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Incoming RTP traffic blocked by SPA112 ATA: UDP port unreachable

Hi folks,

I'm using a Cisco SPA112 ATA behind a NAT, where port 5060,5061 and 16384-16482 are forwarded. Registration to the SIP proxy also works fine. However, I'm struggling with audio issues, meaning that the RTP session is not setup properly.

When investigating this issue at the packet-level, I found that the ATA itself is blocking traffic:

21:00:21.857655 IP 192.168.x.y > 82.197.a.b: ICMP 192.168.x.y udp port 16452 unreachable, length 208

The blocked port number depends per session, but is always between 16384 and 16482.

Actually, the issue sounds very much like in [1]. However, the proposed solution (disabling CDP) is not of any help to me, since it's disabled on my ATA by default. Any clue what could be the reason for this behaviour? Your help is greatly appreciated.


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