One of our clients has a Draytek Vigor 2920- their natted Snom phones
behind it are registered to an Asterisk 1.4 server on an external public IP.
I’ve set QOS, bandwidth management and turned off the SIP ALG via telnet
but I’m still having some problems with some of the phones losing
registration if Asterisk is restarted.
I can see the phones sending SIP REGISTER messages, but they never arrive
at the server; this happens in about half of the phones- with no
consistency as to which lose registration.
It looks like the router is swallowing the messages, or there’s some kind
of NAT problem. Other clients at other sites are fine.
The problem clears if the phone is rebooted (renegotiates a new nat path?)
Any help warmly appreciated.