.NODE

Changing NTP Synchronization Periods

Problem

You want to adjust how often routers send NTP packets to verify clock synchronization.

Solution

NTP does not allow poll rates to be changed manually; however, there are algorithms that adaptively shape this parameter within the NTP protocol.

Discussion

NTP is an extremely efficient protocol that actively monitors all aspects of network timing to adjust its configuration accordingly. Upon initialization of NTP on a router, it sets its poll cycle to about once every 64 seconds. As the local clock becomes synchronized and stable, the router will adaptively back off the poll cycle to a maximum of 1,024 seconds (roughly 17 minutes):

Router>show ntp associations

 address ref clock st when poll reach delay offset disp
*~172.25.1.1 130.207.244.240 2 440 1024 377 1.6 -3.23 5.6
+~172.25.1.3 204.152.184.72 2 829 1024 377 1.7 8.06 0.9
* master (synced), # master (unsynced), + selected, - candidate, ~ configured
Router>

Notice that the poll cycle for the two configured servers above has been throttled back to 1024 seconds. This indicates that the router is in a stable network and the time services are consistently accurate. This also illustrates NTP's remarkable efficiency.

See Also

Recipe 14.5

Router Configuration and File Management

Router Management

User Access and Privilege Levels

TACACS+

IP Routing

RIP

EIGRP

OSPF

BGP

Frame Relay

Handling Queuing and Congestion

Tunnels and VPNs

Dial Backup

NTP and Time

DLSw

Router Interfaces and Media

Simple Network Management Protocol

Logging

Access-Lists

DHCP

NAT

First Hop Redundancy Protocols

IP Multicast

IP Mobility

IPv6

MPLS

Security

Appendix 1. External Software Packages

Appendix 2. IP Precedence, TOS, and DSCP Classifications

Index

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Cisco IOS Cookbook
Cisco IOS Cookbook (Cookbooks (OReilly))
ISBN: 0596527225
EAN: 2147483647
Year: 2004
Pages: 505
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