Topology Time since last change incorrect

[Simon Merckx]

I have 5300XL core switches.

When I do a show span detail:

one of them reports time since last topology change: 1 hour

but the root switch(also 5300XL) reports: 25 hours

In the documentation:
Once an STP topology is stable, establishing an Ethernet link on a switch port results in a topology change. This happens every time a user powers up their PC (assuming that the PC is directly connected to a switch port), resets the PC, or brings up the PC's network stack. The establishment of this link causes the topology change count to increment in:

1. the switch to which the end node is directly attached; and
2. "upstream" switches. That is, the root switch and the switches between the root switch and the switch to which the end node is directly connected.

So the root switch should also receive the topology change and should also report 1 hour since last change?

Why is the root switch not receiving the topology change. The root switch reported by al the switches is the same.

[Matt Hobbs]

What version firmware are you running, and are you running the older 802.1D (STP) by any chance?

[Simon Merckx]

I am running version: E.09.03
I am using normal STP not RSTP

[Matt Hobbs · Accepted solution]

I thought you might be running STP. The switches only count TCN's and not TC's in their 'show span' topology counter. So depending on where in the network the TCN is coming from you may see different values on each of your switches. This can aid in troubleshooting if you need to find the source of the TCN. Generally though the root switch should have the lowest time since last topology change since all TCN's should be reaching it.

At this stage, I'd recommend updating to the latest firmware, in fact E.11.03 defaults to MSTP now. This has a spanning-tree legacy-mode command to better interoperate with STP if you need it. It also should include more information in the 'show span detail' to help troubleshoot any STP related issues.

[Simon Merckx]

Is an upgrade of my firmware the solution?
Are their known issues with my version and the TCN's not reaching the root switch?

I have read al the release notes between my version and the latest. There is nothing that looks like my problem.

[Simon Merckx]

I have found the probleem. Somebody connected a switch with a lower spanning tree priority number to our netwerk. That switch became the new root switch.

That happend without my knowledge.
Sorry for wasting your time.

Thanks for the replies.

[Matt Hobbs]

With the latest firmware you can also use the new root-guard feature amongst a bunch of other spanning-tree enhancements.

[Simon Merckx]

Problem found:
Root switch was wrong.