Failing DNS resolution causes BGP sessions to flap

[Maria Matejka]

Hello!

this is going to be fixed by going multithreaded, then the BGP sessions will be independent on DNS resolution in RPKI.

Basically, BIRD 3 is the solution and there is not much of a hurry to fix this in BIRD 2. Also, you can just add the record to /etc/hosts, as you may want the RPKI to load before DNS is reachable.

Maria

On 21 October 2024 10:17:50 GMT-04:00, "Ondřej Caletka" <ondrej at caletka.cz> wrote:
>Dear BIRD users,
>
>I have recently noticed an interesting issue. A newly set up BGP session between BIRD on our side and a remote party running whatever was taken down every hour or so. The reason for the session being terminated was Received: Hold timer expired.
>
>Looking at the logs, it turned out that this was caused by broken DNS resolver on the machine where BIRD is running. Whenever BIRD was trying to resolve the host name of the RPKI Validator cache, it got stuck for 24 seconds. This was apparently enough for the other BGP speaker to consider it dead and take the session down (the hold timers were shortened from the standard values there).
>
>Oct 15 13:45:51 vrtr-4.mtg.ripe.net bird[907]: rpki_validator: Cannot resolve hostname 'rpki-validator.mtg.ripe.net': >
>Oct 15 13:45:51 vrtr-4.mtg.ripe.net bird[907]: I/O loop cycle took 24009.001 ms for 1 events
>Oct 15 13:45:51 vrtr-4.mtg.ripe.net bird[907]: Kernel dropped some netlink messages, will resync on next scan.
>Oct 15 13:45:51 vrtr-4.mtg.ripe.net bird[907]: peer_as2852_v4: Received: Hold timer expired
>Oct 15 13:46:55 vrtr-4.mtg.ripe.net bird[907]: peer_as2852_v4.ipv4: Automatic RPKI reload not active for import
>
>This case was fixed by making sure DNS resolver works, but I still wonder whether this is a known limitation or whether this is something that can possibly be improved.
>
>--
>Best regards,
>
>Ondřej Caletka

-- 
Maria Matejka (she/her) | BIRD Team Leader | CZ.NIC, z.s.p.o.
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