Bidirectional Forwarding

Is BFD a checking mechanism for L2 or L3 remote link?
Wikipedia does not state it clearly.

Find more posts tagged with

Comments

You can use it instead of relying on say your OSPF/EIGRP/BGP Hellos to do Fast Hellos (sub-second link failure detection) done in Layer 2 instead of Layer 3.

You'll detect dead peers faster, done in hardware(else it'll drown your device).

Wiki might not say a lot about the topic but there's plenty of articles on it

dppagc

joetest your answer is contradictory.
OSPF/EIGRP/BGP is layer 3.
However, you mentioned BFD is for layer 2.
This is where I am confused.

joetest

I can see how it's confusing.

BDF is a forwarding path failure detection protocol.

Back in the day it was designed for directly connected peers meaning it was designed to detect Layer-3 next-hop failures and had to be on a shared/directly connected subnet (no more than 1 IP hop away). As for BFD in Layer 2 I meant it should be done in the forwarding plane(hardware) and not the control plane (like OSPF/EIGRPs Hellos) using CEF.

Nowadays you can set up a BFD session with IP connectivity between the routers. So long you allow UDP packets to flow all the way through your routers you can use Multihop created BFD Sessions.
A really nice blog post about on packetpushers: http://packetpushers.net/using-bfd-to-detect-wan-forwarding-errors/

So I think the answer to your question would be both if I understand correctly.

dppagc

Hi joetest,

Can you give a configuration example for layer 2 connectivity for e.g. between 2 cisco 2960 swittches. I am not sure whether this can work though.

joetest

dppagc wrote: »

Hi joetest, Can you give a configuration example for layer 2 connectivity for e.g. between 2 cisco 2960 swittches. I am not sure whether this can work though.

Seems you can't do it on a switch without IP Base. http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960xr/software/15-2_4_e/configuration_guide/b_1524e_consolidated_2960xr_cg/b_1524e_consolidated_2960xr_cg_chapter_01001111.pdf