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Newsgroups: comp.os.linux.announce,comp.os.linux.help,comp.os.linux.admin,news.answers,comp.answers
From: terryd@extro.ucc.su.oz.au (Terry Dawson)
Subject: Linux NET-2 HOWTO
Keywords: Linux, Networking, TCP/IP, NET-2, SLIP
Summary: HOWTO on configuration of TCP/IP networking and SLIP under Linux.
Followup-To: poster
Approved: linux-announce@tc.cornell.edu (Matt Welsh)
Archive-name: Linux/HOWTO/NET-2-HOWTO
Last-modified: 05 Dec 93
This is the Linux NET-2 HOWTO (previously known as the NET-2-FAQ).
This document explains how to configure TCP/IP and SLIP with the new
``NET-2'' networking code in Linux kernels 0.99.pl13 and above.
Please mail me if you have questions or comments. --terryd
This is the Linux NET-2 HOWTO v1.9, 05 December 1993
By Terry Dawson <terryd@extro.ucc.su.oz.au> and
Matt Welsh <mdw@sunsite.unc.edu>
CHANGES from previous version:
correction to broadcast address calculation, thanks Andr'as Salamon
tcp/ip tutorials added thanks to Gilbert Callaghan
These annotations at the suggestion of Andy Burgess
Shadow password section updated - thanks Rick Sladkey
added Slip Server section - thanks Fred
added /etc/net/diphosts section - thanks Fred
enhanced the netmask description a little
Revamped for 0.99.14
Added Index
*** FTP site maintainers: This document should be stored in the docs/HOWTO
*** directory on your Linux archive as ``NET-2-HOWTO''. You may also wish
*** to link this file to ``NET-2-FAQ'' (its previous name). This document
*** also supercedes the old Linux NET-FAQ.
"Real Programmers don't write documentation." --Ancient Proverb
INDEX for this version
To search for a particular section, search for '^N.S' where
N is the section, and S is the Subsection.
0. Introduction
0.1 Disclaimer
0.2 Questions already?
0.3 Related documentation
0.4 New versions of this document
0.5 Feedback
1. NET-2 Supported Functionality
1.1 Supported Ethernet cards
2. Getting the NET-2 Software
2.1 Unpacking the software
2.2 Putting things in the right place
2.3 Creating the device interfaces
3. Building the Kernel
3.1 Configuring the NET-2 kernel code
3.2 Building the kernel
4. Configuring NET-2 TCP/IP
4.1 Before you begin
4.2 /etc/rc.d/rc.inet1 and /etc/rc.d/rc.inet2
4.2.1 Editing rc.inet1
4.2.2 Editing rc.inet2
4.2.2.1 "To named or not to named... that is the question."
4.3 /etc/hosts
4.3.1 Important note
4.4 /etc/networks
4.5 /etc/host.conf
4.6 /etc/resolv.conf
4.7 /etc/HOSTNAME
4.8 /etc/rc.local
4.9 Other files
5. Configuring SLIP
5.1 Static SLIP server connections
5.2 Dynamic SLIP server connections
5.3 Using DIP
5.4 Configuring your Linux Machine as a SLIP Server
5.5 /etc/net/diphosts
5.6 Configuring Plip interfaces
5.6.1 PLIP Cabling Diagram
6. Are You Stuck?
7. Common Problems and Solutions
8. Known bugs
9. Miscellaneous
------------------------------------------------------------------------------
0. Introduction
This is the NET-2 HOWTO, which is a rewrite of the earlier NET-FAQ for
the new NET-2 TCP/IP code in Linux kernels 0.99.pl10 and above.
The NET-2 code is the new kernel-based networking support for Linux,
written by Fred van Kempen <waltje@uwalt.nl.mugnet.org>. It is based
on the NET-1 code by Ross Biro <bir7@leland.stanford.edu>, device
drivers by Donald Becker <becker@super.org>, SLIP drivers by
Laurence Culhane <loz@holmes.demon.co.uk>, and the D-Link driver by
Bj0rn Ekwall <bj0rn@blox.se>. The NET-2debugged code is maintained
by Alan Cox <iiitac@pyr.swan.ac.uk>. Many others too numerous to
mention have provided support, bug fixes, and help.
This NET-2 HOWTO is by Terry Dawson and Matt Welsh. It covers setup
and configuration of TCP/IP under Linux using NET-2. It also hopefully
answers some of the many questions about the NET-2 code and common
problems that people have. It does not cover using TCP/IP (i.e.
using telnet, FTP, etc.) I'd like to keep this document as short as
possible... :)
0.1 Disclaimer
The NET-2 code is under development, which means that it may
not be as stable and easy to configure as you may like it to be.
code is relatively new and bug fixes are being posted every day, so if
you run into a large number of problems just hang in there. The
software is in two stages of development at the moment. The version
supplied in the standard kernel distribution is version NET-2D
and is being progressively debugged and made more stable by
Alan, until NET-2E, which is currently undergoing Beta testing,
is ready for general release.
NOTE: In this document, `NET-2' does not refer to the Berkeley
Software Distribution NET-2 release of BSD UNIX. Yes, the names
are conflicting. In this HOWTO, `NET-2' refers only to the new
generation of TCP/IP code in the Linux kernel.
0.2 Questions already?
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 comp.os.linux.help,
or, if you believe it to be specifically related the NET-2 kernel
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 revisons of code, a detailed account of the
problem, and the circumstances that caused it to happen are essential.
Traces 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
whether it be SLS, Slackware, Yggadsril, TAMU, MCC, Pro, or other,
please contact the people who created the distribution for support
before attempting to report it to the list, or the NET-2 developers
directly. The developers of the NET-2 code _cannot_ and _will not_
offer support for NET-2 as distributed in any form, other than as
specified in this document, or as per distributed Alpha test
instructions.
Please do NOT bug the NET-2 developers directly unless you have a
_development_-related issue (especially Fred: he has to pay $$$ for
his e-mail access).
To join the NET channel of the Linux-activists mailing list
send mail to
linux-activists-request@niksula.hut.fi
with the line
X-Mn-Admin: join NET
at the top of the message body (not the subject).
Note that the SLIP channel of the mailing list has been disabled and
the NET channel should be used for SLIP discussions as well.
Remember, keep in mind that the NET channel is for development
discussions only.
0.3 Related documentation
There is now a book from the Linux Documentation Project entitled
`Linux Network Administration Guide' by Olaf Kirch. It covers all
aspects of setting up and using networking under Linux, including
TCP/IP, UUCP, mail, news, etc.
This book supplements the NET-2 HOWTO and covers all of the
other aspects of using TCP/IP. This guide simply covers setup of
NET-2, i.e., "How to put your machine on the net."
You should read the Ethernet HOWTO (from sunsite.unc.edu:
/pub/Linux/docs/HOWTO) if you are using an Ethernet network
with NET-2. The Ethernet HOWTO explains all of the ins and outs
of using and configuring Ethenet devices for Linux.
