Routing question

[Dan Alexander]

We have a server that sits on 3 different subnets. Say the subnets are A B and C. I would like for a system on subnet A to reach this server on subnet A, and the server to talk back to it on subnet A. Same thing with the other subnets, B and C. As of now it looks like a system on subnet A, comes into the server on subnet A, but the server talks back over another net, B or C. I want to make sure we can isolate the net traffic, by keeping the systems talking on the same subnets! Any help would be great! Thanks in advance...

[Ron Kinner]

Devices on directly connected subnets should not have a problem. IF the subnet that the distant server is on is remotely connected to subnet A and is not a member of subnet A then the routing tables come into play. You would have to use
route add
to add the subnet to the routing table and assign the correct gateway on subnet A. And repeat for all such subnets.

However, let's make sure that things are going the wrong way.

traceroute ServerOnSubnetA

this should show you each stop on the way from your box to the ServerOnSubnetA. If it's a member of Subnet A then it will need only one hop. IF it is going out a different path then it will need mulitple hops to get where it needs to go if at all.

Ron

[Christian Tremblay]

routes added with the route command will not survive a reboot, if you want to make your changes permanent do not forget to edit your
/etc/rc.config.d/netconf file.

[Kenneth_18 · Accepted solution]

It seems that assymetric routing is taking place in your server.

Normally, for directly attached lan i/f in a particular subnet, when it receives a packet coming from the same subnet, it would reply back on that same subnet.

For your case, it seems that there is an assymetric route configured in your server forcing packets received from subnet A to have an outgoing reply to other interfaces of your server which may or may not have a direct or inderect connection to the remote server on subnet A.

Check your routing table by issuing "netstat -rn". The gateway address for subnet A should be the ip address of your i/f card connected to subnet A. That goes for subnet B & C also.