[asterisk-dev] SIP replies to via or to ip/port (according toRFC)

Nick Lewis Nick.Lewis at atltelecom.com
Thu Dec 17 05:10:05 CST 2009

>1) Force an rport parameter in the first Via header. The (default)
>described in paragraph A above will do the rest.
>2) Force symmetric RTP.

I think that strictly speaking it is down to the UAC behind the firewall
request RFC3581 behaviour by adding an empty rport rather than the
UAS adding it unilaterally. However I agree with this approach so that
the setting is nat=yes (rather than nat=route or nat=never) asterisk 
will operate "as if" the UAC had added the rport parameter. 

The situation with nat=no is more tricky - perhaps the default could be 
changed to nat=never and nat=no depecated. 

It may be worth having another setting nat=compliant that just does as
requires i.e. if rport is received then use both symmetric rtp and

Also we need to consider an option nat=auto that operates as per nat=yes
only for contact addresses and

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