This NET-2 HOWTO supercedes the earlier ``Linux NET-FAQ'' by Phil
Copeland and Matt Welsh. The NET-FAQ is for Linux kernels previous
to 0.99.pl10, running the older version of the TCP/IP code.
This document used to be called the NET-2-FAQ, before the Linux HOWTO
project was underway. Thus, the NET-2-FAQ and the NET-2 HOWTO are
the same.
0.4 New versions of this document
New versions of this document can be retrieved via anonymous
FTP from sunsite.unc.edu:/pub/Linux/docs or directly from me
(terryd@extro.ucc.su.oz.au). It will also be posted to the newsgroups
comp.os.linux.announce, comp.os.linux.help, and news.answers.
You can find news.answers FAQ postings, including this one, archived
on rtfm.mit.edu:/pub/usenet.
0.5 Feedback
Please send any comments, updates, or suggestions to me,
terryd@extro.ucc.su.oz.au. The sooner I get feedback about this
document, the sooner I can update and correct it. If you find any
problems with it, please mail me, instead of posting to one of the
newsgroups. I may miss your corrections. Thanks.
Please send any money to either Fred, Linus, or the Free Software
Foundation. They have made this happen.
1. NET-2 Supported Functionality
The NET-2 code is a complete kernel implementation of TCP/IP for
Linux, including many features not found in the original networking
code. NET-2 supports many popular Ethernet cards, real IP routing,
SLIP (Serial Line IP) for TCP/IP connections over a serial line, such
as the phone line via modem, and PLIP (Parallal Line IP) for local
connection of two machines using your printer ports.
1.1 Supported Ethernet cards
NET-2 supports the following Ethernet cards:
3com 3c503, 3c503/16
Novell NE1000, NE2000
Western Digital WD8003, WD8013
Hewlett Packard HP27245, HP27247, HP27250 (these drivers could
do with more testing)
The following clones are reported to work:
WD-80x3 clones: LANNET LEC-45
NE2000 clones: Alta Combo, Artisoft LANtastic AE-2, Asante Etherpak
2001/2003, D-Link Ethernet II, LTC E-NET/16 P/N 8300-200-002,
Network Solutions HE-203, SVEC 4 Dimension Ethernet, 4-Dimension
FD0490 EtherBoard 16, D-Link DE-600, SMC Elite 16.
Please see the Ethernet HOWTO for more complete information.
As mentioned above NET-2 also supports SLIP in the kernel. Therefore
if you don't have an Ethernet connection you can do TCP/IP over the
phone line, provided you have a SLIP server nearby (many universities
and businesses provide SLIP access to employees/students) and a
compatible modem (usually 14.4 v.42bis, depending on your SLIP server).
Two possible modems are the US Robotics Sportster, or the Infotel
144DF Internal.
2. Getting the NET-2 Software
Before you can configure TCP/IP on your system you need to get the
appropriate software. This includes the current version of the Linux
kernel (0.99.pl14 or above), TCP/IP configuration programs and files
(e.g., /etc/ifconfig, /etc/hosts), and finally a set of network
application programs (such as telnet, ftp, rlogin, etc.).
You may already have all of the items below. Check and make
sure that you do. For example, some distributions come with all
of the NET-2 configuration files, binaries, libraries, and kernel
installed, so there's no reason to get the following files.
Note: they may not be in the places specified in this HOWTO.
If you DO have the NET-2 software already, skip to section 3 on
configuration. If you do NOT have the NET-2 software, follow the
directions below.
The current kernel version is found in
nic.funet.fi:/pub/OS/Linux/PEOPLE/Linus/linux-0.99.14.tar.gz.
This is a gzipped tar file; .gz is the new extension used by gzip.
If you have the old version of gzip, "zcat foo.gz | tar xvf -" works.
The current libraries (libc-4.4.4), can be found in
sunsite.unc.edu:/pub/Linux/GCC/image-4.4.4.tar.z. (You'll probably
want to install the include files in inc-4.4.4.tar.z as well! See the
READMEs there for details.) You'll need at least ver 4.4.2 to use
NET-2, as there were problems with earlier versions that affected
routing and netmasks.
The current NET-2 configuration file distribution is in
tsx-11.mit.edu:/pub/linux/packages/net/net-2/sources/net/net-010.tar.z.
This package includes network configuraiton programs such as
ifconfig, route, netstat etc.
The TCP/IP application binaries and setup files are found in
tsx-11.mit.edu:/pub/linux/packages/net/net-2/binaries.
Get the three files in this directory: net-base.tar.z, net-std.tar.z,
and net-ext.tar.z. As some of the internals of the networking code
have changed, you will also need to get and install the files that
are in the tsx-11.mit.edu:/pub/linux/packages/net/new-net-2 directory,
as they correct some problems you will experience if you opt _not_
get and install them :)
If you use shadowed password (Most SLS users do), then you may find
that the standard network programs do not support them. There used
to be a specially modified package of binaries about, but these were
intended as a short term fix, and have been removed. Recent work on
the standard libraries will mean that as of version 4.5.x of libc,
the shadow password handling will no longer need to be in the
application, and will be handled externally. I have been assured that
4.5.x is due for release shortly.
2.1 Unpacking the software
You don't need to unpack any of the following if you already have all
of the NET-2 software installed.
First, unpack the kernel sources in /usr/src. This will put all
of the kernel sources under /usr/src/linux (the usual place).
# cd /usr/src
# zcat linux-0.99.14.tar.z | tar xvf -
Next, unpack the libraries.
(The following is a summary, please read the detailed instructions
that come with the libraries for complete installation details)
# cd /
# zcat image-4.4.4.tar.z | tar xvf -
Now, make the links to the new libraries in /lib. BE VERY CAREFUL
that you do not delete the previous links. Do everything in
one step, as so:
# ln -sf /lib/libc.so.4.4.4 /lib/libc.so.4
# ln -sf /lib/libm.so.4.4.4 /lib/libm.so.4
Next, unpack the net-base package, which contains the basic
utils and configuration files in /etc. Note that net-base makes
symlinks in /etc for all of your TCP/IP configuration files to /conf.
Therefore, BE WARNED: Before you unpack the following tar files,
make a backup of your files in /etc. Unpacking net-base will overwrite
many of the files in /etc with symbolic links to other places.
For example, /etc/hosts is a symlink to /conf/net/hosts. Why is this
done? Because Fred's Linux/PRO distribution of Linux keeps all
machine-specific configuration files in /conf. And because this is
the way he does it, we may as well too. In general it makes things
easier to locate. If you want to keep all of your net files in
/etc, that's fine, but you'll have to put them there by hand.
Make a backup of everything in /etc before you unpack net-base.
