[asterisk-users] Phone -> NAT/FIREWALL -> Internet -> NAT/Firewall-> Asterisk

[John Millican]

Hello,
CentOS 6.x and Asterisk 11.x
I have an interesting, to me at least, situation.  Using a Polycom
501(also tried with X-Lite). I have set up Asterisk to accept
registration from the Polycom and it registers successfully but then
withing 30 seconds on the CLI I get the message that the Polycom is
unreachable.  The phone still shows that it is registered and if I try
to place a call from the phone to my Cell, my cell rings once and then
stops.  I get a packet retransmission error:
WARNING[1303]: chan_sip.c:4174 retrans_pkt: Retransmission timeout
reached on transmission 689874757 at 192.168.0.100 for seqno 2 (Critical
Response)
Followed by:
n_sip.c:4203 retrans_pkt: Hanging up call xxxxxxxxxx at 192.168.0.100 - no
reply to our critical packet
I am "assuming" that there is a problem with NAT.  I have externip set
in sip.conf.
Any pointers to what I am missing?
Thanks,
JohnM