2 ports on router using same subnet?

[JEDI]

I have 2 switches and 1 router (26xx).

I want to connect both switches to the router, and if 1 switch fails then the traffic automatically goes through the other switch.

I read that you can't have 2 ports on one router using the same subnet? If this is true, how can I (easily) implement the above?

THX

 

[tjmaxz]

I'm assuming you are talking about a Cisco router. I'm not sure why you would want to do that, because if one switch fails, don't you have to manually reconnect all the cables to the 2nd switch? If you have 2 NIC cards on the PC and each connected to a different switch, wouldn't you have assigned them into different subnets anyways?

 

[Kadarin]

Isn't it possible on the Cisco to configure a vlan and create a virtual interface to route packets outside of that vlan? If your switches support spanning-tree, that would be one way of doing it.

 

[JEDI]

but to do spanning tree, won;t the 2 ports on the router need to be bridged?

 

[ScottMac]

You cannot have the same network address (or subnet address) on two ports (or if you do, you can't route between them and it FUBARs the routing tables). In a Cisco, you can do Integrated Route-Bridge (IRB) - the two (or more) interfaces are bridged, then the bridged pair route to the rest of the ports of the router.

Spanning tree has nothing to do with it.

Good Luck

Scott

 

[spidey07]

Its not something you would want to do. In order for them to be on the same subnet you would do some bridging as Scott said.

The only other thing I can think of is maybe HSRP on the two interfaces, although I don't know if that is really possible since both ethernet ports are on the same router.

Maybe describe what your requirements are and we can come up with a solution. If one switch fails then that whole network is down anyway. For real redundancy you'd use two routers with HSRP between them. That way if a switch fails the other router takes over as the default gateway for any clients.

 

[Kadarin]

Originally posted by: ScottMac
You cannot have the same network address (or subnet address) on two ports (or if you do, you can't route between them and it FUBARs the routing tables). In a Cisco, you can do Integrated Route-Bridge (IRB) - the two (or more) interfaces are bridged, then the bridged pair route to the rest of the ports of the router.

Spanning tree has nothing to do with it.

Good Luck

Scott

I'm used to Foundry equipment here.. say for example where you'd create a Layer 2 vlan containing e1 and e2, and create a virtual interface ve1 for that vlan. Switch 1 links to e1 and switch 2 connects to e2. Switch 1 and 2 are also connected to each other. Use spanning tree to block the redundant port and provide failover. Can you not do this on the Cisco box? What am I missing?