Then unpack it from / (the root directory):
# cd /
# zcat net-base.tar.z | tar xvvofp -
Also, unpack net-std.tar.z, which contains the network clients and
daemons (e.g., telnet and telnetd). Unpack it from / as well:
# cd /
# zcat net-std.tar.z | tar xvvofp -
If you wish to use tin (a newsreader), or DIG (the DARPA Internet
Groper), unpack the net-ext package from /:
# cd /
# zcat net-ext.tar.z | tar xvvofp -
Now unpack the fixed versions of rlogin/telnetd from the files:
# cd /tmp
# gzip -dc ftpd.tar.z | tar xvf -
# gzip -dc telnet-rlogin.tar.z | tar xvf -
you will then need to copy the binaries to where the old
version currently live.
Finally, unpack the net-010 package, which contains the sources
for the TCP/IP setup programs (ifconfig, arp, route, etc.) and the
configuration files. This is unpacked into /usr/src/net-010.
# mkdir /usr/src/net-010
# cd /usr/src/net-010
# zcat net-010.tar.z | tar xvvofp -
** Important information for Shadow Password users **
If you are using the SLS distribution, then replace any blank
passwords in /etc/passwd with :x: instead of ::.
Otherwise rshd/rlogind will let anyone become these user ids.
This is an SLS setup bug and will by default allow anyone remote
access to your machine, with root priveledges!
2.2 Putting things in the right place
With the standard NET-2 distribution, all of the configuration files
are in /conf/net, with links in /etc. For example, /etc/hosts
is a link to /conf/net/hosts. However, if you are using a
standard pre-packaged distribution of Linux such as SLS, /conf/net
probably isn't used... that is, /etc/hosts is just /etc/hosts.
So, when I say "/conf/net/hosts", I mean "/etc/hosts", and vice
versa.
Just keep in mind that the TCP/IP software only looks in /etc and
/usr/etc for configuration files. Therefore, it makes sense to
keep all of your files in /etc and /usr/etc as they should be.
HOWEVER, Fred has decided to put the files in /conf/net with LINKS
in /etc. Either way, it doesn't matter. When we say "/etc/hosts",
it doesn't matter if /etc/hosts is an actual file or a link to
/conf/net/hosts.
If you just unpacked NET-2 above (i.e. you don't already have the
files from installing SLS), then you don't have the configuration
files in /conf/net (you only have the symlinks in /etc).
The easiest way to get the configuration files in /conf/net is
to copy them from the net-010 distribution:
# mkdir -p /conf/net
# chown -R root.root /conf; chmod -R 755 /conf
# cp /usr/src/net-010/etc/* /conf/net
You should make sure that all of the symlinks to /conf/net in /etc
can be resolved (that is, try to "more" or "cat" each file, make
sure you don't get any errors). Also note that some files will
be duplicated: for example, /etc/inetd.conf is a symlink to
/usr/etc/inetd.conf. However, from the cp command above you also
have a /conf/net/inetd.conf, which can be deleted (remember that
all of the programs still look in /etc, not /conf. So whatever is
in /etc is the file which is actually being used).
2.3 Creating the device interfaces
In previous version it was necessary to create a number of
device files for the NET-2 code. This is no longer the case.
If you have any of the following files created you should delete
them:
rm /dev/net /dev/arp /dev/unix /dev/inet
rm /dev/ip /dev/icmp /dev/tcp /dev/udp
rm /dev/wd0 /dev/wd1 /dev/wd2 /dev/wd3
rm /dev/ec0 /dev/ec1 /dev/ec2 /dev/ec3
rm /dev/ne0 /dev/ne1 /dev/ne2 /dev/ne3
should clean them all.
3. Building the Kernel
You're now ready to build the new 0.99.pl14 kernel with the NET-2
code enabled.
3.1 Configuring the NET-2 kernel code
A 'make config' will take you through configuring the kernel
Select the drivers you desire by answering 'yes' when prompted.
Note, you will be prompted for "Network Device Support?", but
the label after it might suggest that this is for Ethernet only,
this is not the case, and you must answer 'yes' to this, even if
you only desire the slip or plip drivers to be configured.
You will be asked later about each of the ethernet drivers,
slip and plip in turn.
The Ethernet HOWTO also contains much useful information for
configuring Ethernet devices in the kernel.
3.2 Building the kernel
You can now build the kernel as you normally would (see the file
/usr/src/linux/README if you've never done this before). Essentially
this entails editing /usr/src/linux/Makefile to set root device and
default display mode. (*Note: keyboard is now handled by loadable
keymaps as of 0.99.pl10; grab the file keytable.tar.z from your
nearest Linux ftp site).
Finally do 'make dep' and 'make'. You now have a new 0.99.14 kernel
with NET-2 set up. I wouldn't reboot it quite yet as we still have
to configure the NET-2 programs before it will work correctly.
4. Configuring NET-2 TCP/IP
The final step is to modify the various setup files to get NET-2
working. After this is ready you can boot your new kernel and
go happily netting (if all goes well).
In this section I'll describe each of the major TCP/IP setup files,
what they do, and what you need to do to configure them.
If you're using SLIP, see section 5.0 on configuring SLIP. The
discussion below is for Ethernet connections only. SLIP users
should FIRST read all of section 4.0 and then apply the changes
discussed in section 5.0.
4.1 Before you begin
Before you can configure NET-2 TCP/IP, you need to find out
the following information about your network setup. Your network
admins can tell you most of these things.
* IP address: this is the unique machine address in dotted-decimal
format. An example is 128.253.153.54. Your network admins will
provide you with this number.
If you're only configuring loopback mode (i.e. no SLIP, no ethernet
card, just TCP/IP connections to your own machine---called
"loopback") then your IP address is 127.0.0.1.
* Your network mask ('netmask'). For performance reasons, it is
desirable to limit the number of hosts on any particular segment
of a network. If you have a large number of addresses allocated
to you, you might break those addresses up into large chunks,
and create subnetworks, and then allow each individual network
segment be a subnetwork of the whole network. The network mask
is a pattern of bits, which when overlayed onto an address on your
network, will tell you which subnet that address lives on. This is
very important for routing, and if you find, for example, that you
can happily talk to people outside your network, but not to some
people within your network, there is a good chance that you have
an incorrect mask specified.
Your network administrators 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 Class B
networks use 255.255.0.0. The NET-2 code will automatically select
a mask that assumes no subnetting as a default if you do not specify
a mask.
The masks chosen by default are as follows:
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, try the other. If this
doesn't work, ask your local net guru for help.
This applies equally well to the loopback port. Since the
loopback ports address is always 127.0.0.1, the netmask for
this port is always 255.0.0.0. You can either specify this
explicitly or rely on the default mask.
* Your network address. This is your IP address masked with the netmask.
For example, if your netmask is 255.255.255.0, and your IP address
is 128.253.154.32, your network number (IP addr AND netmask) is
128.253.154.0. With a netmask of 255.255.0.0,
this would be 128.253.0.0.
If you're only using loopback, you don't have a net address.
