Web GUI only available through IPv6: how can I fix this?

Hi everybody,

I’ve installed Syncthing on a Ubuntu 12.04 amd64 system and am not able to open the web GUI page remotely. I have changed the config.xml file accordingly to the instructions, but it seems that the web page is only available through ipv6 and not through ipv4. (The strange thing is that synchronization works as expected, as the corresponding UDP port is available both as ipv4 and ipv6).

Here is what syncthing writes at startup:

$ syncthing -no-browser
[monitor] 11:38:55 INFO: Starting syncthing
[KVNRW] 11:38:55 INFO: syncthing v0.10.30 (go1.4.2 linux-amd64 default) unknown-user@syncthing-builder 2015-03-29 07:46:44 UTC
[KVNRW] 11:38:55 INFO: My ID: ...
[KVNRW] 11:38:56 INFO: Starting web GUI on
[KVNRW] 11:38:57 INFO: Starting UPnP discovery...
[KVNRW] 11:39:03 INFO: UPnP discovery complete (found 0 devices).
[KVNRW] 11:39:03 INFO: Starting local discovery announcements
[KVNRW] 11:39:03 INFO: Starting global discovery announcements

The fact that syncthing writes in the log messages seem to indicate that everything should work as expected. However, I cannot browse the web GUI remotely, only locally. (If you’re curious, running telnet ADDRESS 8080 remotely produces the message “Unable to connect to remote host: Connection timed out”). Connecting to ADDRESS using SSH works as expected.

Here is what I see using netstat:

# netstat -4 -lnp | grep sync
udp   0      0*             5782/syncthing
# netstat -6 -lnp | grep sync
tcp6  0      0 :::22000      :::*           LISTEN      5782/syncthing  
tcp6  0      0 :::8080       :::*           LISTEN      5782/syncthing  
udp6  0      0 :::34953      :::*                       5782/syncthing  
udp6  0      0 :::21025      :::*                       5782/syncthing  
udp6  0      0 :::21026      :::*                       5782/syncthing  

I do not really understand where is the problem. May anybody provide some hints about where to look for a solution? (E.g., is there any debugging features of syncthing useful for my problem? or Linux commands similar to netstat that can help me in pinpointing the source of the problem…)

Thanks a lot, Maurizio.

This sounds like a firewall.

(The sockets showing as tcp6/udp6 is normal. This is how they look when they are listening on both IPv4 and IPv6.)

Thanks a lot! I quickly checked the existence of a firewall before posting, but your answer made me double-check. It turns I was wrong: I just used ps aux | grep iptables and found no entry, but iptables is a kernel module and should be looked for using lsmod.

Once I realized this, I opened 8080 and now the web GUI is accessible remotely as well. Maurizio.