Preventing Loops
Do not allow loops, such as NTP --> DTS --> NTP, to form.
Run the null time-provider (dts_null_provider.c) only if you have a local time source. If you do not have a local time source, you can run the null time-provider, but do not disseminate NTP time anywhere in the local set.
The following figure shows a configuration that is not recommended. This configuration only works as long as the remote NTP Stratum 2 node does not fail.
Configuration Before Stratum 2 Node Fails
If the remote NTP Stratum 2 node fails, the Stratum 3 node starts accepting time from the Stratum 8 node. Once this occurs, the Stratum 3 node drops to Stratum 9 and the Stratum 4 node drops to Stratum 10, as shown in the following figure.
Configuration After Stratum 2 Node Fails
The scenario in the preceding figure shows the creation of a loop:
1. From the node that is labeled Stratum 8, proceed to the NTP node that is labeled Stratum 9.
2. From the NTP node that is labeled Stratum 9, continue to the node that is labeled Stratum 10.
3. DTS then feeds the time back to the node that is labeled Stratum 8, creating a loop.
If this occurs, time in the NTP and DTS subnetwork can drift from UTC.