* Your broadcast address. This is your IP address masked with the
netmask, and then possibly ORed with the subnetmask inverted.
Such that for a Class C network, with netmask 255.255.255.0,
your broadcast address will be your network address (calculated
above) ORed with 0.0.0.255.
For example:
Your IP address is: 128.253.154.32
Your netmask is: 255.255.255.0
netmask inverted is: 000.000.000.255
then:
Your broadcast address should be: 128.253.154.255.
Note that for historical reasons, some networks are setup to use
the network address as the broadcast address, if you have any doubt,
check with your net admin.
If you have access to a sniffer, or some other device capable of
providing a trace of your network, then you might be able to
determine both the network and broadcast addresses by looking at the
traffic on your network. Keep an eye open (or filter all traffic
except) for ethernet frames destined for the ethernet broadcast
address: ff:ff:ff:ff:ff:ff, if it is an IP datagram, then look at
the destination ip address. If the IP source address is your router,
and the protocol ID is not ARP, then what you are seeing might be a
routing broadcast. The destination IP address in this case will be
the IP broadcast address of your network. You can then work out the
IP network address. But again, if in doubt then consult your network
admin, or check the configuration of a known working machine.
If you're only using loopback, you don't have a broadcast address.
* Your gateway address. This is the address of the machine which
is your "gateway" to the outside world (i.e. machines not on your
subnet). In general the gateway machine has an IP address identical
to yours but with a ".1" in the last position; e.g. if your IP
address is 128.253.154.32, your gateway might be 128.253.154.1.
Your network admins will provide you with the IP address of your
gateway.
If you're only using loopback, you don't have a gateway address.
If your network is not connected to the Internet, that is, it
is a standalone network, then you don't have a gateway, and
therefore don't need a gateway address.
* Your nameserver address. Most machines on the net have a name
server which translates hostnames into IP addresses for them.
Your network admins will tell you the address of your name server.
You can in fact run a nameserver on your own machine by running
named, in which case the nameserver address is 127.0.0.1. However,
But it is not required that you run named at all; see section
4.2.2.1.
If you're only using loopback, you don't have a nameserver
address. (After all, you're only connecting to yourself.)
NET-2 supports full routing, multiple routes, subnetworking (at
this stage on byte boundaries only), the whole nine yards. The above
describes most basic TCP/IP configurations. Yours may be quite
different: when in doubt, consult your local network gurus and check
out the man pages for "route" and "ifconfig" included with the net-010
package. Configuring TCP/IP networks is very much beyond the scope of
this document; the above should be enough to get most people started.
4.2 /etc/rc.d/rc.inet1 and /etc/rc.d/rc.inet2
For the non-UNIX wizard: "rc" files are run at bootup time by the
"init" program and start up all of the basic system programs, such
as sendmail, cron, etc. as well as the NET-2 daemons (such as inetd).
For NET-2 the rc files are found in /etc/rc.d. It doesn't really
matter where you keep them, as long as init can find them. (We'll
go into this later).
First things first. The file /etc/rc.d/rc.inet1 configures the basic
TCP/IP interface to your machine, using two programs: /etc/ifconfig
and /etc/route. These two programs tell the kernel how to route and
manage TCP/IP connections to your system, by setting things such as
the IP address, network mask, and so on.
Note that in the previous NET-1 code, the "config" program was
used. However, the "standard" for UNIX system TCP/IP configuration
is to use ifconfig and route, and this has been implemented with NET-2.
THEREFORE: Get rid of your old "rc.net" if you have one. You
should only run rc.inet1 and rc.inet2 at boot time. If you run your old
"rc.net" instead, you'll get error messages about "old-style ioctl"
and things probably won't work at all.
NOTE: SLS uses "rc.net" instead of "rc.inet1" and "rc.inet2". Just
make sure that your "rc.net" uses "ifconfig" and "route" instead
of the old "config" program. In other words, be sure that your
rc.net is a new, NET-2 style rc.net. If it is not, get rid of it
and replace it with rc.inet1 and rc.inet2, as described below.
If you run SLS, the file "rc.net" contains the code for both rc.inet1
and rc.inet2.
Below you're going to edit rc.inet1 to use the correct ifconfig and
route commands for your machine. But first, you need to know the
information about your network setup in section 4.1, above.
4.2.1 Editing rc.inet1
Edit the file /etc/rc.d/rc.inet1. This file uses the "ifconfig" and
"route" commands to configure your network interface at boot time.
Remember that SLS uses just rc.net.
You may need to do some heavy surgery on this file to get it to look
right; it may be easier to delete it and start from scratch. Given
the information above, a possible rc.inet1 should look like:
#!/bin/sh
# rc.inet1: configure the network interface
HOSTNAME=`hostname`
# Attach the loopback device.
/etc/ifconfig lo 127.0.0.1 # uses default netmask 255.0.0.0
/etc/route add 127.0.0.0 # Network address for loopback network
# IF YOU HAVE AN ETHERNET CONNECTION, use these lines below to configure the
# eth0 interface. If you're only using loopback or SLIP, don't include the
# rest of the lines in this file.
# Edit for your setup.
IPADDR="128.253.154.32" # REPLACE with YOUR IP address!
NETMASK="255.255.255.0" # REPLACE with YOUR netmask!
NETWORK="128.253.154.0" # REPLACE with YOUR network address!
# Note: NETWORK MUST be in
# /etc/networks
BROADCAST="128.253.154.255" # REPLACE with YOUR broadcast address, if you
# have one. If not, leave blank and edit below.
GATEWAY="128.253.154.1" # REPLACE with YOUR gateway address!
/etc/ifconfig eth0 ${IPADDR} netmask ${NETMASK} broadcast ${BROADCAST}
# If you don't have a broadcast address, change the above line to just:
# /etc/ifconfig eth0 ${IPADDR} netmask ${NETMASK}
/etc/route add ${NETWORK} # MUST HAVE AN ENTRY IN
# /etc/networks !!!
/etc/route add default gw ${GATEWAY} metric 1 # Add this line only if your
# network is not standalone
# End of rc.inet1
This is a basic rc.inet1 to run the ifconfig and route commands
needed to set up a basic TCP/IP connection. Edit this for your setup.
To ensure that this will be run at boot time, make sure that you
include the command
/bin/sh /etc/rc.d/rc.inet1
in your /etc/rc, or in your /etc/inittab (if you're running the
sysvinit package). In general, make sure that rc.inet1 is run
BEFORE rc.inet2 at boot time. You may wish to run rc.inet1 and
rc.inet2 from /etc/rc or /etc/rc.local. Or you can run them from
/etc/inittab. Either way is fine, but don't run one without the other.
4.2.2 Editing rc.inet2
The rc.inet2 script is also run at boot time, AFTER rc.inet1.
It starts up various TCP/IP daemons such as inetd, portmapper,
and so on. Remember that SLS uses just rc.net.
