Enabling Root Guard - Cisco 4500M Software Manual

Enabling Root Guard

Figure 15-5 BackboneFast after Indirect Link Failure
Switch A
(Root)
If a new switch is introduced into a shared-medium topology as shown in
not activated, because the inferior BPDUs did not come from the recognized designated bridge
(Switch B). The new switch begins sending inferior BPDUs that say it is the root switch. However, the
other switches ignore these inferior BPDUs, and the new switch learns that Switch B is the designated
bridge to Switch A, the root switch.
Figure 15-6 Adding a Switch in a Shared-Medium Topology
Switch C
Enabling Root Guard
To enable root guard on a Layer 2 access port (to force it to become a designated port), perform this task:
Command
Step 1
Switch(config)# interface {{fastethernet |
gigabitethernet | tengigabitethernet} slot / port }
Step 2
Switch(config-if)# [no] spanning-tree guard root
Software Configuration Guide—Release 12.2(25)EW
15-8
L1
Link failure
L2
BackboneFast transitions port
through listening and learning
states to forwarding state
Switch C
Switch A
(Root)
Blocked port
Switch B
L3
Switch B
(Designated Bridge)
Added switch
Purpose
Specifies an interface to configure.
Enables root guard.
You can use the no keyword to disable Root Guard.
Chapter 15 Configuring STP Features
Figure 15-6, BackboneFast is
OL-6696-01