C3750, NTP and Routing

dave.barton · ‎11-13-2006

Hi all,

I have a problem with NTP on a couple of 3750 switches which are routing between VLANs.

Switch A is connected to Switch B (via a trunk port with no pruning) and both are running NTP. Both have multiple IP addresses and act as gateways to the VLANs they serve. They are running OSPF to share their routing information.

Switch A will respond to NTP requests from a machine routed by Switch B.

Switch B will respond to NTP requests from a machine routed by Switch A.

However,

Switch A will NOT respond to NTP requests from a machine routed by Switch A.

Switch B will NOT respond to NTP requests from a machine routed by Switch B.

When I enable debugging on NTP packets. I don't even see the request from a machine the switch is responsible for routing. I do however see the requests from machines that the switch is not responsible for routing.

Any advice on how to troubleshoot further?

Many thanks,

Ben

amit-singh · ‎11-13-2006

Hi Ben,

Please paste the switch configurations and a brief topology if possible.

-amit singh

dave.barton · ‎11-13-2006

Ive edited the configs slightly for security purposes, but everything essential is there:

Topology wise.

We have three 3750 switch stacks. These act as our core switches.

We are running VLANs and do not have any routers.

Part of our network (servers 10.0.0.0/16) is routed by a checkpoint firewall, allowing us to easily control what is allowed between VLANs.

The desktop portion of our network (with an Active Directory, 10.1.0.0/16) is routed by the core switches.

There is a static route between the switches and the firewall to allow traffic to pass between our two network sections.

I am testing from a linux client attached directly to Bradwell (one of the core switches) on VLAN 102. This is a desktop VLAN routed by the switches.

I am attempting to sync ntp with 10.1.0.1 or 10.1.2.254 - both of which are IPs on Bradwell.

The attached config is of Bradwell. The other core switches have a fairly identical config, except they act as a gateway for other VLANs.

Cheers,

Ben