If I have only one rtp proxy should I use set_rtp_proxy_set("0")? I think openser should be smart enough to figure it out if there is only one rtp proxy.

It looks like there is a cut and paste error in the 1.3 nathelper wiki.

1.6.3. set_rtp_proxy_set()

Sets the Id of the rtpproxy set to be used for the next [un]force_rtp_proxy() command.

This function can be used from REQUEST_ROUTE, ONREPLY_ROUTE, BRANCH_ROUTE.

Example 1-17. fix_nated_contact usage

...

set_rtp_proxy_set("2");

force_rtp_proxy();

Rob

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