Newsgroups: comp.os.linux.announce,,comp.os.linux.admin,
From: (Terry Dawson)
Subject: Linux NET-2 HOWTO (part 1/3)
Message-ID: <>
Followup-To: poster
Summary: HOWTO configure TCP/IP networking, SLIP, PLIP, and PPP under Linux.
Keywords: Linux, Networking, TCP/IP, NET-2, SLIP
Sender: (Matt Welsh)
Organization: Cornell Univ. CS Dept, Ithaca NY 14853
Date: Fri, 18 Nov 1994 17:11:12 GMT
Approved: (Matt Welsh)
Lines: 1512

Archive-name: linux/howto/networking/part1
Last-modified: 18 Nov 94

  Linux NET-2/NET-3 HOWTO
  Terry Dawson,
  v2.7, 08 Oct 1994

  This document aims to describe how to obtain, install and configure
  the Linux NET-2 and NET-3 networking software. Some answers to some of
  the more frequently asked questions are also included.

  1.  Introduction.

  This is the Linux NET-2-HOWTO. This document is a complete rewrite of
  the earlier NET-FAQ, and of the subsequent NET-2-HOWTO versions 1.0+,
  for the new NET-2 and NET-3 tcp/ip networking code for Linux kernels
  1.0 and above.

  1.1.  Changes from the previous release.

          Added details of the new ARCNet driver - thanks Avery.
          Added tcpdump location details

          Fixed symlink to dip and chmod problem - thanks Lamar.
          Updated Matt Dillon's slip management suite version

  1.2.  A brief development history of Linux Networking.

  Ross Biro <> wrote the original kernel based
  networking code for Linux. He used ethernet drivers written by Donald
  Becker <>, a slip driver written by
  Laurence Culhane <>, and a D-Link driver by
  Bj0rn Ekwall <>.

  The further development of the Linux networking code was later taken
  up by Fred van Kempen <>, who took Ross's code and
  produced the NET-2 release of network code. NET-2 went through a
  number of revisions until release NET-2d, when Alan Cox
  <> took Fred's NET-2d code and set about
  debugging the code with the aim of producing a stable and working
  release of code for incorporation into the standard kernel releases.
  This code was called NET-2D(ebugged), and has been incorporated into
  the standard kernel releases since some time before Linux vers 1.0 was

  PPP support was added by Michael Callahan, <>
  and  Al Longyear, <>, originally as patches to the
  kernel, and in later releases as an option.

  Fred continued developing his kernel network code, and produced
  NET-2E.  A reference for it if you are interested in looking at Fred's
  new work is listed later on in this document.

  With the release of Linux vers 1.0, Linus made a decision to continue
  supporting Alan's code as the `standard' network kernel code.

  The latest revision of the code, NET-3, appears in kernel releases
  1.1.5 and later, and is essentially the same code, but with many
  fixes, corrections and enhancements.

  Alan has added such features as IPX and AX.25 modules.  Florian La
  Roche, <> has produced an updated distribution of
  network applications.

  Unless otherwise stated, this document will refer to the network code
  included in the standard kernel releases. On the whole this document
  will serve for Fred's code as well, but as the development paths are
  now seperate, it is possible that there will be differences between
  the two.

  2.  Disclaimer.

  The Linux networking code is a brand new implementation of kernel
  based tcp/ip networking. It has been developed from scratch, and is
  not a port of any existing kernel networking code.

  Because it is a fresh implementation it may still have a number of
  bugs or problems with it, and there may be a number of fixes and
  patches released.  If you are worried about problems then just stick
  to the version of network code released with the standard kernel
  releases and utility sets. The networking code has a small team of
  dedicated people working on it, with a cast of thousands testing the
  code, and collecting and reporting bugs and problems.  Any problem you
  experience is likely to have already been reported, and be being
  worked on, and will possible be corrected soon, so be patient, or if
  you can help, offer your assistance.

  We do not, and cannot, know everything there is to know about the
  Linux network software. Please accept and be warned that this document
  probably does contain errors. Please read any README files that are
  included with any of the various pieces of software described in this
  document for more detailed and accurate information. We will attempt
  to keep this document as error-free and up-to-date as possible.
  Versions of software are current as at time of writing.

  NOTE: While its name may appear similar to the Berkeley Software
  Distribution NET-2 release, the Linux network code actually has
  nothing at all to do with it. Please don't confuse them.

  3.  Questions already ?

  `The only stupid question is the unasked one.'

  If you have general configuration questions, and you have been unable
  to find the answers after reading the other various HOWTO and FAQ
  files, then you would be best served to post them to, or, if you believe your question to be
  specifically related to the Linux Network code, then you could post it
  to the NET mailing list. Please include as much relevant information
  as possible, there is nothing more annoying than to have a bug or
  problem reported without sufficient information to even begin
  searching for it.

  Version numbers and revisions of code, a detailed account of the
  problem, and the circumstances that caused it to occur, are essential.
  Trace and debug messages where available should also be considered

  If you have a question relating to the configuration of, or problems
  experienced with, any linux distribution, regardless of who has
  provided it, please contact the prople who created the distribution
  first, before attempting to report the problem to the network code
  developers. The reason for this is that some of the distributions use
  non-standard directory structures, and supply test/non-standard
  versions of code and utilities. The developers of the NET-2 code
  cannot be expected to offer support for the network code as
  distributed in any form, other than as described in this document, or
  as per distributed Alpha/Beta test instructions.

  To join the Linux NET channel on the mail list server, send mail to:

       with the line:

       X-Mn-Admin: join NET

       at the top of the message body (not the subject line).

  Remember, keep in mind that the NET channel is for development discus-
  sions only.

  Note also that a PPP list has been established. To join it, use the
  same procedure as for joining the NET channel, except specify PPP in
  place of NET in the X-Mn-Admin: field.

  Note also that a HAMS list has been established. This list has been
  established for the discussion of programs related to Amateur Radio.
  To join it, follow the same procedure as for joining the NET or PPP
  channels, except specify HAMS in place of NET in the X-Mn-Admin:

  4.  Related Documentation.

  If you are looking for information about tcp/ip networking that this
  HOWTO does not cover, then you might try the following sources, as
  they provide some very useful information.

  Olaf Kirch has written a substantial document as part of the Linux
  Documentation Project entitled the Linux Network Administration Guide.
  This is an excellent document. It covers all aspects of setting up and
  using the tcp/ip networking under Linux, including NFS, UUCP, mail,
  News, nameserver etc.

  Olaf's book supplements this HOWTO, taking up where this document
  leaves off. This document covers the installation and configuration of
  the NET code, i.e. `How to put your machine on the net'. If you are
  new to unix networking, then I strongly urge you to obtain a copy and
  read it first. It will answer a lot of questions for you that are not
  within the scope of this document.

  The current release version is available in:


  There are various versions of the document in this directory. The most
  common formats are supported, being plain ascii, Postscript, DVI,
  Latex and groff.

  The Linux Network Administrators Guide is Copyright (c) by Olaf Kirch.

  You should also read the other HOWTO documents relevant to networking
  with Linux.

  They are:

  The Ethernet-HOWTO
  ( which you
  should read if you intend using an ethernet card with Linux. It
  includes much more detail on how to select, install and configure an
  ethernet card for Linux.

  The Serial-HOWTO (
  if you intend using slip or ppp in server mode.

  The Mail-HOWTO ( and
  the News-HOWTO ( for
  some specific information on setting up Mail and News on your system.

  The UUCP-HOWTO ( if
  you will be connecting to the net via UUCP.

  For more general information on Unix network configuration another
  good place to look for help on setting up your network is the O'Reilly
  and Associates book TCP/IP Network Administration, (the one with the
  Crab on the cover). Keep in mind that the Linux Network code is now a
  fairly standard implementation of tcp/ip networking, this means that
  the commands to configure and use it will work in much the same way as
  for those for other unix operating systems. Keep in mind though that
  some of the arguments and options might differ slightly from those in
  the book.

  If you are after some basic tutorial information on tcp/ip networking
  generally, then you might take a look at the following documents:


  If you are after some more detailed information on tcp/ip networking
  then I highly recommend:

       "Internetworking with TCP/IP"
       by Douglas E. Comer

       ISBN 0-13-474321-0
       Prentice Hall publications.

  4.1.  New versions of this document.

  The latest released version of this document can be retrieved by
  anonymous ftp from:


  via the World Wide Web from the Linux Documentation Project Web Server
  (, at page: NET-2-HOWTO
  ( or directly from
  me, <>. It will also be posted to the
  newsgroups: comp.os.linux.announce,, and
  news.answers periodically.

  You can find news.answers FAQ postings, including this one, archived

  4.2.  Feedback.

  Please send any comments, updates, or suggestions to me,
  <>. The sooner I get feedback, the sooner I
  can update and correct this document. If you find any problems with
  it, please mail me instead of posting to one of the newsgroups, as I
  may miss it. Thanks.

  5.  NET-2/NET-3 Supported functionality.

  The NET code is a complete kernel based implementation of tcp/ip for
  Linux.  The NET-2 and NET-3 versions of code support:

     Ethernet Cards
        Most popular ethernet cards are supported.

     SLIP (Serial Line IP) and PPP
        for tcp/ip networking over serial lines such as the telephone
        via modem, or a local cable between two machines.

     Van Jacobsen Header Compression
        for compressing the tcp/ip headers to improve slip performance
        over low speed lines.

     PLIP (Parallel Lines IP)
        to allow local connections between two machines using your
        printer ports.

     NFS (Networked File System)
        to allow you to remotely mount another machines filesystems.

     AX.25 (A protocol used by Amateur Radio Operators)
        Alan Cox has some experimental code available.

     PI Card (An 8530 SCC based card used by Amateur Radio Operators)
        An experimental PI Card driver is available.

     IPX/SPX (Novell)
        to allow you to write custom SPX/IPX applications, or to use
        Linux as an IPX router.

  The NET-2 and NET-3 network code does not yet currently support:

     NCP (Novell) support
        to allow Linux to serve and mount Novell network devices. This
        is being worked on.

     Lan types other than ethernet
        This means token ring, arcnet, FDDI, etc. An experimental Token
        Ring driver is being developed. An experimental ARCNet driver
        has also been developed (details further on).

     ISDN Support
        this is being developed.

  5.1.  Supported Ethernet cards.

  The standard linux kernel release supports the following type of
  Ethernet cards:

  o  NE2000/NE1000 and close compatibles.

  o  WD80*3 and close compatibles.

  o  SMC Ultra

  o  3c501 (obselete and very slow)

  o  3c503 and close compatibles.

  o  3c509/3c579

  o  HP PCLAN (however a newer kernel is required for the HP PCLAN+)

  o  AT1500 and NE2100 (LANCE and PCnet-ISA) and close compatibles.

  o  AT1700 (not clones)

  o  DEPCA and close compatibles.

  o  D-Link DE600 pocket adaptor and close compatibles.

  o  AT-LAN-TEC/RealTek pocket adaptor and close compatibles.

  Additional drivers are available in the 1.1.* and later development

  The Ethernet-HOWTO contains a lot of very useful information on the
  supported ethernet cards, including information on how to choose an
  ethernet card if you are intending to puchase some specifically for

  As mentioned above, Linux supports other means of network connection
  if you don't have access to an ethernet card or connection. Many
  universities and businesses worldwide offer some form of dial-up
  network access. Generally these forms of access will offer an option
  of either SLIP or PPP access, so you will be well catered for. All you
  will need is a telephone modem, the one you already have may well be
  good enough, and to configure your Linux system appropriately. There
  are sections below that describe exactly what you need.

  6.  Getting the NET-2/NET-3 software.

  Before you can configure the networking software you must obtain all
  of the bits and pieces that make it up. These include the current
  version of the kernel code (version 1.0 or later), the correct system
  libraries, the tcp/ip configuration programs and files (e.g.
  /sbin/ifconfig, /etc/hosts etc.), and finally a set of network
  application programs (such as telnet, ftp, rlogin etc.).

  If you obtained Linux from a distribution you may already have all
  that you need. Check and make sure that you do. For example, some
  Linux distributions come with all of the network configuration files,
  binaries, libraries, and kernel installed, so there's no reason to get
  the following files.

  NOTE: they may be in directories and files different to those
  specified in this HOWTO document

  If you DO have the network software, skip to the `Configuring the
  kernel' section. If you DO NOT have the network software follow the
  following directions.

  6.1.  The kernel source.

  Version 1.0 of the Linux kernel is the production version. Any of the
  Linux kernels after that release are enhancements or bug fixes. If you
  feel at all concerned about the possibility of having to patch and
  modify the kernel source, then you should stick to this release, as it
  will do most of what you want it to. In the case of the networking
  code though, I strongly suggest you just take a deep breath and follow
  the newer releases of code, as there have been many changes in the
  newer version kernels that affect networking. I know you hear it from
  everyone and everywhere, but when trying out any new version of kernel
  software you should always ensure that you have sufficient backups of
  your system just in case something goes seriously wrong while you are

  The current kernel version is found in:


  This is a gzipped file, so you will need gzip to uncompress it.

  To install it, try:

       # cd /usr/src
       # mv linux linux.old
       # gzip -dc v.1.1.45.tar.gz | tar xvf -

  You may also find some files called patch46.gz ... in the same
  directory. These are patch files. If you have a linux kernel that is
  version 1.1.45 then what this means is that you have linux kernel
  version 1.1.0 with patches 1 to 45 applied, so you won't need to apply
  any of these.  If there are any patch files that are greater than the
  version of kernel you have, you should obtain all of those above, and
  apply them, in sequence, with something like the following commands:

       # cd /usr/src
       # gzip -dc .../patch1.gz | patch -p0
       # gzip -dc .../patch2.gz | patch -p0
       # gzip -dc .../patch3.gz | patch -p0


  6.2.  The libraries.

  You'll want at least version 4.4.2 of libc, as there were problems
  with earlier version that affected subnet masks.

