标签为 ‘NTP’的文章

NTP Summarize


As everyone knows, the NTP is sync clock protocol.
That knowledge less other protocol.
But there are some attention:
1. When you config more than one server in customer network.
Please don’t use the same stratum.
Base on the stratum, refer to
If customer use same stratum, it would instability and lost sync.

2013-1-22 更新
There are two reason will lead NTP flapping(lost sync):
1. If you have 2 ntp servers this sort of behavour can happen if the ntp parameters from those servers are similar. This is likely if your peering to two N7Ks. Note also that “prefer” is not a priority selection on XR.
2. NTP version mismatch between V3 and V4

Refer to “Prefer” option, may solve this problem, in most of the case but this is not a 100% solution. If the time from the “preferred” source reaches the client earlier than other configured peers, it is taken to be authoritive and independent of the current time and offset. And we sync to it, but before the NTP client is synchronized to this preferred peer (which should take a few seconds in general or a maximum of 5 minutes), if time updates from other configured peers reach the NTP client, the clock selection algorithms are applied to all of these and we have all the time sources pass through the selection algorithms and NTP tunes the client’s time to some peer, considering the other factors of offset, sync distance and dispersion.

We do have more than 2 servers at the same stratum level, in the CASE, We should try using prefer option to see if we have no issues with time stabilities. But if we have the two servers almost at the same distance, even “prefer” option would not help much.

So it is advisable to to have one server per stratum level.


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