Cisco 7609 User Manual

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Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
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Chapter 15 Configuring STP and IEEE 802.1s MST
Configuring IEEE 802.1s MST
Specifying the Link Type
Rapid connectivity is established only on point-to-point links. Spanning tree views a point-to-point link
as a segment connecting only two switches running the spanning tree algorithm. Because the switch
assumes that all full-duplex links are point-to-point links and that half-duplex links are shared links, you
can avoid explicitly configuring the link type. To configure a specific link type, enter the spanning-tree
linktype command.
Restarting Protocol Migration
A switch running both MSTP and RSTP supports a built-in protocol migration process 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, or 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.
To restart the protocol migration process (force the renegotiation with neighboring switches) on the
entire switch, you can use the clear spanning-tree detected-protocols privileged EXEC command. To
restart the protocol migration process on a specific interface, enter the clear spanning-tree
detected-protocols interface interface-id privileged EXEC command.
Configuring IEEE 802.1s MST
Release 12.1(13)E and later releases support MST. These sections describe how to configure MST:
• Enabling MST, page 15-34
• Displaying MST Configurations, page 15-36
• Configuring MST Instance Parameters, page 15-39
• Configuring MST Instance Port Parameters, page 15-40
• Restarting Protocol Migration, page 15-40
Enabling MST
To enable and configure MST on the switch, perform these tasks in privileged mode:
Command Purpose
Step 1
Router# show spanning-tree mst configuration
Displays the current MST configuration.
Step 2
Router(config)# spanning-tree mode mst
Configures MST mode.
Step 3
Router(config)# spanning-tree mst configuration
Configures the MST region by entering the MST
configuration submode.
Router(config)# no spanning-tree mst
configuration
Clears the MST configuration.

Cisco 7609 Specifications

General

Brand	Cisco
Model	7609
Category	Network Router
Language	English