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Static Route Unreachable Question

Hi,

I have a basic question that a few co-workers and I are tossing around.

Scenario:

Router A has two static routes as follows.

0.0.0.0 0.0.0.0 Router B

0.0.0.0 0.0.0.0 Router C 200

If Router B goes down but the layer 2 link stays up, what happens to the traffic destined for Router B?

Does it get dropped at Router A or does it hit the LAN to Router B but times out?

Does anyone have an article to forward me to with a good explanation?

I'm aware the route stays in the routing table in Router A causing a problem but am not sure what happens to the traffic.

Thanks all. I'm hoping for a Cisco article to reference but haven't been able to find anything yet.

-Jamie

3 REPLIES

Re: Static Route Unreachable Question

Hi,

it depends on the layer 2 technology you have.

A) Frame-relay: the router will send the frames down the specified DLCI and the frame relay switch will drop them (PVC down in the FR switch) or forward them to the point, where the PVC is broken.

B) Ethernet:

1) ARP entry for Router B still present. The router will send the traffic into the LAN switch with Router B MAC as destination. The LAN switch will flood the traffic to all ports in the VLAN (unknown traffic). There the traffic will be dropped.

2) ARP entry for Router B is timed out.

The router will arp for the next hop, i.e. for the IP of router B. As no ARP reply will be received, no valid ethernet frame can be created and the traffic is dropped locally in your router with the default route.

Hope this helps! Please rate all posts.

Regards, Martin

New Member

Re: Static Route Unreachable Question

Thanks Martin. I'm not sure about number one though. If the ARP entry is valid, it is assigned a port to pass traffic to. Why would it flood the switch like a broadcast? Please comment if I'm understanding it wrong.

-Jamie

Bronze

Re: Static Route Unreachable Question

Hi.

I am not sure about 1 st point which martin mentation.

But i am very much sure about 2nd point of martin..

-minu

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