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Configuring NTP on c4948

Last year our RSM /Cat5509 failed and a decision was made to replace it with a layer 3 switch ie: Cat4948 rather than try to source another RSM/Cat5509.

Our telemetry server logs have highlighted that although NTP was being distributed out from our clock unit plugged into the cat5509/RSM before the change out. Once the Cat4948 was installed NTP stopped being distributed to the rest of the network. The NTP configuration was copied directly from the RSM to the new 4948.

The clock/sync unit is plugged directly into one of the ports on the Cat4948 and NTP is being picked up by the Cat4948 (see below). However, the 3660 that is directly connected into the Cat4948 (Ethernet port to Ethernet port) does not seem to be picking NTP up from the Cat4948.

It appears that whilst the Cat4948 is able to pick up NTP from the sync unit, the Cat 4948 is not re-distributing NTP

Original config on the RSM:

R_BAC_RSM

!

ntp clock-period 17179974

ntp update-calendar

ntp server 149.191.41.29

!

END

-------------------------------------------------------

Current config on the Cat4948

L3_BAC_4948_COMMS#

!

ntp clock-period 17179292

ntp update-calendar

ntp server 149.191.41.29

!

END

A 'show ntp status' on the Cat4948 reveals correctly that it is getting sysnc from the clock unit (149.191.41.29) on the 41 subnet vlan

L3_BAC_4948_COMMS# sh ntp status

Clock is synchronized, stratum 2, reference is 149.191.41.29

nominal freq is 250.0000 Hz, actual freq is 250.0083 Hz, precision is 2**18

reference time is CBCD7FF0.FC3CD1E5 (14:34:40.985 UK Thu May 8 2008)

clock offset is -974.0229 msec, root delay is 4.71 msec

root dispersion is 982.67 msec, peer dispersion is 8.64 msec

L3_BAC_4948_COMMS#

------------------------------------------------------------------------------------

3660 (connected to the Cat4948 via an ethernet port)

R_BAC_3660#

!

!

ntp clock-period 17180228

ntp server 149.191.41.29

!

END

R_BAC_3660#

R_BAC_3660# sh ntp status

Clock is unsynchronized, stratum 16, no reference clock

nominal freq is 250.0000 Hz, actual freq is 249.9947 Hz, precision is 2**24

reference time is CAE5A980.B4E2B4EA (17:06:08.706 UTC Wed Nov 14 2007)

clock offset is 0.6322 msec, root delay is 2.59 msec

root dispersion is 0.95 msec, peer dispersion is 0.32 msec

R_BAC_3660#

2 REPLIES
Hall of Fame Super Gold

Re: Configuring NTP on c4948

Suhale

The information that you posted shows clearly that the 4948 is learning NTP time from the server at 149.191.41.29. And it shows that the 3660 is attempting to learn NTP from the same server but is not. There are several things that might cause this:

- is there an IP connectivity issue? Can the 3660 ping the NTP server? Did something perhaps change in the routing logic on the 4948?

- is there something that is filtering traffic (firewall or interface access list) that might be filtering the NTP attempt from the 3660 or filtering responses back from the server?

One alternative to consider might be to change the config of the 3660 and have it learn NTP from the 4948 rather than from the same server that the 4948 is learning from.

HTH

Rick

Community Member

Re: Configuring NTP on c4948

Hi Rick -

Thanks for your informative reply. I will carry out your recommendations and let you know what happens :-)

Suhale

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