eigrp and managed ethernet

For some reason when I lose layer 3 connectivity between two managed Ethernet sites EIGRP does not bounce.Is this because the physical interface does not bounce?

Correct. Eigrp neighbor connectivity has a short-cut when L2 connectivity goes down, otherwise it will use the eigrp neighbor hold-down timer. You can decrease that timer:

interface fa0/0
  ip hello-interval eigrp p x
  ip hold-time eigrp p y

where p is your eigrp as-number, and x is how often you want the hello (in seconds) and y is the max hold-down timer. Generally y is = x * 3


Yeah. If the link-layer failure is hidden from your routing protocol, then
the routing protocol has to rely on its timer setting. When your EIGRP's
hold-time expires, peering would bounce.


Because EIGRP hellos are sent via IP multicast, layer 3 connectivity is
required to establish and maintain adjacencies. However, layer 3 failures
aren't detected for, at most, 15 seconds by default on an Ethernet link.

Stephen Kratzer
Network Engineer
CTI Networks, Inc.