NTP Master

[DEENA VERAPPAN]

     Hi All,

I'm lloking for some help regarding setting up NTP. Currently the source for NTP within our network is our core 6500.Currently the NTP source for the 6500 are internet based NTP Servers. I would like to configure the 6500 to respond to NTP messages as the NTP Master. However will the 6500's source remain as the internet based NTP Servers?? In other words if the 6500is configured to be NTP Master, where would it get it's time from??

Thank you for your help.

Cheers

Deena

P.S.

Current NTP configuration is:

ntp clock-period 17180262

ntp source Vlan1

ntp update-calendar

ntp server 138.23.180.126

ntp server 132.246.168.164

ntp server 209.87.233.53

[Reza Sharifi]

Hi,

The way your NTP is set up currently is correct.  Usually you want a server that has Internet access or receive timing from GPS (Sync Server) to be your NTP server. Then the routers and switches point to that server.

From the command reference guide:

Because Cisco's implementation of NTP does not support directly attached  radio or atomic clocks, the router is normally synchronized, directly  or indirectly, to an external system that has such a clock. In a network  without Internet connectivity, such a time source may not be available.  The ntp master command is used in such cases.

If the system has ntp master configured, and  it cannot reach any clock with a lower stratum number, the system will  claim to be synchronized at the configured stratum number, and other  systems will be willing to synchronize to it via NTP.

http://www.cisco.com/en/US/docs/ios/12_1/configfun/command/reference/frd3003.html

HTH

[DEENA VERAPPAN]

Hi Reza,

Thanks for the reply, the information was very useful.

Just to clarify, if my core 6500 is set to master, it will reply to requests for time from within the network, however it, (the core 6500) will request time from the servers configured namely:

ntp server 138.23.180.126

ntp server 132.246.168.164

ntp server 209.87.233.53

Is this correct??

Thanks again for your help.

Cheers

Deena

[Richard Burts · Accepted solution]

Deena

If your 6500 has learned authoritative NTP time from an Internet time source then your 6500 will respond to requests from your other routers and switches without requiring any configuration such as master.

The suggestion about configuring your 6500 as ntp master should be only about an alternative if your 6500 should lose its connection to its Internet time source. If you do configure your 6500 as master be sure to specify a stratum that is several numbers higher than the stratum from which it is learning its ntp time.

HTH

Rick

[Joseph W. Doherty · Accepted solution]

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Posting

Besides what the others have already posted, wanted to also emphasis the need for ntp update-calendar if you configure your 6500 as a NTP master (good idea on all equipment that supports a calendar).

This because if the 6500 reloads and also loses its NTP authority, all the downstream devices will at least have a reasonable time.

[DEENA VERAPPAN]

Thanks Guys, for the assistance and advice.

Much appreaciated.