Communication to external NTP clocks through VPRNs is supported in two ways: communication with external servers and peers, and communication with external clients.
Communication with external servers and peers are controlled using the same commands as used for access via base routing (see Network Time Protocol (NTP) in the 7450 ESS, 7750 SR, 7950 XRS, and VSR Basic System Configuration Guide). Communication with external clients is controlled via the VPRN routing configuration. The support for the external clients can be as unicast or broadcast service. In addition, authentication keys for external clients are configurable on a per-VPRN basis.
Only a single instance of NTP remains in the node that is time sourced to as many as five NTP servers attached to the base or management network.
The NTP show command displays NTP servers and all known clients. Because NTP is UDP-based only, no state is maintained. As a result, the show command output only displays when the last message from the client was received.