Configuring Spanning Tree
165
Configuring Spanning Tree
T
he configuration of spanning tree is pretty simple unless you want to
change your timers or add multiple spanning tree instances; then it can get
complex. The timers and more advanced configurations are covered in
Chapter 5.
STP is enabled on all Cisco switches by default. However, you may want
to change your spanning tree configuration to have many spanning tree
instances. This means that each VLAN can be its own spanning tree. This is
known as Per-VLAN spanning tree.
To enable or disable spanning tree on a set-based switch, use the set
spantree [parameter]
command. This is performed on a VLAN-by-
VLAN basis rather than a port-by-port configuration:
Todd5000> (enable) set spantree disable 1-1005
Spantrees 1-1005 disabled.
Todd5000> (enable) set spantree enable 1-1005
Spantrees 1-1005 enabled.
The above configuration shows the disabling of spanning tree on an indi-
vidual VLAN basis. To enable spanning tree on an individual VLAN basis,
use set spantree enable [VLAN(s)]. Cisco recommends that you do not
disable spanning tree on a switch, particularly on uplinks where a loop can
occur.
On a chassis with a Supervisor Engine III or III F with a NFFC or NFFC II, you
cannot enable spanning tree on a per-VLAN basis. You must enable spanning
tree on every VLAN using the set spantree enable all command.
To enable or disable spanning tree on a Cisco IOS-based switch, use the
spantree
command or the no spantree command. The configuration
below shows how to enable and disable spanning tree on a 1900 switch:
1900A#config t
Enter configuration commands, one per line. End with
CNTL/Z
1900A(config)#spantree ?
<1-1005> ISL VLAN index
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