[c-nsp] IOS XR BFD

[Oliver Boehmer (oboehmer)]

Nick 'tarantul' Novikov <> wrote on Sunday, July 05, 2009 18:02:

> On Sun, Jul 5, 2009 at 4:59 PM, Pavel Lunin<plunin at senetsy.ru> wrote:
>> You know, I might also be missing something, but I don't see much
>> difference from iBGP's point of view. Traffic anyway goes through
>> RRs on the way from the core to outside as well as between ASBRs and
>> RRs know only defaults. What advantage does iBGP on subifs give
>> here? I'd understand if you had a link or an LSP between ASBRs and
>> wanted to exclude a possibility of passing plain IP traffic from one
>> ASBR to another through RRs, but in this case... am I missing
>> something? How loops are avoided now? 
> 
> 1. RR1 have 0/0 from ASBR1 (as best route) and send packets to RR1
> 2. ASBR1 have BGP session with ASBR2 and destination prefix close
> through ASBR2 
> 3. ASBR1 send packets back to RR1
> 4. Go to p.1
> 
> Ok, I can configure separated L2 path for ASBR1-ASBR2:
> ASBR1 -trunk- RR1 - xconnect - RR2 -trunk- ASBR2
> But if xconnect fails, I get the situation described above for the BGP
> timeout (3*60 seconds by default)
> To avoid this possible to configure the BGP session from ASBR subif
> and use BDF for fast session drop if L2 connect fails.

or, as I mentioned in another post, enable MPLS on ASBRs and RRs to get
the traffic tunnelled, and you can use ISIS BFD and next-hop tracking
and/or BGP-PIC for speedy convergence.

> And my question is not how I should be in this situation.
> What is the logical explanation that BFD does not work in internal
> neighbors? 

because it hasn't been developed to work in this scenario under XR,
which is likely due because it's not a commonly deployed setup.

	oli