  The current libraries (libc-4.5.26) can be found in:


  You will need at least the following files:

  o  image-4.5.26.tar.gz

  o  inc-4.5.26.tar.gz

  o  extra-4.5.26.tar.gz

  o  release.libc-4.5.26

  You MUST read release.libc-4.5.26 before you install the libraries.
  Please note the single line in the release document regarding deleting
  the older version of /usr/lib/libgcc.* or else your compiles will not
  link properly. Please note that to use release 4.5.26 you will also
  need at least GCC version 2.5.7, and Linux kernel 1.0 or later.

  6.3.  The network configuration tool suite.

  You will need the utility suite that provides tools to configure your
  network support.

  The current NET-2 utility suite is available from:


  Because the kernel networking code is still changing some changes to
  the network tools have been necessary as new kernels are released, so
  you will need to choose the version that is appropiate for the kernel
  version you intend to use.

  The filenames reflect the earliest version of kernel that the tools
  will work with. Please choose the filename whose version equals, or is
  less than the version of kernel source you intend to use.

  To build and install the tools, you should try:

       # cd /usr/src
       # mkdir net-tools
       # cd net-tools
       # gzip -dc net-tools-1.1.38.tar.gz | tar xvf -
       # make config
       # make

       If everything makes ok, then:

       # make install

  If you use a kernel version 1.1.26 or earlier you should look in:


  In this directory you will find three versions of the network tools.
  The following table lists net-032 package name with the relevant
  kernel versions:

       net-0.32d-net3.tar.gz     1.1.12+
       net-0.32b.tar.gz          1.1.4+
       net-0.32.old.tar.gz       pre 1.1.4 kernels

  These packages include the essential network configuration programs
  such as ifconfig, route, netstat etc. These will be discussed later.

  6.4.  The network applications.

  You will want a number of network application programs. These are
  programs like telnet, ftp, finger and their daemons at least. Florian
  La Roche, <> has put together a fairly complete
  distribution of network applications in both binary and source form.
  The tcp/ip application binaries and some sample config files are found


  If there are newer versions then use the newer versions. Please read
  the README file first just to make sure that you have the necessary

  Be sure to make backups of any config files important to you. If this
  is a new installation you probably don't have any. You can unpack each
  of the packages above with the command:

       # cd /
       # gzip -dc filename.tar.z | tar xpvlf -

  IMPORTANT NOTE: Florian has built and prepackaged these tar files for
  your convenience. Florian has attempted to make them as complete as
  possible and has included a distribution of the binaries found in the
  net-tools-n.n.nn releases. Unfortunately Florian has chosen not to use
  the same directory structure as Alan did when he prepared the
  installation script for the net-tools. This will mean that you should
  be very careful when installing them. Florian will change this later
  so that this difference is not a problem, but until then, I suggest
  you do the following instead of the above:

       -  Unpack the binaries somewhere safe:
       # cd /usr/src
       # mkdir NetKit
       # cd NetKit
       # gzip -dc NetKit-A-0.07.bin.tar.gz | tar xpvlf -
       # gzip -dc NetKit-B-0.06.bin.tar.gz | tar xpvlf -

       -  Remove Florians copies of the network tools previously described:
       # rm ./bin/hostname ./sbin/route ./sbin/ifconfig ./sbin/netstat
       # rm ./usr/sbin/arp ./usr/sbin/rarp ./usr/sbin/slattach

       -  Copy Florian's files into their new home:
       # cp -vrpd . /

  6.5.  Additional drivers or packages.

  If you want to add some developmental, or Alpha/Beta test code, such
  as AX.25 support, you will need to obtain the appropriate support
  software for those packages. Please check the relevant sections for
  those packages in this document for more detail.

  7.  Configuring the kernel.

  Before you can use any of the network tools, or configure any network
  devices, you must ensure that your kernel has the necessary network
  support built into it. The best way of doing this is to compile your
  own, selecting which options you want and which you don't.

  Assuming you have obtained and untarred the kernel source already, and
  applied any patches that you might need to have applied to get any
  nonstandard or developmental software installed, all you have to do is
  edit /usr/src/linux/drivers/net/CONFIG. This file has many comments to
  guide you in editing it,and in general you will need to edit very
  little, as it has sensible defaults. In my case I don't need to edit
  it at all.  This file is really necesary if your ethernet card is an
  unusual one, or is one that isn't automatically detected by the
  ethernet driver. It allows you to hard code some of the elements of
  your ethernet hardware. For example, if your ethernet card is a close,
  but not exact clone of a WD-8013, then you might have to configure the
  shared memory address to ensure the driver detects and drives the card
  properly. Please check the Ethernet-HOWTO for more definitive
  information on this file and its effect on ethernet cards. This file
  also contains configurable parameters for PLIP, though the defaults
  should again be ok unless you have a particularly slow machine.

  When you are happy that the CONFIG file is suitable for your purposes,
  then you can proceed to build the kernel. Your first step will be to
  edit the top level Makefile to ensure the kernel will be built with
  the appropriate VGA settings, and then you must run the kernel
  configuration program:

       # cd /usr/src/linux
       # make config

  You will be asked a series of questions. There are four sections
  relevant to the networking code. They are the General setup,
  Networking options, Network device support, and the Filesystems
  sections. The most difficult to configure is the Network device
  support section, as it is where you select what types of physical
  devices you want configured. On the whole you can just use the default
  values for the other sections fairly safely. The following will give
  you an idea of how to proceed:

       * General setup
       Networking support (CONFIG_NET) [y] y

  In the General setup section you simply select whether you want
  network support or not. Naturally you must answer yes.

  * Networking options
  TCP/IP networking (CONFIG_INET) [y] y
  IP forwarding/gatewaying (CONFIG_IP_FORWARD) [y] y
  * (it is safe to leave these untouched)
  PC/TCP compatibility mode (CONFIG_INET_PCTCP) [n] n
  Reverse ARP (CONFIG_INET_RARP) [n] n
  Assume subnets are local (CONFIG_INET_SNARL) [y] y
  Disable NAGLE algorithm (normally enabled) (CONFIG_TCP_NAGLE_OFF) [n] n
  The IPX protocol (CONFIG_IPX) [n] n

  The second half of the Networking options section allows you to enable
  or disable some funky features that you can safely accept the defaults
  on until you have some idea why you want to change them.

       * Network device support
       Network device support? (CONFIG_NETDEVICES) [y]
       Dummy net driver support (CONFIG_DUMMY) [n]
       SLIP (serial line) support (CONFIG_SLIP) [y] y
        CSLIP compressed headers (SL_COMPRESSED) [y] y
       PPP (point-to-point) support (CONFIG_PPP) [y] y
       Load balancing support (experimental) (CONFIG_SLAVE_BALANCING) [n] n
       Do you want to be offered ALPHA test drivers (CONFIG_NET_ALPHA) [n] n
       Western Digital/SMC cards (CONFIG_NET_VENDOR_SMC) [y] y
       WD80*3 support (CONFIG_WD80x3) [y] y
       SMC Ultra support (CONFIG_ULTRA) [n] n
       3COM cards (CONFIG_NET_VENDOR_3COM) [n] n
       Other ISA cards (CONFIG_NET_ISA) [n] n
       PLIP (parallel port) support (CONFIG_PLIP) [n] n
       EISA and on board controllers (CONFIG_NET_EISA) [n] n
       Apricot Xen-II on board ethernet (CONFIG_APRICOT) [n] n
       Pocket and portable adaptors (CONFIG_NET_POCKET) [n] n

  This section is the most important, and the most involved. It is where
  you select what hardware devices you want to support. You can see that
  I have selected SLIP support with header compression, PPP, the WD80*3
  driver, and nothing else. Simply answer `y' to whatever you want to
  play with, and `n' to that you don't.

       * Filesystems
       /proc filesystem support (CONFIG_PROC_FS) [y]
       NFS filesystem support (CONFIG_NFS_FS) [y]

  If you wish to run an NFS client then you will want to include the NFS
  filesystem type. You will need to include the /proc filesystem because
  a number of the network utilities use it.

  After you have completed the configuration, all that remains is to
  actually compile the kernel:

       # make dep
       # make

  Don't forget to make zlilo if the new kernel compiles and tests ok.

  8.  Configuring the Network Devices.

  If everything has gone ok so far, then you will have a Linux kernel
  which supports the network devices you intend to use, and you also
  have the network tools with which to configure them. Now comes the fun
  part! You'll need to configure each of the devices you intend to use.
  This configuration generally amounts to telling each device things
  like what its IP address will be, and what network it is connected to.

  In past versions of this document I have presented near complete
  versions of the various configuration files and included comments to
  modify or delete lines from them as appropriate. From this version
  onwards I will take a slightly different approach which I hope will
  result in you having a complete set of uncluttered configuration files
  that you have built from scratch so you know exactly what is in them,
  and why. I'll describe each of these files, and their function, as we
  come to them.

  8.1.  Configuring the special device files in /dev

  You do not need to configure any special device files in the /dev
  directory for Linux Networking. Linux does not need or use them as
  other operating systems might. The devices are built dynamically in
  memory by the kernel, and since they are only names there is no need
  for them to have an appearance directly to you. The kernel provides
  all of the programming hooks and interfaces that you need to utilise
  them effectively.

  8.2.  What information do I need before I begin ?

  Before you can configure the networking software, you will need to
  know a number of pieces of information about your network connection.
  Your network provider or administrator will be able to provide you
  with most of them.

  8.2.1.  IP Address.

  This is the unique machine address, in dotted decimal notation, that
  your machine will use. An example is Your network
  administrator will provide you with this information.

  If you will be using a slip or plip connection you may not need this
  information, so skip it until we get to the slip device.

  If you're using the loopback device only, ie no ethernet, slip or plip
  support, then you won't need an ip address as the loopback port always
  uses the address

  8.2.2.  Network Mask (`netmask').

  For performance reasons it is desirable to limit the number of hosts
  on any particular segment of a network. For this reason it is common
  for network administrators to divide their network into a number of
  smaller networks, known as subnets, which each have a portion of the
  network addresses assigned to them. The network mask is a pattern of
  bits, which when overlayed onto an address on your network, will tell
  you which subnetwork it belongs to. This is very important for
  routing, and if you find for example, that you can happily talk to
  people outside your network, but not to some people on your own
  network, then it is quite likely that you have specified an incorrect
  subnet mask.

  Your network adminstrators will have chosen the netmask when the
  network was designed, and therefore they should be able to supply you
  with the correct mask to use. Most networks are class-C subnetworks
  which use as their netmask. Other larger networks use
  class-B netmasks ( The NET-2/NET-3 code will
  automatically select a default mask when you assign an address to a
  device. The default assumes that your network has not been subnetted.

  The NET-2/NET-3 code will choose the following masks by default:

       For addresses with the first byte:
       1-127         (Class A)
       128-191       (Class B)
       192+     (Class C)

  if one of these doesn't work for you, try another. If this doesn't
  work ask your network administrator or local network guru (dime a
  dozen) for help.

  You don't need to worry about a netmask for the loopback port, or if
  you are running slip/plip.

  8.2.3.  Network Address.

  This is your IP address masked (bitwise AND) with your netmask.  For

       If your netmask is: 
       and your IP address is:    &&
       your Network address is:     =

  8.2.4.  Broadcast Address.

  `A shout is a whisper that everyone hears whether they need to or not'

  This is normally your network address logically ORed with your netmask
  inverted. This is simpler than it sounds. For a Class-C network, with
  network mask, your Broadcast Address will be your
  network address (calculated above), logically ORed with, the
  network mask inverted.

  A worked example might look like:

       If your netmask is:      !
       the netmask inverted is:       0.  0.  0.255    =
       If your Network address is:      ||
       Your broadcast address is:    =

  Note that for historical reasons some networks use the network address
  as the broadcast address. If you have any doubts contact your network

  If you have access to a sniffer, or some other device capable of
  providing you with a trace of your network traffic, then you might be
  able to determine both the network and broadcast addresses by watching
  other traffic on the lan. Keep an eye open for, (or filter everything
  except), ethernet frames destined for the ethernet broadcast address:
  ff:ff:ff:ff:ff:ff.  If any of them has an IP source address of your
  local router, and the protocol ID is not ARP, then check the
  destination IP address, because this datagram may well be a RIP
  routing broadcast from your router, in which case the destination IP
  address will be your broadcast address.

  Once again, if you're not sure, check with your network administrator,
  they'd rather help you, than have you connect your machine

  8.2.5.  Router (`Gateway') Address.

  `There must be some way out of here.'

  This is the address of the machine that connects your network to the
  rest of the Internet. It is your `gateway' to the outside world. A
  couple of conventions exist for allocating addresses to routers which
  your network might follow, they are: The router is the lowest numbered
  address on the network, the router is the highest numbered host on the
  network.  Probably the most common is the first, where the router will
  have an address that is mostly the same as your own, except with a .1
  as the last byte. eg. if your address is, then your
  router might be The router can in fact have any address
  valid on your network and function properly, the address doesn't
  matter at all. There may in fact even be more than one router on your
  network. You will probably need to talk to your network adminstrator
  to properly identify your router address.

  If you're using only loopback then you don't need a router address. If
  you're using PPP then you also don't need your router address, because
  PPP will automatically determine the correct address for you. If
  you're using SLIP, then your router address will be your SLIP server

  8.2.6.  Nameserver Address.

  Most machines on the net have access to a name server which translates
  human tolerable hostnames into machine tolerable addresses, and vice
  versa. Your network administrators will again tell you the address of
  your nearest nameserver. You can in fact run a nameserver on your own
  machine by running named, in which case your nameserver address will
  be, the loopback port address.  However it is not required
  that you run named at all; see section `named' for more information.

  If you're only using loopback then you don't need to know the
  nameserver address since you're only going to be talking to your own

  8.2.7.  NOTE for SLIP/PLIP/PPP users.

  You may or may not in fact need to know any of the above information.
  Whether you do or not will depend on exactly how your network
  connection is achieved, and the capabilities of the machine at the
  other end of the link. You'll find more detail in the section relevant
  to configuration of the SLIP/PLIP and PPP devices.

