There appears to be a configuration error in the context of IPv6 for the host community.openhab.org. The hostname resolves to a DNS AAAA record pointing to IPv6 address 2a0a:4cc0:c1:1dd2::
$ dig AAAA community.openhab.org
; <<>> DiG 9.18.39-0ubuntu0.24.04.2-Ubuntu <<>> AAAA community.openhab.org
[…]
;; QUESTION SECTION:
;community.openhab.org. IN AAAA
;; ANSWER SECTION:
community.openhab.org. 160 IN AAAA 2a0a:4cc0:c1:1dd2::
This address is not reachable, though. I tried from different networks (different ISPs, different autonomous systems), and both pings and traceroutes always get stuck somewhere along the way:
$ ping6 community.openhab.org
PING community.openhab.org (2a0a:4cc0:c1:1dd2::) 56 data bytes
From 2a01:[...] icmp_seq=13 Destination unreachable: Address unreachable
The address belongs to a validly assigned address block, owned by Netcup GmbH. But given the huge number of trailing zeroes, it doesn’t really look like a host address. Therefore, the most likely reason for this problem is that the DNS AAAA record is simply wrong, because someone added a network address instead of the host address there.
Why is this a problem? Well, it makes accessing the forum unnecessarily slow when you’re coming from an IPv6-capable network. My IPv6-connected hosts always try to connect using the IPv6 address first, and retry with IPv4 only after timing out. The first connection to the server is therefore significantly delayed.
How to fix? Correct the DNS entry. Or, if the server is actually not reachable via IPv6 at all, remove the DNS entry, so that all clients go for IPv4 right away.
