is that network outage related to those topology change events?

[hanyawad]

hello,

my client has a switched network of 2 core switches of 4506 and 6 access layer switches most of them are 2960s.

every few days my client experience a random brownout in the network for few minutes. today they had a brownout for few minutes started at 3:14pm.

i took a look at the trap report i found continuous events of bridge topology changes. i attached this file i hope any one has experienced this before to share his knowledge and experience.

regards,

Makar

[Rolf Fischer]

Makar,

STP topology changes are not a bad thing - at least if they are not happening continuously.

After a topology change, age timer expiry of the CAM tables are set to 15 seconds, so  blackholing traffic by using old entries is avoided.

I use

show spanning-tree details | include exec|occur|from

to trace where topology changes came from.

We can see that Fa4/40 is flapping which is the reason for generating a TCN when changing to forwarding state.

That's normal and desired behavior.

But I wonder if Fa4/40 is an uplink?

If not, you should configure spanning-tree portfast and I'd also recommend BPDUGuard on access-ports.

I suppose your primary core switch is configured as STP root for all of your VLANs?

HTH

Rolf

[hanyawad]

fischer,

thanks for your reply. acually i understand it is good thing for generating a TCN but in my scinario it happens continuously and also the major issue i have is the random brownout in my network. so one of the causes which i'm suspecting is STP storm that might happens from continuous flapping links like fa4/40 and then makes the trunk links in this VLAN to go through the blocking state at the point of the brownout. does what i say make sense or i'm confused?

Makar

[jimmysands73_2]

By brownout are you saying its electrical issues?  This cause a lot of weirdness....if devices are going up/down due to the brownout.

[Rolf Fischer]

I think you mean an outage / temporary loss of connectivity, don't you?

You have to distinguish cause and effect. There is a flapping link, which could indicate a physical problem, and this flapping link causes STP topology changes.

Does Fa4/40 connect another STP-aware switch?

If so: Find out why it's flapping.

If not: Configure spanning-tree portfast for edge-ports; after that a link status change will not cause topology changes any more.

HTH,

Rolf