  8.3.  /etc/rc.d/rc.inet1,2 or /etc/

  While the commands to configure your network devices can be typed
  manually each time, you will probably want to record them somewhere so
  that your network is configured automatically when you boot your

  The `rc' files are specifically designed for this purpose. For the
  non-unix-wizard: `rc' file are run at bootup time by the init program
  and start up all of the basic system programs such as syslog, update,
  and cron. They are analagous to the MS-DOS autoexec.bat file, and rc
  might stand for `runtime commands'. By convention these files are kept
  under the /etc directory. The Linux Filesystem Standard doesn't go so
  far as to describe exactly where your rc files should go, stating that
  it is ok for them to follow either the BSD (/etc/rc.*) or System-V
  (/etc/rc.d/rc*) conventions.  Alan, Fred and I all use the System-V
  convention, so that is what you will see described here. This means
  that these files are found in /etc/rc.d and are called rc.inet1 and
  rc.inet2. The first rc file that gets called at bootup time is
  /etc/rc, and it in turn calls others, such as rc.inet1, which in turn
  might called rc.inet2.  It doesn't really matter where they are kept,
  or what they are called, so long as init can find them.

  In some distributions the rc file for the network is called and
  is in the /etc subdirectory. The file on these systems is
  simply the rc.inet1 and the rc.inet2 files combined into one file that
  gets executed. It doesn't matter where the commands appear, so long as
  you configure the interfaces before starting the network daemons and

  I will refer to these files as rc.inet1 and rc.inet2, and I keep them
  in the /etc/rc.d, so if you are using one of the distributions that
  uses, or you want to keep the files somewhere else, then you
  will have to make appropriate adjustments as you go.

  We will be building these files from scratch as we go.

  8.3.1.  rc.inet1

  The rc.inet1 file configures the basic tcp/ip interaces for your
  machine using two programs: /sbin/ifconfig, and /sbin/route.  ifconfig

  /sbin/ifconfig is used for configuring your interfaces with the
  parameters that they require to function, such as their IP address,
  network mask, broadcast addresses and similar. You can use the
  ifconfig command with no parameters to display the configuration of
  all network devices. Please check the ifconfig man page for more
  detail on its use.  route

  /sbin/route is used to create, modify, and delete entries in a table
  (the routing table) that the networking code will look at when it has
  a datagram that it needs to transmit. The routing table lists
  destination address, and the interface that that address is reachable
  via. You can use the route command with no parameters to display the
  contents of the routing table. Please check the route man page for
  more detail on its use.

  8.3.2.  rc.inet2

  The rc.inet2 file starts any network daemons such as inetd, portmapper
  and so on. This will be covered in more detail in section `rc.inet2',
  so for the moment we will concentrate on rc.inet1. I have mentioned
  this file here so that if you have some other configuration, such as a
  single file you will understand what the second half of it
  represents. it is important to remember that you must start your
  network applications and daemons after you have configured your
  network devices.

  8.4.  Configuring the Loopback device (mandatory).

  The loopback device isn't really a hardware device. It is a software
  construct that looks like a physical interface. Its function is to
  happily allow you to connect to yourself, and to test network software
  without actually having to be connected to a network of any kind. This
  is great if you are developing network software and you have a slip
  connection.  You can write and test the code locally, and then when
  you are ready to test it on a live network, eatablish your slip
  connection and test it out. You won't hurt others users if your
  program misbehaves.

  By convention, the loopback device always has an IP address of and so you will use this address when configuring it.

  The loopback device for Linux is called `lo'. You will now make the
  first entry into your rc.inet1 file. The following code fragment will
  work for you:

  # rc.inet1   --  configures network devices.
  # Attach the loopback device.
  /sbin/ifconfig lo
  # Add a route to point to the loopback device.
  /sbin/route add
  # End loopback

  You have used the ifconfig program to give the loopback interface its
  IP address, and route program to create an entry in the routing table
  that will ensure that all datagrams destined for will be
  sent to the loopback port.

  There are two important points to note here.

  Firstly, the netmask and broadcast addresses have been allowed to take
  the default values for the loopback device described earlier in
  section `Network Mask'. To see what they are, try the ifconfig program
  without any arguments.

       # ifconfig
       lo        Link encap Local Loopback
                 inet addr  Bcast  Mask
                 UP BROADCAST LOOPBACK RUNNING  MTU 2000  Metric 1
                 RX packets 0 errors 0 dropped 0 overrun 0
                 TX packets 30 errors 0 dropped 0 overrun 0

  Secondly, its not obvious how the route command chose the loopback
  device as the device for the route to  The route program is
  smart enough to know that belongs to the network supported
  by the loopback device. It works this out by checking the IP address
  and the netmask. You can use the route command with no arguments to
  display the contents of the routing table:

       # route
       Kernel routing table
       Destination     Gateway         Genmask         Flags Metric Ref    Use Iface       *            U     0      0       30 lo

  Note: You might want to use the -n argument if your name resolver is
  not yet configured properly. The -n argument tells route to just
  display the numeric addresses, and to not bother looking up the name.

  8.5.  Configuring an ethernet device. (optional)

  You'll only be interested in this section  if you wish to configure an
  ethernet card, if not then skip on ahead to the next section.

  To configure an ethernet card is only slightly more complicated than
  configuring the loopback device. This time you should probably specify
  explicitly the network mask and the broadcast address, unless you are
  sure that the defaults will work ok, and they probably will.

  For this you will need the IP address that you have been assigned, the
  network mask in use on your network, and the broadcast address in use.

  The first ethernet device for a Linux system is called `eth0', the
  second `eth1' and so forth. You will now add a section to your
  rc.inet1 file. The following code fragment will work for you if you
  change the addresses specified for real ones:

       # Attach an ethernet device
       #  configure the IP address, netmask and broadcast address.
       /sbin/ifconfig eth0 IPA.IPA.IPA.IPA
       /sbin/ifconfig eth0 netmask NMK.NMK.NMK.NMK
       /sbin/ifconfig eth0 broadcast BCA.BCA.BCA.BCA
       # add a network route to point to it:
       /sbin/route add -net NWA.NWA.NWA.NWA device eth0
       # End ethernet


        represents your IP Address.

        represents your netmask.

        represents your Broadcast address.

        represents your Network Address.

  Note the use of the -net argument to the route command.  This tells
  route that the route to be added is a route to a network, and not to a
  host. There is an alternative method of achieving this, you can leave
  off the -net if you have the network address listed in the
  /etc/networks file. This is covered later in section `/etc/networks'.

  8.6.  Configuring a SLIP device (optional)

  SLIP (Serial Line Internet Protocol) allows you to use tcp/ip over a
  serial line, be that a phone line with a dialup modem, or a leased
  line of some sort.  Of course to use slip you need access to a slip-
  server in your area. Many universities and businesses provide slip
  access all over the world.

  Slip uses the serial ports on your machine to carry IP datagrams. To
  do this it must take control of the serial device. Slip device names
  are named sl0, sl1 etc. How do these correspond to your serial devices
  ? The networking code uses what is called an ioctl (i/o control) call
  to change the serial devices into slip devices. There are two programs
  supplied that can do this, they are called dip and slattach

  8.6.1.  dip

  dip (Dialup IP) is a smart program that is able to set the speed of
  the serial device, command your modem to dial the remote end of the
  link, automatically log you into the remote server, search for
  messages sent to you by the server, and extract information for them
  such as your IP address, and perform the ioctl necessary to switch
  your serial port into slip mode. dip has a powerful scripting ability,
  and it is this that you can exploit to automate your logon procedure.

  dip comes supplied in the net-032/net-tools package.  There have been
  a number of other versions of dip produced which offer a variety of
  new features. You will find them at:


  The dip-uri version seems to be the more popular, but I suggest you
  take a close look at each to determine which offers enhancements that
  you find useful.

  8.6.2.  slattach

  slattach on the other hand is a very simple program, that is very easy
  to use, but does not have the sophistication of dip.  slattach is
  ideal to use where you have a permanent connection to your server,
  such as a physical cable, or a leased line.

  8.6.3.  When do I use which ?

  You would use dip when your link to the machine that is your slip
  server is a dialup modem, or some other termporary link. You would use
  slattach when you have a leased line, perhaps a cable, between your
  machine and the server, and there is no special action needed to get
  the link working. See section `Permanent Slip connection' for more

  Configuring slip is much like configuring an Ethernet interface (read
  section `Configuring an ethernet device' above). However there are a
  few key differences.

  First of all, slip links are unlink ethernet networks in that there is
  only ever two hosts on the network, one at each end of the link.
  Unlike an ethernet that is available for use as soon are you are
  cabled, with slip, depending on the type of link you have, you may
  have to initialise your network connection in some special way.

  If you are using dip then this would not normally be done at boot
  time, but at some time later, when you were ready to use the link.  It
  is possible to automate this procedure. If you are using slattach then
  you will probably want to add a section to your rc.inet1 file.  This
  will be described soon.

  There are two major types of slip servers: Dynamic IP address servers
  and static IP address servers. Almost every slip server will prompt
  you to login using a username and password when dialing in. dip can
  handle logging you in automatically.

  8.6.4.  Static slip server with a dialup line and DIP.

  A static slip server in one in which you have been supplied an IP
  address that is exclusively yours. Each time you connect to the
  server, you will configure your slip port with that address. The
  static slip server will answer your modem call, possibly prompt you
  for a username and password, and then route any datagrams destined for
  your address to you via that connection. If you have a static server,
  then you may want to put entries for your hostname and IP address
  (since you know what it will be) into your /etc/hosts. You should also
  configure some other files such as: rc.inet2, host.conf, resolv.conf,
  /etc/HOSTNAME, and rc.local. Remember that when configuring rc.inet1,
  you don't need to add any special commands for your slip connection
  since it is dip that does all of the hard work for you in configuring
  your interface. You will need to give dip the appropriate information,
  and it will configure the interface for you after commanding the modem
  to establish the call, and logging you into your slip server.

  If this is how your slip server works then you can move to section
  `Using Dip' to learn how to configure dip appropriately.

  8.6.5.  Dynamic slip server with a dialup line and DIP.

  A dynamic slip server is one which allocates you an IP address
  randomly, from a pool of addresses, each time you logon. This means
  that there is no guarantee that you will have any particular address
  each time, and that address may well be used by someone else after you
  have logged off.  The netework administrator who configured the slip
  server will have assigned a pool of address for the slip server to
  use, when the server receives a new incoming call, it finds the first
  unused address, guides the caller through the login process, and then
  prints a welcome message that contains the IP address it has
  allocated, and will proceed to use that IP address for the duration of
  that call.

  Configuring for this type of server is similar to configuring for a
  static server, except that you must add a step where you obtain the IP
  address that the server has allocated for you and configure your slip
  device with that.

  Again, dip does the hard work, and new versions are smart enough to
  not only log you in, but to also be able to automatically read the IP
  address printed in the welcome message, and store it so that you can
  have it configure your slip device with it.

  If this is how your slip server works then you can move to section
  `Using Dip' to learn how to configure dip appropriately.

  8.6.6.  Using DIP.

  As explained earlier, dip is a powerful program that can simplify and
  automate the process of dialling into the slip server, logging you in,
  starting the connection, and configuring your slip devices with the
  appropriate ifconfig and route commands.

  Essentially to use dip you'll write a `chat script', which is
  basically a list of commands that dip understands that tell dip how to
  perform each of the actions you want it to perform. See sample.dip in
  the net-032 package for an explanation.  dip is quite a powerful
  program, with many options. Instead of going into all of them here you
  should looks at the man page, README and sample files from tsx-11, and
  the net-032 distribution.

  You may notice that the sample.dip script assumes that you're using a
  static slip server, so you know what your IP address is beforehand.
  For dynamic slip servers, the newer versions of dip include a command
  you can use to automatically read and configure your slip device with
  the IP address that the dynamic server allocates for you. The
  following sample was supplied by Paul Mossip, and is probably a good
  starting point for you. You might like to save it as /etc/dipscript:

  # Connection script for SLIP to

    # Fetch the IP address of our target host.

    # Set the desired serial port and speed.
    port /dev/cua0
    speed 38400

    # Reset the modem and terminal line.

    # Prepare for dialing.
    send ATZ1\r
    wait OK 4
    if $errlvl != 0 goto error
    dial 666-0999                    ## Change to your server's number!
    if $errlvl != 0 goto error
    wait CONNECT 60
    if $errlvl != 0 goto error

    # We are connected.  Login to the system.
    sleep 3
    send \r\n\r\n
    wait gracelands> 20              ## Change to your server's prompt
    if $errlvl != 0 goto error
    send login\n
    wait name: 10                    ## Wait username: prompt
    if $errlvl != 0 goto erro
    send elvisp\n                    ## Change to your own!
    wait ord: 10                     ## Wait password prompt
    if $errlvl != 0 goto error
    send alive\n                     ## Change to your own!
    wait gracelands> 10
    if $errlvl != 0 goto error
    send slip\n                      ## Change to suit your server
    wait SLIP 30                     ## Wait for SLIP prompt
    if $errlvl != 0 goto error
    get $local remote 10             ## Assumes the server sends your IP..
    if $errlvl != 0 goto error       ## address as soon as you enter slip.
    get $remote gracelands           ## slip server address from /etc/hosts
    print CONNECTED to $remote with address $rmtip we are $local
    mode SLIP
    goto exit
    print SLIP to $host failed.
  # End dip script

---End of part 1/3---

Newsgroups: comp.os.linux.announce,,comp.os.linux.admin,
From: (Terry Dawson)
Subject: Linux NET-2 HOWTO (part 2/3)
Message-ID: <>
Followup-To: poster
Summary: HOWTO configure TCP/IP networking, SLIP, PLIP, and PPP under Linux.
Keywords: Linux, Networking, TCP/IP, NET-2, SLIP
Sender: (Matt Welsh)
Organization: Cornell Univ. CS Dept, Ithaca NY 14853
References: <>
Date: Fri, 18 Nov 1994 17:11:50 GMT
Approved: (Matt Welsh)
Lines: 1508

Archive-name: linux/howto/networking/part2
Last-modified: 18 Nov 94

---This is part 2/3---

  The above example assumes you are calling a dynamic slip server, if
  you are calling a static slip server, then remove the following two

  get $local remote 10             ## Assumes the server sends your IP..
  if $errlvl != 0 goto error       ## address as soon as you enter slip.

