Linux NET-2/NET-3 HOWTO
Terry Dawson,
[email protected]
v2.3, 03 Jul 1994
This document aims to describe how to obtain, install and configure
the Linux NET-2 and NET-3 networking software.
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.
Additions:
Z8530 SCC Driver information.
sliplogin based slip server config.
installing kernel patches.
Corrections:
typing mistakes, thanks everyone who contributed here.
moved PPP out of developmental and into Advanced configurations.
Some PPP and other corrections from Al Longyear. Ta.
1.2. A brief development history of Linux Networking.
Ross Biro <
[email protected]> wrote the original kernel based
networking code for Linux. He used ethernet drivers written by Donald
Becker <
[email protected]>, a slip driver written by
Laurence Culhane <
[email protected]>, and a D-Link driver by
Bj0rn Ekwall <
[email protected]>.
The further development of the Linux networking code was later taken
up by Fred van Kempen <
[email protected]>, 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
<
[email protected]> 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
released.
PPP support was added by Michael Callahan, <
[email protected]>
and Al Longyear, <
[email protected]>, 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
and corrections.
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
comp.os.linux.help, 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
mandatory.
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 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:
[email protected]
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
discussions 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.
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:
sunsite.unc.edu
/pub/Linux/docs/linux-doc-project/network-guide/*
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
(
ftp://sunsite.unc.edu/pub/Linux/docs/HOWTO/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 (
http://sunsite.unc.edu/mdw/HOWTO/Serial-HOWTO.html)
if you intend using slip or ppp in server mode.
The Mail-HOWTO (
http://sunsite.unc.edu/mdw/HOWTO/Mail-HOWTO.html) and
the News-HOWTO (
http://sunsite.unc.edu/mdw/HOWTO/News-HOWTO.html) for
some specific information on setting up Mail and News on your system.
The UUCP-HOWTO (
http://sunsite.unc.edu/mdw/HOWTO/UUCP-HOWTO.html) 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:
athos.rutgers.edu
/runet/tcp-ip-admin.doc
/runet/tcp-ip-admin.ps
/runet/tcp-ip-intro.doc
/runet/tcp-ip-intro.ps
4.1. New versions of this document.
The latest released version of this document can be retrieved by
anonymous ftp from:
sunsite.unc.edu
/pub/Linux/docs/HOWTO/NET-2-HOWTO
/pub/Linux/docs/HOWTO/other-formats/NET-2-HOWTO.{tex,ps,dvi}
via the World Wide Web from the Linux Documentation Project Web Server
(
http://sunsite.unc.edu/mdw/linux.html), at page: NET-2-HOWTO
(
http://susnite.unc.edu/mdw/HOWTO/NET-2-HOWTO.html) or directly from
me, <
[email protected]>. It will also be posted to the
newsgroups: comp.os.linux.announce, comp.os.linux.help, and
news.answers periodically.
You can find news.answers FAQ postings, including this one, archived
on rtfm.mit.edu:/pub/usenet.
4.2. Feedback.
Please send any comments, updates, or suggestions to me,
<
[email protected]>. 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.
The NET-2 and NET-3 network code does not yet currently support:
SPX/IPX/NCP (Novell) support
to allow Linux to serve and mount Novell network devices. This
is being worked on. It can though act as an IPX router.
Lan types other than ethernet
This means token ring, arcnet, FDDI, etc. An experimental Token
Ring driver is being developed.
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 and close compatibles.
o 3c501 and close compatibles (not recommended).
o 3c503 and close compatibles.
o 3c509/3c579 and close compatibles.
o HP PCLAN and close compatibles.
o AT1500 and NE2100 (LANCE and PCnet-ISA) and close compatibles.
o AT1700 and close compatibles.
o DEPCA and close compatibles.
o D-Link DE600 pocket adaptor and close compatibles.
o D-Link DE620 pocket adaptor (with newer kernel releases)
o AT-LAN-TEC/RealTek pocket adaptor and close compatibles.
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
Linux.
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 release 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 could stick to this release, and 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 their have been many changes in the
newer version kernels that affect networking.
