Sean A. Walberg wrote:
That said, Bill brought up the idea of ARP tables. This has two problems:
1 - If the link is idle for a while, the arp cache will clear, and be seen as a failure 2 - There are lots of layer 2 networks that don't use ARP. The ethernet code is separate from the ipv4 code.
In addition, this is a common problems on hardware routers. Even a box that's specifically designed to be a router can't do it without resorting to ICMP tests and policy routing.
Good comments Sean. I agree with your comments and it agrees with what I saw when I was doing testing of default route failover a few years back. The only way I could get it to work efectively was for a program ping the gateways to see if they are up and change the default routes when it noticed a failure.
On the otherhand when the NIC dies (layer 1 ?) layer 3 finds out about it but routing does need to be aware of the interface. I think it tries to send packets to a host out the same interface that it received packets from the host.
-- Bill