May 2011
Intermediate to advanced
788 pages
23h 34m
English
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Configuring NTP
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.
NTP Client
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.
Note
On Nexus switches with multiple VDCs, only the default VDC may have NTP configured.
ntp server 132.163.4.102 ntp server 193.67.79.202 ntp server 152.1.58.124 ntp server 128.118.46.3 ntp server 129.6.15.29 ntp server 64.236.96.53 ntp server 208.184.49.9
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
command 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
15.0(1)M4:
R1-PBX#sho ntp associations address ref clock st when poll reach delay offset disp ~127.127.1.1 .LOCL. 7 7 16 37 0.000 0.000 437.71 ~128.118.46.3 .INIT. 16 - 64 0 0.000 0.000 15937. ~208.184.49.9 .INIT. 16 - 64 0 0.000 0.000 15937. +~129.6.15.29 .ACTS. 1 63 64 ...Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.