Suspicious Routers

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Asterisk Users 1 Comment

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 —

One thought on - Suspicious Routers

  • Darryl,

    Most of the cheaper NAT implementations appear to assume that there’s ever only just one client on the LAN side sending traffic from port A to a server port on the WAN side. For TCP this assumption is a nice hack with not too much risk, for UDP applications which send traffic from a well known port to a well known port, this is killing.

    I’ve added a full chapter on this problem in our manual that gets sent to customers, which basically says to reconfigure the SIP clients to all use a different source port for SIP traffic. This should be applicable to most UDP based protocols.

    I think this is valid for most routers below a certain price point
    ($250?), perhaps those running Linux might not be affected.