Cisco IP 7940 Configuration Manual page 6

5. Go to the "SIP" tab
6. Go to the "NAT Support Parameters" section
7. Set the "Handle VIA rport" field to "yes"
8. Set the "Insert VIA rport" field to "yes"
9. Set the "STUN Enable" field to "yes"
10. Set the "STUN Server" field to "stunserver.org" – to allow the phone to
discover its external IP Address, and the port mappings that will be applied
to the traffic sent and received by the phone ,the default port is 5060 for
TCP and 10000-12000 for RTP
11. Click the "Submit All Changes" button at the bottom of the page. Your phone
will restart.
Cisco IP Phone Configuration Guides
Figure 2-2
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