The current kernel version is found in:
ftp.funet.fi
/pub/OS/Linux/PEOPLE/Linus/v1.1/v1.1.23.tar.gz
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.1.1.23.tar.gz | tar xvf -
You may also find some files called patch1.gz ... in the same
directory. These are patch files. If you have a linux kernel that is
version 1.1.23 then what this means is that you have linux kernel
version 1.0 with patches 1 to 23 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 with the following command:
# 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:
sunsite.unc.edu
/pub/Linux/GCC/
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:
sunacm.swan.ac.uk
/pub/misc/Linux/Networking/Programs/System/net032/*
In this directory you will find a number of versions of the network
tools. 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 following table lists
net-032 package name with the relevant kernel versions:
net3-net032d.tar.gz 1.1.12+
net032b.tar.gz 1.1.4+
net032.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. The
tcp/ip application binaries and setup files are found in:
tsx-11.mit.edu
/pub/linux/packages/net/net-2/binaries/net-std.tar.z
/pub/linux/packages/net/net-2/binaries/net-ext.tar.z
NOTE: The net-base.tar.z package is now obselete and should not be
used. It contains the original version of the network configuration
utilities which will not work with the newer kernel releases. It does
though however, contain a number of sample configuration files which
will be useful for you to look at, so you might get it and untar it in
a safe place (under /tmp perhaps) so that you can have a look at them.
You can unpack each of the packages above with the command:
# cd /
# gzip -dc filename.tar.z | tar xvvofp -
Please note that these are quite old versions of the network
applications. These packages do however give you a good idea of where
each of the programs go. In general you will find that the client
programs will go in /usr/bin and the daemon programs (server) will go
in /usr/etc. There are new versions of the network applications
available in both binary and source form, from:
sunacm.swan.ac.uk
/pub/misc/Linux/Networking/Programs/BSD/*
You will need to copy these into the same places, with the same
permissions, as those you are replacing. A packaged release of the
newer applications will be released soon.
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 if 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 withheader 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. 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.
8.1.1. IP Address.
This is the unique machine address, in dotted decimal notation, that
your machine will use. An example is 128.253.153.54. 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 127.0.0.1.
8.1.2. 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, 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 255.255.255.0 as their netmask. Other larger networks use
class-B netmasks (255.255.0.0). 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:
1-127 255.0.0.0 (Class A)
128-191 255.255.0.0 (Class B)
192+ 255.255.255.0 (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.
8.1.3. Network Address.
This is your IP address masked (bitwise AND) with your netmask. For
example:
If your netmask is: 255.255.255.0
and your IP address is: 128.253.154.32 &&
---------------
your Network address is: 128.253.154.0 =
8.1.4. 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 255.255.255.0, your Broadcast Address will be your
network address (calculated above), logically ORed with 0.0.0.255, the
network mask inverted.
A worked example might look like:
If your netmask is: 255.255.255.0 !
the netmask inverted is: 0. 0. 0.255 =
If your Network address is: 128.253.154.0 ||
----------------
Your broadcast address is: 128.253.154.255 =
Note that for historical reasons some networks use the network address
as the broadcast address. If you have any doubts contact your network
administrator.
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
misconfigured.
8.1.5. 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 128.253.154.32, then your
router might be 128.253.154.1. 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
address.
8.1.6. 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 127.0.0.1, 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
machine.
8.1.7. 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.
8.2. /etc/rc.d/rc.inet1,2 or /etc/rc.net
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
machine.
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. For NET-2/NET-3 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 rc.net and
is in the /etc subdirectory. The rc.net 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
applications.
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 rc.net, 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.
8.2.1. rc.inet1
The rc.inet1 file configures the basic tcp/ip interaces for your
machine using two programs: /sbin/ifconfig, and /sbin/route.
8.2.1.1. 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.
8.2.1.2. 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.
8.2.2. 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 rc.net 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.
8.3. 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 fucntion 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
127.0.0.1 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:
#!/bin/sh
#
# rc.inet1 -- configures network devices.
#
# Attach the loopback device.
/sbin/ifconfig lo 127.0.0.1
#
# Add a route to point to the loopback device.
/sbin/route add 127.0.0.1
# 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 127.0.0.1 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 127.0.0.1 Bcast 127.255.255.255 Mask 255.0.0.0
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 127.0.0.1. The route program is
smart enough to know that 127.0.0.1 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
127.0.0.0 * 255.0.0.0 U 0 0 30 lo
#
8.4. 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
#
Where: IPA.IPA.IPA.IPA represents your IP Address. NMK.NMK.NMK.NMK
represents your netmask. BCA.BCA.BCA.BCA represents your Broadcast
address. NWA.NWA.NWA.NWA 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'.
8.5. 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
8.5.1. 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 package. There have been a number of
other versions of dip produced which offer a variety of new features.
You will find them at:
sunsite.unc.edu
/pub/Linux/system/Network/serial/dip*
The dip-uri 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.
8.5.2. 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.
8.5.3. 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
information.
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.
8.5.4. 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.
8.5.5. 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.
