Work with a Firewall with NAT 98SIPxNano IP-PBX Getting Started Guide B • Firewalls and NATWork with a Firewall with NATIf you are using multiple phones behind a firewall with NAT, and if that firewall has only a single external IPaddress, you must open a unique set of external SIP and RTP/RTCP port/address pairs for each phone thatmakes calls through the firewall.When you set up these ports for your firewall, you associate the phone’s IP address with each one. This processis sometimes called port mapping; that is, mapping a port on the external or public side of the firewall to a spe-cific port and device IP address inside the firewall.Note The RTP ports specified for a phone must be consecutive.However, when you have multiple phones behind the firewall, you use different ports for each one. For exam-ple, open unique SIP port 5060 for phone A, port 5061 for phone B, and 5062 for phone C. Then open arange of eight unique, consecutive RTP/RTCP ports for each phone: 8000 to 8007 for phone A, 8008 to 8015for phone B, 8016 to 8023 for phone C.The configuration for your firewall may look something like this:IP address forphone A: 192.168.0.3phone B: 192.168.0.4phone C: 192.168.0.5You must also make sure that each phone’s Port for inbound SIP TCP messages, the Starting port forinbound SIP UDP messages, and the Starting port for RTP/RTCP packets reflect these values:Table 12. Parameter settings for certain phonesParameter Setting: Phone A192.168.0.3Phone B192.168.0.4Phone C192.168.0.5SIP_TCP_PORT 5060 5061 5062SIP_UDP_PORT 5060 5061 5062PHONESET_RTP_PORT_START 8000 8008 8016
