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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 STP
• Ensure that trunks carry all of the VLANs mapped to an instance or do not carry any VLANs at all
for this instance.
• Do not connect switches with access links because access links may partition a VLAN.
• Complete any MST configuration involving a large number of either existing or new logical VLAN
ports during a maintenance window because the complete MST database gets reinitialized for any
incremental change (such as adding new VLANs to instances or moving VLANs across instances).
Configuring STP
These sections describe how to configure STP on VLANs:
• Enabling STP, page 15-23
• Enabling the Extended System ID, page 15-24
• Configuring the Root Bridge, page 15-25
• Configuring a Secondary Root Bridge, page 15-26
• Configuring STP Port Priority, page 15-27
• Configuring STP Port Cost, page 15-29
• Configuring the Bridge Priority of a VLAN, page 15-30
• Configuring the Hello Time, page 15-32
• Configuring the Forward-Delay Time for a VLAN, page 15-32
• Configuring the Maximum Aging Time for a VLAN, page 15-33
• Enabling Rapid-PVST, page 15-33
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.
• With Release 12.1(11b)E and later releases, when you are in configuration mode you can enter
EXEC mode-level commands by entering the do keyword before the EXEC mode-level command.
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.
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