Disabling Stp - Cisco Catalyst 2950 Software Configuration Manual

Chapter 10 Configuring STP
Caution Switches that are not running spanning tree still forward BPDUs that they receive so that the other
switches on the VLAN that have a running spanning-tree instance can break loops. Therefore, spanning
tree must be running on enough switches to break all the loops in the network; for example, at least one
switch on each loop in the VLAN must be running spanning tree. It is not absolutely necessary to run
spanning tree on all switches in the VLAN; however, if you are running spanning tree only on a minimal
set of switches, an incautious change to the network that introduces another loop into the VLAN can
result in a broadcast storm.
Note If you have already used all available spanning-tree instances on your switch, adding another VLAN
anywhere in the VTP domain creates a VLAN that is not running spanning tree on that switch. If you
have the default allowed list on the trunk ports of that switch, the new VLAN is carried on all trunk ports.
Depending on the topology of the network, this could create a loop in the new VLAN that will not be
broken, particularly if there are several adjacent switches that have all run out of spanning-tree instances.
You can prevent this possibility by setting up allowed lists on the trunk ports of switches that have used
up their allocation of spanning-tree instances. Setting up allowed lists is not necessary in many cases and
can make it more labor-intensive to add another VLAN to the network.
Spanning-tree commands determine the configuration of VLAN spanning-tree instances. You create a
spanning-tree instance when you assign an interface to a VLAN. The spanning-tree instance is removed
when the last interface is moved to another VLAN. You can configure switch and port parameters before
a spanning-tree instance is created; these parameters are applied when the spanning-tree instance is
created.

Disabling STP

STP is enabled by default on VLAN 1 and on all newly created VLANs up to the spanning-tree limit
specified in
When STP is disabled and loops are present in the topology, excessive traffic and indefinite packet
Caution
duplication can drastically reduce network performance.
Beginning in privileged EXEC mode, follow these steps to disable STP on a per-VLAN basis:
Command
Step 1
configure terminal
Step 2 no spanning-tree vlan vlan-id
Step 3
end
Step 4 show spanning-tree vlan vlan-id
Step 5 copy running-config startup-config
To re-enable STP, use the spanning-tree vlan vlan-id global configuration command.
78-11380-04
Table 10-3. Disable STP only if you are sure there are no loops in the network topology.
Purpose
Enter global configuration mode.
Disable STP on a per-VLAN basis.
For vlan-id, the range is 1 to 4094 when the enhanced software image is
installed and 1 to 1005 when the standard software image is installed. Do
not enter leading zeros.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Catalyst 2950 Desktop Switch Software Configuration Guide
Configuring Spanning-Tree Features
10-11