NTP question

[mr7]

Hi all,

I have a two site A & B in two cities, connected through oversea ISDN. Site B is stub that no Internet access.

Also, as the ISDN is expensive so I don't want site B router sync it's time to site A through ISDN, it will make the ISDN keep up and down. But it is a must to make the router has a precise time as the access-list inside are reference to the time based access-list.

i) How can I configure the NTP so that once it is synced, no more packets send?

ii) Any suggested time source (may be a software in a WIN 2000 PC, or a simple device that plugs into the network) for our router to sync to in site B? Can this device becomes a time source (ntp master) and provide time service but no need to reference to another outside time source?

Thanks,

BBD

[Richard Gallagher]

One solution could be to have the router at site B configured to get it's clocking from a public NTP server. But when you configure the dialer-list to define interesting traffic to bring the ISDN line up deny NTP.

This way NTP traffic will not bring the ISDN line up, but when the line is NTP will be able to synchronise, and keep it's clock failry accurate. The internal clock should keep good time when not connected via ISDN.

Or alternatively you could try installing a NTP deamon on one of the machines at site B, but one again you are relying on the internal clock of that machine. If it's just for controlling the time-based ACLs then if the clock is a few minutes out I do not see this being a big problem.