[j-nsp] BGP timer

[Jeff Haas]

BFD holddown is the right feature for this.
WARNING: BFD holddown is known to be problematic between Juniper and Cisco implementations due to where each start their state machines for BFD vs. BGP.

It was a partial motivation for BGP BFD strict:
https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-bfd-strict-mode

BGP BFD strict was added in 23.2R1.

-- Jeff


On 4/28/24, 05:13, "juniper-nsp on behalf of Thomas Bellman via juniper-nsp" <juniper-nsp-bounces at puck.nether.net <mailto:juniper-nsp-bounces at puck.nether.net> on behalf of juniper-nsp at puck.nether.net <mailto:juniper-nsp at puck.nether.net>> wrote:


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Juniper Business Use Only
On 2024-04-27 09:44, Lee Starnes via juniper-nsp wrote:


> Having difficulty finding a way to prevent BGP from re-establishing after a
> BFD down detect. I am looking for a way to keep the session from
> re-establishing for a configured amount of time (say 5 minutes) to ensure
> we don't have a flapping session for a. link having issues.


Isn't that what the holddown-interval setting does? It is limited
to 255 seconds (4 minutes 15 seconds), though, and for BGP it is
only allowed for EBGP sessions, not iBGP sessions.


The documentation also says that you need to set holddown-interval
on *both* ends. I'm gueesing that the holddown only prevents your
end from initiating the BGP session, but that it will still accept
a connection initiated from the other end.


https://www.juniper.net/documentation/us/en/software/junos/cli-reference/topics/ref/statement/bfd-liveness-detection-edit-protocols-bgp.html <https://www.juniper.net/documentation/us/en/software/junos/cli-reference/topics/ref/statement/bfd-liveness-detection-edit-protocols-bgp.html>


I haven't used BFD for BGP myself, though, only for static routes
on a couple of links. But there I do use holddown-interval, and
at least when I set it up several years ago, it seemed to do what
I expected: after the link and the BFD session came up again, it
waited (in my case) 15 seconds before enabling my static route
again.




--
Thomas Bellman, National Supercomputer Centre, Linköping Univ., Sweden
"We don't understand the software, and sometimes we don't understand
the hardware, but we can *see* the blinking lights!"