Bidirectional Forwarding

dppagc

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

joetest

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