Simple Traversal of UDP over NAT (STUN) ? is a protocol thatenables a VoIP device, such as the DVG-2001S or an IP phone, todetect the presence and type of NAT behind which the phone isplaced. The DVG-2001S supports STUN and can intelligently modifythe private IP address and port in its SIP/SDP message by using theNAT mapped public IP address and port through a series of STUNqueries against a STUN server located on the public Internet. Thiswill allow SIP signaling and RTP media to successfully traverse aNAT without requiring any configuration changes on the NAT.
Below is a list of Public STUN servers
- stun.fwd.org (no DNS SRV record)
- stun01.sipphone.com (no DNS SRV record)
- stun.softjoys.com (no DNS SRV record)
- stun.voipbuster.com (no DNS SRV record)
- stun.voxgratia.org (no DNS SRV record)
- stunserver.org see their usage policy