Hi, Hoping someone might have some insight... I currently have a Debian 7 system (freeswitch 1.4) with Aastra 6731i phones and a single Polycom 335. Everything works fine. I built a Debian 8 system (freeswitch 1.6) as a drop-in replacement. Inbound calls work fine on the 2 different brands of phones (Aastra, and Polycom), but the Aastra phones cannot make outbound calls. Or rather, they can, but there is no audio. Outbound calls via the Polycom work fine. I did packet captures when making an outbound call with each type of phone, and when using the Aastra phones, there is no response received by the FS box after the Invite. I literally unplug the Debian 7 system and plug in the Debian 8 system. They are identically IP'ed, same SIP and RTP ports, etc. I can move the Debian 8 box to e.g. my home network, and then the Aastra phones work fine. So, it seems this is some kind of firewall/nat problem, but why would the Polycom still work? Is there some configuration parameter on the Aastra phones I should look at? Any thoughts appreciated. Thanks, Tim