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Webcast-Catalyst9k
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Problem in Spanning-Tree

Hi,

I am facing a problem in spanning-tree implementation and need to know the Cisco gurus opnion. The scnario is explained below

Device-1 7609

Device-2 2960 and 3750

Device-3 Non cisco switches

Now D1 has Multiple spanning-tree defined witth following counters parameter

spanning-tree mst hello-time 1

spanning-tree mst forward-time 4

spanning-tree mst max-age 10

spanning-tree mst 0-1 priority 24576

While D2 and 3 has the same values for these parameters.

Two instances are defined in addition to instance 0

instance-1 includes vlan used in D3

instance-2 includes vlan in D2

All switches in D2 and D3 are connected to D1 i.e. 7609.

All vlans in D2 are defined in instance 1 of D1

All vlans in D3 are defined in instance 2 of D1

D1 is the root for MST topology.

The problem is that everytime we define a vlan in D1-instance-2. the whole segment get disturbed, high CPU and eventually a major outage occurs.

My question is

Should I put all vlans in one instance.

In a region, all devices should have all the vlans in similar instance? e.g. if D2 has vlans in instance-1 should I define the same D3 or vice versa?

Let me know if more information is required

1 REPLY
Hall of Fame Super Silver

Re: Problem in Spanning-Tree

Hello Kashan,

my understanding of MST is that all devices need to agree on:

region name

region revision number

the Vlan mappings have to be consistent on all devices.

So :

All switches in D2 and D3 are connected to D1 i.e. 7609.

All vlans in D2 are defined in instance 1 of D1

All vlans in D3 are defined in instance 2 of D1

D1 is the root for MST topology.

Have you defined on D2 devices that the range of vlans in D3 are in instance 2 ?

and the opposite on devices in D3 ?

see

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/spantree.html

another note:

actually only BPDUs of instance 0 are sent out ports so at least one vlan has to stay wih instance 0. But on this point I'm not sure there have been other threads about MST with different opinions on this.

Hope to help

Giuseppe

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