chi-node-14 failed to return with IPv4 on reboot
tonight i rebooted chi-node-14 and it failed to assign itself an IPv4 address.
it seems the trouble as the DAD (Duplicate Address Detection) algo failed to complete correctly:
-- Journal begins at Fri 2023-07-07 11:56:06 UTC, ends at Fri 2023-07-21 03:13:01 UTC. --
Jul 21 02:33:23 chi-node-14 systemd[1]: Starting Raise network interfaces...
Jul 21 02:33:29 chi-node-14 ifup[4084]: Waiting for DAD... Timed out
Jul 21 02:33:29 chi-node-14 ifup[3903]: ifup: failed to bring up eth0
Jul 21 02:33:29 chi-node-14 systemd[1]: networking.service: Main process exited, code=exited, status=1/FAILURE
Jul 21 02:33:29 chi-node-14 systemd[1]: networking.service: Failed with result 'exit-code'.
Jul 21 02:33:29 chi-node-14 systemd[1]: Failed to start Raise network interfaces.
the server was (thankfully!) still reachable over IPv6 so I added a quick hack to the interfaces(5) file:
dad-attempts 0
... which seems to have fixed the problem in the short term.
in the long term, there are few more questions here:
- why the hell did this fail in the first place?
- is this specific to this site? this server? a misconfiguration on our side or the other?
- is this going to happen again? on another server?
- is it safe to turn DAD off? abolish patriarchy and all, but it's just an acronym dude, chill out?
- is this something that would happen with systemd-networkd as well and do we want to switch already?
a bunch of links i found in my search:
- https://unix.stackexchange.com/questions/192869/why-is-my-dad-slow
- https://www.agwa.name/blog/post/beware_the_ipv6_dad_race_condition
- https://www.the-art-of-web.com/system/ipv6-dad-tentative/
- https://github.com/systemd/systemd/issues/650
- https://serverfault.com/questions/1110760/error-restarting-networking-service
- https://dataplane.org/jtk/blog/2022/12/ipv6dad/
i basically read none of those, and only found this and jumped on it:
https://manpages.debian.org/unstable/ifupdown/interfaces.5.en.html#dad-attempts
so maybe further research is needed here...
Edited by anarcat