  When dip is given the get $local command it searches the incoming text
  from the remote end for a string that looks like an IP address, ie
  strings numbers seperated by `.' characters. This modification was put
  in place specifically for dynamic slip servers, so that the process of
  reading the IP address granted by the server could be automated.

  The example above will automaticaly create a default route via your
  slip link, if this is not what you want, you might have an ethernet
  connection that should be your default route, then remove the default
  command from the script.  After this script has finished running, if
  you do an ifconfig command, you will see that you have a device sl0.
  This is your slip device.  Should you need to, you can modify its
  configuration manually, after the dip command has finished, using the
  ifconfig and route commands.

  Please note that dip allows you to select a number of different
  protocols to use with the mode command, the most common example is
  cslip for slip with compression. Please note that both ends of the
  link must agree, so you should ensure that whatever you select agrees
  with what your server is set to.

  The above example is fairly robust and should cope with most errors.
  Please refer to the dip man page for more information. Naturally you
  could, for example, code the script to do such things as redial the
  server if it doesn't get a connection within a prescribed period of
  time, or even try a series of servers if you have access to more than

  8.6.7.  Permament slip connection using a leased line and slattach.

  If you have a cable between two machines, or are fortunate enough to
  have a leased line, or some other permanent serial connection between
  your machine and another, then you don't need to go to all the trouble
  of using dip to set up your serial link. slattach is a very simple to
  use utility that will allow you just enough functionality to configure
  your connection.

  Since your connection will be a permanent one, you will want to add
  some commands to your rc.inet1 file. In essence all you need to do for
  a permament connection is ensure that you configure the serial device
  to the correct speed and switch the serial device into slip mode.
  slattach allows you to do this with one command. Add the following to
  your rc.inet1 file:

       # Attach a leased line static slip connection
       #  configure /dev/cua0 for 19.2kbps and cslip
       /sbin/slattach -p cslip -s 19200 /dev/cua0 &
       /sbin/ifconfig sl0 IPA.IPA.IPA.IPA pointopoint IPR.IPR.IPR.IPR up
       # End static slip.


        represents your IP address.

        represents the IP address of the remote end.

  slattach allocated the first unallocated slip device to the serial
  device specified. slattach starts with sl0. Therefore the first
  slattach command attaches slip device sl0 to the serial device
  specified, and sl1 the next time, etc.

  slattach allows you to configure a number of different protocols with
  the -p argument. In your case you will use either slip or cslip
  depending on whether you want to use compression or not.  Note: both
  ends must agree on whether you want compression or not.

  8.7.  Configuring a PLIP device. (optional)

  plip (Parallel Line IP), is like slip, in that it is used for
  providing a point to point network connection between two machines,
  except that it is designed to use the parallel printer ports on your
  machine instead of the serial ports. Because it is possible to
  transfer more than one bit at a time with a parallel port, it is
  possible to attain higher speeds with the plip interface than with a
  standard serial device. In addition, even the simplest of parallel
  ports, printer ports, can be used, in lieu of you having to purchase
  comparitively expensive 16550AFN UART's for your serial ports.

  Please note that some laptops use chipsets that will not work with
  PLIP because they do not allow some combinations of signals that PLIP
  relies on, that printers don't use.

  The Linux plip interface is compatible with the Crywyr Packet Driver
  PLIP, and this will mean that you can connect your Linux machine to a
  DOS machine running any other sort of tcp/ip software via plip.

  When compiling the kernel, there is only one file that might need to
  be looked at to configure plip. That file is
  /usr/src/linux/driver/net/CONFIG, and it contains plip timers in mS.
  The defaults are probably ok in most cases. You will probably need to
  increase them if you have an especially slow computer, in which case
  the timers to increase are actually on the other computer.

  To configure a plip interface, you will need to add the following
  lines to your rc.inet1 file:

       # Attach a PLIP interface
       #  configure first parallel port as a plip device
       /sbin/ifconfig plip0 IPA.IPA.IPA.IPA pointopoint IPR.IPR.IPR.IPR up
       # End plip


        represents your IP address.
        represents the IP address of the remote machine.

  The pointopoint parameter has the same meaning as for slip, in that it
  specifies the address of the machine at the other end of the link.

  In almost all respects you can treat a plip interface as though it
  were a slip interface, except that neither dip nor slattach need be,
  nor can be, used.

  8.7.1.  PLIP cabling diagram.

  plip has been designed to use cables with the same pinout as those
  commonly used by the better known of the MS-DOS based pc-pc file
  transfer programs.

  The pinout diagram (taken from /usr/src/linux/drivers/net/plip.c)
  looks as follows:

       Pin Name    Connect pin - pin
       ---------   -------------------------------
       GROUND      25 - 25
       D0->ERROR   2 - 15
       ERROR->D0   15 - 2
       D1->SLCT    3 - 13
       SLCT->D1    13 - 3
       D2->PAPOUT  4 - 12
       PAPOUT->D2  12 - 4
       D3->ACK     5 - 10
       ACK->D3     10 - 5
       D4->BUSY    6 - 11
       BUSY->D4    11 - 6
       D5          7*
       D6          8*
       D7          9*
       STROBE      1*
       FEED        14*
       INIT        16*
       SLCTIN      17*

  Notes: Do not connect the pins marked with an asterisk `*'.  Extra
  grounds are 18,19,20,21,22,23, and 24.

  If the cable you are using has a metallic shield, it should be
  connected to the metallic DB-25 shell at one end only.

  Warning: A miswired PLIP cable can destroy your controller card. Be
  very careful, and double check every connection to ensure you don't
  cause yourself any unnecessary work or heartache.

  While you may be able to run PLIP cables for long distances, you
  should avoid it if you can. The specifications for the cable allow for
  a cable length of about 1 metre or so. Please be very careful when
  running long plip cables as sources of strong electromagnetic fields
  such as lightning, power lines, and radio transmitters can interfere
  with and sometimes even damage your controller. If you really want to
  connect two of your computers over a large distance you really should
  be looking at obtaining a pair of thin-net ethernet cards and running
  some coaxial cable.
  9.  Routing. (mandatory)

  After you have configured all of your network devices you need to
  think about how your machine is going to route IP datagrams. If you
  have only one network device configured then your choice is easy, as
  all datagrams for any machine other than yours must go via that
  interface. If you have more than one network interface then your
  choice is a little more complicated. You might have both an ethernet
  device and slip connection to your machine at home. In this situation
  you must direct all datagrams for your machine at home via your slip
  interface, and all else via the ethernet device. Routing is actually a
  very simple mechanism, but don't worry if you find it slightly
  difficult to understand at first; everybody does.

  You can display the contents of your routing table by using the route
  command without any options.

  There are four commonly used routing mechanisms for unix network
  configurations.  I'll briefly discuss each in turn.

  9.1.  Static/Manual Routes.

  Static routing, as its name implies, is `hard coded' routing, that is,
  it will not change if your network suffers some failure, or if an
  alternate route becomes available. Static routes are often used in
  cases where you have a very simple network with no alternate routes
  available to a destination host, that is, there is only one possible
  network path to a destination host, or where you want to route a
  particular way to a host regardless of network changes.

  In Linux there is a special use for manual routes, and that is for
  adding a route to a slip or plip host where you have used the ifconfig
  pointopoint parameter. If you have a slip/plip link, and have the
  pointopoint parameter specifying the address of the remote host, then
  you should add a static route to that address so that the ip routing
  software knows how to route datagrams to that address. The route
  command you would use for the slip/plip link via leased line example
  presented earlier would be:

       #/sbin/route add IPR.IPR.IPR.IPR


        represents the IP address of the remote end.

  9.2.  Default Route.

  The default route mechanism is probably the most common and most
  useful to most end-user workstations and hosts on most networks. The
  default route is a special static route that matches every destination
  address, so that if there is no more specific route for a datagram to
  be sent to, then the default route will be used.

  If you have a configuration where you have only a single ethernet
  interface, or a single slip interface device defined then you should
  point your default route via it. In the case of an ethernet interface,
  the Linux kernel knows where to send datagrams for any host on your
  network. It works this out using the network address and the network
  mask as discussed earlier. This means that the only datagrams the
  kernel won't know how to properly route will be those for people not
  on your network. To make this work you would normally have your
  default route point to your router address, as it is your means of
  getting outside of your local network. If you are using a slip
  connection, then your slip server will be acting as your router, so
  your default route will be via your slip server.

  To configure your default route, add the following to your rc.inet1
  after all of your network device configurations:

       # Add a default route.
       /sbin/route add default gw RGA.RGA.RGA.RGA


        represents your Router/Gateway Address.

  9.3.  Proxy ARP.

  This method is ugly, hazard prone and should be used with extreme
  care, some of you will want to use it anyway.

  Those with the greatest need for proxy arp will be those of you who
  are configuring your Linux machine as a slip dial-in server. For those
  of you who will be using PPP, the PPP daemon simplifies and automates
  this task, making it a lot safer to use.

  Normally when a host on your ethernet network wants to talk to you, it
  knows your IP address, but doesn't know what hardware (ethernet)
  address to send datagrams to. The ARP mechanism is there specifically
  to provide that mapping function between network address and hardware

  If you want to use your machine as a server for other machines, you
  must get your machine to answer ARP requests for their IP addresses on
  their behalf, as they will not be physically connected to the ethernet
  network. Lets say that you have been assigned a number of IP addresses
  on your local network that you will be offering to dial-in slip users.
  Lets say those addresses are:, and that you have
  an ethernet card with a hardware address of 00:00:C0:AD:37:1C. (You
  can find the hardware address of your ethernet card by using the
  ifconfig command with no options). To instruct your Linux server to
  answer arp requests by proxy for these addresses you would need to add
  the following commands to the end of your rc.inet1 file:

  # Proxy ARP for those dialin users who will be using this
  #           machine as a server:
  /sbin/arp -s 00:00:C0:AD:37:1C pub
  /sbin/arp -s 00:00:C0:AD:37:1C pub
  /sbin/arp -s 00:00:C0:AD:37:1C pub
  /sbin/arp -s 00:00:C0:AD:37:1C pub
  /sbin/arp -s 00:00:C0:AD:37:1C pub
  # End proxy arps.

  The pub argument stands for `publish'. It is this argument that
  instructs your machine to answer requests for these addresses, even
  though they are not for your machine. When it answers it will supply
  the hardware address specified, which is of course its own hardware

  Naturally you will need to ensure that you have routes configured in
  your linux server that point these addresses to the slip device on
  which they will be connecting.

  If you are using PPP, you don't need to worry about manually messing
  with the arp table, as the pppd will manage those entries for you if
  you use the proxyarp parameter, and as long as the IP addresses of the
  remote machine and the server machine are in the same network. You
  will need to supply the netmask of the network on the server's pppd
  command line.

  9.4.  gated - the routing daemon.

  gated could be used in place of proxy arp in some cases, and would
  certainly be much cleaner, but its primary use is if you want your
  linux machine to act as an intelligent ip router for your network.
  gated provides support for a number of routing protocols. Among these
  are RIP, BGP, EGP, HELLO, and OSPF. The most commonly used in small
  networks being rip. rip stands for `Routing Information Protocol'. If
  you run gated, configured for rip, your linux machine will
  periodically broadcast a copy of its routing table to your network in
  a special format. In this way, all of the other machines on your
  network will know what addresses are accessible via your machine.

  gated can be used to replace proxy arp when all hosts on your network
  run either gated or routed. If you have a network where you use a
  mixture of manual and dynamic routes, you should mark any manual
  routes as `passive' to ensure that they aren't destroyed by gated
  because it hasn't received an update for them.

  gated would normally be started from your rc.inet2 which is covered in
  the next section. You might already see a daemon called routed
  running. gated is superior to routed in that it is more flexible and
  more functional. So you should use gated and not routed.

  9.4.1.  Obtaining gated

  Gated is available from:


  gated.linux.tgz is the source, so you probably won't need it unless
  you wish to recompile the binaries for some reason.

  9.4.2.  Installing gated

  The gated binary distribution comprises three programs and two sample
  configuration files.

  The programs are:

        the actual gated daemon.

        the operational user interface for gated. gdc is for controlling
        the gated daemon, stopping and starting it, obtaining its status
        and the like.

        a diagnostic tool to query the known routes of a gateway using
        either a `rip query' or a `rip poll'.

  The configuration files are:

        this is the actual configuration file for the gated daemon. It
        allows you to specify how gated will behave when it is running.
        You can enable and disable any of the routing protocols, and
        control the behaviour of those routing protocols running.

        a text file that describes the version number of the gated

  The gated binary distribution will not install the gated files in the
  correct place for you. Fortunately there aren't very many, so its
  fairly simple to do.

  To install the binaries try the following:

       # cd /tmp
       # gzip -dc .../gated.linux.bin.tgz | tar xvf -
       # install -m 500 bin/gated /usr/etc
       # install -m 444 bin/gated.conf bin/gated.version /etc
       # install -m 555 bin/ripquery bin/gdc /sbin
       # rm -rf /tmp/bin

  I keep the networking daemons in /usr/etc, if yours are somewhere else
  then naturally you'll have to change the target directory. The sample
  gated configuration file included configures gated to emulate the old
  routed daemon.
  To install the man files, try the following:

       # cd /tmp
       # gzip -dc .../ | tar xvf -
       # install -m 444 man/*.8 /usr/man/man8
       # install -m 444 man/*.5 /usr/man/man5
       # rm -rf /tmp/man

  The man files contain concise and detailed information on the
  configuration and use of gated. For information on configuring gated,
  refer to the gated-config man page.

  10.  Configuring the network daemons.

  As mentioned earlier, there are other files that you will need to
  complete your network installation. These files concern higher level
  configurations of the network software. Each of the important ones are
  covered in the following sub-sections, but you will find there are
  others that you will have to configure as you become more familiar
  with the network suite.

  10.1.  /etc/rc.d/rc.inet2 (the second half of

  If you have been following this document you should at this stage have
  built an rc file to configure each of your network devices with the
  correct addresses, and set up whatever routing you will need for your
  particular network configuration. You will now need to actually start
  some of the higher level network software.

