Access Layer switches getting dropped in network

[Anuj Singhi]

I have two 4506 core switches to which various model switches are connected forming redundancy in access layer. Yesterday most of the access layer switches started dropping over network with 1 out of 5 ping being successfull. When we rebooted the secondary core switch the issue got resolved but as soon as it came up issue reoccurred. We disabled all the downlink connections of the switches in secondary core switch which has provided us a workaround but we are still not sure what might have caused the issue.

There are no loop or mac flooding logs in any of the switches, neither there were any spanning tree logs. Access layer switches are configured with trunk configuration.

We have pvst running on the core switches. Can anybody suggest what could be the root cause of it. 

[devils_advocate]

Are you using VSS between the 4506's or something like HSRP?

What does STP show from the Core perspective when the issue occurs, presumably all the ports on the root bridge are in the designated state?

[Anuj Singhi]

They are running in HSRP and yes all the ports were DP. Could running rapid pvst resolve the issue on both switches?

[devils_advocate]

You need to make sure your root bridge for the STP is the same as your HSRP active router.

Is this a new setup or an existing setup which stopped working properly?

You need to understand whether you actually have a bridging loop first.

What do the logs show when it happens?

Has your primary and secondary root bridges been defined manually?

Are the access switches all configured with the default STP priority?

[Anuj Singhi]

Root bridge is same as HSRP active router and this is an old setup which suddenly stopped working. We have not setup primary and secondary as manual. 

Secondary switch however is not acting as secondary stp root from what we can see

Yes all the access switches are configured with default STP priority.

[devils_advocate]

Secondary switch however is not acting as secondary stp root from what we can see

You need to ensure the STP is configured to follow the HSRP active.

If Switch 1 is the STP primary root bridge and also the HSRP active, you need to configure switch 2 to be the secondary.

Presumably the 4506 devices are connected together?

Can you post the configs from both switches?

Ideally you need to boot the second one up out of hours and check the STP status.