RTP to non-standard port when call goes to voicemail

Asterisk Asterisk SIP
1

I have encountered an issue where on a SIP trunk between two Asterisk servers, only calls that are not answered, go to a non-standard RTP port and the Voicemail service is not handled by Asterisk

Example 1 - Everything Works
A Calls B, B answers. Good to go

Example 2 - No RTP in Voicemail
A calls B, B lets the call go to Voicemail. Voicemail Application activates, but no RTP is received.

After receiving RTP pakcets from the far side server the near side responds on a non-standard port. Shown in the trace below.

I have checked the rtp.conf and the start and end range match on both sides.

[general]
prtpstart=10000
rtpend=20000

Anything else I should look for. I am looking at any firewall port forwarding or blocking, but I do not think thats the case here.

image

2

prtpstart? Is that a typo or did you copy it exactly as it is?

3

Where is the trace for the failure case?

4

ah. yeah that is a typo in the post, that is not present in the config file. cant seem to find an option to edit the original post though.

5

I cant provide the whole trace, but if there’s a portion of it that would be helpful I can see about getting that.

6

Portions generally don’t help. You have to understand the full situation and everything involved. For example you mention a firewall, if NAT is involved then it could be using a UDP port mapping outside of the configured page.

7

And the portion that was obviously missing was the one that exhibited the symptoms.

8

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