Configuring Mst Instance Port Parameters; Restarting Protocol Migration - Cisco 7604 Configuration Manual

Configuring Prestandard 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 router running both MSTP and RSTP supports a built-in protocol migration mechanism that enables
the router to interoperate with legacy 802.1D switches. If this router 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 router 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 router does not automatically revert to the MSTP mode if it no longer receives 802.1D
BPDUs because it cannot determine whether the legacy router has been removed from the link unless
the legacy router is the designated router. A router also might continue to assign a boundary role to a
port when the router to which it is connected has joined the region.
To restart the protocol migration process (force the renegotiation with neighboring switches) on the
entire router, you can use the clear spanning-tree detected-protocols privileged EXEC command. Use
the clear spanning-tree detected-protocols interface interface-id privileged EXEC command to restart
the protocol migration process on a specific interface.
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
20-40
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 20 Configuring STP and Prestandard IEEE 802.1s MST
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
(default)
(default)
(default)
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