this is an issue which I've been discussing with Brian West on IRC and in e-mail correspondence, which I thought I should bring to the list so that others can look at it as well. The configuration My external SIP profile has its ext-sip-ip and ext-rtp-ip set to stun:stun.freeswitch.org. This is necessary for nat traversal. I have an internal-ipv6 profile as well, which is working, but for some reason it's interfering with calls on the external profile (which of course is an IPv4 profile). The symptom is the following line in outgoing SIP messages while attempting to establish a call to a gateway via the external profile: o=FreeSWITCH 1245193059 1245193060 IN IP6 stun:stun.freeswitch.org in response to which, the other side returns a 488 (invalid session description). I can confirm that ext-sip-ip and ext-rtp-ip are *not* set in the internal-ipv6.xml profile, but they are said as explained above in the external profile, where the problem lies. This looks like a bug to me but I want to rule out misconfiguration first. This has been tested on revision 13806.