We have an HP Layer 3 Switch that is doing IP routing between vlans. The general set up is that the switch has an IP address on each VLAN and IP routing is enabled. On our servers VLAN, we have a firewall that has a connection to the outside world.

To set a IP route on the HP router, we use IOS command

ip route 0.0.0.0 0.0.0.0 192.168.2.1

where 192.168.2.1 is the address of our firewall, and the zeros essentially mean to route all traffic that the switch doesn't know what to do with out the firewall as a gateway.

We're in the middle of an ISP and firewall change. I set up the new firewall and ran the IOS command

ip route 0.0.0.0 0.0.0.0 192.168.2.254

(the address of the new firewall). Things started working nicely. When I reviewed the configuration of the switch though, I noticed that it did not replace the previous ip route command, but just added another route.

Now, I know how to remove the old firewall route (no ip route 0.0.0.0 0.0.0.0 192.168.2.1), but what is the effect of having these two 0.0.0.0 routes? Is it switch implosion? Will a server just respond back over the route it receives the request from?

I've read elsewhere that having two default gateways is an impossibility by definition, but I'm curious about this situation that our switch allowed.

Thanks!