IRC not working over HE.net 6in4 tunnel? read on...
I recently switched VPS's (to Digital Ocean) and because my new co-location provider does not come with native IPv6, I had to use a tunnel. Naturally I chose tunnelbroker.net. However, after reestablishing all important services, I noticed that TCP ports in the range 6666-6669 don't work -- not on IPv6 anyways. These are usually used by IRC servers.
I did a bit of detective work on trying to figure out what was going on. Initially looking for solutions on the internet, but all I found were other people having this same problem with tunnelbroker.net tunnels.
Now, it seems that the packets are getting into their network.
Look over this TCP traceroute example:
$ tcptraceroute6 irc6 6666
1 tube (2607:f2c0:f00e:999::1) 0.198 ms 0.260 ms 0.188 ms
2 2607:f2c0:1::2:14 (2607:f2c0:1::2:14) 12.108 ms 13.040 ms 11.939 ms
3 2607:f2c0:1:2120::2 (2607:f2c0:1:2120::2) 12.876 ms 11.137 ms 10.982 ms
4 10gigabitethernet4-3.core1.tor1.he.net (2001:470:1:2de::1) 11.704 ms 14.839 ms 19.287 ms
5 10gigabitethernet7-3.core1.chi1.he.net (2001:470:0:1e2::2) 21.271 ms 21.266 ms 22.184 ms
6 tserv1.chi1.he.net (2001:470:0:6e::2) 27.561 ms 26.941 ms 27.180 ms
7 * * *
8 * * *
9 * * *
10 * * *
In the above example, you can see that the TCP traceroute breaks after
getting to tserv1.chi1.he.net.
Let's compare it to a port that works, like 5000 -- also used by IRC but for server-to-server communication.
$ tcptraceroute6 irc6 5000
1 tube (2607:f2c0:f00e:999::1) 0.259 ms 0.228 ms 0.261 ms
2 2607:f2c0:1::2:14 (2607:f2c0:1::2:14) 13.000 ms 11.475 ms 12.787 ms
3 2607:f2c0:1:2120::2 (2607:f2c0:1:2120::2) 11.347 ms 10.918 ms 11.036 ms
4 10gigabitethernet4-3.core1.tor1.he.net (2001:470:1:2de::1) 19.952 ms 11.974 ms 21.632 ms
5 10gigabitethernet7-3.core1.chi1.he.net (2001:470:0:1e2::2) 26.053 ms 24.848 ms 21.408 ms
6 tserv1.chi1.he.net (2001:470:0:6e::2) 27.132 ms 26.866 ms 26.718 ms
7 mytunnel-2-pt.tunnel.tserv9.chi1.ipv6.he.net (2001:470:1f10:999::2) 46.349 ms 46.849 ms 41.896 ms
Note that in this case the packets make it through to the tunnel end point.
The unfortunate part of this exercise is that in the world of tunnelled IPv6, a lot of things happen between "6" and "7".
Fortunately, all you need to do is go to the tunnelbroker.net website,
select your tunnel, and go to the Advanced tab. Here you will find a button to
unblock IRC.
I did this, and all of a sudden my packets went though.
Yey!