Configuring Mst Instance Port Parameters; Restarting Protocol Migration - Cisco 4500M Software Manual

Configuring MST

Configuring MST Instance Port Parameters

To configure MST instance port parameters, perform this task:
Command
Step 1
Switch(config-if)# spanning-tree mst x cost y
Step 2
Switch(config-if)# spanning-tree mst x port-priority y
Step 3
Switch(config-if)# Ctrl-Z
Step 4
Switch# show spanning-tree mst x interface y
This example shows how to configure MST instance port parameters:
Switch(config)# interface fastethernet 4/4
Switch(config-if)# spanning-tree mst 1 ?
cost
port-priority
Switch(config-if)# spanning-tree mst 1 cost 1234567
Switch(config-if)# spanning-tree mst 1 port-priority 240
Switch(config-if)# ^Z
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 will stay 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 4000 family 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#
Software Configuration Guide—Release 12.2(25)EW
16-12
Change the interface spanning tree path cost for an instance
Change the spanning tree port priority for an instance
(default)
Prio.Nbr Vlans mapped
Back BLK 1234567 240.196
Chapter 16 Understanding and Configuring Multiple Spanning Trees
Purpose
Configures the MST instance port cost.
Configures the MST instance port priority.
Exits configuration mode.
Verifies the configuration.
port guard :none
bpdu filter:disable
bpdu guard :disable
1-10
(default)
(default)
(default)
OL-6696-01