8.5.6. 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 knoware.nl.mugnet.org
#
# Fetch the IP address of our target host.
main:
# Set the desired serial port and speed.
port /dev/cua0
speed 38400
# Reset the modem and terminal line.
reset
# 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.
login:
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
done:
print CONNECTED to $remote with address $rmtip we are $local
default
mode SLIP
goto exit
error:
print SLIP to $host failed.
exit:
#
# End dip script
The above example assumes you are calling a dynamic slip server, if
you are calling a static slip server, then remove the following two
lines:
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
one.
8.5.7. 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 fucntionality 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.
Where: IPA.IPA.IPA.IPA represents your IP address. IPR.IPR.IPR.IPR
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.
8.6. 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.
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
Where: IPA.IPA.IPA.IPA represents your IP address. IPR.IPR.IPR.IPR
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.
8.6.1. 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
--------- -------------------------------
INIT 16 - 16
SLCTIN 17 - 17
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*
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.
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 though you have more than one network interface then
your choice is a little more complicated. You might for example 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
Where: 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
#
Where: 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 simpifies 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
address.
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: 128.253.154.120-124, 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 your rc.inet1 file:
#
# Proxy ARP for those dialin users who will be using this
# machine as a server:
#
/sbin/arp -s 128.263.154.120 00:00:C0:AD:37:1C pub
/sbin/arp -s 128.263.154.121 00:00:C0:AD:37:1C pub
/sbin/arp -s 128.263.154.122 00:00:C0:AD:37:1C pub
/sbin/arp -s 128.263.154.123 00:00:C0:AD:37:1C pub
/sbin/arp -s 128.263.154.124 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
address.
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 and would certainly be much
cleaner, but its primary use is if you want your linux machine to act
as an ip router. gated provides support for a number of routing
protocols, the one 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 accesible via your machine.
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.
There are a couple of gated distributions floating around, and I don't
have details of any of them at the moment. I'll try and get some more
information into the next version of this document.
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 rc.net)
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, <
[email protected]>
#
# Constants.
NET="/usr/etc"
IN_SERV="lpd"
LPSPOOL="/var/spool/lpd"
# 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 ]
then
echo -n "syslogd "
${NET}/syslogd
fi
# Start the SUN RPC Portmapper.
if [ -f ${NET}/rpc.portmap ]
then
echo -n "portmap "
${NET}/rpc.portmap
fi
# Start the INET SuperServer
# This is a MUST HAVE, so leave it in.
if [ -f ${NET}/inetd ]
then
echo -n "inetd "
${NET}/inetd
else
echo "no INETD found. INET cancelled!"
exit 1
fi
# Start the NAMED/BIND name server.
if [ ! -f ${NET}/named ]
then
echo -n "named "
${NET}/named
fi
# Start the ROUTEd server.
if [ -f ${NET}/routed ]
then
echo -n "routed "
${NET}/routed -q #-g -s
fi
# Start the RWHO server.
if [ -f ${NET}/rwhod ]
then
echo -n "rwhod "
${NET}/rwhod -t -s
fi
# Start the U-MAIL SMTP server.
if [ -f XXX/usr/lib/umail/umail ]
then
echo -n "umail "
/usr/lib/umail/umail -d7 -bd </dev/null >/dev/null 2>&1 &
fi
# Start the various INET servers.
for server in ${IN_SERV}
do
if [ -f ${NET}/${server} ]
then
echo -n "${server} "
${NET}/${server}
fi
done
# Start the various SUN RPC servers.
if [ -f ${NET}/rpc.portmap ]
then
if [ -f ${NET}/rpc.ugidd ]
then
echo -n "ugidd "
${NET}/rpc.ugidd -d
fi
if [ -f ${NET}/rpc.mountd ]
then
echo -n "mountd "
${NET}/rpc.mountd
fi
if [ -f ${NET}/rpc.nfsd ]
then
echo -n "nfsd "
${NET}/rpc.nfsd
fi
# Fire up the PC-NFS daemon(s).
if [ -f ${NET}/rpc.pcnfsd ]
then
echo -n "pcnfsd "
${NET}/rpc.pcnfsd ${LPSPOOL}
fi
if [ -f ${NET}/rpc.bwnfsd ]
then
echo -n "bwnfsd "
${NET}/rpc.bwnfsd ${LPSPOOL}
fi
fi
echo network daemons started.
# Done!
10.3. Name Resolution.
Name Resolution is the process of converting a hostname in the
familiar dotted notatiion (e.g. tsx-11.mit.edu) 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
complex.
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
127.0.0.1 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 loomer.vpizza.com). You may also wish to include entries for
your gateways and network addresses.