  Now would be a really good time to read Olaf's Network Administrators
  Guide, as it really should be considered the definitive document for
  this stage of the configuration process. It will help you decide what
  to include in this file, and more importantly perhaps, what not to
  include in this file. For the security conscious it is a fair
  statement to say that the more network services you have running, the
  more likely the chance of your system having a security hole: Run only
  what you need.

  There are some very important daemons (system processes that run in
  the background) that you will need to know a little about. The man
  pages will tell you more, but they are:

  10.1.1.  inetd.

  inetd is a program that sits in the background and manages internet
  connection requests and the like. It is smart enough that you don't
  need to leave a whole bunch of servers running when there is nothing
  connected to them.  When it sees an incoming request for a particular
  service, eg telnet, or ftp, it will check the /etc/services file, find
  what server program needs to be run to manage the request, start it,
  and hand the connection over to it. Imagine it as a master server for
  your internet servers. It also has a few simple standard services
  inbuilt. These are echo, discard and generate services used for
  various types of network testing.

  10.1.2.  syslogd.

  syslogd is a daemon that handles all system logging. It accepts
  messages generated for it and will distribute them according to a set
  of rules contained in /etc/syslogd.conf. For example, certain types of
  messages you will want to send to the console, and also to a log file,
  where others you will want only to log to a file. syslogd allows you
  to specify what messages should go where.

  10.2.  A sample rc.inet2 file.

  The following is a sample rc.inet2 file that Fred built. It starts a
  large number of servers, so you might want to trim it down to just
  those services that you actually want to run. To trim it down, simply
  delete or comment out the stanzas (if to fi) that you don't need. All
  each stanza does is test that the relevant module is a file, that it
  exists, echoes a comment that you can see when you boot your machine,
  and then executes the commands with the arguments supplied to ensure
  that it runs happily in the background. For more detailed information
  on each of the deamons, check either the Network Administrators Guide
  or the relevant man pages.

  #! /bin/sh
  # rc.inet2      This shell script boots up the entire INET system.
  #               Note, that when this script is used to also fire
  #               up any important remote NFS disks (like the /usr
  #               distribution), care must be taken to actually
  #               have all the needed binaries online _now_ ...
  # Version:      @(#)/etc/rc.d/rc.inet2  2.18    05/27/93
  # Author:       Fred N. van Kempen, <>

  # Constants.

  # At this point, we are ready to talk to The World...
  echo -e "\nMounting remote file systems ..."
  /bin/mount -t nfs -v            # This may be our /usr runtime!!!

  echo -e "\nStarting Network daemons ..."
  # Start the SYSLOG daemon.  This has to be the first server.
  # This is a MUST HAVE, so leave it in.
  echo -n "INET: "
  if [ -f ${NET}/syslogd ]
          echo -n "syslogd "

  # Start the SUN RPC Portmapper.
  if [ -f ${NET}/rpc.portmap ]
          echo -n "portmap "

  # Start the INET SuperServer
  # This is a MUST HAVE, so leave it in.
  if [ -f ${NET}/inetd ]
          echo -n "inetd "
          echo "no INETD found.  INET cancelled!"
          exit 1

  # Start the NAMED/BIND name server.
  if [ ! -f ${NET}/named ]
          echo -n "named "

  # Start the ROUTEd server.
  # NOTE: routed is now obselete. You should now use gated.
  #if [ -f ${NET}/routed ]
  #        echo -n "routed "
  #        ${NET}/routed -q #-g -s

  # Start the GATEd server.
  if [ -f ${NET}/gated ]
          echo -n "gated "

  # Start the RWHO server.
  if [ -f ${NET}/rwhod ]
          echo -n "rwhod "
          ${NET}/rwhod -t -s

  # Start the U-MAIL SMTP server.
  if [ -f XXX/usr/lib/umail/umail ]
          echo -n "umail "
          /usr/lib/umail/umail -d7 -bd </dev/null >/dev/null 2>&1 &

  # Start the various INET servers.
  for server in ${IN_SERV}
          if [ -f ${NET}/${server} ]
                  echo -n "${server} "

  # Start the various SUN RPC servers.
  if [ -f ${NET}/rpc.portmap ]
          if [ -f ${NET}/rpc.ugidd ]
                  echo -n "ugidd "
                  ${NET}/rpc.ugidd -d
          if [ -f ${NET}/rpc.mountd ]
                  echo -n "mountd "
          if [ -f ${NET}/rpc.nfsd ]
                  echo -n "nfsd "

          # Fire up the PC-NFS daemon(s).
          if [ -f ${NET}/rpc.pcnfsd ]
                  echo -n "pcnfsd "
                  ${NET}/rpc.pcnfsd ${LPSPOOL}
          if [ -f ${NET}/rpc.bwnfsd ]
                  echo -n "bwnfsd "
                  ${NET}/rpc.bwnfsd ${LPSPOOL}

  echo network daemons started.
  # Done!

  10.3.  Name Resolution.

  Name Resolution is the process of converting a hostname in the
  familiar dotted notation (e.g. into an IP address
  which the network software understands. There are two principal means
  of achieving this in a typical installation, one simple, and one more

  10.3.1.  /etc/hosts

  /etc/hosts contains a list of ip addresses and the hostnames they map
  to. In this way, you can refer to other machines on the network by
  name, as well as their ip address. Using a nameserver (see section
  `named') allows you to do the same name->ip address translation
  automatically. (Running named allows you to run your own nameserver on
  your linux machine).  This file needs to contain at least an entry for with the name localhost. If you're not only using loopback,
  you need to add an entry for your ip address, with your full hostname
  (such as You may also wish to include entries for
  your gateways and network addresses.

  For example, if has the ip address,
  the /etc/hosts file would contain:

       # /etc/hosts
       # List of hostnames and their ip addresses               localhost loomer
       # end of hosts

  Once again you will need to edit this file to suit your own needs. If
  you're only using loopback, the only line in /etc/hosts should be for, with both localhost and your hostname after it.

  Note that in the second line, above, there are two names for and just loomer.  The first name is
  the full hostname of the system, called the "Fully Qualified Domain
  Name", and the second is an alias for it. The second allows you to
  type only rlogin loomer instead of having to type the entire hostname.
  You should ensure that you put the Fully Qualified Domain Name in the
  line before the alias name.

  10.3.2.  named - do I need thee ?

  `I dub thee ..'

  named is the nameserver daemon for many unix-like operating systems.
  It allows your machine to serve the name lookup requests, not only for
  itself, but also for other machines on the network, that is, if
  another machine wants to find the address for `',
  and you have this machines address in your named database, then you
  can service the request and tell other machines what `goobers' address

  Under older implementations of Linux tcp/ip, to create aliases for
  machine names, (even for your own machine), you had to run named on
  your Linux machine to do the hostname to IP address conversion. One
  problem with this is that named is comparitively difficult to set up
  properly, and maintain.  To solve this problem, a program called was made available on Linux systems to translate your
  /etc/hosts file into the many files that make up named database files.
  However even with this problem overcome, named still uses CPU overhead
  and causes network traffic.

  The bottom line is this: You do not need to run named on your Linux
  system. The SLS instructions will probably tell you to run to setup named. This is simply unnecessary unless you
  want to make your Linux system function as a nameserver for other
  machines, in which case you probably should learn some more about
  named anyway. When looking up hostnames, your linux machine will first
  check the /etc/hosts file, and then ask the nameserver out on the net.

  The only reason you may want to run named would be if:

  o  You're setting up a network of machines, and need a nameserver for
     one of them, and don't have a nameserver out on the net somewhere.

  o  Your network administrators want you to run your Linux system as a
     nameserver for some reason.

  o  You have a slow slip connection, and want to run a small cache-only
     nameserver on your Linux machine so that you don't have to go out
     on the serial line for every name lookup that occurs. If you're
     only going to be connecting to a small number of hosts on the net,
     and you know what their addresses are, then you can put them in
     your hosts file and not need to query a nameserver at all.
     Generally namelookup isn't that slow and should work fine over a
     slip link anyway.

  o  You want to run a nameserver for fun and excitement.

  In general, you do NOT need to run named: this means that you can
  comment it out from your rc.inet2 file, and you don't have to run If you want to alias machine names, for example, if you
  want to refer to as just loomer, then you can add as
  alias in /etc/hosts instead. There is no reason to run named unless
  you have a specific requirement to do so. If you have access to a
  nameserver, (and your network administrators will tell you its
  address), and most networks do, then don't bother running named.

  If you're only using loopback, you can run named and set your
  nameserver address to, but since you are the only machine
  you can talk to, this would be quite bizzarre, as you'd never need to
  call it.

  10.3.3.  /etc/networks

  The /etc/networks file lists the names and addresses of your own, and
  other, networks. It is used by the route command, and allows you to
  specify a network by name, should you so desire.

  Every network you wish to add a route to using the route command
  should have an entry in the /etc/networks file, unless you also
  specify the -net argument in the route command line.

  Its format is simliar to that of /etc/hosts file above, and an example
  file might look like:

  # /etc/networks: list all networks that you wish to add route commands
  #                for in here
  default         # default route    - recommended
  loopnet       # loopback network - recommended
  mynet    # Example network CHANGE to YOURS
  # end of networks

  10.3.4.  /etc/host.conf

  The system has some library functions called the resolver library.
  This file specifies how your system will lookup host names. It should
  contain at least the following two lines:

       order hosts,bind
       multi on

  These two lines tell the resolve libraries to first check the
  /etc/hosts file, and then to ask the nameserver (if one is present).
  The multi entry allows you to have multiple IP addresses for a given
  machine name in /etc/hosts.

  This file comes from the implementation of the resolv+ bind library
  for Linux. You can find further documentation in the resolv+(8) man
  page if you have it. If you don't, it can be obtained from:


  This file contains the resolv+.8 man page for the resolver library.

  10.3.5.  /etc/resolv.conf

  This file actually configures the system name resolver, and contains
  two types of entries: The addresses of your nameservers (if any), and
  the name of your domain, if you have one. If you're running your own
  nameserver (i.e running named on your Linux machine), then the address
  of your nameserver is, the loopback address.

  Your domain name is your fully qualified hostname (if you're a
  registered machine on the Internet, for example), with the hostname
  component removed.  That is, if your full hostname is, then your domain name is, without the
  hostname loomer.

  For example, if you machine is, and has a
  nameserver at the address, then your /etc/resolv.conf
  file would look like:


  You can specify more than one nameserver. Each one must have a
  nameserver entry in the resolv.conf file.

  Remember, if you're running on loopback, you don't need a nameserver.

  10.3.6.  Configuring your Hostname - /etc/HOSTNAME

  After you have configured everything else, there is one small task
  that remains, you need to configure your own machine with a name. This
  is so that application programs like sendmail can know who you are to
  accept mail, and so that your machine can identify itself to other
  machines that it might be connected to.

  There are two programs that are used to configure this sort of
  information, and they are commonly misused. They are hostname and

  If you are using a release of net-tools earlier than 1.1.38 then you
  can include a command in your /etc/rc file that looks like this:

       /bin/hostname -S

  and this will cause the hostname command to read a file called
  /etc/HOSTNAME which it expects will contain a "Fully Qualified Domain
  Name", that is, your machines hostname including the domainname. It
  will split the F.Q.D.N. into its DNS hostname and domainname
  components and set them appropriately for you.

  For example, the machine above would have the file /etc/HOSTNAME:

  If you are using the hostname that came with net-tools-1.1.38 or
  later, then you would add a command at the end of your
  /etc/rc.d/rc.inet1 file like:


  or if you have upgraded from a previous release, you could add:

       /bin/hostname -F /etc/HOSTNAME

  and it would behave in the same way as for the earlier version.

  The /bin/domainname command is for setting the N.I.S.  domain name NOT
  the D.N.S. domain name. You do not need to set this unless you are
  running NIS, which is briefly described later.

  10.4.  Other files.

  There are of course many other files in the /etc directory which you
  may need to dabble with later on. Instead of going into them here, I'm
  going to provide the bare minimum to get you on the net. More
  information is available in Olaf's Network Administration Guide. It
  picks up where this HOWTO ends, and some more information will be
  provided in later versions of this document.

  Once you have all of the files set up, and everthing in the right
  place, you should be able to reboot you new kernel, and net away to
  your hearts content.  However I strongly suggest that you keep a
  bootable copy of your old kernel and possibly even a `recovery disk',
  in case something goes wrong, so that you can get back in and fix it.
  You might try HJLu's `single disk boot disk', or `disk1' from an SLS

  11.  Advanced Configurations.

  The configurations above have described how a typical Linux
  workstation might be configured for normal end-user operation. Some of
  you will have other requirements which will require slightly more
  advanced configurations. What follows are examples of some the more
  common of these.

  11.1.  PPP - Point to Point Protocol.

  The Point to Point Protocol is a modern and efficient protocol for
  conveying multiple protocols, tcp/ip for one, across serial links,
  that a lot of people use in place of slip. It offers enhanced
  functionality, error detection and security options. It corrects a
  number of deficiencies that are found in slip, and is suitable for
  both asynchronous links and synchronous links alike.

  An important feature of PPP operation is dynamic address allocation,
  and this feature will almost certainly be exploited by your PPP
  server. This feature allows a PPP client, with a specially formatted
  frame, to request its address from the server. In this way
  configuration is somewhat less messy than with slip, since this
  ability to retrieve your address must occur outside of the protocol.

  The authors of the Linux port are Michael Callahan,
  <> and  Al Longyear, <>.
  Most of this information has come from the documentation that
  accompanies the PPP software. The documentation is quite complete, and
  will tell you much more than I present here.

  The Linux PPP code has come out of Alpha testing and is now available
  as a public release. The 1.0.0 Linux PPP code is based on Paul
  Mackerras's free PPP for BSD-derivative operating systems. The 1.0.0
  release is based on version 2.1.1 of the free PPP code.

  The PPP code comes in two parts. The first is a kernel module which
  handles the assembly and disassembly of the frames, and the second is
  a set of protocols called LCP, IPCP, UPAP and CHAP, for negotiating
  link options, bringing the link into a functioning state and for
  11.1.1.  Why would I use PPP in place of SLIP ?

  You would use PPP in place of SLIP for a few reasons. The most common

     Your Internet Provider supports only PPP
        The most obvious reason you would use PPP in favour of SLIP is
        when your Internet Provider supports PPP and not SLIP. Ok, I
        said it was obvious.

