Network port scanners can be used to enumerate SIP User Agents, Registrars, Proxy servers, and other SIP-enabled systems. SIP usually listens on TCP or UDP port 5060.
Other protocols required for VoIP calls, such as RTP, listen on static/dynamic ports other than port 5060. While port 5060 is used to set up the session using SIP, the actual media transmission uses other ports.
Here's how to enumerate SIP devices on a network, step by step:
Download Nmap from http://insecure.org/nmap/.
nmap on the command line (Windows) or shell (Unix) to retrieve the syntax of the tool.
Enter the following nmap command on the command line/shell to enumerate SIP User Agents and other intermediate ...