Spanning tree issue with trunks

[Marseb]

Hi all,

I have a problem in our netwerk with recently installed Procurve switches and was looking for some help.

The situation:
Switch A (5406 ZL)
Switch B (5406 ZL)
Switch C (2610)

Switch A and B are directly connected to eachother with a trunk of 4. Total 4Gb

Switch C is connected to A and B with a 1Gb per link. When switch C was connected spanning tree blocked the link between A and B. This link has a Cost of 10.000 and a priority of 64.

The links from A to C and from B to C have a cost of 20.000 and a priority of 128.

In a test setup with 3 switches (2610) no matter what I do, the trunk will be the active link or become the active link when it was interupted and returns.

What to do/configure?

[Krzysztof Oledzki]

Which one is you STP root switch? I guess it is the "Switch C". You should be able to check it with "sh spanning-tree".

The solution is pretty simple: make sure one of your 5406 becomes the root, you should be able to do this with "spanning-tree priority 0"

[Tijl van der Steeg]

I agree. Costs are only relevant when you have multiple links on one switch, not to set priorities between switches

"sh span" should help you

[Marseb]

I looked at the spanning-tree config on switch C but did not see if it the root.

This the result:
Multiple Spanning Tree (MST) Information

STP Enabled : Yes
Force Version : MSTP-operation
IST Mapped VLANs : 1-4094
Switch MAC Address : 0024a8-07d6c0
Switch Priority : 32768
Max Age : 20
Max Hops : 20
Forward Delay : 15

Topology Change Count : 125
Time Since Last Change : 5 days

CST Root MAC Address : 0008a2-01c8b0
CST Root Priority : 32768
CST Root Path Cost : 200000
CST Root Port : 2

IST Regional Root MAC Address : 0024a8-07d6c0
IST Regional Root Priority : 32768
IST Regional Root Path Cost : 0
IST Remaining Hops : 20

Root Guard Ports :
TCN Guard Ports :
Protected Ports :
Filtered Ports :

[Krzysztof Oledzki]

No, it seems that it is not a root. If it is, you will see:

"CST Root Port : This switch is root"

instead of:

"CST Root Port : 2"

But wait. AFAIK port #2 is only capable of 10/100, so it seems that you root switch is connected by this port, so your topology looks probably like this:

root(?)
|
|
(port #2)
2610
/ \
/ \
5406 5406

What device do you have there on that port?

[Shadow13]

hi,

Just to unblock the port between A and B, do as they said.

use this commands in A or B

#spannint-tree instance 0 priority 1

this will make that switch the ROOT and will unblock the trunk link between the 2 switches.

and just for clarification, would you please use #show lldp info remote-device
in switch C, just to check the ROOT MAC address belongs to which device in your network.


Regards,
Islam Hassan

[Marseb]

I'm looking into what device is on switch C behind port 2. I can't resolve it physically (large factory) so i'm trying to resolve the IP based on the mac. (not yet succesfull)

The "show lldp info remote-device" command returns 2 entries, the link to switch A and the link to switch B. It does not talk about the STP root (port 2).

[Krzysztof Oledzki]

OK, if it is an independent network all you need to do (and definitely should!) is to split spanning trees by enabling bpdu filtering on that port:

spanning-tree 2 bpdu-filter

If your switch supports pvst-filter then use this:

spanning-tree 2 bpdu-filter pvst-filter

BTW: you should also consider enabling bpdu-protection/pvst-protection on ports you don't use to connect your switches together.