Failure to access /_cockpit/ when connecting via IPv6

Pioneer behind router.

When attempting access of Cockpit from the WebGUI using a IPv6 routeable IPv6 address, I can get to the Login page, but after submitting credentials, I get a error page:

journalctl has:

– Boot 63ff2368109e477fa79f710099b649cb –
Aug 13 12:30:24 freebird systemd[1]: Starting cockpit.service - Cockpit Web Service…
Aug 13 12:30:24 freebird systemd[1]: Started cockpit.service - Cockpit Web Service.
Aug 13 12:33:24 freebird systemd[1]: cockpit.service: Deactivated successfully.
Aug 13 12:33:24 freebird systemd[1]: cockpit.service: Consumed 3.570s CPU time.
Aug 13 12:33:34 freebird systemd[1]: Starting cockpit.service - Cockpit Web Service…
Aug 13 12:33:35 freebird systemd[1]: Started cockpit.service - Cockpit Web Service.
Aug 13 12:35:06 freebird systemd[1]: cockpit.service: Deactivated successfully.
Aug 13 12:40:58 freebird systemd[1]: Starting cockpit.service - Cockpit Web Service…
Aug 13 12:40:58 freebird systemd[1]: Started cockpit.service - Cockpit Web Service.
Aug 13 12:42:32 freebird systemd[1]: cockpit.service: Deactivated successfully.
Aug 13 12:42:32 freebird systemd[1]: cockpit.service: Consumed 1.188s CPU time.
Aug 14 06:22:49 freebird systemd[1]: Starting cockpit.service - Cockpit Web Service…
Aug 14 06:22:49 freebird systemd[1]: Started cockpit.service - Cockpit Web Service.
Aug 14 06:24:24 freebird systemd[1]: cockpit.service: Deactivated successfully.
Aug 14 06:24:24 freebird systemd[1]: cockpit.service: Consumed 1.200s CPU time.
Aug 14 09:18:13 freebird systemd[1]: Starting cockpit.service - Cockpit Web Service…
Aug 14 09:18:13 freebird systemd[1]: Started cockpit.service - Cockpit Web Service.
Aug 14 09:19:50 freebird systemd[1]: cockpit.service: Deactivated successfully.
Aug 14 09:19:50 freebird systemd[1]: cockpit.service: Consumed 1.640s CPU time.
Aug 14 11:25:15 freebird systemd[1]: Starting cockpit.service - Cockpit Web Service…
Aug 14 11:25:16 freebird systemd[1]: Started cockpit.service - Cockpit Web Service.

There’s nothing different in the log between successful access and this failure. I think I’ve been able to access Cockpit over IPv6 previously, but I don’t know for certain.

If I change the url to an IPv4 address, I can reach the Cockpit UI (after allowing a browser security exception for self-signed cert).

All other url accesses using the IPv6 that I’ve tried have worked without problem (accessing apps & plinth config stuff, etc).

rickbol