10-22
Catalyst 3550 Multilayer Switch Software Configuration Guide
78-11194-03
Chapter 10 Configuring STP
Configuring Basic STP Features
Disabling STP
STP is enabled by default on VLAN 1 and on all newly created VLANs up to the spanning-tree limit
specified in
Table 10-3
. Disable STP only if you are sure there are no loops in the network topology.
Caution
When STP is disabled and loops are present in the topology, excessive traffic and indefinite packet
duplication can drastically reduce network performance.
Beginning in privileged EXEC mode, follow these steps to disable STP on a per-VLAN basis:
To re-enable STP, use the spanning-tree vlan vlan-id global configuration command.
Configuring the Root Switch
The switch maintains a separate spanning-tree instance for each active VLAN configured on it. A bridge
ID, consisting of the switch priority and the switch MAC address, is associated with each instance. For
each VLAN, the switch with the lowest bridge ID becomes the root switch for that VLAN.
Forward-delay time
15 seconds.
Maximum-aging time
20 seconds.
Port Fast
Disabled on all interfaces.
BPDU guard
Disabled on the switch.
UplinkFast
Disabled on the switch.
BackboneFast
Disabled on the switch.
Root guard
Disabled on all interfaces.
EtherChannel guard
Enabled on the switch.
Table 10-3
Default STP Configuration (continued)
Feature
Default Setting
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
no spanning-tree vlan vlan-id
Disable STP on a per-VLAN basis.
For vlan-id, the range is 1 to 1005. Do not enter leading zeros.
Step 3
end
Return to privileged EXEC mode.
Step 4
show spanning-tree vlan vlan-id
Verify your entries.
Step 5
copy running-config startup-config
(Optional) Save your entries in the configuration file.