ARP in VLAN

ehuarte · ‎09-10-2008

Hi;

We have two 6500 in the backbone that have configured several VLAN gateways.

The thing is that if any computer of a VLAN, we configure a gateway of another VLAN and the computer still works.

How we can solve this issue?

Thanks. Regards

Giuseppe Larosa · ‎09-10-2008

Hello Eneko,

your switch has probably the ip proxy-arp enabled on the SVI VLan

With proxy-arp a router answers arp requests for ip addresses that are not in the subnet: once the computer associates the mac address with the gateway it can send traffic to other subnets.

you can check this with

sh ip int vlan X

to change

int vlan X

no ip proxy-arp

on all SVI vlans

Notice : you change on the fly the vlan of the port connected on the pc it has the MAC address in the ARP table and so it works even if the proxy-arp is disabled.

All SVis on the C6500 share the same MAC address so the change on the fly doesn't isolate the PC you need to clear the arp cache on the pc to see the no ip proxy-arp effect

Hope to help

Giuseppe