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I have a Cisco 877W which I'm using for my home ADSL connection (and as a refresher in Cisco IOS). I've got a working config in-place with my PPPoA connection coming online correctly, and VLANs and other settings configured as I want them, but I can't crack the NTP configuration.

For NTP, I have the following defined

ntp server source Dialer0
ntp server source Dialer0
ntp server source Dialer0
ntp server source Dialer0

This setup works fine when issued in Global Configuration Mode when the Dialer0 interface (ATM0.1) is up. The configuration fails at startup though:

Translating ""...domain server ( (

ntp server source Dialer0
% Invalid input detected at "^" marker.

This is repeated for the other servers defined.

Obviously the DNS lookup for the server(s) fails because the DNS servers cannot be accessed because the external interface is not yet online.

Is there a way to delay the NTP configuration until afte the Dialer0 interface is fully initialised? Can the NTP commands be triggered by the Line Protocol on the Dialer0 interface transitioning to the up state? Alternatively, can the NTP commands be delayed for 5 minutes after the router has finished initialising?

Any advice, or pointers to useful documentation or examples gratefully received ...

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surely it doesn't try just once? – SpacemanSpiff Jul 13 '11 at 21:37
The error shown after a reload actually removes the NTP configuration from running-config (but not from startup-config), so in essence, yes, it tries to resolve the NTP server name(s) once then gives up! – Mike Insch Jul 13 '11 at 21:50
now that stinks! bumping this post as their has to be a good answer for this scenario – SpacemanSpiff Jul 13 '11 at 23:29

OK, I think I might have solved this - though my head hurts now! Posting for others who might encounter this ...

I've removed my NTP server setup from the config and substituted the following:

kron policy-list ntp
 cli ntp server source Dialer0
 cli ntp server source Dialer0
 cli ntp server source Dialer0
 cli ntp server source Dialer0

kron occurrence ntp-init in 5 oneshot
 policy-list ntp

Now, after a reload the router waits 5 minutes before configuring NTP, which seems to work OK so far ... It's a bit of a hack though - there's probably a better way !

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The problem with this approach is that after the 5 minute delay has passed, two things happen: 1. the kron occurrence ... command is removed from running-config, and the individual ntp server source Dialer0 commands are present in running-config. To be effective, every future config change also requires that the kron occurrence ... command is re-entered, and that no ntp server X ... is entered for each server before doing copy running-config startup-config - so this is only useful as a workaround, it's not a true solution. – Mike Insch Jul 15 '11 at 13:20

on my 1841 (15.1(3)T) IOS will attempt to resolve the ntp server name at boot time before the interfaces are online, which obviously fails. I 'fixed' the issue by using ntp server address instead of host name.

share|improve this answer
This is the only workaround I have found so far myself. Pretty stupid of a mistake coming from Cisco. – gparent Nov 14 '12 at 16:49

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