Spanning-Tree Topology Question

tobin_jim · ‎11-09-2009

Hi There,

Should all switches participating in and trunking the same vlan agree on the time of the last topology change for that vlan.

The switches on my LAN are reporting various values.

4507-01#show span vlan 71 det | in last change

Number of topology changes 26 last change occurred 6w6d ago

4507-02#show span vlan 71 det | in last change

Number of topology changes 37 last change occurred 4w4d ago

N5_1SWL#show span vlan 71 det | in last change

Number of topology changes 13 last change occurred 1y4w ago

I would have thought that a topology change on one switch would have been reported to the root and passed to the other switches from there.

Is the topology change repoted only locally significant to the switch?

Jim

Giuseppe Larosa · ‎11-09-2009

Hello Jim,

the switches should agree on STP "uptime" on the vlan.

Have you enabled STP features like STP loop guard that could make one switch to ignore some changes?

I've checked in a campus of mine on two devices one is at distribution and one access layer and they match

sh spanning-tree vlan 9 det

VLAN0009 is executing the ieee compatible Spanning Tree protocol

Bridge Identifier has priority 0, address 001d.4605.4009

Configured hello time 2, max age 20, forward delay 15

We are the root of the spanning tree

Topology change flag not set, detected flag not set

Number of topology changes 1299 last change occurred 00:57:06 ago

from Port-channel10

VLAN0009 is executing the rstp compatible Spanning Tree protocol

Bridge Identifier has priority 32768, sysid 9, address 0022.90a4.c380

Configured hello time 2, max age 20, forward delay 15, transmit hold-count 6

Current root has priority 0, address 001d.4605.4009

Root port is 257 (TenGigabitEthernet5/1), cost of root path is 2

Topology change flag not set, detected flag not set

Number of topology changes 757 last change occurred 00:57:27 ago

Hope to help

Giuseppe