Nexus 7000 - BFD with Loopback support

[john_sev]

Without going into a ridiculous amount of details just yet, the problem is as follows.

Let's take this topology:

N7K2 --iBGP-- N7K1

                            |

                         eBGP

                            |

                       Router1

The situation as is:

1.) N7K1 has an iBGP peering with N7K2

2.) N7K2 has an eBGP peering with Router1

3.) N7K2 gets the routes from Router1 via N7K1

The problem today is that if N7K1 goes down, N7K2 will only withdraw the BGP routes originated by Router1 when the BGP holdtimer expires (15 seconds in this case), and since it's the main WAN link, this would need to be less than 5 seconds. Normally, BFD would solve the problem, however, we're running iBGP on loopbacks between the 2 N7Ks, and I can't seem to find any clear documentation on how to run BFD between two loopbacks for N7K.

Has anyone tried something like this before?

(And before you go into "why isn't this connected redundant", the topology is larger than this, and it's actually a DC redundancy problem, it's genuinely that the timers would benefit from BFD)

[cofee]

Hi,

Please check out this link, you may find it useful.

http://kemot-net.com/blog/nexus-ibgp-with-bfd

[john_sev]

I'm sure that if you look into the article you'll quickly see that the loopback part isn't mentioned, which is the biggest challenge. Under Nexus config (and for that matter on a lot of other platforms) you can't go and set up bfd configuration under your loopback. 

That's on p2p if ibgp peering, which is a lot easier (and then indeed, BFD works with a few quirks in configuration)

My feeling is that this is mhop bfd (loopback-to-loopback would end up being mhop) so the adjacency in bfd doesn't even come up (or I can't seem to find the right config to do it)