2 Nics in the same network. Routing problems.

Tmor · n00b Joined: 10 Mar 2005 Posts: 30

Hi,

I have 2 NICs that are both DHCP enabled and I need to be able to talk to them both them. They are both on the same subnet. The problem is in the routing. When DHCP brings up BOTH interfaces it adds 2 default routes. One for each interface on the subnet. This problem only seemed to appear when I started using 2005.1 and the new /etc/conf.d/net parameters.

When no interfaces are up there is only the loopback route.

When one interface (eth0) is up there is a DEFAULT route pointing to the gateway and eth0 is pingable.

jamapii · l33t Joined: 16 Sep 2004 Posts: 637

You can write a postup() shell function in /etc/conf.d/net, that determines the number of default routes, and if it's 2, it removes one of them:

Tmor · n00b Joined: 10 Mar 2005 Posts: 30

Yes, that would definately solve the problem of the route, but the interface wouldnt be reachable. To complicate matters more, the two nics are in two different switches and all the switches are in the same network.

Am I just missing a fundamental network problem? It would seem that both interfaces should be able to default back to their respective gateways, which in this case is the firewall with the IP 10.x.x.1 and both be active because the have different MAC/IP addresses which the switches can handle. Spanning-Tree is active and there are no loops in the network.

Now if I am in the same subnet I can talk with both interfaces, but any traffic incoming from another subnet cannot. I have duplicated this several times locally and I dont believe its a firewall configuration and I dont want to NAT any external to internal addresses (although I know that would work flawlessly).

Now, I dont have to have DHCP. I can manually define anything.

The network setup kind of looks like this:

Tmor · n00b Joined: 10 Mar 2005 Posts: 30

bump. anyone know how to get 2 interfaces active on the same subnet?
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bigfunkymo · Apprentice Joined: 23 Jan 2004 Posts: 237

Just out of curiosity, what exactly are you trying to accomplish here?
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Taladar · Posted: Sun Sep 04, 2005 6:54 pm Post subject:

You are likely to end up with all packages going to one interface anyway if both are on the same logical subnet. To avoid that you would have to change routing to your PC and employ some kind of load balancing. Something like that would be needed for outgoing packages too.

So I second the question "what are you trying to do?"

UberLord · Posted: Mon Sep 05, 2005 7:22 am Post subject:

Posters are right "What are you trying to do?" The first interface will always be used.

However, I do this as well so that when my wireless connection fails, my wired connection takes over (or vice versa if some dumbass knocks the power off my desk phone (ip phone, PC gets cat5 from phone)).

baselayout-1.12.0 solves this by enforcing different metrics for each interface
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