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