Cisco SPA2102-SF Administration Guide - Page 53

Configuring Your System for ITSP Interoperability Firewalls and SIP 3 STEP 6 Click Submit All Changes. STEP 7 View the syslog messages to determine whether your network uses symmetric NAT. Look for a warning header in the REGISTER messages, such as Warning: 399 spa "Full Cone NAT Detected." Firewalls and SIP To enable SIP requests and responses to be exchanged with the SIP proxy at the ITSP, you must ensure that your firewall allows both SIP and RTP unimpeded access to the Internet. • Make sure that the following ports are not blocked: • SIP ports-UDP port 5060 through 5063, which are used for the ITSP line interfaces • RTP ports-16384 to 16482 • Also disable SPI (Stateful Packet Inspection) if this function exists on your firewall. Configuring SIP Timer Values The default timer values should be adequate in most circumstances. However, you can adjust the SIP timer values as needed to ensure interoperability with your ISTP. For example, if SIP requests are returned with an "invalid certificate" message, you may need to enter a longer SIP T1 retry value. To view the default settings or to make changes, open the Voice > SIP page, and scroll down to the SIP Timer Values section. For field descriptions, see "SIP Timer Values (sec) section," on page 129 of Appendix B. Cisco Small Business ATA Administration Guide 53