Have to delete/recreate extensions with SRTP/DTLS enabled

@Hawkeye wrote:

Hi, been at this for hours and hours.
For a long time, there was no issue like this. This seems to have started about a week ago.

The problem in a nutshell is inbound calls hangup soon as they are answered by end point.

First noticed this issue on cell phone with Bria. Subsequently found same issue in our Grandstream phones.

For some reason, when end point is configured with:
Transport = UDP
SRTP = yes
DTLS = yes

We could not answer a call as the call would immediately hangup. Seems the reason is:

[2017-03-20 11:57:39] WARNING[4386][C-0000003b]: chan_sip.c:10760 process_sdp: Failed to receive SDP offer/answer with required SRTP crypto attributes for audio

Below is part of a call:

<--- SIP read from UDP:xxx.xx.72.210:57225 --->
SIP/2.0 200 OK
Via: SIP/2.0/UDP xx.xx.85.115:5060;branch=z9hG4bK37cfe498;rport=5060
From: "JOHN TRUCKING" ;tag=as0c9703b7
To: ;tag=1040663773
Call-ID: 21ce57fa54030f9445391dee7f41f74c@xx.xx.85.115:5060
CSeq: 102 INVITE
Contact:
Supported: replaces, path, timer
User-Agent: Grandstream GXP2130 1.0.7.97
Allow: INVITE, ACK, OPTIONS, CANCEL, BYE, SUBSCRIBE, NOTIFY, INFO, REFER, UPDATE, MESSAGE
Content-Type: application/sdp
Content-Length: 212

v=0
o=320 8002 8000 IN IP4 xxx.xx.72.210
s=SIP Call
c=IN IP4 xxx.xx.72.210
t=0 0
m=audio 5008 RTP/AVP 0 101
a=sendrecv
a=rtpmap:0 PCMU/8000
a=ptime:20
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
<------------->
--- (12 headers 11 lines) ---
Found RTP audio format 0
Found RTP audio format 101
Found audio description format PCMU for ID 0
Found audio description format telephone-event for ID 101
[2017-03-20 11:57:39] WARNING[4386][C-0000003b]: chan_sip.c:10760 process_sdp: Failed to receive SDP offer/answer with required SRTP crypto attributes for audio
sip_route_dump: route/path hop:
Transmitting (NAT) to xxx.xx.72.210:57225:
ACK sip:320@xxx.xx.72.210:57225 SIP/2.0
Via: SIP/2.0/UDP xx.xx.85.115:5060;branch=z9hG4bK1867acbe;rport
Max-Forwards: 70
From: "JOHN TRUCKING" ;tag=as0c9703b7
To: ;tag=1040663773
Contact:
Call-ID: 21ce57fa54030f9445391dee7f41f74c@xx.xx.85.115:5060
CSeq: 102 ACK
User-Agent: FPBX-13.0.190.19(13.14.0)

The above partial call is AFTER changing SRTP to NO, Transport to UDP Only and DTLS to NO.

Decided to change configuration for a few extensions in FreePBX and End points and go plain vanilla. NO SRTP, NO DTLS. UDP Only

The only fix was to delete the extensions in FreePBX and recreate them. After recreating the extensions with no SRTP, No DTLS and transport set to UDP only, inbound calls worked as they should.

We use wild card CA Signed certificates. Not real sure if the certificate is the cause but why the error above regarding SRTP when SRTP is set to OFF is beyond me.

Thanks.

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