07-05-2015 04:42 AM - edited 03-08-2019 12:50 AM
Hi,
Just need some help here. A bit confused of what went wrong. I'm just setting up a home lab environment and I have observed this weird behaviour.
For some reason both of my L3 switches (3560) have elected themselves to be the root bridge for VLAN 101, I have configured SW1 to the the root bridge for VLAN 101 and SW2 the root bridge for VLAN 102. I have an additional 2 L2 switches in my lab network.
This is a really basic configuration and I haven't done any VLAN prunning and all VLAN's are allowed through the trunks. All switches are within the same VTP domain and the mode is set to transparent.
I also came across a similar thread however the solutions/bug is for the Cisco 3550, and I'm running a 3560 switch.
https://supportforums.cisco.com/discussion/9556911/spanning-tree-multiple-roots
Any assistance would be greatly appreciated.
SW1 output:
VLAN0101
Spanning tree enabled protocol rstp
Root ID Priority 28773
Address 0014.a8e3.1600
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 28773 (priority 28672 sys-id-ext 101)
Address 0014.a8e3.1600
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/23 Desg FWD 19 128.25 P2p
Fa0/24 Desg FWD 19 128.26 P2p
SW2 output:
VLAN0101
Spanning tree enabled protocol rstp
Root ID Priority 24677
Address 0012.d9a4.bc80
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24677 (priority 24576 sys-id-ext 101)
Address 0012.d9a4.bc80
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/23 Desg FWD 19 128.25 P2p
Fa0/24 Desg FWD 19 128.26 P2p
07-06-2015 01:56 AM
Hi,
This is a curious issue. Can you please provide the following outputs from both your 3560 switches?
show cdp neighbor
show vlan brief
show int trunk
show run
Thank you!
Best regards,
Peter
07-06-2015 02:19 AM
A network diagram might help... are you sure there's at least one "path" for Vlan101 between the two switches (and without any BPDU filtering on the way)?
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