Cisco 521SG Administration Guide - Page 126

Configuring SIP, SPCP, and NAT Managing NAT Transversal with Cisco IP Phones 4 NAT Mapping with Session Border Controller We recommend that you choose an service provider that supports NAT mapping through a Session Border Controller. With NAT mapping provided by the service provider, you have more choices in selecting a router. NAT Mapping with SIP-ALG Router NAT mapping can be achieved by using a router that has a SIP Application Layer Gateway (ALG). By using a SIP-ALG router, you have more choices in selecting an service provider. NAT Mapping with a Static IP Address You can configure NAT mapping on the phone to ensure interoperability with the service provider. • You must have an external (public) IP address that is static. • The NAT mechanism used in the router must be symmetric. See Determining Whether the Router Uses Symmetric or Asymmetric NAT. Use NAT mapping only if the service provider network does not provide a Session Border Controller functionality. To configure NAT mapping on the phone: 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 • Send Resp To Src Port STEP 3 Enter the public IP address for your router EXT IP field. STEP 4 Click the Ext_n tab and navigate to NAT Settings. STEP 5 Set NAT Mapping Enable to yes. Cisco Small Business SPA300 Series, SPA500 Series, and WIP310 IP Phone Administration Guide 125