spanning-tree

[fsebera]

show spantree stat 4/5 306

Does anyone know why does the MAC address reported on "topology change last recvd. from" that actually belongs to a non-ROOT and (non-secondary root)

DOWNSTREAM switch show up on my user port 4/5 as the reason for the topology change?

I thought since my PC was disconnected/connected on port 4/5, my PC mac address would show up as the source and reason for the topology change.

Am I reading the output incorrectly?

I read the output as the MAC address 00-0a-f4-f7-12-fe came in on port 4/5.

The ROOT and 2nd ROOT switches are UPSTREAM.

I disabled portfast on port 4/5 and disconnected/reconnected my PC.

show spantree stat 4/5 306 provided the below output.

--snip--

Vlan based information & statistics

spanningtree type ieee

spanningtree multicast address 01-80-c2-00-00-00

bridge ID priority 24882

(bridge priority: 24576, sys ID ext: 306)

bridge mac address 00-09-b6-11-be-00

bridge hello time 2 sec

bridge forward delay 15(15) sec

topology change initiator: 4/5

last topology change occured: Wed Mar 9 2005, 18:37:07

topology change FALSE

topology change time 35

topology change detected FALSE

topology change count 377

topology change last recvd. from 00-0a-f4-f7-12-fe

--snip--

Thanks for responding

Frank

[Georg Pauwen]

Hello Frank,

the output shows that your port 4/5 is responsible for the topology change, and normally, the ´topology change last received´ MAC address should be the one of the upstream switch, that is, the switch in the direction to the root. Since TCN BPDUs are sent out blocked and non-blocked ports, it might just be that the downstream switch with MAC address 00-0a-f4-f7-12-fe received and transmitted the TCN faster than the root port on your switch where the topology change has occurred. You could check the physical topology to find out if, for some reason, the path through blocked ports is actually shorter than though non-blocking ports.

You might want to check this document as background reading:

Understanding Spanning-Tree Protocol Topology Changes

http://www.cisco.com/en/US/partner/tech/tk389/tk621/technologies_tech_note09186a0080094797.shtml

Regards,

GP

[ankurbhasin]

Hello Frank,

"topology change last recvd. from 00-0a-f4-f7-12-fe"

this means tcn is sourced by 00-0a-f4-f7-12-fe mac address. So we need to trace this mac address in your network and find out whats happening on that switch which is generating tcn.

This entry is the only means which tell us which switch is generating TCN and sending to the root bridge.

Regards,

Ankur