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New Member

NTP Configuration

I have a setup in which Windows2000 Server is configured as a NTP Server. Now I have around 50 Routers and Switches those i want to synchronise their clocks to the Windows2000 Server.

I donot have external clock source. Their is no authentication for ntp configuration.

Somehow the Switches and Routers are unable to synchronise their time with that ntp server.

Is there special configuration required?

Mansoor Hafeez


Re: NTP Configuration

If there's no authentication, then simple

ntp server

is enough to get NTP sync.

Make sure that your server actually permits unicast client connections from IP addresses that belong to your network devices. Some server software by default don't allow client connections.

When everything correctly configured, one possible reason for clock not beeing synchronized is fluctation of clock on the server itself or large network jitter.

What does 'sh ntp as' and 'sh ntp st' say? Also try 'debug ntp select' and 'debug ntp validity'.

New Member

Re: NTP Configuration

After running the 'debug ntp validity', the following message is displaying

"1w5d: NTP: packet from failed validity tests 20"

Everytime I am receiving the same message

Hall of Fame Super Silver

Re: NTP Configuration


The error failed validity tests 20 indicates that your device considers the other device time to be unsynchronized. Are you sure that the device at has valid synched time?



Re: NTP Configuration

Taking into account your environment, I'd reverse roles and configure one or better two Cisco routers as NTP servers and let everything else to be sync'ed from them. Cisco routers have reasonably good (stable) internal clock and Windows machines are able to sync from them. You can even do further hierarchical setup - configure your PDC to sync from Cisco and then let all Windows workstations to sync from PDC (if I'm correct they'd do this anyway).

New Member

Re: NTP Configuration

Setting up Time Server in Windows 2000 Server will not be able to sync Routers and Switches clock as both uses different version.

In Windows its SNTP -Simple Network Time Protocol.

In Routers/Switches its NTP - Network Time Protocol.

You can configure any Router/Switch as a NTP Server, in which "calender" command works. It will act as Server and will update all the clients.

In case that command is not available in any of the Router/ Switch, either you can buy hardware NTP Server or you can configure any Router as NTP Server but in this case the Router which is acting as NTP Server's clock will get reset in case of reboot/reload.

I hope this will solve your query.



New Member

Re: NTP Configuration

Download tardis200 from and its manual from, install it on your PC.

Configure your Tardis accordingly (See section 7 of the downloaded manual) Note, your Tardis is installed to run as a service when you load your windows; it is important to configure the Tardis to broadcast NTP time information using broadcasts and multicasts.

On your router interface connected to this network where Tardis was installed, run [ntp broadcast] command and [ntp master] command from the global config mode. On the other router interfaces, configure [ntp broadcast client] to receive update from the ntp master

I hope this will be of help.