Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

NTP redundancy

Hi All,

When config NTP, suppose the server is R1 and if I want the R1 fail, other routers will use R2 as time source. How can I config it? Thank You!

Best Regards

Teru Lei

1 ACCEPTED SOLUTION

Accepted Solutions
Silver

Re: NTP redundancy

As thisisshanky said you can have multiple NTP statements in your config, to chose R1 as the primary use the prefer keywork:

ntp server prefer

ntp server

4 REPLIES

Re: NTP redundancy

I think, you can configure multiple NTP server commands one after the other.

Silver

Re: NTP redundancy

As thisisshanky said you can have multiple NTP statements in your config, to chose R1 as the primary use the prefer keywork:

ntp server prefer

ntp server

New Member

Re: NTP redundancy

Just would like to know if configured multiple NTP server, will it send the NTP queries to all the configured NTP server address or just the prefer one ?? and how to tweak the NTP queries timers to be longer from routers (client) ?? seems to be no way ???

Silver

Re: NTP redundancy

Keep in mind that to accurately maintain time in the face of failing time servers, at least three servers must be continuously queried.

Given that caveat, there are a number of tricks you can play to reduce NTP traffic. My favorite for large hub and spoke networks is to configure all the spokes to use a single server IP, minimizing traffic. The trick is that the IP is not a real server but rather an IP address which is defined (as a loopback interface) on every hub router. The hub routers then use multiple real time servers to keep on time. This approach avoids forwarding spoke time requests across the hub network even when dialed in or otherwise connected to a backup hub router. Of course, this approach assumes that any failures which would cause a hub router to lose time would also cause it to lose the ability to provide any other services to the spokes trying to use it.

WARNING: any time you have multiple routers with duplicate IP addresses, you need to ensure that you understand all the ramifications. In particular, make sure there is a loopback on the router with a globally unique higher IP address before defining the duplicated IP. Picking up the duplicated IP address as the router ID in a routing protocol can have undesireable side effects.

Good luck and have fun!

Vincent C Jones

www.networkingunlimited.com

304
Views
0
Helpful
4
Replies
CreatePlease login to create content