[asterisk-users] Suspicious routers

Darryl Moore darryl at moores.ca
Tue Sep 9 14:35:27 CDT 2014

Hello list,

I have again come across a router which behaves very badly with my IAX2
packets. This time I've documented it and thought I'd share to see if
anyone else has seen similar issues.

I have two asterisk servers running behind a dlink DI-604 Internet
router. Both are trying to use the same IAX account to connect to the
same remote asterisk server to place phone calls. Niether register with
the remote box. They both only use it to place outgoing calls when the
need arises. They do both monitor quality though, and one works while
the other does not.

Using tcpdump to see the IAX traffic on both machines yields the following.

---- machine #1 ----

15:27:04.325773 IP > UDP
15:27:05.327026 IP > UDP
15:27:24.325523 IP > UDP
15:27:25.326783 IP > UDP
15:27:44.324648 IP > UDP
15:27:45.325916 IP > UDP
15:28:04.324285 IP > UDP
15:28:05.325570 IP > UDP
15:28:24.323868 IP > UDP
15:28:25.325132 IP > UDP

As you can see this machine is trying desperately to talk to the remote
server, but there is never any response.

----- machine #2 -----

15:27:04.364718 IP > UDP
15:27:05.363308 IP > UDP
15:27:24.362713 IP > UDP
15:27:25.365736 IP > UDP
15:27:33.182751 IP > UDP
15:27:33.205658 IP > UDP
15:27:33.205936 IP > UDP
15:27:44.362897 IP > UDP
15:27:45.364978 IP > UDP
15:28:04.362375 IP > UDP
15:28:05.365890 IP > UDP

Oh look here's the responses! It would appear that all the responses to
the packets from both machines are being sent to the one machine.


I've seen and suspected this before, and changing the old cheap routers
has generally fixed this, but I'm wondering if anyone else has seen this
before, and if there are other routers I need to worry about. I don't
yet have an automated way to test routers for this, but I'm seriously
thinking about coming up with something.


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