Configuring Mst Instance Port Parameters; Restarting Protocol Migration - Cisco 7609 Configuration Manual

Configuring IEEE 802.1s MST

Configuring MST Instance Port Parameters

To configure MST instance port parameters, perform these tasks:
Command
Step 1
Router(config-if)# spanning-tree mst x cost y
Step 2
Router(config-if)# spanning-tree mst x
port-priority y
Step 3
Router# show spanning-tree mst x interface y
This example shows how to configure MST instance port parameters:
Router(config)# interface fastEthernet 4/4
Router(config-if)# spanning-tree mst 1 ?
cost
port-priority
Router(config-if)# spanning-tree mst 1 cost 1234567
Router(config-if)# spanning-tree mst 1 port-priority 240
Router(config-if)# ^Z
Router# 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
Router#

Restarting Protocol Migration

A switch running both MSTP and RSTP supports a built-in protocol migration mechanism that enables
the switch to interoperate with legacy 802.1D switches. If this switch receives a legacy 802.1D
configuration BPDU (a BPDU with the protocol version set to 0), it sends only 802.1D BPDUs on that
port. An MSTP switch can also detect that a port is at the boundary of a region when it receives a legacy
BPDU, an MST BPDU (version 3) associated with a different region, or an RST BPDU (version 2).
However, the switch does not automatically revert to the MSTP mode if it no longer receives 802.1D
BPDUs because it cannot determine whether the legacy switch has been removed from the link unless
the legacy switch is the designated switch. A switch also might continue to assign a boundary role to a
port when the switch to which it is connected has joined the region.
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
15-40
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 15
Purpose
Configures the MST instance port cost.
Configures the MST instance port priority.
Verifies the configuration.
port guard :none
bpdu filter:disable
bpdu guard :disable
1-10
Configuring STP and IEEE 802.1s MST
(default)
(default)
(default)
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