We had a similar issue when we migrated to debain a while back; flapping sessions, weird timeouts, etc. Tweaking `net.ipv6.route.max_size' helped. Some clues: - https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=861115#10 - https://bird.network.cz/pipermail/bird-users/2020-February/014270.html Regards, Honghao Zeng

On Mar 22, 2021, at 4:29 PM, Pavlo Astakhov <jared@jared.kiev.ua> wrote:

Hello, all

I got a weird question. We recently migrated two our routers from CentOS 7 to Debian 10, installed Bird, placed config files back - and since then we are observing BGP flaps.

Moreover, flaps are observed on IPv6 peers only:

Name Proto Table State Since Info device1 Device --- up 2021-03-18 15:42:27 direct1 Direct --- up 2021-03-18 15:42:27 kernel1 Kernel master4 up 2021-03-18 15:42:27 kernel2 Kernel master6 up 2021-03-18 15:42:27 static1 Static master4 up 2021-03-18 15:42:27 static2 Static master6 up 2021-03-18 15:42:27 UPLINK BGP --- up 2021-03-18 15:42:31 Established UPLINKv6 BGP --- up 2021-03-22 21:11:12 Established AR1 BGP --- up 2021-03-18 15:42:31 Established AR1v6 BGP --- up 2021-03-19 23:42:55 Established AR2 BGP --- up 2021-03-18 15:42:28 Established AR2v6 BGP --- up 2021-03-20 15:37:38 Established BR2 BGP --- up 2021-03-18 15:42:28 Established BR2v6 BGP --- up 2021-03-21 11:03:33 Established ospf4 OSPF master4 up 2021-03-18 15:42:27 Running ospf6 OSPF master6 up 2021-03-18 15:42:27 Running

Flaps are unregular, currently we saw no coincedences with anything. The network is stable, our and peers configs were not changed, Bird version too (2.0.7 on both CentOS and Debian).

The only message about this in logs is hold-related:

2021-03-22 21:01:10 <WARN> Kernel dropped some netlink messages, will resync on next scan. 2021-03-22 21:04:33 <WARN> Kernel dropped some netlink messages, will resync on next scan. 2021-03-22 21:06:10 <WARN> Kernel dropped some netlink messages, will resync on next scan. 2021-03-22 21:10:12 <RMT> UPLINKv6: Error: Hold timer expired 2021-03-22 21:10:13 <WARN> Kernel dropped some netlink messages, will resync on next scan. 2021-03-22 21:10:15 <WARN> Kernel dropped some netlink messages, will resync on next scan. 2021-03-22 21:10:16 <WARN> Kernel dropped some netlink messages, will resync on next scan. 2021-03-22 21:10:16 <WARN> Kernel dropped some netlink messages, will resync on next scan.

Could you please suggest some way to go except of returning to CentOS?

Thank you in advance.

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