Enforce SRTP but ONLY on the internal leg/side

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bort900

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Feb 28, 2025
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Hi all,

New Fusion/Freeswitch user here, coming from years of asterisk/FreePBX.

I am trying to setup my instance so that my endpoints register with TLS and are forced to use RTP media encryption. After reading some posts, I set the following Switch Variables for ONLY the 'SIP Profile: Internal' internal_ssl_enable = true and rtp_secure_media = mandatory. (both using the 'set' command)

Using a SIP client I verified that i can only place a call with media encryption enabled on my SIP client. Unencrypted calls are declined with a Not Acceptable here. So far so good.

Next I added a basic outbound route, and the call goes thru, BUT i noticed via the CLI and sngrep the SDP sent from my box to my provider has a crypto line! I am definitely not registering TLS with my provider, but they seem to accept RTP/SAVP on an outbound call. Weird but OK. The real problem is i can not call into my PBX. The CLI shows 'Crypto not negotiated but required'

It seems to me that the rtp_secure_media = mandatory is propigating up/down the call path even though i only have it set on the 'Internal' Profile. I've verified my gateway is set to the 'external' profile.

I have read that some people put stuff in the dialplan, but after a few days of looking at this, i am still not sure what or where i would put something in dialplan without affecting other functions or impacting security.

My ask is: What missing from the internal/external concepts thats making not work as i would expect? that is, TLS/SRTP ONLY on the internal side of the call leg? Is there a documented way to implement this that i am just missing?

This is on a fresh Debian 12 install of the latest FusionPBX install script. I am using LetsEncrypt for TLS. I am happy to provide any screenshots or logs. Thanks all!
 
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