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New Member

NTP Synchronize problem

Hi,

I have configured NTP server properly and it was working fine.  But due to some reason I had to configure "Ip routing" on switch.  After that I have been facing this problem. i.e. NTP is not synchronized.

Again when I remove "Ip routing" command then its working fine.  Could any one can give me some idea why its happening.

Thanks

Goutam

15 REPLIES

Re: NTP Synchronize problem

Hi,

I have configured NTP server properly and it was working fine.  But due to some reason I had to configure "Ip routing" on switch.  After that I have been facing this problem. i.e. NTP is not synchronized.

Again when I remove "Ip routing" command then its working fine.  Could any one can give me some idea why its happening.

Thanks

Goutam

Hi Goutam,

Can you share the diagramtic representaion of the network and the ntp configuration in switch.

Ganesh.H

New Member

Re: NTP Synchronize problem

Hi,

Please find the diagram, how the NTP server is connected to switches and configuration.

Thanks

Goutam

New Member

Re: NTP Synchronize problem

Hi,

Please find the diagram of NTP server connectivity to switch and configuration.

Re: NTP Synchronize problem

Hi,

Please find the diagram of NTP server connectivity to switch and configuration.

Hi Goutam,

Can you share the show ntp assoiciation output from access switch and from the original post you have mentioned when you enabled ip routing clock never sycronize what this means when you configure ip routing in core switch clock never syncronize is it ?

Ganesh.H

New Member

Re: NTP Synchronize problem

Hi,

Please find the output

ST-DC-SW-SVR-3750-2#sh ntp associations

      address         ref clock     st  when  poll reach  delay  offset    disp
~10.128.90.254    127.127.7.1       8  25615    64    0     1.8   -0.08  16000.
* master (synced), # master (unsynced), + selected, - candidate, ~ configured

When I am configuring "ip routing" on access switch, its never synchronized.  Core switch is showing synchronized...

Re: NTP Synchronize problem

Hi Goutam

what kind of access switch do you have ? is it layer 2 or layer 3 ? can you give a show ip interface brief on your access switch and send it to us please ? can you also post "show log" incase it has any NTP logs ?

Regards

Raj

New Member

Re: NTP Synchronize problem

Hi Raj,

Please find the log and interface details.  This switches are L2 Switch.

Re: NTP Synchronize problem

Hi,

Please find the output

ST-DC-SW-SVR-3750-2#sh ntp associations

      address         ref clock     st  when  poll reach  delay  offset    disp
~10.128.90.254    127.127.7.1       8  25615    64    0     1.8   -0.08  16000.
* master (synced), # master (unsynced), + selected, - candidate, ~ configured

When I am configuring "ip routing" on access switch, its never synchronized.  Core switch is showing synchronized...

Hi Goutam,

First i would like to suggest you configure in your core switch as ntp master with startum value lower than the actual ntp server 172.18.136.2 startum value and check the following things from access switch to reach the core switch.

As per the above logs following observation can be done:-

The 'reach' counter shows a value of 0 for the following configured NTP server IP address(es):

10.128.90.254

This means that the router did not receive at least the last eight NTP packets it expects to receive. Usually this counter shows a value of "377" which means that device has received at least the last eight NTP packets.

Check out the below things between the access switch and core switch:-


1. Make sure that NTP server IP address(es) mentioned above is reachable by pinging the server IP address(es).
2. Enable the debug ntp packet command to make sure that NTP packets are received from the server(s).
3. Make sure that NTP packets are not blocked by the access-list statement.

4.Verify that the 'stratum' value configured on the server is valid for your setup.configure a high stratum number to ensure that this router does not overridethe clock on another system with a lower stratum number. The lower stratum number indicates a more reliable clock.

And as Raj suggested also share the details for the acces switches is it a L2 or L3.

Hope to help

Ganesh.H

New Member

Re: NTP Synchronize problem

Hi Ganesh,

I have checked and found that,  when I remove "Ip routing" command from access switch, its works fine and able to ping core switch ip 10.128.90.254 (ntp server).  But when I enable "Ip routing" command on access switch.. it stop to ping to Core switch ip 10.128.90.254.

and please tell me how do i change "Startum" and make it fixed.

NTP packet is not  blocked anywhere in the network, if it is then it should not ping after removing "ip routing" command.  I think something related to "ip routing" command.

Ok I will all the points again.  Request all of you to check this type of problem, if i can solve anyhow.

Re: NTP Synchronize problem

Hi Ganesh,

I have checked and found that,  when I remove "Ip routing" command from access switch, its works fine and able to ping core switch ip 10.128.90.254 (ntp server).  But when I enable "Ip routing" command on access switch.. it stop to ping to Core switch ip 10.128.90.254.

and please tell me how do i change "Startum" and make it fixed.

NTP packet is not  blocked anywhere in the network, if it is then it should not ping after removing "ip routing" command.  I think something related to "ip routing" command.

Ok I will all the points again.  Request all of you to check this type of problem, if i can solve anyhow.

Hi Goutam,

As you have told access switches are L2 switch then Switch(config)#ip default-gateway {ip address} is the command for routing the traffic towards the default gateway and confirm also after removing the ip routing NTP is not sync right ?

As you have configured ntp master in core switches just add startum value like ntp master starum value lower than the actual ntp server.

HTH

Ganesh.H

Hall of Fame Super Gold

Re: NTP Synchronize problem

The router is configured to synchronize it's clock to "10.128.90.254".  The symbol "~" means that it's configured but it's not synchronizing.  What I'd like to know is what is "10.128.90.254"?  Is this a Server configured as an authoritative time source?  Another network appliance?

What router is this?  Can you configure SNTP and does it work?

Can you ping "10.128.90.254"?

New Member

Re: NTP Synchronize problem

Hi Leolaohoo,

If you see the diagram I have attached before,  this IP 10.128.90.254 is Core switch in my network, which is working Master/NTP server for all the access switches in Network.

But in case of Core switch the NTP server is in different network i.e. 172.18.136.2 (NTP Server IP).

Connectivity is like... Core Switch is synchronizing with NTP Server 172.18.136.2 and Access switches are synchronizing with Core Switch (10.128.90.254)

Everythis were working fine....the problem i am facing when configuring "ip routing" command.

Purple

Re: NTP Synchronize problem

   You probably have no route to the ntp server that you were using before. If it was setup as a layer 2 switch before then you were probably using the ip default-gateway command pointing to a specific address. When you turn on ip routing on the switch that default gateway command  will no longer work and you have to define a default static route pointing to that same address that used to be in the default gateway comand , instead of using  " ip default-gateway x.x.x.x you have to change it to ip route 0.0.0.0 0.0.0.0 x.x.x.x   which will be what the address was in the former gateway command. Not knowing why you had to turn routing on or what network changes you made it is speculation , I know you have to turn on routing in a lot of cases just to configure QOS parameters.

New Member

Re: NTP Synchronize problem

Hi Glen,

Before "Ip routing" was not enable on Access Switch.  and NTP was working fine.

Suddenly one day, one of the access switch crashed and same I have discussed with cisco experties, and they have recommended to enable "Ip routing" to avoid crash in future.

Purple

Re: NTP Synchronize problem

So did you check to see if you are using a default gateway command or a default static route?  Have no idea why they would tell you changing it from a layer 2 switch to a layer 3 functional switch , that should make no difference of why it crashed , we have hundreds of 3560's setup as L2 only..  I would post your config on the switch you are talking about.

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