All SIP phone become UNREACHABLE

We have an asterisk box, with around 200 SIP peers online, and a total of 550 configured. The asterisk box is in the same LAN as all the phones. For some reason all phones become UNREACHABLE suddenly, and after a little while come back again to be REACHABLE.
We tried version 1.2.13 and 1.2.14 and the problem always exists. We even tried installing a new box, with a fresh linux (Centos 4.4) and the problem still exists.
The seems to be no network problems. There is never any packet loss between the phones and the Asterisk.

Any ideas ?


This sounds like a DNS issue.

If you have any sip trunks and you havent limited the number of register attempts it can knock all the phones out.

registerattempts = 3 will mean that only 3 attempts will be made