[Asterisk-Users] grandstream sip phone (NTP)

[Stephen R. Besch]

I have solved the time server problem with the Grandstream by having my 
* box's NTP service mirror a public NTP server.  I had to do this 
because my phones are all on the 192.168 subnet, which is non-routable. 
For example, assuming that the NTP service is configured and running on 
your * box, create an NTP mirror which allows access from machines on 
192.168.10.X by adding the following line to the ntp.conf file:

restrict 192.168.10.0 mask 255.255.255.0 notrust nomodify notrap

The IP range and netmask arguments are obvious.  The 3 option flags tell 
the ntp daemon that none of the machines that might communicate over 
this subnet are to be trusted as time servers, none of them are to be 
allowed to update the ntp daemon running on the asterisk server, and 
none of them will be able to use the trap service for logging purposes.

Finally, I also like to set up a different (from the one used by the 
phones for SIP and RTP) IP address for the NTP server (so the * box has 
2 addresses on the 192.168 net). It goes without saying that the 
asterisk box must also have a public IP address so that it can 
synchronize itself with a remote time server. In my setup, I have one 
net card for the public address, while the 2 192.168 addresses are on a 
second card.

-- 
Stephen R. Besch, Ph.D.
SachsLab
320 Cary Hall
SUNY at Buffalo
Buffalo, NY 14214
(716) 829-3289 x106