linux-ethernet.html

Linus guide, Linus guide, Linus guide,

<P>Basically, if your network has machines that are assigned IP addresses
that are 192.168.1.*, you represent the whole network with 192.168.1.0. If
your network's machines have IP addresses of 192.168.2.*, then your whole
network would be represented by 192.168.2.0 and you would type <TT>route
add -net 192.168.2.0 netmask 255.255.255.0 eth0</TT> in order to get your
Linux machine to contact the rest of the network.</P>

<P>That should also work for networks with no hubs, if you connect the
computers all to each other using those RJ-58 cables (the ones that
look like TV wiring). I haven't tried it myself but few people use
that kind of setup these days.</P>

<P>All of the above will allow you to contact hosts within your
network. Now you have to be able to contact hosts outside your own
local network, especially those on the Internet. You'll have to
configure a gateway, a machine that's connected to the Internet and
that is willing to share its connection with you. For example, if the
machine with the IP address 192.168.1.5 is your gateway to the
Internet, you would type this (as root) to send requests for addresses
that are out of your network:</P>

<PRE>
route add default gw 192.168.1.5 eth0
</PRE>

<P>If you are connected to the Internet through a dialup connection using
PPP (which most people are), you would do something different, depending
on what machine the Internet connection is running off of. If the machine
you're working on is the machine that's connected to the Internet through
PPP, then you would type something like this:</P>

<PRE>
route add default ppp0
</PRE>

<P>That will configure your system to send requests for packets that are
not in your network to the Internet through your modem. (I hope you're
still following along; if you don't understand I'm not doing a good
job...)</P>

<P>You might want to use <A
HREF="http://sunsite.unc.edu/LDP/HOWTO/mini/IP-Masquerade.html">IP
Masquerading</A>, a way to share your Internet connection with others on
your network. The way it basically works is when a request is sent from a
machine within your network, your machine takes a look at it and if it's
&quot;addressed&quot; to an Internet address, your machine sends the
packet out through your connection, whether it be Ethernet or PPP.</P>

<P>If you've got a host within your LAN that's your gateway to the
Internet, then you would use <TT>route add default gw 192.168.1.5</TT>, if
192.168.1.5 is the IP address of the gateway. When your connection is
shared this way instead of IP masquerading, each machine on the network
(known as a <B>node</B>) has its own IP address on the Internet.</P>

<A NAME="startup"></A>
<H3><A NAME="4">Putting IP Assignment and Routing in Startup</A></H3>

<P>The information about routing and your IP address on your Ethernet
network would be very inconvenient to type in every single time you want
to be connected to the rest of the network, so we'll put it in your system
startup files.</P>

<P>One easy (but very sloppy) way is to put the following example
lines in the file <TT>/etc/rc.d/rc.sysinit</TT>:</P>

<PRE>
route add -net 192.168.1.0 eth0
ifconfig eth0 192.168.1.1 up
</PRE>

<P>I don't recommend doing it that way, but it's quick, it's simple
and it's almost guaranteed to work. Should you choose to go that route
(no pun intended), put the lines at the bottom of the file
<TT>rc.sysinit</TT>. The right way to do it would be to use the
<B>linuxconf</B> program in Red Hat for your network
settings. Alternatively you can edit <TT>/etc/sysconfig/network</TT>,
<TT>/etc/sysconfig/network-scripts/ifcfg-eth0</TT>, and
<TT>/etc/hosts</TT>. If you're a true beginner, go ahead and use
<B>pico</B> to edit these text files if you have no experience with
Unix editors such as <B>vim</B> or <B>emacs</B>.</P>

<P>Your <TT>/etc/sysconfig/network</TT> file may look something like
this:</P>

<PRE>
NETWORKING=yes
HOSTNAME=methuselah.lan
DOMAINNAME=lan
GATEWAY=192.168.1.5
GATEWAYDEV=eth0
FORWARD_IPV4=no
TIMESERVERATBOOT=no
TIMESERVERTYPE=ntp
TIMESERVERHOST=(none)
TIMESERVERRESYNC=(none)
</PRE>

<P>And your <TT>/etc/sysconfig/network-scripts/ifcfg-eth0</TT>:</P>

<PRE>
DEVICE=eth0
IPADDR=192.168.1.1
NETMASK=255.255.255.0
NETWORK=192.168.1.0
BROADCAST=192.168.1.255
ONBOOT=yes
</PRE>

<P>Finally, your <TT>/etc/hosts</TT>:</P>

<PRE>
127.0.0.1               localhost localhost.localdomain
192.168.1.1             methuselah.lan methuselah
</PRE>

