12-28-2012 07:46 PM - edited 03-07-2019 10:49 AM
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
12-29-2012 01:38 AM
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
12-29-2012 09:09 AM
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
12-29-2012 10:14 AM
By brownout are you saying its electrical issues? This cause a lot of weirdness....if devices are going up/down due to the brownout.
12-29-2012 12:36 PM
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
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