linux routing

I am trying to make set up router on redhat linux 7.2 and no luck. Here i smy situation:

linux box with two NICs (REALTEK) with public IPs. Let say on one NIC has ip 217.75.74.1 with mask 255.255.255.0 and second NIC has ip 217.75.75.1 with mask 255.255.255.0. Now thereis a 217.75.74.0 network on one side an 217.75.75.0 on the oter.

Here is where i get stuck. I ping from 217.75.74.0 network the router and i get respons from both 217.75.74.1 AND 217.75.75.1. But this is where it ends. I can't ping any further. Let's say a ping from host 217.75.74.2 host with ip 217.75.75.2 no luck, ping won't go through. What I am doing wrong?

i tried enabling ip_forward - still no luck. Please help.
lmx-netAsked:
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ken_330Commented:
hey .
   u got only two valid IPS...so u should expect any response since u dont have any nodes with that address right?

   if not please elaborate it clearly .
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lmx-netAuthor Commented:
What do you mean two valid IPs? I have two whole subnets ... I can pretty much pick from 252 IPs on each side ... So my gateway one (1st NIC) has IP 217.75.74.1 and the other gateway (2nd NIC in the linux box) has IP 217.75.75.1. And then I can pick what ever IP, so lets say from 217.75.74.20 i want to ping 217.75.75.35 and no luck ... The ping simply wont go pass the second NIC in the linux box.
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JaemCommented:
1) you need to do
echo 1 > /proc/sys/net/ipv4/ip_forward
on the linux box (router)
2) you need to tell the other boxes on 217.75.74.0/24 and 217.75.75.0/24 the route to the other network.

boxes on 217.75.74.0/24
either
route add -net 217.75.75.0/24 gw 217.75.74.1
or
route add default gw 217.75.74.1

boxes on 217.75.75.0/24
either
route add -net 217.75.74.0/24 gw 217.75.75.1
or
route add default gw 217.75.75.1

One nice way to debug it, is use tcpdump and ping and look where the connections break.
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lmx-netAuthor Commented:
Thanks Jaem, The thing is i have tried the ip_forward, but I will try it again. The other thing is, the IPs on one side are spread all over one city and the others are spread another city. So I can't really go around and add a route to everybodys computer. Somehow it has to be dona on the linux box. What can be done?
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JaemCommented:
Do you use DHCP to allocate the IP addresses? Then you should be able to give the boxes the name of the router. But basically, if a box on 217.75.74.0/24 wants to talk to one on 217.75.75.0/24, it needs to know the route to get outside its network, and the responding box needs the same info. Else have you tried ping/tcpdump to track the packets? It could tell you where they get lost.
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CleanupPingCommented:
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