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17-27
Catalyst 2960 and 2960-S Switch Software Configuration Guide
OL-8603-09
Chapter 17 Configuring MSTP
Configuring MSTP Features
Specifying the Link Type to Ensure Rapid Transitions
If you connect a port to another port through a point-to-point link and the local port becomes a
designated port, the RSTP negotiates a rapid transition with the other port by using the
proposal-agreement handshake to ensure a loop-free topology as described in the “Rapid Convergence”
section on page 17-11.
By default, the link type is controlled from the duplex mode of the interface: a full-duplex port is
considered to have a point-to-point connection; a half-duplex port is considered to have a shared
connection. If you have a half-duplex link physically connected point-to-point to a single port on a
remote switch running MSTP, you can override the default setting of the link type and enable rapid
transitions to the forwarding state.
Beginning in privileged EXEC mode, follow these steps to override the default link-type setting. This
procedure is optional.
To return the port to its default setting, use the no spanning-tree link-type interface configuration
command.
Designating the Neighbor Type
A topology could contain both prestandard and IEEE 802.1s standard compliant devices. By default,
ports can automatically detect prestandard devices, but they can still receive both standard and
prestandard BPDUs. When there is a mismatch between a device and its neighbor, only the CIST runs
on the interface.
You can choose to set a port to send only prestandard BPDUs. The prestandard flag appears in all the
show commands, even if the port is in STP compatibility mode.
Beginning in privileged EXEC mode, follow these steps to override the default link-type setting. This
procedure is optional.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Specify an interface to configure, and enter interface
configuration mode. Valid interfaces include physical ports,
VLANs, and port-channel logical interfaces. The VLAN ID
range is 1 to 4094. The port-channel range is 1 to 6.
Step 3
spanning-tree link-type point-to-point Specify that the link type of a port is point-to-point.
Step 4
end Return to privileged EXEC mode.
Step 5
show spanning-tree mst interface interface-id Verify your entries.
Step 6
copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Specify an interface to configure, and enter interface
configuration mode. Valid interfaces include physical ports.
Step 3
spanning-tree mst pre-standard Specify that the port can send only prestandard BPDUs.