MSTP problem

Unanswered Question
Jul 9th, 2007

I have a network with four cisco switches

3560(12.2(25)SEC)---trunk---3560GS1(12.2(25)SEE3)---trunk---3560GS2(12.2(25)SEE3)(GEth0/26)---trunk---3550(12.2(37)SE)(GEth0/1)

Switches are has same MST region and has same MST instance.

3560(0014.A80B.3B80):

spanning-tree mode mst

spanning-tree extend system-id

!

spanning-tree mst configuration

name XXX

revision 10

instance 1 vlan 500

instance 2 vlan 508

instance 3 vlan 511

instance 4 vlan 725

instance 5 vlan 706

instance 6 vlan 504-506, 509-510, 512-513, 700-705, 707-724, 726-799

3560GS1(0018.19CF.CC00):

spanning-tree mst configuration

name XXX

revision 10

instance 1 vlan 500

instance 2 vlan 508

instance 3 vlan 511

instance 4 vlan 725

instance 5 vlan 706

instance 6 vlan 504-506, 509-510, 512-513, 700-705, 707-724, 726-799

!

spanning-tree mst 1-4 priority 28672

spanning-tree mst 5-6 priority 24576

3560GS2(0015.FA9A.DD80):

spanning-tree mode mst

spanning-tree extend system-id

!

spanning-tree mst configuration

name XXX

revision 10

instance 1 vlan 500

instance 2 vlan 508

instance 3 vlan 511

instance 4 vlan 725

instance 5 vlan 706

instance 6 vlan 504-506, 509-510, 512-513, 700-705, 707-724, 726-799

!

spanning-tree mst 5 priority 28672

3550(0012.80F6.6E00):

spanning-tree mode mst

spanning-tree extend system-id

!

spanning-tree mst configuration

name XXX

revision 10

instance 1 vlan 500

instance 2 vlan 508

instance 3 vlan 511

instance 4 vlan 725

instance 5 vlan 706

instance 6 vlan 504-506, 509-510, 512-513, 700-705, 707-724, 726-799

!

spanning-tree mst 0-6 priority 61440

Switch 3560 is root for CIST.

Problem:

MSTP is not stable, sometime 3550 send BPDU with TC, because his port GEth0/1 setting BOUNDARY and switching to PVST mode. What is cause maybe?

debug 3550 in attachment

Attachment: 
I have this problem too.
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Francois Tallet Mon, 07/09/2007 - 09:12

Hi Sergey,

ge0/1 on the 3550 seems to be receiving two kinds of bpdus.

-Some MST bpdus from region, with better information (root port).

-Some RSTP bpdus, probably tagged (probably coming from a switch running Rapid-PVST).

What is exactly g0/1? What is it connected to? Is is a shared segment (or it is connected to an emulated LAN with different peers?). You usually expect a single peer from a point-to-point link.

Another possibility is that this port is connected to a third party bridge that floods PVST+ bpdus. In that case, the bpdus that are causing this flapping you see in the debug may be caused by some remote devices sending PVST+ bpdus (again, probably some Rapid-PVST devices) across the L2 network handled by the third party boxes.

Regards,

Francois

zaikini_23 Mon, 07/09/2007 - 21:45

Thank you Francois. I have found the reason of the arisen problem. It's remote-span vlan 706 on 3560GS2 for monitoring some ports. This vlan was allowed between 3560GS2 and 3550. I blocked it, but I want monitoring ports traffic and my server wouldn't connect to 3560GS2. I shall search for the decision of this problem. Thanks once again Francois, good luck:)

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