NTP Failover Scenario

[R_Acuti]

Scenario:

- 2 non-Cisco NTP server appliances are on the network.

- The NTP servers are peered with each other. Only one has a GPS input.

- The NTP topology is "flat", all routers and switches poll these NTP servers directly.

If a network outage causes the NTP server with the GPS input to become inaccessible, how long will it take before the routers and switches seek NTP from the other NTP server?

I am testing this scenario in my lab and after missing several polls, the routers still insist that their "master" is the unavailable NTP server.  I'm disconnecting the ethernet cable from the NTP server to simulate the outage.

Thoughts?

[marce1000]

>"master" is the unavailable NTP server.

 Well I guess that's normal if  it's not on the network , but as far as fail over is concerned issue command as 'show ntp associations" subsequently , within 10-secs (e.g.) ; in order to check whether another ntp server is chosen to sync with. To checkout the latter issue the various 'show ntp...' commands ; check which ntp server gets marked with asterix and is synced with.

M.

[R_Acuti]

Right, I've been checking

ntp status

ntp associations

ntp associations detail

and nothing changes. The <*> sticks with the NTP server that is unavailable. The <+> sticks with the NTP server that is available. Show ntp associations detail still indicates that the unavailable server is "our _master" even after long periods of time.

The polling intervals are pretty long at 1024 seconds, but I've been patient and waited.  The "when" indicates that polls to the "our_master" NTP server are being missed, but none of the routers are shifting the <*> to the other server.

The routers will shift from one server to another if I make one server look unattractive by altering its time suddenly, but not if I simply remove it from the network.

[R_Acuti]

Apparently I just haven't been patient enough. NTP is rarely a protocol that changes instantly. After allowing a longer period of time, my routers have all failed over to the only available NTP server.