You will probably want to comment out most of this file, especially
if you're not planning on using NFS (Network File System). You
MUST leave the stanza to run inetd and syslogd uncommented. Note
that if you DON'T uncomment everything but inetd and syslogd,
you may run into network problems at first. The best bet is to
comment all of these things out, get yourself on the network, and
then worry about configuring the rest of the clients in rc.inet2.
If you're not going to be using NFS, you can comment out the lines
to run: ugidd, mountd, nfsd, pcnfsd, and bwnfsd.
You can comment out the stanza to run "umail" unless you have that
package. In general, most of the things found in rc.inet2 are "sold
separately". I recommend starting only inetd and syslog at first
until you get everything going.
4.2.2.1 "To named or not to named... that is the question."
Named is the nameserver daemon that runs under TCP/IP. It allows
your machine to serve the name lookup requests of other machines...
that is, if a machine wants to find the IP address for
"goober.norelco.com", and you have this machine's IP address in your
named database, then you can service the request and tell other
machines what goober's address is.
Under older implementations of Linux TCP/IP, to create aliases for
machine names (even for your own machine), you were required to run
named on your Linux box to store name->IP address translations. The
problem with this is that named is generally difficult to setup and
maintain. To solve this problem, a program called "hostcvt.build"
was made available on Linux systems to translate your /etc/hosts file
(see section 4.3) into named database files. However, even with
this problem out of the way, running named on your system will cause
some amount of CPU load and 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 set up named. This is simply unnecessary, UNLESS
you want to make your Linux system a nameserver for some reason.
Now, instead of putting hostnames into the named database, you can
simply include them in the file /etc/hosts (section 4.3). When
looking up names, your Linux system will first look in /etc/hosts
and then ask the nameserver out on the net (if you have one).
The only reason you may want to run named would be if:
a) 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
elsewhere);
b) Your network admins want you to run your Linux system as a
nameserver for some reason; or,
c) 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 phone line every time a name lookup
occurs. (If you are only going to lookup a small number of
machine names, and you know what they are, you can put their
addresses in /etc/hosts instead.) Generally name lookup isn't
that slow, and should work fine over most SLIP connections.
d) 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 rc.inet2, and you don't have to run
hostcvt.build. If you want to alias machines, for example you want
to refer to "loomer.vpizza.com" just as "loomer", you can add an
alias in /etc/hosts instead. There is no reason to run named unless
you truly want a full nameserver on your machine. If you already
have a nameserver (most machines on the Internet do, and your net
admins will tell you its address), 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 that's pointless. (No pun
intended.) You don't need a nameserver at all if you use only
loopback; the only hostname you know is your own, and it's in
/etc/hosts (see section 4.3, below).
4.3 /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 by IP address. Using a nameserver (see section 4.1)
also allows you to do the name->IP address translation automatically.
(Running named allows you to run your own nameserver on your Linux
box. See section 4.2.2.1 above.)
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 contain an antry for your IP address, with your full hostname
(such as loomer.vpizza.com). You may also wish to include entries
for your gateway and network addresses.
For example, if "loomer.vpizza.com" has the IP address
"128.253.154.32", my /etc/hosts file would look like:
# /etc/hosts: List of hostnames and IP addresses
127.0.0.1 localhost
128.253.154.32 loomer.vpizza.com loomer
# end of hosts
Once again, edit this for 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 machine. The second is an alias---it
allows me to just use "rlogin loomer" without having to type in the
entire name.
4.3.1 Important note
The line "%%IP%% %%HOST%% %%ALIAS%%" needs to be deleted from
this file! This is a "tag" line used by Fred's experimental net
config scripts. Matt Welsh is now writing a new set of scripts which
don't use these lines. In any of these files, you see curious lines
with entries such as "%%NAME%%", these lines MUST be deleted. If you
don't delete them, you may have lots of strange errors and overflowing
syslog files.
4.4 /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
MUST have an entry in /etc/networks
Its format is similar to that of the /etc/hosts file, (Sec 4.3)
and an example one 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 - mandatory
loopnet 127.0.0.0 # loopback network - mandatory
mynet 128.253.154.0 # Example network CHANGE to YOURS
#
# end of networks
4.5 /etc/host.conf
This file specifies how your system will lookup names.
It should contain the two lines:
order hosts,bind
multi on
These two lines tell the resolve libraries to first check the
/etc/hosts file for any names to lookup, and then 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 the man page available).
4.6 /etc/resolv.conf
This file contains two types of entires: 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., you're running named
on your Linux machine: see section 4.2.2.1), then the address of
your nameserver is just 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
chopped off. That is, if your full hostname is loomer.vpizza.com,
your domain name is just "vpizza.com", without the hostname ("loomer").
For example, if your machine is goober.norelco.com, and has a
nameserver at the address 128.253.154.5, your /etc/resolv.conf would
look like:
domain norelco.com
nameserver 127.253.154.5
You can specify more than one nameserver. Each one
must have a "nameserver" line of its own in resolv.conf.
If you're only using loopback, you don't have a nameserver.
4.7 /etc/HOSTNAME
This is a new file; it contains the full hostname of your machine
(with the domain name). For example, the machine above would have
the file /etc/HOSTNAME:
goober.norelco.com
That's all.
4.8 /etc/rc.local
Change the line in /etc/rc.local (or /etc/rc, depending on your
setup) which sets your system's hostname, to
/bin/hostname -S
(You have a new hostname in /bin.) This sets your hostname from
the name found in /etc/HOSTNAME. If you don't like this (personally
I don't), just do:
/bin/hostname -S <your-hostname>
For example,
/bin/hostname -S loomer.vpizza.com
It IS important that you give a full hostname (with domain name)
in /etc/HOSTNAME. This allows the hostname command to set the
host AND domainname in one shot.
IMPORTANT: The hostname found in /etc/HOSTNAME *must* be a valid
hostname. This means that it must be found in /etc/hosts (or that
your nameserver must be able to resolve it, but you should put it
in /etc/hosts in case your nameserver is down).
4.9 Other files
There are of course many other files in /etc 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 will
be provided in later versions of the NET-2 HOWTO.
Once you have all of the files set up, and everything in the
right place, you should be able to reboot your new kernel and
net away to your heart's content. However, I strongly suggest
that you keep a bootable copy of your old kernel and even possibly
a "recovery disk" (say, the SLS a1 disk, or HJLu's single disk
boot disk) in case you hosed your /etc/rc files, for example,
and can't login when you boot.
5. Configuring SLIP
SLIP (Serial Line Internet Protocol) allows you to use TCP/IP
over the phone line, with a modem (no need for an Ethernet card).
Of course, to use SLIP you'll need access to a dial-in SLIP server
in your area. Many universities and businesses provide SLIP access
all over the world.
Configuring SLIP is much like configuring an Ethernet interface
(please read section 4.0 above). However, there are a few key
differences.
