20-22
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 20 Configuring STP and Prestandard IEEE 802.1s MST
Configuring STP
Configuring STP
These sections describe how to configure STP on VLANs:
•
Enabling STP, page 20-22
•
Enabling the Extended System ID, page 20-24
•
Configuring the Root Bridge, page 20-24
•
Configuring a Secondary Root Bridge, page 20-26
•
Configuring STP Port Priority, page 20-27
•
Configuring STP Port Cost, page 20-28
•
Configuring the Bridge Priority of a VLAN, page 20-30
•
Configuring the Hello Time, page 20-31
•
Configuring the Forward-Delay Time for a VLAN, page 20-32
•
Configuring the Maximum Aging Time for a VLAN, page 20-32
•
Enabling Rapid-PVST, page 20-33
Note
The STP commands described in this chapter can be configured on any LAN port, but they are in effect
only on LAN ports configured with the
switchport
keyword.
Caution
We do not recommend disabling spanning tree, even in a topology that is free of physical loops. Spanning
tree serves as a safeguard against misconfigurations and cabling errors. Do not disable spanning tree in
a VLAN without ensuring that there are no physical loops present in the VLAN.
Enabling STP
Note
STP is enabled by default on VLAN 1 and on all newly created VLANs.
You can enable STP on a per-VLAN basis. The Cisco 7600 series router maintains a separate instance
of STP for each VLAN (except on VLANs on which you disable STP).
To enable STP on a per-VLAN basis, perform this task:
Command
Purpose
Step 1
Router(config)#
spanning-tree vlan
vlan_ID
Enables STP on a per-VLAN basis. The
vlan_ID
value
can be 1 through 4094, except reserved VLANs (see
Table 20-5 on page 20-21
).
Router(config)#
default spanning-tree vlan
vlan_ID
Reverts all STP parameters to default values for the
specified VLAN.
Router(config)#
no
spanning-tree vlan
vlan_ID
Disables STP on the specified VLAN; see the following
Cautions for information regarding this command.