For example, if loomer.vpizza.com has the ip address 128.253.154.32,
the /etc/hosts file would contain:
# /etc/hosts
# List of hostnames and their ip addresses
127.0.0.1 localhost
128.253.154.32 loomer.vpizza.com 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
127.0.0.1, with both localhost and your hostname after it.
Note that in the second line, above, there are two names for
128.253.154.32: loomer.vpizza.com 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 `goober.norelco.com',
and you have this machines address in your named database, then you
can service the request and tell other machines what `goobers' address
is.
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
hostcvt.build 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
hostcvt.build to setup named. This is simply unnecessary unless you
want to make your Linux system fucntion 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
hostcvt.build. If you want to alias machine names, for example, if you
want to refer to loomer.vpizza.com 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 127.0.0.1, 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 0.0.0.0 # default route - recommended
loopnet 127.0.0.0 # loopback network - recommended
mynet 128.253.154.0 # 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:
sunsite.doc.ic.ac.uk
/computing/comms/tcpip/nameserver/resolv+/resolv+2.1.1.tar.Z
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 127.0.0.1, 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
loomer.vpizza.com, then your domain name is vpizza.com, without the
hostname loomer.
For example, if you machine is goober.norelco.com, and has a
nameserver at the address 128.253.154.5, then your /etc/resolv.conf
file would look like:
domain norelco.com
nameserver 127.253.154.5
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. /etc/HOSTNAME
This is a new file, it contains the full hostname of your machine with
the domain name included. It is used by the hostname command, to save
you having to supply the hostname as an argument. For example, the
machine above would have the file /etc/HOSTNAME:
goober.norelco.com
That's all.
10.3.7. Setting your machine's name.
After you have all of your network daemons, and all of the network
code, up and running, there is one small task that remains to do, and
that is to set the hostname for your machine. This is achieved by
adding a command to your /etc/rc.local, or your /etc/rc file, after
rc.inet2, or your rc.net has been run. You may already have this
command in your file, so all you will have to do is modify it to your
hostname.
# /etc/rc or /etc/rc.local
...
...
/bin/hostname -S
...
...
This command expects your hostname to be found in /etc/HOSTNAME. If
you've opted not to bother with the /etc/HOSTNAME file, then you can
use this form:
# /etc/rc or /etc/rc.local
...
...
/bin/hostname -S loomer.vpizza.com
...
...
Note that in some distributions a different hostname program is used,
and this will not accept the -S argument, nor does it use the
/etc/HOSTNAME file, so you ignore the comment relating to those.
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
distribution.
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,
<
[email protected]> and Al Longyear, <
[email protected]>.
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
authentication.
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
are:
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
this.
11.1.2. Where to obtain the PPP software.
The ppp software is available from:
sunsite.unc.edu
/pub/Linux/system/Networking/serial/ppp-2.1.2a.tar.gz
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.
11.1.3.1. 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/config.in. 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.
11.1.3.2. 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
directory.
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
ok.
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.
11.1.4.1. 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
arguments.
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 192.1.1.17:
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 192.1.1.17: says to set the ppp interfaces address to 192.1.1.17.
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.
11.1.4.2. 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.
11.1.4.3. 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:
#!/bin/sh
exec /usr/etc/pppd passive :192.1.2.23
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
script.
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:
[email protected]
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.
11.2.1.1. Where to get sliplogin
sliplogin can be obtained from:
sunsite.unc.edu
/pub/Linux/system/Network/serial/sliplogin.tar.gz
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.
11.2.1.2. 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.
11.2.1.3. 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
features.
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:
normal
to enable normal uncompressed slip.
compress
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.
11.2.1.4. 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.
11.2.1.5. 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
documented.
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
[email protected] */
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:
Sfredm:ij/SMxiTlGVCo:1004:10:UUNET:/tmp:/usr/bin/dip-i
^^ ^^ ^^ ^^ ^^ ^^ ^^
| | | | | | \__ 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
/etc/net/diphosts.
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.
11.2.2.1. 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::145.71.34.1:SLIP uwalt:CSLIP,1006
^ ^ ^ ^ ^ ^
| | | | | \___ MTU
| | | | \_________ protocol (SLIP, CSLIP,
| | | | KISS)
| | | \___________________ comment field
| | \________________________________ IP address of the other
| | side, or host.domain.name
| \___________________________________ unused (compat. with passwd)
\________________________________________ login name (as returned by
getpwuid(getuid()))
An example /etc/net/diphosts entry for a remote slip user might be:
Sfredm::145.71.34.1:SLIP uwalt:SLIP,296
which specifies a slip link with MTU of 296, or
Sfredm::145.71.34.1:SLIP 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 - automount2amd.pl.