First of all, dialing in and connecting to your SLIP server is
usually done at boot time, usually by a program called "dip"
(found in the "dip" subdir of the net-010 package). "Dip" not only
dials and logs you into the SLIP server, but it also initiates the
SLIP connection and runs the appropriate ifconfig and route commands
to initialize the device. Therefore, the only lines needed in
/etc/rc.d/rc.inet1 are the few commands to initilize the loopback
connection at the top (see section 4.2.1 above).
If you're not using DIP, you may indeed have to edit rc.inet1 for
your SLIP parameters.
Also, there are two types of SLIP servers: Dynamic IP address
servers and static IP address servers. Dynamic servers allocate
a new, different IP address to you every time you dialin and
initiate a connection. Static servers give you the same address
every time. Almost every SLIP server will also prompt you for
a username and password when dialing in: DIP can handle logging
you in automatically.
Essentially, configuring a SLIP connection is just like configuring
for loopback or ethernet. The main differences are discussed below.
Read section 4.0 above for information on configuring your TCP/IP
files, and apply the changes below.
5.1 Static SLIP server connections
If you have a static-allocation server (same IP address every time),
then you may want to put entries for your hostname and IP address
(since you know what your IP address is!) in /etc/hosts. You should
also configure the other files listed in section 4.0: rc.inet2,
host.conf, resolv.conf, /etc/HOSTNAME, and rc.local). Remember that
when configuring rc.inet1, you don't need to run the ifconfig and
route commands other than the two for the loopback interface (if
you're using DIP to dial your connection).
In general, your gateway is the IP address of your SLIP server.
Because DIP handles the configuration of the route, you probably
don't need to know this, but in some cases you might have to run the
appropriate ifconfig or route commands in /etc/rc.d/rc.inet1 to
get it to work correctly. Instead of using "eth0" as your interface
name, SLIP connections use "sl0". Keep in mind that you can't
ifconfig sl0 until you have dialed the connection and connected to
the SLIP server.
Also, you may need to use the "pointopoint" argument to ifconfig if
DIP does not do it correctly. For example, if your SLIP server's
address is 44.136.8.5, and your IP address is 128.253.154.32, you may
need to run the command
# /etc/ifconfig sl0 128.253.154.32 pointopoint 44.136.8.5
See the man pages for ifconfig in the net-010 package.
5.2 Dynamic SLIP server connections
If your SLIP server allocates a new IP address to you every time
you dialin, you don't know your IP address at all, so you can't
include an entry in /etc/hosts for your machine. (If you want, you
can place your hostname in /etc/hosts with the address 127.0.0.1).
Most dynamic SLIP servers tell you your IP address when you initiate
the connection. For example, it may print a string such as, "Your IP
address is 128.253.154.10. Server address is 128.253.154.1." DIP will
need to know these numbers when it configures the connection. See
section 5.3 below on using DIP.
If you use DIP, it does all of the work of configuring the
connection when you dialin, so rc.inet1 only needs the two lines
to configure the loopback address (see section 4.2.1 above).
Also, see section 5.1 above. You need to configure all of
the files listed in section 4.0. Your gateway address (should you
need to know it) will be the address of the SLIP server. Also,
you may need to run ifconfig on sl0 using the SLIP server's address
as the "pointopoint" argument (see section 5.1 above). However, if
you use DIP, it should be able to do all of the ifconfig and route
commands for you.
One good way to figure out how to configure SLIP on your machine is
to find someone else who uses the SLIP server (it can be on a PC,
Mac, UNIX box, whatever) and find out what numbers they use.
5.3 Using DIP
DIP can simplify the process of dialing into the SLIP server, logging
in, starting the connection, and configuring the sl0 device with
the appropriate ifconfig and route commands.
Essentially, to use DIP you'll write a "chat script" which is
basically a list of commands to send to DIP along with commands for
logging in, starting the connection, and so on. See "sample.dip"
in the net-010 package for an explanation. DIP is quite a powerful
program, with many options. Instead of going into all of them here
you should look at the READMEs and the sample files from tsx-11 and
the net-010 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, you'll probably need to use the command
"dip -t" and use the DIP "local" and "remote" commands by hand after
the SLIP server prints your IP address. For example,
loomer:~% dip -t
DIP>port cua0 (My modem is on /dev/cua0.)
DIP>speed 57600 (Set the baud rate.)
DIP>reset (Reset modem and terminal line.)
DIP>send att\r\n (Send modem init string...)
DIP>dial 2446000 (Dial SLIP server.)
DIP>term (Enter interactive mode.)
Welcome to Annex Server...
Annex login: mdw1
Annex password:
User mdw1 authenticated.
Annex> slip (From SLIP server prompt, give "slip" command to start
SLIP connection.)
SLIP inititated.
Your IP address is 128.254.254.10, server address is 128.254.254.1.
^] (Hit DIP break key to get back to DIP prompt.)
DIP> local 128.254.254.10 (Give local command to specify my IP address.)
DIP> remote 128.254.254.1 (Specify server's IP address.)
DIP> mtu 1500 (Set SLIP MTU value.)
DIP> mode SLIP (Start the SLIP mode from DIP.)
loomer:~%
Now we're running in SLIP mode, and everything should work. The command
# /etc/ifconfig sl0
will tell you the current interface parameters; you may need to set
some of these by hand if DIP didn't get the correctly. Also, some have
found that they need to use the route command to change their operating
parameters. DIP sets a route for the address of your SLIP server, but
you may need to delete this route and add it as your gateway instead.
For example, with a SLIP server address of 128.253.154.1, use the
commands:
# /etc/route del 128.253.154.1
# /etc/route add default gw 128.253.154.1
In later versions of dip, and I too profess to be confused as to
exactly which version it might be, this procedure will not work,
and you should instead use the dip
default
command instead. This will automatically point your default route
via your slip link.
It should be simple to modify the code for DIP in the file attach.c
to run the route and ifconfig commands that work for you automatically.
Of course, typing all of those DIP commands may be time consuming. It
may be possible to write a DIP chat script to run all of the commands
up through dialing the connection and logging in, and then "exit" the
script to let you type the "local" and "remote" commands by hand.
Furthermore, there are patches for DIP by Paul Mossip
(mossip@vizlab.rutgers.edu) which modify the "get" command to grab
the IP address of your host and the server from the output of
the SLIP server. This should allow you to do all of the dialing and
configuration within a chat script just as you would with static
SLIP servers. This patch was recently posted to comp.os.linux.announce.
(Check the c.o.l.a archives on sunsite.unc.edu.)
Fred is planning to modify DIP for easier use by those with dynamic
SLIP servers (including the above patch) soon.
