Building Telephony Systems with OpenSIPS - Second Edition

Chapter 10. SIP NAT Traversal

NAT, also known as Network Address Translation, was the solution found to solve the shortage of IP version 4 addresses. It uses a small range of IP addresses (in most cases, a single IP address) on the external port of a firewall and a range of private addresses (see RFC 1918) on the internal port of the firewall.

Unfortunately, NAT affects SIP communication because SIP uses IP addresses inside its headers. In this chapter, we will look at some ways to solve the NAT traversal challenge.

In this chapter, we will cover the following topics:

• Explaining why and where NAT breaks SIP communications
• Describing the different types of NAT devices and their implications
• Describing the most common solutions available for NAT traversal ...