Cisco Catalyst 4500 Series, Software Configuration Manual

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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 23 Configuring STP and MST
Configuring STP
BPDU: sent 3, received 3417
Switch#
Enabling the Extended System ID
Note
The extended system ID is enabled permanently on chassis that support 64 MAC addresses.
Use the spanning-tree extend system-id comman d to enable the extended system ID on chassis that
support 1024 MAC addresses. See the “Understanding the Bridge ID” section on page 23-2 .
To enable the extended system ID, perform this task:
Note When you enable or disable the extended system ID, the bridge IDs of all active STP instances are
updated, which might change the spanning tree topology.
This example shows how to enable the extended system ID:
Switch# configure terminal
Switch(config)# spanning-tree extend system-id
Switch(config)# end
Switch#
This example shows how to verify the configuration:
Switch# show spanning-tree summary | include extended
Extended system ID is enabled.
Configuring the Root Bridge
A Catalyst 4500 series switch maintains an instance of spanning tree for each active VLAN configured
on the switch. A bridge ID, consisting of the bridge priority and the bridge MAC address, is associated
with each instance. For each VLAN, the switch with the lowest bridge ID becomes the root bridge for
that VLAN. Whenever the bridge priority changes, the bridge ID also changes, resulting in the
recomputation of the root bridge for the VLAN.
Command Purpose
Step 1
Switch(config)# spanning-tree extend system-id
Enables the extended system ID.
Disables the extended system ID.
Note
You cannot disable the extended system ID on
chassis that support 64 MAC addresses or when
you have configured extended range VLANs (see
Table 23-4 on page 23-7 ).
Step 2
Switch(config)# end
Exits configuration mode.
Step 3
Switch# show spanning-tree vlan vlan_ID Verifies the configuration.