[asterisk-users] configure SRTP port range?

Joshua C. Colp jcolp at digium.com
Sat Feb 23 10:39:11 CST 2019

On Sat, Feb 23, 2019, at 12:17 PM, hw wrote:


> > Any source to UDP ports X to Y (10000 to 20000 by default) allow.
> Are you saying that the ports specified in rtp.conf ('rtpstart' and 
> 'rtpend') specify with ports asterisk uses regardless whether RTP or 
> SRTP is being used?  Is that why you speak of "media" (ports)?
> (That would have been and would answer my original question: Where to 
> specify the SRTP ports?)

> > What you can't do is limit the rule based on the source of media, except for circumstances where you know for sure the source.
> > 
> > Note that RTP ports in Asterisk aren't open all the time and only listen when a call is using it, and they also learn the source of media - blocking out other sources.
> > 
> ok
> After opening the ports specified in rtp.conf, both RTP and SRTP were 
> working in the test calls I made.  But:
> How do clients know which media ports to use?  Is asterisk telling them 
> that?
> I. e., can I (basically) rely on the clients to use the media ports in 
> rtp.conf, or did I just get lucky that by chance the clients happened to 
> use these ports when I made the test calls?

It's exchanged as part of call setup using SDP. SDP specifies where media should be sent, the codecs that can be used, and also controls hold/unhold. Each side provides SDP which is parsed, interpreted, negotiated, and used.

Joshua C. Colp
Digium - A Sangoma Company | Senior Software Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - US
Check us out at: www.digium.com & www.asterisk.org

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