system (GPS), as the time source for the operating system. Prior to the support of NTP-PTP interworking,
only backplane time was supported for the operating system time.
NTP-PTP interworking also provides the means to communicate status changes between PTP and NTP
processes. It also supports the unambiguous control of the operating system time and backplane time in the
event of bootup, switchovers or card and process failures.
For information regarding configuring NTP-PTP interworking, refer to
System Management Configuration
Guide for Cisco NCS 5000 Series Routers
. For information regarding commands, refer to
System Management
Command Reference for Cisco NCS 5000 Series Routers
.
Configuring Poll-Based Associations
No specific command enables NTP; the first NTP configuration command that you issue enables NTP.
Note
You can configure the following types of poll-based associations between the router and other devices (which
may also be routers):
•
Client mode
•
Symmetric active mode
The client and the symmetric active modes should be used when NTP is required to provide a high level of
time accuracy and reliability.
When a networking device is operating in the client mode, it polls its assigned time serving hosts for the
current time. The networking device then picks a host from all the polled time servers to synchronize with.
Because the relationship that is established in this case is a client-host relationship, the host does not capture
or use any time information sent by the local client device. This mode is most suited for file-server and
workstation clients that are not required to provide any form of time synchronization to other local clients.
Use the
server
command to individually specify the time-serving hosts that you want your networking device
to consider synchronizing with and to set your networking device to operate in the client mode.
When a networking device is operating in the symmetric active mode, it polls its assigned time-serving hosts
for the current time and it responds to polls by its hosts. Because this is a peer-to-peer relationship, the host
also retains time-related information about the local networking device that it is communicating with. This
mode should be used when there are several mutually redundant servers that are interconnected via diverse
network paths. Most stratum 1 and stratum 2 servers on the Internet today adopt this form of network setup.
Use the
peer
command to individually specify the time-serving hosts that you want your networking device
to consider synchronizing with and to set your networking device to operate in the symmetric active mode.
When the router polls several other devices for the time, the router selects one device with which to synchronize.
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147
Implementing NTP
Configuring Poll-Based Associations