     You have a normally noisy serial line
        PPP provides a frame check sequence for each and every frame
        transmitted, SLIP does not. If you have a noisy serial line, and
        you are using SLIP, your error correction will be performed end
        to end, that is between your machine and the destination
        machine, whereas with PPP the error detection occurs locally,
        between your machine and the PPP server. This makes for faster
        recovery from errors.

     You need to make use of some other feature PPP offers.
        PPP provides a number of features that SLIP does not. You might
        for example want to carry not only IP, but also DECNET, or
        AppleTalk frames over your serial link. PPP will allow you to do

  11.1.2.  Where to obtain the PPP software.

  The ppp software is available from:


  This file contains the kernel source, and the pppd source and binary.
  Version 1.0.0 is meant for use with kernels 1.0.x and 1.1.x. No
  support is currently available for Fred's Net-2E kernel.

  11.1.3.  Installing the PPP software.

  Installation of the PPP software is fairly straightforward.  The kernel driver.

  Some support for ppp has been built into the kernel for some time.
  Configuring the kernel is fairly easy, the following should work ok:

       # cd /usr/src
       # gzip -dc ppp-2.1.2a.tar.gz | tar xvf -
       # cp /usr/src/ppp-2.1.2a/linux/ppp.c /usr/src/linux/drivers/net
       # cp /usr/src/ppp-2.1.2a/pppd/ppp.h /usr/src/linux/include/linux

  You will then need to uncomment the CONFIG_PPP line in
  /usr/src/linux/ If you are running a version of the kernel
  that is 1.1.4 or higher, then you will also need to comment out or
  delete the macro definition of NET02D in the file
  /usr/src/linux/drivers/net/ppp.c. If you are running an even more
  recent version then you make not to make any changes at all.

  You can then do a make config, select PPP support, and follow with a
  make dep;make.

  When you reboot with the new kernel you should see messages at boot
  time that look something like these:

       PPP: version 2.1.1 (4 channels)
       TCP compression code copyright 1989 Regents of the University of California
       PPP line discipline registered.

  Now, try looking at the contents of /proc/net/dev. It should look
  something like this:

         Inter-|   Receive                  |  Transmit
          face |packets errs drop fifo frame|packets errs drop fifo colls carrier
             lo:      0    0    0    0    0        0    0    0    0     0    0
           ppp0:      0    0    0    0    0        0    0    0    0     0    0
           ppp1:      0    0    0    0    0        0    0    0    0     0    0
           ppp2:      0    0    0    0    0        0    0    0    0     0    0
           ppp3:      0    0    0    0    0        0    0    0    0     0    0

  This indicates that the kernel driver is installed correctly.  pppd

  If you want to recompile pppd, type make in the pppd subdirectory of
  the installation.  There will be some warnings when compiling lcp.c,
  upap.c and chap.c but these are OK.

  If you want to recompile chat, consult README.linux in the chat

  To install, type make install in the chat and pppd directories.   This
  will put chat and pppd binaries in /usr/etc and the pppd.8 manual page
  in /usr/man/man8.

  pppd needs to be run as root. You can either make it suid root or just
  use it when you are root. make install will try to install it suid
  root, so if you are root when you try to install it, it should work

  11.1.4.  Configuring and using the PPP software.

  Like slip, you can configure the PPP software as either a client or a
  server.  The chat performs a similar function to the dip program in
  that it is used to automate the dialling and login procedure to the
  remote machine, unlike dip though, it does not perform the ioctl to
  convert the serial line into a PPP line. This is performed by the pppd
  program. pppd can act as either the client or the server. When used as
  a client, it normally invokes the chat program to perform the
  connection and login, and then it takes over by performing the ioctl
  to change the line discipline to ppp and then steps out of the way to
  let you operate.

  Please refer to the pppd and chat man pages for more information.
  Please also refer to the README file that comes with the ppp software,
  as its description of the operation of these utilities is much more
  complete than I have described here.  Configuring a PPP client by dial-up modem.

  This is perhaps what most of you will want to do, so it appears first.
  You would use this configuration when you have a network provider who
  supports ppp by dialup modem. When you want to establish your
  connection you simply have to invoke the pppd program with appropriate

  The following example might look a little confusing at first, but it
  is easier to understand if you can see that all it is doing is taking
  a command line for the chat program as its first argument and then
  others for itself later.

       pppd connect 'chat -v "" ATDT5551212 CONNECT "" ogin: ppp word: password'\
             /dev/cua1 38400 debug crtscts modem defaultroute

  What this says is:

  o  Invoke the chat program with the command line:

       chat -v "" ATDT5551212 CONNECT "" ogin: ppp word: password

  Which says: Dial 5551212, wait for the `CONNECT' string, transmit a
  carriage return, wait for the string `ogin:', transmit the string
  `ppp', wait for the string `word:', transmit the string `password',
  and quit.

  o  Use serial device /dev/cua1

  o  Set its speed to 38400 bps.

  o  debug means log status messages to syslog

  o  crtscts means use hardware handshaking to the modem - recommended.

  o  modem means that pppd will attempt to hang up the call before and
     after making the call.

  o  defaultroute instructs pppd to add a routing entry that makes this
     the default route. In most cases this will be what you want.

  o says to set the ppp interfaces address to
     This argument normally looks like x.x.x.x:y.y.y.y, where x.x.x.x is
     your ip address, and y.y.y.y is the ip address of the server. If
     you leave off the server's address, pppd will ask for it, and
     x.x.x.x will be set to your machines ip address.

  Please refer to the pppd and chat man pages for more information.
  Please also refer to the README file that comes with the ppp software,
  as its description of the above is much more complete than I have
  described here.  Configuring a PPP client via a leased line.

  Configuring a PPP client via a leased line is almost as
  straightforward as for configuring slip with slattach. You will still
  use the pppd program, but since you won't need to establish the modem
  link the arguments to the chat program can be much simpler.

  The example I'm presenting here assumes that the ppp server doesn't
  require any special login procedure. I do this because every login
  procedure will be different, and if you are simply running a local
  connection then it is possible that you might have it set up this way.

       pppd connect 'echo connecting...' defaultroute noipdefault debug \
             kdebug 2 /dev/cua0 9600

  This will echo a message to your screen, and set your default route
  via the ppp interface. The noipdefault argument instructs the pppd
  program to request the address to use for this device from the server.
  Debug messages will go to syslog. The kdebug 2 argument causes the
  debug messages to be set to level 2, this will give you slightly more
  information on what is going on. It will use /dev/cua0 at 9600 bps.

  If your ppp server does require some sort of login procedure, you can
  easily use the chat program as in the example for the dialup server to
  perform that function for you.

  Please refer to the pppd and chat man pages for more information.
  Please also refer to the README file that comes with the ppp software,
  as its description of the above is much more complete than I have
  described here.  Configuring a PPP server.

  Configuring a PPP server is similar to establishing a slip server.
  You can create a special `ppp' account, which uses an executable
  script as its login shell. The /etc/passwd entry might look like:

       ppp:EncPasswd:102:50:PPP client login:/tmp:/etc/ppp/ppplogin

  and the /etc/ppp/ppplogin script might look like:

       exec /usr/etc/pppd passive :

  The address that you provide will be the address that the calling
  machine will be assigned.

  Naturally, if you want multiple users to have simultaneous access you
  would have to create a number of startup scripts and individual
  accounts for each to use, as you can only put one ip address in each

  11.1.5.  Where to obtain more information on PPP, or report bugs.

  Most discussion on PPP for Linux takes place on the PPP mailing list.

  To join the Linux PPP channel on the mail list server, send mail to:

       with the line:

       X-Mn-Admin: join PPP

       at the top of the message body (not the subject line).

  Please remember that when you are reporting bugs or problems you
  should include as much information relevant to the problem as you can
  to assist those that will help you understand your problem.

  You might also like to check out:

  RFCS 1548, 1331, 1332, 1333, and 1334. These are the definitive
  documents for PPP.

  W. Richard Stevens also describes PPP in his book `TCP/IP Illustrated
  Volume 1', (Addison-Wessley, 1994, ISBN 0-201-63346-9).

  11.2.  Configuring Linux as a Slip Server.

  If you have a machine that is perhaps network connected, that you'd
  like other people be able to dial into, and provide network services,
  then you will need to configure your machine as a server. If you want
  to use slip as the serial line protocol, then currently you have two
  options as to how to configure your Linux machine as a slip server. I
  will present a summary of both.

  11.2.1.  Slip Server using sliplogin

  sliplogin is a program that you can use in place of the normal login
  shell for slip users that converts the terminal line into a slip line.
  The caller will login as per the standard login process, entering
  their username and password, but instead of being presented with a
  shell after their login, sliplogin is executed which searches its
  configuration file (/etc/slip.hosts) for an entry with a login name
  that matches that of the caller. If it locates one, it configures the
  line as an 8bit clean line, and uses an ioctl call to convert the line
  discipline to slip. When this process is complete, the last stage of
  configuration takes place, where sliplogin invokes a shell script
  which configures the slip interface with the relevant ip address,
  netmask and sets appropriate routing in place. This script is usually
  called /etc/slip.login, but in a similar manner to getty, if you have
  certain callers that require special initialisation, then you can
  create configuration scripts called /etc/slip.login.loginname that
  will be run instead of the default.  Where to get sliplogin

  sliplogin can be obtained from:


  The tar file contains both source, precompiled binaries and a man
  page.  To install the binaries into your /sbin directory, and the man
  page into section 8, do the following:

       # cd /usr/src
       # gzip -dc .../sliplogin.tar.gz | tar xvf -
       # cd src
       # make install

  If you want to recompile the binaries before installation, add a make
  clean before the make install. If you want to install the binaries
  somewhere else, you will need to edit the Makefile install rule.  Configuring /etc/passwd for Slip hosts.

  You need to create some special logins for Slip callers in your
  /etc/passwd file. A convention commonly followed is to use the
  hostname of the calling host with a capital `S' prefixing it. So, for
  example, if the calling host is called radio then you would create a
  /etc/passwd entry that looked like:

       Sradio:FvKurok73:1427:1:radio slip login:/tmp:/sbin/sliplogin

  Note: the caller doesn't need any special home directory, as they will
  not be presented with a shell from this machine, so /tmp is a good
  choice.  Also note that sliplogin is used in place of the normal login
  shell.  Configuring /etc/slip.hosts

  The /etc/slip.hosts file is the file that sliplogin searches for
  entries matching the login name to obtain configuration details for
  this caller. It is this file where you specify the ip address and
  netmask that will be assigned to the caller, and configured for their
  use. A sample entry for host `radio' might look like:

       Sradio    `hostname`    radio    <netmask>    <opt1>    <opt2>

  The /etc/slip.hosts file entries are:

  1. the login name of the caller.

  2. ip address of the server machine, ie this machine.

  3. ip address that the caller will be assigned.

  4. the netmask assigned to the calling machine in hexadecimal notation
     eg 0xffffff00 for a Class C network mask.

  5. optional parameters to enable/disable compression and other

  Note: You can use either hostnames or IP addresses in dotted decimal
  notation for fields 2 and 3. If you use hostnames then those hosts
  must be resolvable, that is, your machine must be able to locate an ip
  address for those hostnames, otherwise the script will fail when it is
  called. You can test this by trying trying to telnet to the hostname,
  if you get the `Trying nnn.nnn.nnn...'  message then your machine has
  been able to find an ip address for that name.  If you get the message
  `Unknown host', then it has not. If not, either use ip addresses in
  dotted decimal notation, or fix up your name resolver configuration.

  The most commonly used optional paramaters for the opt1 and opt2
  fields are:

        to enable normal uncompressed slip.

---End of part 2/3---

Newsgroups: comp.os.linux.announce,,comp.os.linux.admin,
From: (Terry Dawson)
Subject: Linux NET-2 HOWTO (part 3/3)
Message-ID: <>
Followup-To: poster
Summary: HOWTO configure TCP/IP networking, SLIP, PLIP, and PPP under Linux.
Keywords: Linux, Networking, TCP/IP, NET-2, SLIP
Sender: (Matt Welsh)
Organization: Cornell Univ. CS Dept, Ithaca NY 14853
References: <>
Date: Fri, 18 Nov 1994 17:13:11 GMT
Approved: (Matt Welsh)
Lines: 1185

Archive-name: linux/howto/networking/part3
Last-modified: 18 Nov 94

---This is part 3/3---

        to enable van Jacobsen header compression (cslip)

  Naturally these are mutually exclusive, you can use one or the other.
  For more information on the other options available, refer to the man
  pages.  Configuring the /etc/slip.login file.

  After sliplogin has searched the /etc/slip.hosts and found a matching
  entry, it will attempt to execute the /etc/slip.login file to actually
  configure the slip interface with its ip address and netmask.

  The sample /etc/slip.login file supplied with the sliplogin package
  looks like this:

  #!/bin/sh -
  #       @(#)slip.login  5.1 (Berkeley) 7/1/90
  # generic login file for a slip line.  sliplogin invokes this with
  # the parameters:
  #      1        2         3        4          5         6     7-n
  #   slipunit ttyspeed loginname local-addr remote-addr mask opt-args
  /sbin/ifconfig $1 $4 pointopoint $5 mtu 1500 -trailers up
  /sbin/route add $5
  exit 0

  You will note that this script simply uses the ifconfig and route
  commands to configure the slip device with its ipaddress, remote ip
  address and netmask, and creates a route for the remote address via
  the slip device. Just the same as you would if you were using the
  slattach command.  Configuring the /etc/slip.logout file.

  When the call drops out, you want to ensure that the serial device is
  restored to its normal state so that future callers will be able to
  login correctly.  This is achieved with the use of the
  /etc/slip.logout file. It is quite simple, and again, I'll present the
  sample included in the sliplogin package.

       #!/bin/sh -
       #               slip.logout
       /sbin/ifconfig $1 down
       /sbin/route del $5
       exit 0

  All it does is `down' the interface and delete the manual route
  previously created.

