IBM 12.1(22)EA6 User Manual
10-21
Cisco Systems Intelligent Gigabit Ethernet Switch Modules for the IBM BladeCenter, Software Configuration Guide
24R9746
Chapter 10 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
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
By default, the link type is determined 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.
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.
procedure is optional.
To return the switch to its default setting, use the no spanning-tree link-type interface configuration
command.
command.
Restarting the Protocol Migration Process
A switch running MSTP supports a built-in protocol migration mechanism that enables it to interoperate
with legacy IEEE 802.1D switches. If this switch receives a legacy IEEE 802.1D configuration BPDU
(a BPDU with the protocol version set to 0), it sends only IEEE 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).
with legacy IEEE 802.1D switches. If this switch receives a legacy IEEE 802.1D configuration BPDU
(a BPDU with the protocol version set to 0), it sends only IEEE 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 IEEE
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.
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
switch, use the clear spanning-tree detected-protocols privileged EXEC command.
switch, use the clear spanning-tree detected-protocols privileged EXEC command.
To restart the protocol migration process on a specific interface, use the clear spanning-tree
detected-protocols interface interface-id privileged EXEC command.
detected-protocols interface interface-id privileged EXEC command.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface interface-id
Specify the interface to configure, and enter interface
configuration mode. Valid interfaces include physical ports,
VLANs, and port channels. Valid VLAN IDs are 1 to 4094.
Valid port-channel numbers are 1 to 6.
configuration mode. Valid interfaces include physical ports,
VLANs, and port channels. Valid VLAN IDs are 1 to 4094.
Valid port-channel numbers are 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.