It's great to see that Hybrid has IPv6 support, but it's not quite perfect.
Out of the box, while an attempt is made to listen on all interfaces over both
protocols, "address already in use" errors for the listening sockets may appear
in /var/log/ircd/ircd-hybrid.log — with a bit of configuration,
this can be fixed though.
The following is the relevant excerpt of the initial /etc/ircd-hybrid/ircd.conf:
listen {
port = 6665 .. 6669;
};
Messages like this appeared in the log when Hybrid was started:
binding listener socket irc.comssa.org.au[0::/6665]:Address already in use binding listener socket irc.comssa.org.au[0::/6666]:Address already in use binding listener socket irc.comssa.org.au[0::/6667]:Address already in use binding listener socket irc.comssa.org.au[0::/6668]:Address already in use binding listener socket irc.comssa.org.au[0::/6669]:Address already in use
With a bit of research, I found a forum thread with example configuration snippets to prepare services for IPv6, but it didn't quite work for two reasons. The suggested configuration was as follows:
listen {
host = "0.0.0.0"; # Bind to all IPv4
host = "::"; # Bind to all IPv6
port = 6665 .. 6669;
};
The same messages were logged, and clients were still unable to connect over
IPv6. As was the case earlier, netstat -l did not show any
services listening on those ports. I'm not sure if it's a bug in Hybrid, but
listening on a specific interface's IP address seems to be required for IPv6,
although I've never had to do this for other programs like nginx.
listen {
host = "0.0.0.0"; # Bind to all IPv4
host = "2001:470:7c85::1";
port = 6665 .. 6669;
};
I was then able to connect over IPv6, and I was delighted. All seemed well
until a few hours later when a client notified me that they were unable to
connect. They didn't have IPv6. Also broken was qwebirc, which uses IPv4.
Running netstat -l again now showed that Hybrid was listening only over IPv6, as if the second host line overrode the
first.
Digging into the source of Hybrid 8.1.13, the doc/reference.conf showed that host lines are essentially
optional modifiers for the next port line; you need one port line for each interface or address you wish to listen on. The
final configuration that listened properly on both IPv4 and IPv6 for me was:
listen {
host = "0.0.0.0"; # Bind to all IPv4
post = 6665 .. 6669;
host = "2001:470:7c85::1";
port = 6665 .. 6669;
};
As a brief note: like most daemons, sending SIGHUP to the
Hybrid process or running /etc/init.d/ircd-hybrid reload allows
you to use a new configuration without disconnecting any users. To my pleasant
surprise, even when enabling incorrect configurations that ceased to listen
over IPv4, existing IPv4 users still remained connected.