  11.2.2.  Slip Server using dip.

  Let me start by saying that some of the information below came from
  the dip man pages, where how to run Linux as a slip server is briefly

  To configure Linux as a slip server, you need to create some special
  slip accounts for users, where dip (in slave mode) is used as the
  login shell. Fred suggests that he has a convention of having all of
  his slip accounts begin with a capital `S', eg `Sfredm'.

  Because the login program won't accept arguments to the login shell,
  you will need to create a small program that looks like the following:

  /* dip-i.c - from a mail message of Karl kke...@esoc.bitnet */
  int main()
     execlp("dip", "dip", "-i", (char *) 0);

  Compile it with: gcc -O dip-i.c -o dip-i

  Give it permissions 555. I recommend calling it /usr/bin/dip-i as
  shown below.

  A sample /etc/passwd entry for a slip user looks like:

       ^^         ^^        ^^  ^^   ^^    ^^   ^^
       |          |         |   |    |     |    \__ shell program running
       |          |         |   |    |     |         dip -i as login shell
       |          |         |   |    |     \_______ Home directory
       |          |         |   |    \_____________ User Full Name
       |          |         |   \__________________ User Group ID
       |          |         \______________________ User ID
       |          \________________________________ Encrypted User Password
       \___________________________________________ Slip User Login Name

  After the user logs in, the login(1) program, if it finds and verifies
  the user ok, will execute the shell program dip-i which will execute
  the dip command in input mode (-i). dip now scans the
  /etc/net/diphosts file for an entry for the given user name.
  Therefore, each slip user must also have an entry in

  You will have to re-read section `Proxy Arp' to arrange for your
  machine to proxy arp for the slip users who will be using your system
  if you want them to have access to any network that your server
  machine might be connected to.  Configuring /etc/net/diphosts

  /etc/net/diphosts is used by dip to lookup preset configurations for
  remote hosts. These remote hosts might be users dialing into your
  linux machine, or they might be for machines that you dial into with
  your linux machine.

  The general format for /etc/net/diphosts is as follows:

  Suwalt:: uwalt:CSLIP,1006
   ^    ^  ^            ^         ^     ^
   |    |  |            |         |     \___ MTU
   |    |  |            |         \_________ protocol (SLIP, CSLIP,
   |    |  |            |                    KISS)
   |    |  |            \___________________ comment field
   |    |  \________________________________ IP address of the other
   |    |                                    side, or
   |    \___________________________________ unused (compat. with passwd)
   \________________________________________ login name (as returned by

  An example /etc/net/diphosts entry for a remote slip user might be:

       Sfredm:: uwalt:SLIP,296

  which specifies a slip link with MTU of 296, or

       Sfredm:: uwalt:CSLIP,1006

  which specifies a cslip-capable link with MTU of 1006.

  When a user logs in, they will receive a normal login, and password
  prompt, at which they should enter their slip-login userid and
  password. If they check out ok, then the user will see no special
  messages, they should just change into slip mode at their end, and
  then they should be able to connect ok, and be configured with the
  parameters from the diphosts file.

  11.3.  Using the Automounter Daemon - AMD.

  This section has been supplied by Mitch DSouza, and I've included it
  with minimal editing, as he supplied it. Thanks Mitch.

  11.3.1.  What is an automounter, and why would I use one ?

  An automounter provides a convenient means of mounting filesystems on
  demand, i.e. when requried. This will reduce both the server and the
  client load, and provides a great deal of flexibility even with non-
  NFS mounts. It also offers a redundancy mechanism whereby a mount
  point will automatically switch to a secondary server should a primary
  one be unavailable. A rather useful mount called the union mount gives
  the automounter the ability to merge the contents of multiple
  directories into a single directory. The documentation msut be read
  thoroughly to make full use of its extensive capabilities.

  A few important points must be remembered - (in no particular order):

  o  amd maps are not compatible with Sun maps, which in turn are not
     compatible with HP maps ad infinitum. The point here however is
     that amd is freely available and compatible with all the systems
     mentioned above and more, thus giving you the ability to share maps
     if amd is installed throughout your network. Mitch uses it with a
     mixture of Linux/Dec/NeXt/Sun machines.

  o  Sun automount maps can be converted to amd style maps by using the
     perl script in the contrib directory -

  o  You must have the portmapper running before starting amd.

  o  UFS mounts do not timeout.

  o  UFS mounts, in the case of Linux only, have been extended to deal
     with all varieties of native filesystems (i.e. minix, ext, ext2,
     xiafs ...) with the default being minix. This undocumented feature
     is accessed in the opts option like:

        ..., opts:=type=msdos,conv=auto

  o  Do not mount over existing directories unless you use a direct
     automount option, otherwise it is like mounting your disk on /home
     when some user directory is /home/fred.

  o  Always turn on full logging with the `-x all' option to amd if you
     have any troubles. Check also what the command:

       % amq -ms

  reports, as it will indicate problems as they occur.

  o  GNU getopt() is too clever for its own good sometimes. You should
     always use `--' before the non-options e.g.

       # /etc/amd -x all -l syslog -a /amd -- /net /etc/

  11.3.2.  Where to get AMD, the automounter daemon.

  amd can be obtained from:


  This contains ready-to-run binaries, full sources and documentation in
  texinfo format.

  11.3.3.  An example AMD configuration.

  You do not configure the automounter from the /etc/fstab file, which
  you will already be using to contain information about your
  fileystems, instead it is command line driven.

  To mount two nfs filesystems using your /etc/fstab file you would use
  two entries that looked like:

       server-1:/export/disk  /nfs/server-1  nfs  defaults
       server-2:/export/disk  /nfs/server-2  nfs  defaults

  i.e. you were nfs mounting server-1 and server-2 on your linux disk on
  the /nfs/server-1 and /nfs/server-2 directories.

  After commenting out, or deleting the above lines from your /etc/fstab
  file, you could amd to perform the same task with the following

       /etc/amd -x all -l syslog -a /amd -- /nfs /etc/amd.server
       |      | |    | |       | |     |  | |  | |             |
       |      | |    | |       | |     |  | |  | |             |
       `------' `----' `-------' `-----' -' `--' `-------------'
        |        |      |         |      |   |    |
        (1)      (2)    (3)       (4)    (5) (6)  (7)


  1. The full amd binary path (obviously optional) depending on your
     $PATH setting, so just `amd' may be specified here.

  2. `-x all' means turn full logging on. Read the documentation for the
     other logging levels

  3. `-l syslog' means log the message via the syslog daemon. This could
     mean put it to a file, dump it, or pass it, to an unused tty
     console. This (syslog) can be changed to the name of a file, i.e.
     `-l foo' will record to a file called foo.

  4. `-a /amd' means use the /amd directory as a temporary place for
     automount points. This directory is created automatically by amd
     and should be removed before starting amd in your /etc/rc scripts.

  5. `--' means tell getopt() to stop attempting to parse the rest of
     the command line for options. This is especially useful when
     specifying the `type:=' options on the command line, otherwise
     getopt() tries to decode it incorrectly.

  6. `/nfs' is the real nfs mount point. Again this is automatically
     created and should not generally contain subdirectories unless the
     `type:=direct' option is used.

  7. The amd map (i.e. a file) named `amd.server' contains the lines:

  # /etc/amd.server
  /defaults    opts:=rw;type:=nfs
  server-1     rhost:=server-1;rfs:=/export/disk
  server-2     rhost:=server-2;rfs:=/export/disk

  Once started and successfully running, you can query the status of the
  mounts with the command:

       % amq -ms

  Now if you say:

       % ls /nfs

  you should see no files. However the command:

       % ls /nfs/server-1

  will mount the host `server-1' automatically. voila! amd is running.
  After the default timeout has expired, this will automatically be
  unmounted. Your /etc/password file could contain entries like:

       mitch:EncPass:20:10:Mitch DSouza:/nfs/server-1/home/mitch:/bin/tcsh
       matt:EncPass:20:10:Matt Welsh:/nfs/server-1/home/matt:/bin/csh

  which would mean that when Linus, Matt, or Mitch are logged in, their
  home directory will be remotely mounted from the appropriate server,
  and umounted when they log out.

  11.4.  Using Linux as a router

  Linux will function just fine as a router. You should run a routing
  daemon such as gated, or if you have simple routing requirements use
  hard coded routes. If you are using a late version kernel (1.1.*) then
  you should ensure that you have answered `y' to:

  IP forwarding/gatewaying (CONFIG_IP_FORWARD) [y] y

  when building your kernel.

  Olaf Kirch's Network Administrators Guide discusses network design and
  routing issues, and you should read it for more information. A
  reference to it is in the "Related Documentation" section of this

  12.  Experimental and Developmental modules.

  There are a number of people developing new features and modules for
  the Linux networking code. Some of these are in quite an advanced
  state (read working), and it is these that I intend to include in this
  section until they are standard release code, when they will be moved

  12.1.  AX.25 - A protocol used by Amateur Radio Operators.

  The AX.25 protocol is used by Amateur Radio Operators worldwide.  It
  offers both connected and connectionless modes of operation, and is
  used either by itself for point-point links, or to carry other
  protocols such as tcp/ip and netrom.

  It is similar to X.25 level 2 in structure, with some extensions to
  make it more useful in the amateur radio environment.

  Alan Cox has developed some kernel based AX.25 software support for
  Linux and these are available in ALPHA form for you to try. Alan's
  code supports both KISS based TNC's (Terminal Node Controllers), and
  the Z8530 SCC driver.

  The User programs contain a P.M.S. (Personal Message System), a beacon
  facility, a line mode connect program, and `listen' an example of how
  to capture all AX.25 frames at RAW interface level.

  Be sure to read /usr/local/ax25/README as it contains more complete
  information regarding this software.

  12.1.1.  Where to obtain the AX.25 software.

  The AX.25 software is available from:


  You will find a number of directories, each containing different
  versions of the code. Since it is closely linked with the kernel code,
  you will need to ensure that you choose the version appropriate for
  the kernel version you are running. The following table shows the
  mapping between the two:

  AX25007                 Prehistoric
  AX25010                 Obsolete
  AX25012                 for release 1.0.* kernels and higher
  AX25016                 for release 1.1.5 kernels
  AX25017                 for release 1.1.6 kernels
  AX25022                 for release 1.1.28 kernels

  In each directory you will find at least two files, one called
  something like krnl022.tgz, and the other called something like
  user022.tgz.  These are the kernel software, and the user programs

  12.1.2.  Installing the AX.25 software.

  The software comes in two parts, the kernel drivers, and the user
  programs.  The kernel drivers.

  To install the kernel drivers, do the following:

       # cd /usr/src
       # gzip -dc krnl022.tgz | tar xvf -

  you will need to uncomment the CONFIG_AX25 define in the
  /usr/src/linux/ file.

  You should then:

       # cd /usr/src/linux
       # make config
       # make dep;make

  Be sure to answer `yes' when you are asked if you should include the
  AX.25 support in the make config step. You will also need to answer
  `yes' to inluding SLIP if you want the AX.25 code to support a KISS
  TNC.  The user programs.

  To install the user programs you should try:

       # cd /
       # gzip -dc user022.tgz | tar xvvof -

  You should then:

       # cd /usr/local/ax25/src
       # make install

  12.1.3.  Configuring and using the AX.25 software.

  Configuring an AX.25 port is very similar to configuring a slip
  device.  The AX.25 software has been designed to work with a TNC in
  kiss mode. You will need to have the TNC preconfigured and connected.

  You use the axattach program in much the same way as you would use the
  slattach program. For example:

       # /usr/local/ax25/bin/axattach -s 4800 /dev/cua1 VK2KTJ &

  would configure your /dev/cua1 serial device to be a kiss interface at
  4800 bps, with the hardware address VK2KTJ.

  You would then use the ifconfig program to configure the ip address
  and netmask as for an ethernet device:

       # /sbin/ifconfig sl0
       # /sbin/ifconfig sl0 netmask
       # /sbin/ifconfig sl0 broadcast
       # /sbin/ifconfig sl0 arp mtu 257 up

  To test it out, try the following:

       /usr/local/ax25/bin/call VK2DAY via VK2RVT

  The call program is a linemode terminal program for making ax.25
  calls. It recognises lines that start with ` ' as command lines.  The
  ` .' command will close the connection.

  You also need to configure some items such as the window to use. This
  necessitates editing only one file. Edit the /usr/local/ax25/etc/ports
  file. This is an ascii file containing one line for each AX.25 port.
  You must have the entries in this file in the same order as you
  configure your AX.25 interfaces.

  The format is as follows:

  callsign baudrate window frequency

  At this stage not much of this information is used, it will be picked
  up and used in later developments.

  I haven't had a chance to try this code out yet. Please refer to the
  man pages in /usr/local/ax25/man and the README file in
  /usr/local/ax25 for more information.

  12.2.  Z8530 SCC driver.

  The Zilog Z8530 SCC provides Synchronous/Asynchronous, HDLC, NRZI
  encoding and other capabilities. There are a number of peripheral
  cards that use the Z850 as the basis of their design. A driver has
  been written by Joerg Reuter, <>, and
  is available on:


  Please read the README file that accompanies the driver for more

  12.3.  Ottawa PI/PI2 card driver.

  The Ottawa PI card is a Z8530 SCC based card for IBM PC type machines
  that is in common usage by Amateur Radio operators worldwide. While it
  is most commonly used by Amateur Radio Operators, it could be pressed
  into service in other fields where it is desirable to have the
  features of a Z8530. It supports a high speed half duplex (single DMA
  channel) port, and a low speed (<19.2kbps interrupt driven) full
  duplex port. The PI2 is a new version of the card that supports an on
  board radio modem, and improved hardware design.

  A driver for this card has been written by David Perry,
  <>, and is available from:


  Please read the README file that accompanes the driver for more

  12.4.  NIS - Sun Network Information System.

  There are in fact two NIS implementations being distributed. Firstly
  there is a rudimentary implementation in the standard libc ditribution
  which however requires binding to servers via ypbind before use.  A
  more clean implementation tending towards the NIS+ implementation is
  called NYS, is written by Peter Eriksson, <> and is
  available from:


  An NIS style server can be retrieved from:


  Check there are no newer versions, as this information might now be
  slightly dated.