<P>(Something else to note about <TT>/etc/hosts</TT> is that it might
be the reason that your sendmail or Samba startup is slow on bootup;
because it can't figure out what to do with the hostname that you set
for your computer.)</P>

<!-- We need some info here about DHCP on boot up. I will add it
later, some time.>

<P>The equivalent I found on Slackware a while back was that you can
just edit <TT>/etc/rc.d/rc.inet1</TT> (or the other rc.inet* file) and
it will set it for you automatically. You specify the values of
certain things like your IP address and broadcast address (and more,
of course).</P>

<P>So if you're going to edit one of those files, just go ahead and use
your favorite text editor (pico, vim, vi, emacs, joe, jed; the list goes
on).</P>

<A NAME="winconfig"></A>
<H3><A NAME="5">Windows 95 Configuration</A></H3>

<P>On the Windows 95 machine, if you have one on the network, start by
clicking on the Start button, then going to <B>Settings</B>, then
<B>Control Panel</B>, and finally <B>Network</B>.</P>

<P>In the Network dialog box, if you haven't already, add a TCP/IP service
for your Ethernet card, if you haven't already. Highlight TCP/IP for your
Ethernet adapter, and click on the Properties button. Fill in the
information that you need, such as the gateway IP address (the Linux box
if it's running IP masquerading), the nameserver (your ISP's nameserver),
the IP address assigned to your machine within your network (such as
192.168.1.2), and any other stuff you might have to fill in.</P>

<P>You can also run <B>winipcfg</B> to see if you currently have an IP
address on the network.</P>

<P>That's about all I know about setting up the Windows box, so let's move
on. Hopefully you have whatever other machines (nodes) on the network
already set up.</P>

<A NAME="testconnect"></A>
<H3><A NAME="6">Testing Your Connection</A></H3>

<P>To test if your connection works, try pinging another host on your
network. Let's say your machine is 192.168.1.1 and the other machine, the
one you're going to ping, is <B>192.168.1.2</B>. This is what you'd type
to start pinging the host:</P>

<PRE>
ping 192.168.1.2
</PRE>

<P>If lines periodically appear and look something like this, your
connection works:</P>

<PRE>
64 bytes from 192.168.1.2: icmp_seq=0 ttl=32 time=1.2 ms
64 bytes from 192.168.1.2: icmp_seq=1 ttl=32 time=1.0 ms
64 bytes from 192.168.1.2: icmp_seq=2 ttl=32 time=1.0 ms
64 bytes from 192.168.1.2: icmp_seq=3 ttl=32 time=1.0 ms
64 bytes from 192.168.1.2: icmp_seq=4 ttl=32 time=1.1 ms
</PRE>

<P>To stop pinging, type Control-C (Ctrl+C) to get back to the prompt.</P>

<A NAME="othersources"></A>
<H3><A NAME="7">Other Sources of Information</A></H3>

<UL>
<LI><A HREF="http://sunsite.unc.edu/LDP/HOWTO/Ethernet-HOWTO.html" TARGET="_top">Linux Ethernet-HOWTO</A> - Hardware info</LI>
<LI><A HREF="http://sunsite.unc.edu/LDP/HOWTO/NET-3-HOWTO.html" TARGET="_top">Linux NET-3-HOWTO</A> - Network configuration info</LI>
<LI><A HREF="http://sunsite.unc.edu/LDP/HOWTO/mini/IP-Masquerade.html" TARGET="_top">IP Masquerading mini-HOWTO</A> - Sharing your Internet connection with other computers within your network</LI>
</UL>

<A NAME="books"></A>
<H3><A NAME="8">Related Books</A></H3>

<OL>
<LI><A HREF="http://www.amazon.com/exec/obidos/ASIN/1565924002/joshslinuxguide" TARGET="_top">Linux Network Administrator's Guide (2nd Edition)</A> - Freely available in print.</LI>
</OL>

<HR>

<P>If you have trouble and are wondering how to solve your problem, either
solve it yourself and give me a summary of your scenario, or
alternatively, <A HREF="mailto:[e-mail]">ask for help</A>. And, as
usual, suggestions are always welcome.</P>

<HR>

<P><B><FONT SIZE="-1">Copyright &copy; 1997-2000 <A
HREF="mailto:[e-mail]">Joshua Go ([e-mail])</A>. All rights
reserved. Permission to use, distribute, and copy this document is
hereby granted. You may modify this document as long as credit to me
is given.</FONT></B></P>

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