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Discard SRTP Packet with wrong MAC


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Hi guys,


We have some extensions on a domain that have been working fine and connected for 90 days plus.


Recently 3 of the extensions were restarted and now they will not re-register.


The logfile in the domain of the PBX is showing these for the extensions trying to register: (replaced a few digits with x)



[7] 2016/08/09 11:44:45: Port 59: Discard SRTCP packet from 210.10.xxx.xx:53709 with wrong MAC

[7] 2016/08/09 11:44:45: Port 367: Discard SRTCP packet from 210.10.xxx.xx:62129 with wrong MAC

[7] 2016/08/09 11:44:46: Port 154: Discard SRTCP packet from 210.10.xxx.xx:52753 with wrong MAC


We've connected one of the problem extensions using a different handset at a different location/network without any problem. Haven't tested handsets from the site with the problems on a different location/network as yet.


Any ideas on what could be causing this problem?


Many thanks


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Media encryption is not in a perfect world. The way it was designed with the "Roll over counter" made it hard to implement it without having to guess what the counter value is. SRTP seems to be stable with the implementations that we know, but SRTCP still is a problem with some phone types. For example, if the SDP negotiations between the PBX and the phone agrees on 32-bit MAC, the SRTP packet still must use 80 bit. That might be the problem here. The next software update for the phones might solve the problem (which phones are you using).


The good news is that SRTCP is not essential and you can still talk.

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