[asterisk-users] Asterisk Help

Under asterisk info: Sip registry

12/12                      76.xxx.xxx.xxx   D   N      5066     UNREACHABLE

11/11                      76.xxx.xxx.xxx   D   N      5064     UNREACHABLE

10/10                      76.xxx.xxx.xxx   D   N      5062     UNREACHABLE

All these IP phones are behind NAT. What could be the problem?

Thanks in advance.

Jarga