Appendix A: NAT router requirements for NAT Traversal feature Page 851 of 910
IP Line Description, Installation and Maintenance
Confirm using IP Phone
The NAT router uses a cone NAT if no error message is displayed when the
IP Phone registers to the system. The NAT device does not use a cone NAT
if the IP Phone behind it displays the following error message:
NAT Error! ITG3053
Please try upgrading firmware on the NAT device or
replacing it with a different NAT device that has a cone
NAT implemented.

Time-out configuration

Confirm using natcheck
Time-out configuration cannot be performed using natcheck.
Confirm using IP Phone
If the IP Phone connection times out and the IP Phone reboots, use LD 117 to
lower the NAT Keep Alive Timer value on the Call Server. The reboots could
indicate that the NAT device’s address/port mapping is being cleared because
there is no message traffic from the IP Phone. By lowering the NAT Keep
Alive Timer value in the Call Server, keep-alive messages are sent more
frequently to keep the mapping “alive”.
>ld 117
->chg nkt 20
If lowering the NAT Keep Alive Timer value to the minimum value of 20
seconds doesn’t stop the time-outs, try replacing the NAT device.

Hairpinning

Hairpinning occurs when an IP Phone behind a NAT router can send packets
to the Public IP address and Port of another IP Phone connected to the same
NAT router. Determine if hairpinning is supported on the NAT router.