Slow Layer 3 Switching

[scottholwerda]

We have a 4506 switch with a supervisor IV engine. I configured an ip address to each VLAN interface in the network, and enabled them with the no shut command. I entered the ip routing command, and setup the default gateway to a cisco router that has that was doing the vlan routing and has the path to everywhere in the LAN.

I made sure that there was no other default gateways configured. When I switched the the default gateway from the router to the switch in the appropraite vlan the speed to access anything on another vlan has increased at lease 3 times.

Does anyone have an idea of what the cause could be?

[micah]

Please post configs. It should of course be much faster on the Sup IV.

[Craig Norborg]

Hopefully you put the router on a different subnet than the network now, right? And the vlan interfaces on the 4506 that replaced the router has the same IP addresses as the router used to have on its vlan interfaces (ie: the clients have the same default gateway as before? or do they need to change their gateway?)

Definitely seeing the configurations would help, I'd also like to see what the ip configuration of any of the systems on a vlan is too...

[scottholwerda]

The router is still in place and has a trunked interface for each vlan and subnet. I am trying to make the change transparently, so I am changing the default gateway on teh clients. If I change the gateway on any client to point to the switch everything slows down.

The configuration of the switch is attached.

[Craig Norborg]

Hmm.. I can't be sure without actually debugging what's happening, but I'm betting that your getting some kind of L3 problems, whether it be a loop or just the router and l3 switch fighting somehow... Not a big fan of RIP handling situations like this either.

My recommendation would be to create a separate VLAN and give it a subnet big enough to have your router and l3 switch in it (ie: a 255.255.255.252 subnet is large enough). If you have another ethernet on the router, you could do this while the other link is active if you want.

Then, when your ready, take down the trunk to the router and let the l3 switch assume the IP address the router used to have. Make the l3 switches default gateway point to the IP address you gave the router on the link you just created.

Personally I would use a smarter routing protocol such as EIGRP or OSPF, but RIP should work.