NTP
Modes
Client-Server
- AKA,
server
Time is one way, the clients get time from servers.
Symmetric Active/Passive
- AKA,
peer
Devices have a low-stratum primary reference, but if that primary reference goes down, they can use each other as backups.
Broadcast or multicast
-
AKA,
broadcast -
Same subnet
-
Not as accurate
Config
Provide NTP
!
! 7 is pretty low
!
! good practice is to bind this to a stable interface, like a loopback
!
!
ntp master 7
ntp source Loopback0
Get NTP from another server
!
! NTP should never rely on a single server.
!
! Even my home network relies on seven external NTP servers.
!
!
ntp server pool.ntp.org
A public config
Warning
Does your organization use time in a way that human lives depend on it being correct?
You shouldn’t “just get it off the Internet”
The NTP Pool is generally very high quality, but it is a service run by volunteers in their spare time.
Please talk to your equipment and service vendors about getting local and reliable service setup for you.
See also our terms of service.
We recommend time servers from Meinberg, but you can also find time servers from End Run, Spectracom and many others.
From Using pool.ntp.org.
From this list.
ntp server pool.ntp.org
ntp server time.nist.gov
ntp server time.cloudflare.com
ntp source <loopback-goes-here>
ntp peer <other-router-goes-here>
!
! NTP Master 7 ... if Internet connectivity is lost, and external NTP fails, this box can still serve NTP.
!
ntp master 7
References
Cisco - Best Practices for NTP