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Catalyst 6000 Family Software Configuration Guide—Releases 6.3 and 6.4
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Chapter 8 Configuring Spanning Tree
Using MISTP-PVST+ or MISTP
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Determining MISTP Instances—VLAN Mapping Conflicts
A VLAN can only be mapped to one MISTP instance. If you attempt to map a VLAN to more than one
instance, all of its ports are set to blocking mode. You can use the
show spantree conflicts
command to
determine to which MISTP instances you have attempted to map the VLAN.
This command prints a list of the MISTP instances associated with the VLAN, the MAC addresses of
the root switches that are sending the BPDUs containing the VLAN mapping information, and the timers
associated with the mapping of a VLAN to an MISTP instance. When only one entry is printed or when
all the entries are associated to the same instance, the VLAN is mapped to that instance. If two or more
entries in the list are associated with different MISTP instances, the VLAN is in conflict.
To clear up the conflict, you must manually remove the incorrect mapping(s) from the root switch. The
remaining entry on the list becomes the official mapping.
To determine VLAN mapping conflicts, perform this task in privileged mode:
This example shows there is an attempt to map VLAN 2 to MISTP instance 1 and to MISTP instance 3
on two different switches as seen from a third switch in the topology:
Console> (enable)
show spantree conflicts 2
Inst MAC Delay Time left
---- ----------------- --------- ---------
1 00-30-a3-4a-0c-00 inactive 20
3 00-30-f1-e5-00-01 inactive 10
The Delay timer shows the time in seconds remaining before the VLAN joins the instance. The field
displays
inactive
if the VLAN is already mapped to an instance (the timer has expired), or if the VLAN
is in conflict between instances.
The Time Left timer shows the time in seconds left before the entry expires and is removed from the
table. The timer is restarted every time an incoming BPDU confirms the mapping. Entries pertaining to
the root switch show
inactive
on the root switch itself.
Unmapping VLANs from an MISTP Instance
The keyword
none
is used to unmap the specified VLANs from the MISTP instances to which they are
currently mapped. When you unmap a VLAN from an MISTP instance, the resulting state of all the ports
of the VLAN (if the VLAN exists) is
blocking
.
To unmap a VLAN or all VLANs from an MISTP instance, perform this task in privileged mode:
This example shows how to unmap a VLAN from an MISTP instance:
Console> (enable)
set vlan 6 mistp-instance none
Vlan 6 configuration successful
Task
Command
Determine VLAN mapping conflicts.
show spantree conflicts
vlan
Task
Command
Unmap a VLAN from an MISTP instance.
set vlan
vlan
mistp-instance none