You'll have to play with various values for your routes and gateways
to get everything going correctly. If you have any information on how
you configured your SLIP interface, please drop me a note
(terryd@extro.ucc.su.oz.au). Include info on your SLIP address, server
address, gateway, and so on, and what commands you used to set up
SLIP. There are various possible configurations for SLIP servers and
I'd like to update this NET-2 HOWTO with as many hints as possible. :)
5.4 Configuring your Linux Machine as a SLIP Server
So, you wanna go bleeding edge eh ? Ok. I've asked Fred about how to
do this, and the following is what he has supplied. What I would like
you to do is take the following information, and make what use of it
you can. Then, when you have a slip server successfully working,
I'd like you to send me your configuration scripts, and a description
of how to use it, and send it to me to replace this section. Ok ?
Note: Some of the information below came from the dip man pages,
where in fact how to run Linux as a slip server is briefly documented.
To configure Linux as a slip server, you need to create 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".
A sample /etc/passwd entry for a Slip user looks like:
Sfredm:ij/SMxiTlGVCo:1004:10:UUNET:/tmp:/usr/bin/dip -i
^^ ^^ ^^ ^^ ^^ ^^ ^^
| | | | | | \__ dip 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 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.
5.5 /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, PPP)
| | | \___________________ comment field ("gecos" :-)
| | \________________________________ 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==296, or
Sfredm::145.71.34.1:SLIP uwalt:CSLIP,1006
which specifies a CSLIP-capable link with MTU of 1006.
5.6 Configuring Plip interfaces
PLIP is like SLIP, in that it is used for providing point to point
IP links between machines, except that it is designed to use the
Parallel ports on your machine instead of the serial ports. Because
it is possibel to transfer more than one bit at a time with the
Parallel port, it is possible to attain higher speeds with the
plip interface than with the serial interface. In addition, even
the simplest of parallel ports, printer ports, can be used, in
lieu of you having to purchase conmparatively expensive 16550AFN
UARTs for your serial ports.
When compiling the kernel, there is only one file that might need
to be looked at. That file is net/drv/plip/global.h, and it contains
timers in mS. The defaults are probably going to be fine, unless you
have an especially slow computer, in which case you might have to
increase them on the machine at the other end of the link.
A sample configuration for a dip interface might be:
/etc/rc.d/rc.inet1:
ifconfig pl0 192.148.64.1 broadcast 192.148.255.255 \
netmask 255.255.0.0 pointopoint 212.194.167.1 up
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.
/etc/rc.d/rc.inet2:
route add default pl0 metric 1
In almost all respects, you can treat a plip interface as though
it were a slip interface, except that dip is not, and cannot be
used.
5.6.1 PLIP Cabling Diagram
PLIP has been designed to use cables with the same pinout as those
commonly used by the better known of the dos based pc-pc file transfer
programs. The pinout diagram (taken from net/drv/plip/README) looks as
follows:
GROUND 25 - 25
D0->ERROR 2 - 15 15 - 2
D1->SLCT 3 - 13 13 - 3
D2->PAPOUT 4 - 12 12 - 4
D3->ACK 5 - 10 10 - 5
D4->BUSY 6 - 11 11 - 6
D5 7*
D6 8*
D7 9*
STROBE output 1*
AUTOFD output 14*
INIT output 16*
SLCTIN output 17*
Do not connect the pins marked with an asterisk (`*'). They are
D5 (pin 7), D6 (pin 8) and D7 (pin 9). STROBE is pin 1, FEED is
pin 14.
Extra grounds are on pins 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.
6. Are You Stuck?
Really? Then you should read the man pages for ifconfig and route,
included in the net-010 package, and understand their functions. These
commands have a lot of flexibility, and because everyone's network
setup is different, you may find a way to use ifconfig and route to
get your connection working. If you do, feel free to send me some mail
so I can include it in the next update of the NET-2 HOWTO. Because of
my limited amount of experimental data, most of the discussion above
is about my own setup, and I'd like to generalize it as much as
possible.
Matt is currently writing a set of scripts to simplify NET-2
configuration. You can pick up the pre-alpha release from
tc.cornell.edu, in the file /pub/mdw/netconf-0.3.tar.z. These scripts
maintain a small database of network configuration info, and allow you
to easily modify and configure your network interface. The scripts are
far from complete: Matt has been waiting until the NET-2 interface
itself stabilizes a bit more before upgrading it further.
Another good place to look for help on setting up NET-2 is the
O'Reilly and Associated book ``TCP/IP Network Administration''...
the one with the crab on the cover. Keep in mind that NET-2 is now
a "standard" implementation of TCP/IP---this means that ifconfig
and route work the same under Linux as they do on other UNIX systems.
You might also search out the following documents which are an
excellent source of tutorial information on tcp/ip:
athos.rutgers.edu:/runet
-rw-r--r-- 1 0 0 176218 Oct 20 1989 tcp-ip-admin.doc
-rw-r--r-- 1 0 0 214199 Oct 20 1989 tcp-ip-admin.ps
-rw-r--r-- 1 0 0 92106 Oct 20 1989 tcp-ip-intro.doc
-rw-r--r-- 1 0 0 111478 Oct 20 1989 tcp-ip-intro.ps
Also keep in mind that NET-2 _is_ developing very rapidly---it's
one of the newest additions to the Linux kernel. Thus, all of the
bugs haven't been worked out yet, so there may be some problems.
However, a good rule of thumb is that if you were able to get TCP/IP
working under kernels before 0.99.pl10, you should be able to get it
working under NET-2 as well. There are still some issues dealing with
performance to be fixed, but overall the system works. And, as with
everything in Linux development, time will cure what ails NET-2.
If it's absolutely unusable to you, go back to an earlier kernel
version, and wait until things develop further. The code is still
fairly new.
7. Common Problems and Solutions
Now that the NET-2 HOWTO has been out for a while, I've been
able to gather some common problems (and answers!). Here are
some things which I have learned from hearing from readers.
If you run into a problem which should be included here,
please send it along (even if you have the solution!).
QUESTION: Whan I try to use the network, or use SLIP, I get the
error message "Network not reachable". What should I do?
ANSWER: This message means that a machine somewhere in the path did
not have a route to the destination network. Until you can demonstrate
otherwise, it is the courteous thing to do, assume it is your
machine. This is usually an indication that either your ifconfig or
route commands are in some way wrong. You can look at the status of
your ifconfig by using the command "ifconfig" by itself. This should
tell you what NET-2 thinks your IP address, netmask, etc. are.
You can use the command "route" by itself to get routing information.
This will tell you what routes you have set up and what gateways
(if any).
The best way to test a SLIP or network connection is to use "ping"
with IP addresses only. If you use hostnames, as in "ping loomer",
if some part of name lookup isn't working you'll have trouble.
To test just the network, NOT name lookup, use only IP addresses,
as in "ping 128.253.154.32".
For SLIP connections the best thing to do is to ping your
SLIP server. If nothing comes back, then something is wrong. Try
using "dip -v" which will print debugging information while DIP
is dialing the server. Remember that for some SLIP connections you
may need to use the commands
# route del <your slip server address>
# route add default gw <your slip server address>
or the dip:
default
command (depending on the version of dip you are running),
to get SLIP talking to the server. Once you can talk to the
server, everything SHOULD work (if your server is set up correctly!).
