Restarting Protocol Migration - Cisco Catalyst 4500 Series Configuration Manual

Chapter 20 Configuring STP and MST
Switch# show spanning-tree mst 1 interface fastethernet 4/4
FastEthernet4/4 of MST01 is backup blocking
Edge port:no
Link type:point-to-point (auto)
Boundary :internal
Bpdus (MRecords) sent 125, received 1782
Instance Role Sts Cost
-------- ---- --- --------- -------- -------------------------------
1
Switch#

Restarting Protocol Migration

RSTP and MST have built-in compatibility mechanisms that allow them to interact properly with other
regions or other versions of IEEE spanning-tree. For example, an RSTP bridge connected to a legacy
bridge can send 802.1D BPDUs on one of its ports. Similarly, when an MST bridge receives a legacy
BPDU or an MST BPDU associated with a different region, it is also to detect that a port is at the
boundary of a region.
Unfortunately, these mechanisms cannot always revert to the most efficient mode. For example, an RSTP
bridge designated for a legacy 802.1D stays in 802.1D mode even after the legacy bridge has been
removed from the link. Similarly, an MST port still assumes that it is a boundary port when the bridge(s)
to which it is connected have joined the same region. To force a Catalyst 4500 series switch to
renegotiate with the neighbors (that is, to restart protocol migration), you must enter the clear
spanning-tree detected-protocols command, as follows:
Switch# clear spanning-tree detected-protocols fastethernet 4/4
Switch#
Displaying MST Configurations
To display MST configurations, perform this task:
Command
Step 1
Switch# show spanning-tree mst configuration
Step 2
Switch# show spanning-tree mst [detail]
Step 3
Switch# show spanning-tree mst instance-id [detail]
Step 4
Switch# show spanning-tree mst interface interface
[detail]
Step 5
Switch# show spanning-tree mst instance-id
interface interface [detail]
Step 6
Switch# show spanning-tree vlan vlan_ID
OL-25340-01
(default)
Prio.Nbr Vlans mapped
Back BLK 1234567 240.196
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
port guard :none
bpdu filter:disable
bpdu guard :disable
1-10
Purpose
Displays the active region configuration information.
Displays detailed MST protocol information.
Displays information about a specific MST instance.
Displays information for a given port.
Displays MST information for a given port and a given
instance.
Displays VLAN information in MST mode.
Configuring MST
(default)
(default)
(default)
20-33