Setting up a direct LAN between 2 PCs

Mr_Nightmare · 08-30-2005, 08:17 PM

Dear All,

I am a new user of the Linux OS,

I have 2 PCs with Linux Fedora 2 installed on both. I want to set up a direct LAN connection between both computers while both are running Linux. I know how to do the connection under windows (I got a Cat5 crossover cable), but I have no idea what the commands may be under Linux.

Can anybody please give me a step-by-step procedure on how to complete this task?
I tried to search for a similar topic on this site, but I didn't find any. So I guess this one is one of its kinds!!

Note: I want to do the set up using command lines, not using any GUI tool (otherwise, the task would be very similar to windows...)

charon79m · 08-30-2005, 09:46 PM

I'm no Redhat guy, but I'll give you some direction here...

Check out the directory /etc/sysconfig/networking/

You'll find some info in the devices and the profiles directories that contain the IP info for the interfaces.

I'd assume you are familiar with the IP addressing needed to get the machines talking; if not, just post back and we'll go over it.

Oh, by the way... there is nothing wrong with using the GUI to make changes and then using the command line to see how those changes have affected the text files that hold the configuration.

You can also man ifconfig or ip to learn about addressing your machines.

MrKnisely

sonajiso · 08-31-2005, 12:00 AM

You have 2 choices:
1. Install a DHCP server on one of the boxes
2. Assign static IP's to each system, manually configure the routing - if required at all.

Since you only want to connect two PC's via a crossover cable, I suggest option 2. Its much easier to achieve.This is how you do it:

Lets suppose your computers are A and B. A has 3 NIC's (I believe on redhat they would be numbered eth0 to eth2) while B has 7 NIC's (eth0 - eth6). Let suppose A and B are connected via NIC's A.eth1 and B.eth3. All we have to do is assign static IP's to these 2 and enable arp on each of the 2 interfaces.

Please choose 2 IP's like 10.#.#.# or 192.168.#.#, where # is a base 10 number from 0-254. Choose these 2 IP's carefully. Make sure they do not fall in a range that is already routed "outside" via the other intrfaces. Lets say route returns the following on A:

Code:

192.168.0.0     *               255.255.255.0   U     0      0        0 eth0
10.5.0.0         *               255.255.0.0      U    0       0         0 eth2
loopback        *               255.0.0.0       U     0      0        0 lo
default         192.168.0.1     0.0.0.0         UG    0      0        0 eth0

As part of the above example, I would not want to choose any IP's in the range 192.168.0.0 - 192.168.0.255 and 10.5.0.0 and 10.5.255.255. It is also relatively unwise to choose the IP of the default gateway - if you have any.

So let suppose IP's 192.168.10.100 and 192.168.10.101 satisfy the above restrictions. All you have to do is assign one IP to A and one to B.

As root execute the following on A (Assigns the static IP of 192.168.10.100 to A.eth1):

Code:

ifconfig eth1 up
ifconfig eth1 inet 192.168.10.100 netmask 255.255.255.0 arp

Note that the address resolution protocol is probably enabled by default, but just making sure it's enabled we will pass arp to ifconfig eth1.

As root execute the following on B:

Code:

ifconfig eth3 up
ifconfig eth3 inet 192.168.10.101 netmask 255.255.255.0 arp

Now as a regular user, on A try

Code:

ping 192.168.10.101

..and on B try:

Code:

ping 192.168.10.100

The 2 computers should see one another.
If not, you might have to tweak your routing table. That can be achieved as easily as:

On A:

Code:

route add -net 192.168.10.0 netmask 255.255.255.0 dev eth1

..and on B:

Code:

route add -net 192.168.10.0 netmask 255.255.255.0 dev eth3

Although when an interface is activated, Linux tends to update the routing table as well, so it would be strange if you had to manually update it.

charon79m · 08-31-2005, 07:58 PM

It is important to remember that with ifconfig you are setting up IP addresses for now. Once you reboot your system, you're back to the unconfigured state.

You need to edit the sysconfig files in Fedora to get them changed for good.

MrKnisely