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Cisco IP Phone Models 7905G and 7912G Administrator Guide (SIP)
OL-4277-01
Chapter 8 Profile and Web Page Parameters and Defaults
Parameter Details
22 Process a received = parameter in the VIA header to extract the external IP addresses
used by the Network Address Translation (NAT) router.
• 0=Disable (default).
• 1=Enable.
When a Cisco IP Phone is operating behind a NAT, the NATIP parameter must be set to
the external IP address of the NAT router. This setting allows the correct IP address to
be placed in the Contact and SDP headers.
You may leave the NATIP address set to the default value of 0 (or 0.0.0.0) and let the
phone automatically scan the VIA header for a received = parameter. The parameter, if
present, would indicate that the phone is operating behind a firewall.
The phone proceeds as follows:
1. If the received = parameter is an INVITE response, the current INVITE is canceled
and a new INVITE is sent with the new IP address extracted from the
received =NAT_IP_Address parameter in the Contact header. This step is performed
only if registration is currently in an idle state.
2. If the received = parameter is in a REGISTER response as a result of a REGISTER
command, the phone will cancel all previous registrations and re-register with the
new IP address extracted from the received = NAT_IP_Address parameter in the
Contact header.
Note For the phone to automatically detect its presence behind a NAT, the SIP proxy
server or remote user agent server must include the received = parameter in the
VIA header in the responses to the phone if the proxy detects that the source
address and port do not match those in the VIA header.
23 Reserved. Must be set to 0.
Table 8-9 ConnectMode Parameter (continued)
Bit Description