Administrator Guide

Layer 2 Switching Commands 763
spanning-tree backbonefast
Use the spanning-tree backbonefast command to enable the detection of
indirect link failures and accelerate spanning tree convergence on
STP-PV/RSTP-PV configured switches using Indirect Link Rapid
Convergence (IRC). IRC accelerates finding an alternative path when an
indirect link to the root port goes down. Use the no form of the command to
disable the IRC feature.
Syntax
spanning-tree backbonefast
no spanning-tree backbonefast
Default Configuration
This command has no default configuration.
Command Modes
Global Configuration Mode
User Guidelines
IRC can be configured even if the switch is configured for MST(RSTP) or
RSTP-PV mode. It only has an effect when the switch is configured for
STP-PV mode.
If an IRC-enabed switch receives an inferior BPDU from its designated switch
on a root or blocked port, it sets the maximum aging time on the interfaces
on which it received the inferior BPDU if there are alternative (blocked) paths
to the designated switch. This allows a blocked port to immediately move to
the listening state where the port can be transitioned to the forwarding state
in the normal manner.
Example
console(config)#spanning-tree backbonefast
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