Cisco Catalyst 4500 Series Administration Guide

25-15
Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)E
OL_28731-01
Chapter 25 Configuring Optional STP Features
Enabling BackboneFast
Figure 25-5 shows how BackboneFast reconfigures the topology to account for the failure of link L1.
Figure 25-5 BackboneFast after Indirect Link Failure
If a new switch is introduced into a shared-medium topology as shown in Figure 25-6, BackboneFast is
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 25-6 Adding a Switch in a Shared-Medium Topology
Enabling BackboneFast
Note For BackboneFast to work, you must enable it on all switches in the network. BackboneFast is supported
for use with third-party switches but it is not supported on Token Ring VLANs.
To enable BackboneFast, perform this task:
L1
L2 L3
Switch C
Switch A
(Root)
Switch B
Blocked port
11241
Switch A
(Root)
Switch C
Switch B
(Designated Bridge)
Added switch
11245
Blocked port

Cisco Catalyst 4500 Series Specifications

General

Series	Catalyst 4500 Series
Category	Switch
Layer Support	Layer 2, Layer 3
Form Factor	Modular chassis
Stackable	No
Chassis Slots	3, 6, 7, 10
Power Supply Options	AC, DC
Redundancy	Power supply, Supervisor engine
Network Management	Cisco IOS Software CLI, SNMP, Cisco Prime Infrastructure
Features	Security, QoS
Port Density	Up to 384 ports per chassis
Security Features	802.1X, ACLs, DHCP Snooping, Dynamic ARP Inspection, IP Source Guard
Supervisor Engine	8-E