NTP is a client/server application. Devices participating in NTP are either NTP servers, which provide time to other devices, or NTP clients, which request time from NTP servers. Servers are also clients and can be peered with each other as well. Configuring an IOS or NX-OS device as an NTP client is the simpler of the two models, so we’ll start there.
To configure an IOS or NX-OS device to request accurate time from an
NTP server, use the
ntp server command.
You can list as many NTP servers as you need, each on a separate line.
Here, I’ve listed seven publicly available NTP servers. Using so many
will help illustrate how NTP behaves.
On Nexus switches with multiple VDCs, only the default VDC may have NTP configured.
ntp server 184.108.40.206 ntp server 220.127.116.11 ntp server 18.104.22.168 ntp server 22.214.171.124 ntp server 126.96.36.199 ntp server 188.8.131.52 ntp server 184.108.40.206
Once you’ve configured the NTP servers, you should begin receiving accurate time signals (assuming you can reach them).
To see the status of the NTP servers in IOS, use the
show ntp associations.
In this chapter, I’ll use the IP-PBX system I built in Chapter 30. This is a 2811 router running IOS version
sho ntp associationsaddress ref clock st when poll reach delay offset disp ~127.127.1.1 .LOCL. 7 7 16 37 0.000 0.000 437.71 ~220.127.116.11 .INIT. 16 - 64 0 0.000 0.000 15937. ~18.104.22.168 .INIT. 16 - 64 0 0.000 0.000 15937. +~22.214.171.124 .ACTS. 1 63 64 ...