bfd on FastEthernet interface

[jerryting]

Sir

Network environment is Router A <->L2 Switch <-> Router B Use fastethernet connection in the middle

If in the FastEthernet config

bfd interval milliseconds min_rx milliseconds multiplier interval-multiplier

Whether it can speed up FastEthernet0/0 line protocol to down？

[Joseph W. Doherty]

Yes it can.

With a physical topology like yours, a link between one of the routers and the L2 switch might go down.  If that happens, the router with that link would see the down port, but the other router would still see its link as being up.  In cases like this, you often rely on a dynamic routing protocol's ability to detect it's lost connectivity to its peer, although it doesn't see a link outage.  Depending on the routing protocol, and its configuration, such an outage might go unnoticed for a short while.  For example, OSPF with its default settings, might not notice the outage for up to 40 seconds.

Dynamic routing protocols peer hellos can often be adjusted in their frequency, but not all support subsecond loss detection and those that do can create a lot of overhead.  BFD provides both subsecond loss detection and is "efficient".

[jerryting]

Sir

I did not run any Dynamic routing, I just used static default route to internet int the 2 ISP. but need bfd,So that one of them FastEthernet protocol to down and one of the static routes removed.

it can？

[Joseph W. Doherty · Accepted solution]

I don't believe BFD works with static routes.

However in a case like your, loss of path can be done with IP SLA tracking.

For an example:

http://www.cisco.com/c/en/us/support/docs/ip/ip-routing/200785-ISP-Failover-with-default-routes-using-I.html