  Both of these are fully functional and they have been used extensively
  with no troubles to query Sun servers for NIS information like
  passwd/hosts/group etc.  and don't require binding to arbitrary
  servers. In fact they allow you to specify servers for services and
  have the ability to select a yp/dns/file option for name/passwd/etc.
  resolution of specific services. They are extremely easy to set up,
  and recommended for client machines integrating into larger networks.

  Clearly your network daemons and clients need to be recompiled to link
  with the shared library to make use of the YP facilities.
  This is fairly trivial and an NYS package of all network clients and
  daemons is currently being compiled.

  If you have more detailed information on NIS, please email me.

  12.5.  snmp agent.

  There is an experimental snmp agent for linux, ported by Erik
  Schoenfelder, <>.

  It is available from:


  Please read the file called cmu-snmp2.1.2l2.README, as it contains
  information that you will need to know about the package.

  This package provides a nearly complete MIB-II variable set. At this
  stage though, you can only read variables, not set them.

  nstat.tar.gz contains a formatter of the output from /proc/net/snmp
  called nstat.

  You will need to be running either a new version kernel, or apply
  patches to your kernel source. Details are in the README file.

  12.6.  Experimental ARCNet driver

  There have been a number of people looking for a driver for ARCNet
  cards.  ARCNet cards provide only rates of about 2Mbps, but are
  capable of being supported via longer length cables than for 10base2
  (thinnet) type lans. ARCNet cards are also likely to be fairly cheap,
  as many businesses are gradually replacing their ARCNet networks with
  other lan types.

  Avery Pennarun <> has produced an
  experimental ARCNet driver for Linux. It is ALPHA which means you
  should try it knowing that it probably still contains many errors and
  might even cause you other problems like kernel hangs.

  The source code and kernel patch for the driver are available at:


  Note: For ease of patching you will require kernel version 1.1.51 as
  this is what the patch was made against, though it might also work
  either 1.1.45 and up.

  There are some known bugs, you can obtain details of these by reading
  the top of the arcnet.c file.

  Avery is now at the stage where he needs people to try the driver to
  discover any bugs or problems that he hasn't been able to find, and to
  guage how well it works in other environments.  Avery will happily
  accept any reports via the NET channel, or by email to home at either
  <>, or <Avery.Penna...@NorLinK.Com>.
  Avery has problems with News, so bug reports via any of the Linux
  newsgroups might not make it to him.  Avery wants to know not only if
  you have problems, but also if you have success.

  12.7.  Experimental Token Ring driver

  An experimental Token Ring driver is being developed by Peter De
  Schrijver <>. His latest version, at the time
  of writing was available at:


  12.8.  V.35 interface board

  V.35 is a C.C.I.T.T. standard interface that provides a high speed
  balanced serial interface suitable for speeds up to about 2 Mbps. The
  use of differential pair balanced transmission allows the V.35
  interface to support longer cables than can the more familiar
  V.24/RS232C type interface and higher data rates.

  Pete Kruckenberg <> located a company that
  supplies V.35 interface hardware for ISA bus machines. The company is
  also developing a Linux driver for this card that is nearing Beta
  testing stage.  This would allow you to directly connect your Linux
  machine to a 48/56kbps synchronous leased line. The card supports
  multiple protocols and allows for interface speeds of up to 12 Mbps.

  More information is available from:


  or you can email Dale Dhillon <>

  12.9.  Slip Management Suite

  Matthew Dillon, has assembled a suite of
  programs for managing slip connections, both incoming and outgoing.
  Some of the software's features are automatic dialling out, automatic
  redial on failure, and shifting between slip connections on a single
  serial port.

  Matt has tested the code with version 1.1.x kernels, but says it
  should also compile and run ok with version 1.0.x kernels.

  You can obtain the software from:
  ( or from:

  12.10.  tcpdump utility

  Adam Caldwell <> has ported the tcpdump
  to linux. tcpdump allows you to take traces of network activity by
  intercepting the datagrams on their way in and out of your machine.
  This is useful for diagnosing difficult to identify network problems.

  Both binary and sources are available, and version 3.0 has been tested
  on kernel versions 0.99.15, 1.0.8 and 1.1.28.

  You can find the source and binaries at:
  ( or

  13.  Some Frequently Asked Questions, with brief Answers.

  Following are some questions and answers that are commonly asked.

  13.1.  General questions:

     I have only a dialin terminal access to a machine on the net, can I
        this as a network connection ?"  Yes you can, take a look at
        TERM. TERM allows you you to run network connections over a
        normal terminal session. It requires some modifications to the
        network applications to work with it, but binaries and sources
        are available for the most common ones already. take a look at
        the TERM-HOWTO (
        HOWTO.html) for lots more information.

     I want to build my own standalone network, what addresses do I use
        RFC1597 has specifically reserved some IP addresses for private
        networks.  You should use these as they prevent anything nasty
        happening if you accidentally get connected to the Internet. The
        addresses reserved are:


     Note, reserved network addresses are of classes A, B and C, so you
     are not restricted in your network design or size. Since you won't
     be connecting to the Internet it doesn't matter if you use the same
     address as some other group or network, just so long as the
     addresses you use are unique within your network.

     If is down, how do I get the files specified ?
        `sunacm' is mirrored on:



     How do I know what version of kernel/net code I am running ?
        The network code and kernel now have synchronised version
        numbers, so try:

        uname -a


        cat /proc/version

  13.2.  Error messages:

     I keep getting the error `eth0: transmit timed out'. What does this
        This usually means that your Ethernet cable is unplugged, or
        that the setup parameters for your card (I/O address, IRQ, etc.)
        are not set correctly.  Check the messages at boot time and make
        sure that your card is recognized with the correct Ethernet
        address. If it is, check that there is no conflict with any
        other hardware in your machine, eg you might have a soundblaster
        sharing the same IRQ or i/o control port.

     I get errors `check Ethernet cable' when using the network.
        You probably have your Ethernet card configured incorrectly.
        Double check the settings in /usr/src/linux/drivers/net/CONFIG.
        If this checks out ok, you may in fact have a cabling problem,
        check the cables are plugged in securely.

  13.3.  Routing questions:

     Why do I get the message `obselete route request' when I use the
        route command ?
        You are using a version of route that is older than your kernel.
        You should upgrade to a newer version of route. Refer to the
        "The network configuration tool suite" section of this document
        for information on where to obtain the tool set.

     Why do I get a `network unreachable' message when I try and net-
        This message means that yours, or some other, machine doesn't
        know how to route to the host that you are attempting to ping or
        connect to. If it occurs for all hosts that you try, then it is
        probable that you don't have your default route set up properly,
        reread the `routing' section.

     I can ping my server/gateway, but can't ping or connect to anyone
        This is probably due to a routing problem. Reread the `routing'
        section in this document. If this looks ok, then make sure that
        the host you are attempting to connect to has a route to you. If
        you are a dialin user then this is a common cause of problems,
        ensure that your server is either running a routing program like
        gated or routed, or that it is `prox arping' for you, otherwise
        you will be able to get datagrams to the remote host, but it
        won't know how to return datagrams to you.

  13.4.  Using Linux with fileservers/NFS:

     How do I use my existing Novell fileserver with my Linux machine ?
        If you have the Novell NFS Daemon code then it is easy, just NFS
        mount the Novell volume that you wish to use. If you don't, and
        you are really desperate to be able to do this, and you have a
        spare pc machine laying about, you are in luck. You can run a
        program called Stan's Own Server on the spare PC. First,
        configure the pc as a novell workstation with maps to the
        directories you want to nfs mount, then run SOS, and export
        those drive maps.  SOS is available from

     Files get corrupted when running NFS over a network.
        Certain vendors (Sun primarily) shipped many machines running
        NFS without UDP checksums. Great on ethernet, suicide otherwise.
        UDP checksums can be enabled on most file servers. Linux has it
        enabled by default from pl13 onwards - but both ends need to
        have it enabled...

     Why are my NFS files all read only ?
        The Linux NFS server defaults to read only. RTFM the `exports'
        and nfsd manual pages. With non Linux servers you may also need
        to alter /etc/exports

  13.5.  slip questions:

     What do I do if I don't know my slip servers address ?
        dip doesn't really need to know the address of your slip server
        for slip to function. The remote option was added as a
        convenience so that dip could automate the ifconfig and route
        commands for you. If you don't know, and cannot find out the
        address of your slip server then Peter D. Junger has suggested that he simply used
        his own address wherever a dip script called for a remote
        address. This is a small kludge but it works ok, as the server's
        address never actually appears in the slip headers anyway.

     `dip' only works for root. How do I make it work for others?
        dip needs to be suid root to perform some of the tasks necessary
        to do its job, so check that the file permissions of dip are
        6750. On some systems dip is actually a symbolic link to another
        file, such as dip.uri, if this is how yours is setup then make
        the change to that file instead. Something like `chmod 6750 dip'
        should work ok. Check also that dip is owned by root: `chown
        root:dip dip'.

     With SLIP I can ping my server, and other hosts, but telnet or ftp
        work."  This is most likely caused by a disagreement on the use
        of header compression between your server and your machine.
        Double check that both ends either are, or are not, using
        compression. They must match.

     How can I hang up the phone line when I'm done using SLIP?
        If you use dip to dial out on the SLIP line, just `dip -k'
        should do the trick. If not, try to kill the dip process that is
        running. When dip dies it should hang up the call. To give it
        the best chance to clean up after itself, try killing the
        process in the following sequence: `kill <pid>', `kill -hup
        <pid>', and finally, if the dip process still refuses to die,
        try `kill -9 <pid>'. The same philosophy should be applied to
        all unix processes that you are attempting to kill.

     I see a lot of overrun errors on my slip port, why ?
        The older network tools incorrectly report number of packets
        compressed as the number of packets overrun. This has been
        corrected, and shouldn't occur of you are running the new
        version kernel and tools. If it still is it probably indicates
        that your machine isn't keeping up with the rate of data
        incoming. If you are not using 16550AFN UARTs then you should
        upgrade to them. 16450, or 8250 generate an interrupt for every
        character they receive and are therefore very reliant on the
        processor to be able to find time to stop what it is doing an
        collect the character from them to ensure none get lost. The
        16500AFN has a 16 character FIFO, and they only generate
        interrupts when the FIFO is nearly full, or when they have had
        character waiting, this means that less interrupts get generated
        for the same amount of data, and that less time is spent
        servicing your serial port. If you want to use multiple serial
        ports you should mandatorily upgrade to 16550AFN UARTs anyway.

     Can I use two slip interfaces ?
        Yes. If you have, for example, three machines which you would
        like to interconnect, then you most certainly could use two slip
        interfaces on one machine and connect each of the other machines
        to it. Simply configure the second interface as you did the
        first. NOTE that the second interface will require a different
        IP address to the first. You may need to play with the routing a
        bit to get it to do what you want, but it should work.

     I have a multiport i/o card, how do I use more than 4 slip ports ?
        The kernel slip comes with a default of a maximum of 4 slip
        devices configured, this is set in the
        /usr/src/linux/drivers/net/slip.h file.  To increase it, say to
        16, change the #define SL_NRUNIT to 16, in place of the 4 that
        will be there. You also need to edit
        /usr/src/linux/drivers/net/Space.c and add sections for sl4, sl5
        etc. You can copy the existing driver definition as a template
        to make it easier. You will need to recompile the kernel for the
        change to take effect.

  14.  Known Bugs.

  The Linux networking code is still an evolving thing. It still has
  bugs though they are becoming less frequently reported now. The Linux
  Networking News ( is a World
  Wide Web page maintained by Alan Cox which contains information on the
  status of the NET-3 networking code. You can obtain information on
  what is known and what isn't, by reading the
  /usr/src/linux/net/inet/README file that accompanies the kernel
  source, or by joining the NET channel.

  15.  Copyright Message.

  The NET-2-HOWTO is copyright by Terry Dawson and Matt Welsh. A
  verbatim copy of this document may be reproduced and distributed in
  any medium, physical or electronic without permission of the authors.
  Translations are similarly permitted without express permission if
  such translations include a notice stating who performed the
  translation, and that it is a translation.  Commercial redistribution
  is allowed and encouraged, however, the authors would like to be
  notified of any such distributions.

  Short quotes may be used without prior consent by the authors.
  Derivative works and partial distributions of the NET-2-HOWTO must
  include either a verbatim copy of this file, or make a verbatim copy
  of this file available.  If the latter is the case, a pointer to the
  verbatim copy must be stated at a clearly visible place.

  In short, we wish to promote dissemination of this information through
  as many channels as possible. However, we wish to retain copyright on
  this HOWTO document, and would like to be notified of any plans to
  redistribute it.  Further we desire that ALL information provided in
  this HOWTO be disseminated.

  If you have any questions relating to the conditions of this
  copyright, please contact Matt Welsh, the Linux HOWTO coordinator, at:
  16.  Miscellaneous, and Acknowledgements.

  This HOWTO has been completely rewritten using the new smgl tools that
  Matt Welsh put together. The tools seem to work just fine, and they
  are pretty simple to use. There are so many people who have
  contributed comments and suggestions for this update that I have
  forgotten who you are. Thanks.

  Please, if you have any comments or suggestions then mail them to me.
  I'm fairly busy these days, so I might not get back to you straight
  away, but I will certainly consider any suggestion you have.

  The Linux networking code has come a long way, and it hasn't been an
  easy trip, but the developers, all of them, have done an excellent job
  in getting together something that is functional, versatile, flexible,
  and free for us to use. We all owe them a great debt of thanks. Linus,
  Ross, Fred, Alan, the Alpha/Beta testers, the tools developers, and
  those offering moral support have all contributed to the code as it is

  For those that have an itch they want to scratch, happy hacking, here
  it is.


  Terry Dawson, vk2ktj.

  <>, or <>

			  SCO's Case Against IBM

November 12, 2003 - Jed Boal from Eyewitness News KSL 5 TV provides an
overview on SCO's case against IBM. Darl McBride, SCO's president and CEO,
talks about the lawsuit's impact and attacks. Jason Holt, student and 
Linux user, talks about the benefits of code availability and the merits 
of the SCO vs IBM lawsuit. See SCO vs IBM.

Note: The materials and information included in these Web pages are not to
be used for any other purpose other than private study, research, review
or criticism.