[Asterisk-Users] SIP Phone Unreachable

[Renato Mintz]

Hi Folks,

I found a strange problem trying to install a system on a customer. I
have the following network configuration:

 Asterisk - Router (NAT) - Internet - Router (NAT) - Grandstream Phone

The routers are low end D-Link router + broadband access. The router
near asterisk has 5060 and 10000-10009 ports opened and assigned to
Asterisk server. The router near the phone has default configuration:
outgoing ok, incoming blocked.

I have Qualify = 1000. As soon as * is restarted I get a message
telling the phone is unreachable. Looking at SIP debug I see *
transmitting OPTIONS and receiving OK but it seems that * discards the
OKs, because it always transmits OPTIONS 4 times (and receives 4 OKs),
stop a little and begin transmitting OPTIONS again.

Looking at the SIP messages I found that the Call-ID in the OPTIONS
message uses the Asterisk EXTERNAL IP address but the OK coming from
the GS Phone has its Call-ID with the Asterisk INTERNAL IP address.

I run ethereal near the phone and the OK it sends has Asterisk
EXTERNAL IP address! Somebody is translating the EXTERNAL IP into the
INTERNAL IP at the Call-Id header.

I also run tcpdump at the Asterisk Server and the result is the same
as the sip debug.

My simple conclusion is: the router is opening the SIP message and
translating the Call-Id header IP, but I don't believe in that.

Any clue?

Thanks?

Renato