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/amd.net
11.3.2. Where to get AMD, the automounter daemon.
amd can be obtained from:
sunsite.unc.edu
/pub/Linux/system/Misc/mount/amd920824upl67.tar.gz
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
syntax:
/etc/amd -x all -l syslog -a /amd -- /nfs /etc/amd.server
| | | | | | | | | | | | |
| | | | | | | | | | | | |
`------' `----' `-------' `-----' -' `--' `-------------'
| | | | | | |
(1) (2) (3) (4) (5) (6) (7)
Where:
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:
...
linus:EncPass:10:0:God:/nfs/server-1/home/linus:/bin/sh
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.
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
forward.
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.
12.1.1. Where to obtain the AX.25 software.
The AX.25 software is available from:
sunacm.swan.ac.uk
/pub/misc/Linux/Radio/*
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 Current AX.25 kernel release for 1.0.* kernels
AX25017 Current AX.25 kernel release for 1.1.6+ kernels
patch10-11 Patch from AX.25 010 to 011
In each directory you will find at least two files, one called
something like krnl017.tgz, and the other called something like
user017.tgz. These are the kernel software, and the user programs
respectively.
12.1.2. Installing the AX.25 software.
The software comes in two parts, the kernel drivers, and the user
programs.
12.1.2.1. The kernel drivers.
To install the kernel drivers, do the following:
# cd /usr/src
# gzip -dc krnl017.tgz | tar xvf -
you will need to uncomment the CONFIG_AX25 define in the
/usr/src/linux/config.in 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.
12.1.2.2. The user programs.
To install the user programs you should try:
# cd /
# gzip -dc user017.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 44.136.8.5
# /sbin/ifconfig sl0 netmask 255.255.255.0
# /sbin/ifconfig sl0 broadcast 44.136.8.255
# /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.
I haven't had a chance to try this code out yet. Please refer to the
man pages in /usr/local/ax25/man for more information.
12.2. Z8530 SCC driver for Ottawa PI card.
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.
A driver has been written by Joerg Reuter, <
[email protected]
aachen.de>, and is available on:
ftp.ucsd.edu
/hamradio/packet/tcpip/incoming/sccdrv-1.4a.dl1bke.tar.gz
Please read the README file that accompanies the driver for more
details.
12.3. 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, <
[email protected]> and is
available from:
ftp.funet.fi
/pub/OS/Linux/BETA/NYS/nys-0.26.tar.gz
An NIS style server can be retrieved from:
ftp.funet.fi
/pub/OS/Linux/BETA/NYS/ypserv-0.5.tar.gz
Check there are no newer versions, as this information might now be
slightly dated.
Both of these are fully fucntional 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 libnsl.so 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.
12.4. snmp agent.
There is an experimental snmp agent for linux, ported by Erik
Schoenfelder, <
[email protected]>.
It is available from:
ftp.ibr.cs.tu-bs.de
/pub/local/cmu-snmp2.1.2l2.tar.gz
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.
13. Some Questions and Answers.
Following are some questions and answers that are commonly asked.
I have only a dialin terminal access to a machine on the net, can I
use
this as a network connection ?" Yes you can, take a look at
TERM. TERM allows you you to run network connection 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 (
http://sunsite.unc.edu/mdw/HOWTO/Term-
HOWTO.html) for lots more information.
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
[email protected] 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.
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 /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 will need to
recompile the kernel for the change to take effect.
If sunacm.swan.ac.uk is down, how do I get the files specified ?
`sunacm' is mirrored on:
ftp.Uni-Mainz.DE
/pub/Linux/packages/Net2Debugged
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:
cat /proc/version
I keep getting the error `eth0: transmit timed out'. What does this
mean?
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.
dip doesn't work. How do I make it work ?
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, that is `chmod 6750 dip'. 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
don't
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.
Why do I get a `network unreachable' message when I try and net-
work?
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
remote.
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
routed or gated, 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.
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 `kill -9' the dip process. When
dip dies it should hang up the call.
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
spdcc.com:pub/sos/sossexe.zoo
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
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.
14. Known Bugs.
The Linux networking code is still an evolving thing. It still has
bugs though they are becoming less frequently reported now. For the
most up to date information on what is known and what isn't, read the
/usr/src/linux/net/inet/README file that accompanies the kernel
source, or join 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:
[email protected], or +1 607 256 7372.
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
today.
For those that have an itch they want to scratch, happy hacking, here
it is.
73
Terry Dawson, vk2ktj.
<
[email protected]>, or <
[email protected]>
