Wrong default gateway

[irelandsky]

Hi all,

i've cat 6509 with msfc2 and native IOS. I've configured 14 vlans each one with its ip address.

Normally each client on a vlan have as def gateway the ip address of the interface vlan on the catalyst.

IF i configure the default gateway on a client on Vlan A with the IP address of interface Vlan B ( so wrong ip address) all works fine...and it is very strange. I think that if i configure wrong def gateway the client is not able to go outside of his network, but it isn't true ....why??

Thaks all

Marco

[Georg Pauwen]

Hello,

can you post your configuration ?

Regards,

Georg

[jamey]

Could be proxy-arp. Turn off proxy-arp on the VLAN A interface.

-HTH

[Richard Burts · Accepted solution]

It is almost certainly proxy arp. If the PC is configured with an incorrect default gateway, the PC will attempt to forward to what is configured, and arp for the address that is configured. With proxy arp enabled, the router will respond with its own MAC accress. The PC is happy, it has an address to forward to that works. The packets are sent to the VLAN interface and it makes the proper forwarding decision. If you turn off proxy arp then when the PC arps for its configured default gateway it will not get a response and will not be able to send traffic to any remote destination.

So proxy arp on the router will compensate for errors in configuration of the PCs.