Hello everyone!
Here is what my home network looks like:


| |eth0-----eth0|Comp1|
Internet------ppp0| Gateway |
| |eth1-----eth0|Comp2|

What I want to do is to make so that all computers can access internet
and also can connect(ping) each other...
Gateway can ping Comp2 while eth1 there's no routes on eth0, but when
I enable eth0 connection with something like
route add -net 10.0.0.0 netmask 255.0.0.0 eth0
I can no longer ping comp on eth1
All comps have different IP's and all user proper netmasks.
Cna you plz help me?

I really don't understand your diagram.

However, if you want to configure IP Forwarding and Masquerading (Internet Connection Sharing) on your Linux computer, take a look at this post.
http://www.linuxquestions.org/questi...274#post424274

A hub would be good for you situation
ppp
||
|| <ip forwarding would be used here>
eth0
|
hub
/ \
| |
cptr1 cptr2

I'm sure you could get your computers to all talk w/ your set up but this is much more managable and expandable. And a hub isn't that expensive... $25? $30? I forget.

note: That didn't turn out exactly as I'd hoped, but the bottom two lines point to PC1 and PC2. Every thing else looks about right....

My diagram didn't look how it supposed to be... :/
I have a gateway with two comps connected to it's eth0 and eth1
the problem that I have is that when they both are enabled only eth0
works

Are you using static IPs or DHCP ?

Let's start from the beginning.

Computer1 and computer2 should have different static IPs.
The gateway IP for computer1 should be the IP of eth0 and
the gateway IP for computer2 should be the IP of eth1.

You will need to set up IP Forwarding and Masquerading. Take a look at the link in my previous post.

All of them use static IP's and gateways on Comp1 and Comp2 are ok.
Main comp has same IP's of eth1 and eth0, is it ok?
Here is a bit from my console. When only eth1 route is set up I can ping
10.0.0.6, but when I setup the route for eth0 it stops working...

[root@main root]# route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
10.0.0.0 * 255.0.0.0 U 0 0 0 eth1
127.0.0.0 * 255.0.0.0 U 0 0 0 lo
[root@main root]# ping 10.0.0.6
PING 10.0.0.6 (10.0.0.6) 56(84) bytes of data.
64 bytes from 10.0.0.6: icmp_seq=1 ttl=64 time=0.694 ms
64 bytes from 10.0.0.6: icmp_seq=2 ttl=64 time=0.361 ms
64 bytes from 10.0.0.6: icmp_seq=3 ttl=64 time=0.357 ms

--- 10.0.0.6 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 1998ms
rtt min/avg/max/mdev = 0.357/0.470/0.694/0.159 ms
[root@main root]# route add -net 10.0.0.0 netmask 255.0.0.0 eth0
[root@main root]# route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
10.0.0.0 * 255.0.0.0 U 0 0 0 eth0
10.0.0.0 * 255.0.0.0 U 0 0 0 eth1
127.0.0.0 * 255.0.0.0 U 0 0 0 lo
[root@main root]# ping 10.0.0.6
PING 10.0.0.6 (10.0.0.6) 56(84) bytes of data.
From 10.0.0.4 icmp_seq=1 Destination Host Unreachable
From 10.0.0.4 icmp_seq=2 Destination Host Unreachable
From 10.0.0.4 icmp_seq=3 Destination Host Unreachable

--- 10.0.0.6 ping statistics ---
4 packets transmitted, 0 received, +3 errors, 100% packet loss, time 3036ms
, pipe 3


Thanks

Umm, you can't have two interfaces connected to the same network like that, you're going to have routing conflicts.

Give each NIC on the gateway a different address on a different subnet, and put each of the connected hosts on a unique network.

Something like this:

Ok I got it working!
Thank everyone!