I was setting up a new root-server machine and went for the Debian 7 minimal set-up. Thankfully the root-server provider I am using (hetzner) is connected with IPv4 and IPv6 natively. Awesome stuff!
If you’re using an IPv6 native set-up these days you STILL have to be cautious about possible side-effects with software having bugs and not knowing how to deal with these ginormous ip adresses.
So there’s a well known Jabber / XMPP server that I am using for some years now without any issues. I was even using it on native IPv6 connected machines earlier.
But with the fresh and clean set-up of Debian 7 and IPv6 by the hoster several problems started bubbling up.
1: the ‘there can only be one ipv*’ problem
Turns out that the debian team decided to set a system setting by default that lets IPv6 aware applications bind to IPv6 only. Good thing, you can disable it by adding this to your sysctl.conf:
net.ipv6.bindv6only=0
2: the ‘who resolves first is right’ problem
When you get a IPv6 native machine it might have a resolv.conf consisting of IPv4 and IPv6 name servers. And don’t worry: Everything is going to be all-right as long as the software you’re planning to use is perfectly capably dealing with the answers of both types of servers. The IPv4 ones will default to the A records, the IPv6 ones to the AAAA record.
Now there’s OpenFire. A stable and easy to use XMPP / Jabber server implementation. It’s based upon Java and I am running it with Java 7 on my Debian machine.
Unfortunately in the current 3.9.1 version of OpenFire there’s a bug that leads to Server-to-Server XMPP connections not working when they resolv to IPv6. So for example your Google-Talk contacts won’t work at all.
The bug itself is rather stupid: Seems that OpenFire expects an IPv4 adress from the DNS lookup and crashes on an IPv6 adress.
The solution is as easy as the bug is stupid: Remove the IPv6 defaulting nameservers from your resolv.conf.
# nameserver config
nameserver 2xx.xxx.yyy.99
nameserver 2xx.xxx.yyy.100
nameserver 2xx.xxx.yyy.98
nameserver 8.8.8.8
nameserver 8.8.4.4
#nameserver 2axx:yyy:0:zzzz::add:9898
#nameserver 2axx:yyy:0:zzzz::add:9999
#nameserver 2axx:yyy:0:zzzz::add:1010
Source 1: defaulting to net.ipv6.bindv6only=1
Source 2: http://community.igniterealtime.org/thread/51902