Cisco Nexus 7000 Series Configuration Manual page 77

Configuring NTP
• A peer configured alone takes on the role of a server and should be used as a backup. If you have two
servers, you can configure several devices to point to one server and the remaining devices to point to
the other server. You can then configure a peer association between these two servers to create a more
reliable NTP configuration.
• If you have only one server, you should configure all the devices as clients to that server.
• We recommend that you do not configure (just) two NTP servers. Instead, you should configure one,
three, or four or more NTP servers.
All NTP servers return the time together with an estimate of the current error. When using multiple time
servers, NTP also wants these servers to agree on some time, meaning there must be one error interval
where the correct time must be. When there are just two NTP servers, there might be an issue if both
sources do not fall into the small common range because the NTP client will be unable to determine
which source is more correct.
• You can configure up to 64 NTP entities (servers and peers).
• If you configure NTP in a VRF, ensure that the NTP server and peers can reach each other through the
configured VRFs.
• You must manually distribute NTP authentication keys on the NTP server and Cisco NX-OS devices
across the network.
• If CFS is disabled for NTP, then NTP does not distribute any configuration and does not accept a
distribution from other devices in the network.
• After CFS distribution is enabled for NTP, the entry of an NTP configuration command locks the network
for NTP configuration until a commit command is entered. During the lock, no changes can be made
to the NTP configuration by any other device in the network except the device that initiated the lock.
• If you use CFS to distribute NTP, all devices in the network should have the same VRFs configured as
you use for NTP.
• If you configure NTP in a VRF, ensure that the NTP server and peers can reach each other through the
configured VRFs
• You must manually distribute NTP authentication keys on the NTP server and Cisco NX-OS devices
across the network.
• Use NTP broadcast or multicast associations when time accuracy and reliability requirements are modest,
your network is localized, and the network has more than 20 clients. We recommend that you use NTP
broadcast or multicast associations in networks that have limited bandwidth, system memory, or CPU
resources.
Note
• The NTP source-interface and source configuration has a limitation of getting applied only when
configured on the client. If the configuration is done on the server (the switch with the NTP master),
source address of the outgoing packet will still be that of the received destination address.
Time accuracy is marginally reduced in NTP broadcast associations because information
flows only one way.
Cisco Nexus 7000 Series NX-OS System Management Configuration Guide
Guidelines and Limitations for NTP
49