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New Member

Default gateway detection

How does an IOS router that uses an ethernet accessible IP for its default gateway decide if the default route is available? Let's say that the interface that the router uses is an ethernet interface connected to a hub or switch. As long as the hub/switch is up the interface will sho as interface up, protocol up. If the default route gateway IP does not respond to pings will that "tell" the router to use another route?

Thanks,

Diego

2 REPLIES
Cisco Employee

Re: Default gateway detection

The default-route will stay in the routing table as long as the interface is up/up. If the interface is DOWN, then the route will be deleted from the routing table. When forwarding the traffic the following 2 case apply:

1. If the next-hop is specified, the the router will ARP for the next-hop ip and then forward the traffic.

2.If the next-hop is not known(ip route 0/0 eth0..this is not recommended), the router will ARP for each and every destination. The traffic will be forwarded to the whoever downstream router that responds to the ARp.

Rgds,

gopal

New Member

Re: Default gateway detection

So in case 1 above, when the router ARPs, there will be no reply. Will this delete the route from the tables?

Thanks,

Diego

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