SIP Signaling Messages
By default, the device resolves NAT issues for SIP signaling, using its NAT Detection mechanism. The NAT Detection mechanism checks whether the endpoint is located behind NAT by comparing the source IP address of the incoming UDP/TCP packet (in which the SIP message is received) with the IP address in the SIP Contact header. If the packet's source IP address is a public address and the Contact header's IP address is a local address, the device considers the endpoint as located behind NAT. In this case, the device sends the SIP messages to the endpoint using the packet's source IP address. Otherwise (or if you have disabled the NAT Detection mechanism), the device sends the SIP messages according to the SIP standard (RFC 3261), where requests within the SIP dialog are sent using the IP address in the Contact header and responses to INVITEs are sent using the IP address in the Via header.
If necessary, you can also configure the device to always consider incoming SIP INVITE messages as sent from endpoints that are located behind NAT. When this is enabled, the device sends responses to the INVITE (to the endpoint) using the source IP address of the packet (INVITE) initially received from the endpoint. This is useful in scenarios where the endpoint is located behind a NAT firewall and the device (for whatever reason) is unable to identify NAT using its regular NAT Detection mechanism. This feature is enabled per specific calls using the 'Always Use Source Address' parameter in the IP Groups table (see Configuring IP Groups). If this feature is disabled, the device's NAT detection is according to the settings of the global parameter, 'SIP NAT Detection' parameter (see below procedure).
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To enable the NAT Detection feature (global): |
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1.
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Open the Transport Settings page (Setup menu > Signaling & Media tab > SIP Definitions folder > Transport Settings). |
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2.
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From the 'SIP NAT Detection' drop-down list (SIPNatDetection), select Enable: |
