Cisco SPA508G Administration Guide - Page 127

Configuring SIP, SPCP, and NAT Managing NAT Transversal with Cisco IP Phones 4 STEP 6 (Optional) Set NAT Keep Alive Enable to yes. The service provider might require the phone to send NAT keep alive messages to keep the NAT ports open. Check with your service provider to determine the requirements. STEP 7 Click Submit All Changes. STEP 8 Configure the firewall settings on your router to allow SIP traffic. See Configuring SIP. NAT Mapping with STUN If the service provider network does not provide a Session Border Controller functionality and if the other requirements are met, it is possible to use Session Traversal Utilities for NAT (STUN) to discover the NAT mapping. The STUN protocol allows applications operating behind a network address translator (NAT) to discover the presence of the network address translator and to obtain the mapped (public) IP address (NAT addresses) and the port number that the NAT has allocated for the User Datagram Protocol (UDP) connections to remote hosts. The protocol requires assistance from a third-party network server (STUN server) located on the opposing (public) side of the NAT, usually the public Internet. This option is considered a last resort and should be used only if the other methods are not available. To use STUN • The router must use asymmetric NAT. See Determining Whether the Router Uses Symmetric or Asymmetric NAT. • A computer running STUN server software is available on the network. You can also use a public STUN server or set up your own STUN server. STEP 1 Click Voice > SIP and navigate to NAT Support Parameters. STEP 2 Set the following parameters to yes: • Handle VIA received • Insert VIA received, • Substitute VIA Addr • Handle VIA rport • Insert VIA rport Cisco Small Business SPA300 Series, SPA500 Series, and WIP310 IP Phone Administration Guide 126