Source port SIP 5060 is sometimes not natted


We have recently purchased a Peplink Balance One Core. It works pretty good except for one specific case.

We have some difficulties to access SIP servers on the Internet from LAN devices using source port UDP 5060.

Example: I have multiples phones in the LAN that all use port UDP 5060 as source. When I look at the SIP packets arriving on the SIP server on the Internet, I can see multiple devices where the source port has been natted (to random source ports) but some packets arrive on the server with the source ports still on UDP 5060, meaning the Peplink didn’t NAT these source ports. The returned packets from the server to the phones never reach the internal phones (probably because the Peplink sends the returned traffic to only one LAN device, or to nothing).

The SIP ALG has been deactivated on the Peplink (compatibility mode).

If I change the source port on the phone, then it works.
If I configure the phones to use TCP, it works as well.

Have you already seen this behavior?



This is not the expected behavior. Please perform Network Capture via http://LAN IP/cgi-bin/MANGA/support.cgi when you notice the problem occurs. Then open ticket for us to investigate.


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