Cisco SPA962-NA Administration Guide - Page 25

Chapter 1 Introducing Linksys 900 Series IP Phones Technology Background • SIP ports-By default, UDP port 5060 and 5061 • RTP ports-16384 to 16482 If security is not a concern in your environment, you can consider disabling SPI, if this function exists on your firewall. Network Address Translation This section describes issues that arise when using the LVS system on a network behind a network address translation (NAT) device. It includes the following topics: • NAT Overview, page 1-13 • NAT Types, page 1-14 • Simple Traversal of UDP Through NAT, page 1-14 • SIP-NAT Interoperation, page 1-15 NAT Overview Network Address Translation (NAT) allows multiple devices to share the same public, routable, IP address for establishing connections over the Internet. NAT is typically performed by a router that forwards packets between the Internet and the internal, private network. The association between a private address and port and a public address and port is called a NAT mapping. This mapping is maintained for a short period of time, that varies from a few seconds to several minutes. The expiration time is extended whenever the mapping is used to send a packet from the source device. The ITSP may support NAT mapping using a Session Border Controller (see Figure 1-3). Figure 1-3 NAT Support with Session Border Controller Provided by ITSP 192.168.1.101 192.168.1.102 Private IP address 192.168.1.1 External IP address assigned by ISP NAT Device ISP DHCP server Internet SPA9000 SIP Proxy 192.168.1.100 ITSP Session Border Controller Document Version 3.0 Linksys 900 Series IP Phone Administrator Guide 1-11