7 - Networking

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7 - Networking.
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Linux is known to be one of the best networking operating systems in the
world, perhaps even THE best, unfortionally it's not the easiest OS to
set up a good network in, but I hope that this section will make
exclamation marks out of some question marks.


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The first thing you need to do networking is 2 computers and
network cards attached with a crossed network cable, or connected via a hub,
with normal network cable (doh?).

The next step is to make sure the network cards work properly.

Make sure you have the networking support compiled into the kernel, you need
to have the following checked in the kernel (example is from the Linux 2.2.14
kernel, using `make menuconfig`, you can read more about how you
compile/recompile your kernel in /usr/doc/HOWTO/Kernel-HOWTO):

General setup --->
[*] Networking support
Networking options --->

[*] Kernel/User netlink socket
[*] Network firewalls
<*> Unix domain sockets
[*] TCP/IP networking
[*] IP: advanced router
[*] IP: firewalling
[*] IP: transparent proxy support
[*] IP: masquerading
[*] IP: ICMP masquerading
[*] IP: aliasing support
<*> IP: Reverse ARP
[*] IP: Allow large windows (not recommended if <16Mb of memory)
Network device support --->
[*] Network device support
Ethernet (10 or 100Mbit) --->
[*] Ethernet (10 or 100Mbit)
(In here find your network card and check it.)
Filesystems --->
[*] /proc filesystem support

Then you add this line in your /etc/rc.d/rc.local

echo "1" > /proc/sys/net/ipv4/ip_forward () at boot time


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If you have more then one network card, you may wanna add one as Module and
one hard compiled (*) into the kernel, so that the kernel knows that it's
2 network cards.

Then you need to name then eth0 and eth1, this you *may* have to do
even if you only have 1 network card, but it's not likely.

I have 2 network cards, one "3com 509 B" and one "3com 905"
The first thing I need to do is to is to find the module name for
the network cards.
Go to /lib/modules/2.2.14/misc/ and do an "ls"
(the 2.2.14/ dir will be named after whatever kernel version you have,
`uname -r` to find out)
In there I found a file called 3c59x.o (that's the one I compiled as module),
then I set that as eth0, like this:
I open the file /etc/conf.modules (or /etc/modules.conf depending on the
kernel and system) and add:

alias eth0 3c59x

Then I know the other card is a "3com 509 B" so I go to:
/lib/modules/2.2.14/net/ and in there I find a 3c509.o, so I again
add an alias in /etc/conf.modules:

alias eth1 3c509

Basicly, you will find the network cards you added from the kernel in either
/lib/modules/2.2.14/net/ or /lib/modules/2.2.14/misc/, or say now
that you had a Linux 2.2.15 kernel then it would be:
/lib/modules/2.2.15/net/ and /lib/modules/2.2.15/misc/

And remember to add the cardnames without the .o in the module name, as
3c509.o will be named 3c509 as an alias in /etc/conf.modules.

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Now you wanna add the network card so it starts at boot time and get an IP.
Now you must decide what network IP it should have
(either 192.168.1.* or 10.0.0.* in this example I've used 10.0.0.*)
Open or crate a file called: /etc/sysconfig/network-scripts/ifcfg-eth0
(if it doesn't exist when you open it it will be created.)

In this file type the following:

ONBOOT=yes
DEVICE=eth0
IPADDR=10.0.0.1
NETMASK=255.255.255.0
NETWORK=10.0.0.0
BROADCAST=10.255.255.255
BOOTPROTO=none

The save and quit.

ifcfg-eth0 goes if this is your first network card, if it were your second
network card on the same computer it would be ifcfg-eth1, and then the
DEVICE variable would say DEVICE=eth1.

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After this you need to tell your computer what IP, network name and nick name
it has. This you do in /etc/hosts.
By default you should have this line in your /etc/hosts:

127.0.0.1 localhost localhost.localdomain

Now you add your new hosts, the current computer and the other computer(s),
here I have used the 10.0.0.* IP range.

10.0.0.1 main.bogus.com main
10.0.0.2 sidekick.bogus.com sidekick

Note that there is a TAB separating each of the 3 fields (IP hostname nick).

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After that it's time to set up the forwarding and everything like that using
ipchains.
This you do by adding the following lines to your /etc/rc.d/rc.local

/sbin/ipchains -P forward DENY
/sbin/ipchains -A forward -i eth0 -j MASQ

You may also wanna execute the lines since /etc/rc.d/rc.local only
loads at boot time.

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At this time you may also wanna set up a caching nameserver on your system,
Both to speed up your surfing and to get your LAN (Local Area Network)
to interact in a proper way.

In the following example I've used:

bind-8.2.2P5-1mdk.i586.rpm
and
caching-nameserver-6.0-3mdk.noarch.rpm

(A nameserver is depending on bind)

So after you installed bind and a caching-nameserver this is what you wanna do,
(everything in this example is based on the previously written network
configurations):

First you need to edit a file named /etc/named.conf, where in you add a "zone".
The zones in this example to add, looks like this:

zone "bogus.com" {
type master;
file "bogus.com";
};

zone "0.0.10.in-addr.arpa" {
type master;
file "10.0.0";
};

The first one is for the networked computers hostnames, and the second for
there IP's.

In this example I use 10.0.0.* as the network IP, but another common network
IP is also 192.168.0.* .... those are the two most common/accepted ones.

Then you save and quit that, to go and create the files bogus.com and 10.0.0,
which you do in: /var/named/

First we can create /var/named/bogus.com, and in there type the following:

@ IN SOA ns.bogus.com. main.bogus.com. (
2000020100 ; Serial
28800 ; Refresh
14400 ; Retry
3600000 ; Expire
86400 ) ; Minimum
IN NS localhost.
;1 IN PTR localhost.
localhost A 127.0.0.1
ns A 10.0.0.1
sidekick A 10.0.0.2
main A 10.0.0.1
mail A 10.0.0.1

(What comes before the Serial, 2000020100 is a date, 2000-02-01-00, so
you can type that as your current date.)

Then you save and quit that, and crate the file: /var/named/10.0.0, and in
there you type this:

@ IN SOA ns.bogus.com. main.bogus.com. (
2000020100 ; Serial
28800 ; Refresh
14400 ; Retry
3600000 ; Expire
86400 ) ; Minimum
NS ns.bogus.com.
1 PTR main.bogus.com.
2 PTR sidekick.bogus.com.

Now it's almost time to start the nameserver, but first you wanna add the
nameserver to your /etc/resolv.conf so you have any use of it.

Open /etc/resolv.conf and at the top of it add:

nameserver 10.0.0.1

and leav the rest of the file entry's as they are if there is any, then
save and quit that.

And now it's time to start the nameserver.
To be sure that everything works normally, do these commands:

/usr/sbin/named
/usr/sbin/ndc restart

And then type `nslookup`, that should look like this:

root:~# nslookup
Default Server: main.bogus.com
Address: 10.0.0.1

>

If you get that, just type exit at the ">", and then add the following lines
to /etc/rc.d/rc.local

if
ps aux | grep named | grep -v grep >/dev/null ; then
echo >/dev/null
else
/usr/sbin/named
/usr/sbin/ndc restart
fi

This will check if you have a named running, and if not, it will start it,
note that this is not the 100% correct way to do it, but it's by far they
most lazy way to do it, and it works.

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That was the basics of making a network at home and setting up a nameserver.
I hope it's enough so that anyone can set up a little network at home.