14-14
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-07
Chapter 14 Configuring STP
Configuring Spanning-Tree Features
Changing the Spanning-Tree Mode.
The switch supports three spanning-tree modes: PVST+, rapid PVST+, or MSTP. By default, the switch
runs the rapid PVST+ protocol on all NNIs and ENIs on which spanning tree is enabled.
Beginning in privileged EXEC mode, follow these steps to change the spanning-tree mode. If you want
to enable a mode that is different from the default mode, this procedure is required.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
spanning-tree mode {pvst | mst |
rapid-pvst}
Configure a spanning-tree mode on STP ports on the switch.
• Select pvst to enable PVST+.
• Select mst to enable MSTP (and RSTP). For more configuration
steps, see
Chapter 15, “Configuring MSTP.”
• Select rapid-pvst to enable rapid PVST+ (the default setting).
Step 3
interface interface-id (Recommended only for rapid-PVST+ mode) Specify an STP port to
configure, and enter interface configuration mode. Valid interfaces
include physical NNIs or ENIs with spanning tree enabled, VLANs, and
NNI or ENI port channels. The VLAN ID range is 1 to 4094. The
port-channel range is 1 to 48.
Note If a physical interface is a UNI, before attempting to configure
it as a spanning-tree link, you must enter the port-type nni
interface configuration command or configure the port as an
ENI and enable spanning tree on the port. See
“Enabling
Spanning Tree on an ENI” section on page 14-13.
If the interface is a VLAN, only ports with spanning tree
enabled in the VLAN will run spanning tree.
If the interface is a port channel, all members of the port channel
must be NNIs or ENIs with spanning tree enabled.
Step 4
spanning-tree link-type point-to-point (Recommended only for rapid-PVST+ mode) Specify that the link type
for this port is point-to-point.
If you connect this port to a remote port through a point-to-point link
and the local port becomes a designated port, the switch negotiates with
the remote port and rapidly changes the local port to the forwarding
state.
Step 5
end Return to privileged EXEC mode.
Step 6
clear spanning-tree detected-protocols (Recommended only for rapid-PVST+ mode) If any port on the switch
running spanning tree is connected to a port on a legacy IEEE 802.1D
switch, restart the protocol migration process on the entire switch.
This step is optional if the designated switch detects that this switch is
running rapid PVST+.
Step 7
show spanning-tree summary
and
show spanning-tree interface
interface-id
Verify your entries.
Step 8
copy running-config startup-config (Optional) Save your entries in the configuration file.
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