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How to stop Spanning Tree from blocking VLAN ports (SG500)

Od29
Level 1
Level 1

I've set the spanning tree mode to MSTP and the ports have completely different VLANs.  

 

Diagram.png

SW1 ports 44-47 connects to port 43 on SW2, SW3, SW4, SW5 respectively - all are Trunking with VLAN 10

SW2 port 44 connects to port 44 on SW4 - Trunking VLAN 200.  At this point STP kicks in and blocks the port.

 

SW2 %STP-W-PORTSTATUS: gi1/43 of instance 3: STP status Forwarding
SW2 %STP-W-PORTSTATUS: gi1/43 of instance 4: STP status Forwarding
SW2 %STP-W-PORTSTATUS: gi1/43 of instance 5: STP status Forwarding
SW2 %STP-W-PORTSTATUS: gi1/43 of instance 6: STP status Forwarding
SW4 %STP-W-PORTSTATUS: gi1/44 of instance 6: STP status Blocking
SW4 %STP-W-PORTSTATUS: gi1/44 of instance 1: STP status Blocking
SW4 %STP-W-PORTSTATUS: gi1/44 of instance 0: STP status Blocking
SW4 %LINK-I-Up:  Vlan 200
SW4 %LINK-I-Up:  gi1/44
SW4 %STP-W-PORTSTATUS: gi1/44 of instance 6: STP status Forwarding
SW4 %STP-W-PORTSTATUS: gi1/44 of instance 1: STP status Forwarding
SW4 %STP-W-PORTSTATUS: gi1/44 of instance 0: STP status Forwarding

I don't understand why instance 1 (mapped to VLAN 10) is even in the logs for SW4 gi1/44 - it should only be instance 6 (VLAN 200)

 

I'm really tempted to just disable STP on my trunking ports at this point .. but I hate not understanding why it isn't working.

 

I've written out my setup instructions with all of the CLI commands .. I do these instructions from a hard reset.  I'm running the latest firmware on all the switches too.  Any help would be greatly appreciated.

 

EDIT: Added Diagram

3 Replies 3

balaji.bandi
Hall of Fame
Hall of Fame

i will look at the configuration and feedback on what is wrong here, do you have any network layout of how these switches are connected.

 

i may think that somewhere loop in the network causes this block, that will only confirm once we get a network diagram and review the configs.

BB

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Edited the post and attached a diagram.

Maybe I found the problem ...

 

In the MST configuration I was only including instances in each switch's configuration if those instances were using VLANs that were used on that switch.

So if SW1 didn't use VLAN 14, and VLAN 14 was mapped to MST Instance 2 - I didn't include instance 2 in SW1's MST configuration.

 

When I included all instances / VLANs in the MST configuration - I am still seeing blocked ports - but they are on other instances that the port doesn't use.  The instance it DOES use is not blocked ...   https://pastebin.com/zF5ATH8q