This Best Practice describes how NAT Traversal is enabled and configured within the
In this section:
NAT Traversal (also known as RTP Latching) allows the
In a typical network layout (see below), an SBC 1000 has both a public interface connected to the internet, and a private interface connected to the corporate network. A user's home network is also attached to the network with a NAT router and a SIP phone behind it. In this example, SIP requests arrive at the SBC from the Home SIP Phone wih the SIP Phone's private IP address (i.e., 192.168.10.2). With Inbound NAT Traversal enabled, the SBC 1000 can detect the public IP address (i.e. 134.56.216.210). Once this detection is made, all communication to this endpoint is sent to the public IP, rather than the private IP from the Home SIP Phone.
Typical Network Example
These instructions assume you are logged into the
In the left navigation pane, go to SIP > NAT Qualified Prefix Tables.
Click Apply.
A NAT Qualified Prefix Table must be created before associating it with a Signaling Group. See Step 1 .
Access the Inbound NAT Traversal options.
Do not confuse the Inbound NAT Traversal fields with the Outbound NAT Traversal fields in the SIP IP Details section. The Outbound NAT Traversal fields are used when the SBC is on the private side of a NAT device.
From the Detection drop down list, select Enable.
Configure optional fields (i.e, Secure Media Latching, Secure Media Netmask and Registrar Max. TTL Enabled). For field definitions, see Creating and Modifying SIP Signaling Groups.
Click Apply.
The following are guidelines/recommendations for configuring and using the NAT Traversal feature.
When the Inbound NAT Traversal feature is disabled, registrations from NAT endpoints may show up in the SIP Registrar User Table, but that doesn't mean they've successfully registered. Only when the Public Source IP and Public Source Port are properly detected and displayed in the SIP Registrar User Table, does that mean that a NAT endpoint is properly registered. For details on how to view these fields, see Viewing Registered Users.
We recommend that connecting NAT routers have SIP ALG disabled in order for NAT traversal to function properly.