For Ethernet connections, try pinging your gateway. If you can talk
to your gateway, you should be able to talk to the outside world.
You may need more than one route (that is, more than one gateway).
For example, some universities use one gateway for on-campus
networks and another for off-campus networks.
Either way, try pinging addresses on your local network, and remote
addresses. If you can ping all addresses ok remote to your network,
and some on your local network, but not others on your local network,
then check your netmask setting.
If the "network not reachable" message means that you can't
talk to your gateway. This can be due to several things:
a) Wrong route or ifconfig commands
b) Ethernet card problems (see below)
c) You didn't compile the kernel correctly (see below).
d) There is in fact some sort of network failure elsewhere.
QUESTION: I keep getting the error "eth0: transmit timed out".
What does this mean?
ANSWER: 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.
QUESTION: I get errors "check Ethernet cable" when using the network.
ANSWER: You probably have your Ethernet card configured incorrectly.
For Etherlink cards, in the file /usr/src/linux/net/inet/CONFIG,
change the line
EL_OPTS = -UEL2_AUI
to
EL_OPTS = -DEL2_AUI
This tells the card to use the AUI cable interface.
Just make sure that all of the options for your card are set
correctly in the CONFIG file, and rebuild your kernel.
QUESTION: When I use NET-2, I get a "General protection" error
or a panic from the kernel. How can I fix this?
ANSWER: Remember that the NET-2 code is still on the buggy side,
just because it's in mid-development. If you get a kernel panic
while using NET-2, write down the EIP address (and the other
information given in the panic message). The EIP is the address
where the kernel paniced, usually of the form 0008:xxxxxxxx
where "0008" is the segment descriptor for the kernel text, and
"xxxxxxxx" is the offset into that segment (80386 programmers will
know what this means).
Use the command
nm /usr/src/linux/tools/system | sort -n
or
nm /usr/src/linux/tools/zSystem | sort -n
depending on whether or not you use a compressed kernel (zImage).
This will print a listing of all symbols in the kernel text,
simply scan down the list and look for the function that contains
the EIP address in the kernel dump. There's the culprit.
However, in some cases the EIP can be misleading; the kernel
may panic at a place which is complete irrelevant to where the
actual problem occurred. However, it is a good starting place;
first, locate the function which contains the EIP address, and
then check out the kernel code to see what might be wrong.
Keep in mind that this will only work if you compile your own
kernel and have the "system" file associated with it.
QUESTION: How can I hang up the phone line when I'm done using
SLIP?
ANSWER: If you use dip to dial out on the SLIP line, just
"kill -9" the dip process itself (dip won't die unless you kill
it with SIGKILL or some other signal). When dip dies, the line
should hang up.
If you don't use dip to dial out, either instruct your dialing
program to hang up the line, or kill the dialing process.
QUESTION: With SLIP, I get a connection open, but no data flows.
ANSWER: This could be a number of things. First, check your routes
and be sure that the gateway is set correctly. Attempt to ping
your gateway; if you can't, then something is wrong with the routes.
Another problem could be that your system and the SLIP server
disagree about header compression. With 0.99.pl11 and above,
SLIP automatically compresses packet headers. To turn off header
compression, check the SL_COMPRESS option in the CONFIG file.
In pl14 there will be supplied a 'setencap' command to allow you
to configure compression.
QUESTION: With SLIP, I get a connection, but after sending a small
amout of data, the connection hangs.
ANSWER: Probably an MTU problem. The MTU is the maximum packet
size available for the network. For SLIP, your MTU is set in
your dip dialing script with the "MTU" command. The default value
is 1500, which means that the system can send packets of up to
1500 bytes in size. However, some SLIP servers (Berkeley SLIP,
for example), use a smaller MTU (around 1006). If your MTU is
too large, the SLIP server will fragment the packets, and currently
(NET-2d), IP packet fragmentation isn't supported (see next section).
The solution is to set a smaller MTU (around 512, or lower) in
your dip chat script.
Another thing to check if you are having erratic SLIP problems is
flow control. You need to use hardware (RTS/CTS) flow control
on your modem, and your modem and your computer must agree. XON/XOFF
flow control is not practical for SLIP.
8. Known bugs
There are several known bugs with the NET-2 software. Note that these
may or may not be fixed with a newer version of the NET-2 code;
therefore, I leave them here.
The bugs here are for NET-2d, found in kernels 0.99.pl10, pl11,
and pl12, and pl13, and pl14. NET-2e (currently in Beta), when
released, may or may not have fixed these bugs.
* Bug with route guessing code. If you ifconfig the "lo"
interface before the "eth0" interface in rc.inet1, whenever you
add a route, it will be added to "lo" instead of "eth0".
(Simply use the "route" command by itself; it will display all
of your routes. If your "default" route, which should be out
on the ethernet, is for device "lo" instead of "eth0", then you're
seeing this bug.)
This is just a problem with the route guessing code. Several
things can fix it: 1) ifconfig/route on "eth0" before "lo" in
rc.inet1; or, 2) Set your netmask to 255.0.0.0 (which is reported
to work, but I can't guarantee it). This should be fixed in NET-2e.
* Missing IP packet fragmentation. Packet fragmentation allows the
various protocol layers to "chop up" packets into smaller packets
if the MTU (maximum tranfer unit) of one network differs from
another. NET-2e should contain packet fragmentation/defragmentation
code, but NET-2d currently does not.
pl14 has had fragmentation support fitted.
* Weak NFS support. There have been a number of success stories with
NFS under Linux, however, not all of the support is there. For
one thing, the current NFS buffer size is much smaller---and
therefore much slower---than other implementations of NFS. From
what I understand, this problem is related to the lack of packet
fragmentation code, above. With pl14 and upwards this will probably
be resolved.
9. Miscellaneous
I'm sure that I've missed something. This NET-2 HOWTO was thrown
together with the help of Matt Welsh, Jeff Uphoff, and Alan Cox.
Hopefully it will help someone out there get going with networking
under Linux.
Future plans for the NET-2 HOWTO include a section on setting up
your own Linux LAN (with SLIP and/or Ethernet), adventures in
routing, and the use of netstat and other network administration
under Linux. For now, the information here should be more than
enough. :)
If you have questions about setting up NET-2, feel free to mail me, or
if you have any corrections, additions, or errata for this NET-2 HOWTO,
send me any and all changes (cdiffs are nice, but I'm flexible).
Of course, thanks to Fred, Linus, Ross, Phil, Paul, Don, and everyone
else who helped to develop the NET-2 code and work on previous
versions of TCP/IP for Linux and the NET-FAQ. Finally, Linux has a
complete implementation of TCP/IP. It may not be for everyone yet.
But for those who want to do some hacking---here it is.
Cheers,
Terry Dawson, (terryd@extro.ucc.su.oz.au)
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