Chapter 19
| Spanning Tree Commands
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Command Mode
Interface Configuration (Ethernet, Port Channel)
Command Usage
◆ Specify a point-to-point link if the interface can only be connected to exactly
one other bridge, or a shared link if it can be connected to two or more bridges.
◆ When automatic detection is selected, the switch derives the link type from the
duplex mode. A full-duplex interface is considered a point-to-point link, while a
half-duplex interface is assumed to be on a shared link.
◆ RSTP only works on point-to-point links between two bridges. If you designate
a port as a shared link, RSTP is forbidden. Since MSTP is an extension of RSTP,
this same restriction applies.
Example
Console(config)#interface ethernet 1/5
Console(config-if)#spanning-tree link-type point-to-point
spanning-tree
loopback-detection
This command enables the detection and response to Spanning Tree loopback
BPDU packets on the port. Use the no form to disable this feature.
Syntax
[no] spanning-tree loopback-detection
Default Setting
Enabled
Command Mode
Interface Configuration (Ethernet, Port Channel)
Command Usage
◆ If Port Loopback Detection is not enabled and a port receives it’s own BPDU,
then the port will drop the loopback BPDU according to IEEE Standard 802.1W-
2001 9.3.4 (Note 1).
◆ Port Loopback Detection will not be active if Spanning Tree is disabled on the
switch.
Example
Console(config)#interface ethernet 1/5
Console(config-if)#spanning-tree loopback-detection
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