From: Jay Hennigan (jay@west.net)
Date: Sat Jun 28 2003 - 13:09:33 GMT-3
On Fri, 27 Jun 2003, ccie2be wrote:
> Maybe you could help me (and the rest of the group study community)
> understand some additional ntp config issues.
>
> Specifically, in your example 3, in R2 config, the key# is entered in 3
> different commands which seems very redundant. Is it required in all the
> commands? Would authen failed, for example, if the config didn't have the
> key # in the ntp server x.x.x.x command?
You can have different keys for different peers. That's why the key
number is repeated.
* ntp authentication-key [number] [string] <- Defines key [number]
* ntp trusted-key [number] <- lists keys which this router will trust for
synchronization.
* ntp server|peer [ip addr] key [number] <- Will send packets to this
server or peer with this key.
> Also, if 2 routers are config as NTP Masters, the 1st say, stratum 8 and the
> 2nd stratum 10, and other ntp clients are peering with both masters,
> shouldn't the other routers sync with the master with the lower stratum even
> if they had already sync'ed with the master with the higher stratum?
Possibly not. It depends on how far apart the new master is from
the old. If a device is synced, the NTP algorithm is designed to avoid
sudden large shifts but to "speed up" or "slow down" gradually. If it
is presently synced, a new peer that is "insane" (way out of step) will
be ignored. If you reload or lose NTP entirely and the clock is not
set as master it will sync to the howest stratum server.
> Lastly, at what point (ie, how long should I wait) should I conclude there's
> a problem when 2 2500 routers which are both NTP masters but with different
> stratum levels don't sync up properly?
See above. It depends on how far apart they are. If a device is synced
and a new device appears that is way out of step, perhaps never (for small
values of never). Especially if they're drifting apart rather than closer
together.
> rtr1
> ntp master 6
> ntp server 12.0.0.2
>
> rtr2
> ntp master 9
> ntp server 12.0.0.1
>
> In the above config, shouldn't rtr2 sync up with rtr1 since it has the lower
> stratum? How long should it take?
Set them within a few seconds of each other, and yes. Set them months
apart, probably not.
See:
http://www.cisco.com/en/US/tech/tk648/tk362/technologies_white_paper09186a0080117070.shtml
http://www.oreilly.com/catalog/hardcisco/chapter/ch10.html?CMP=IL7015
-- Jay Hennigan - CCIE #7880 - Network Administration - jay@west.net WestNet: Connecting you to the planet. 805 884-6323 WB6RDV NetLojix Communications, Inc. - http://www.netlojix.com/
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