Cisco Catalyst 2950 Command Reference

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Catalyst 2950 and Catalyst 2955 Switch Command Reference
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Chapter 2 Catalyst 2950 and 2955 Cisco IOS Commands
spanning-tree backbonefast
spanning-tree backbonefast
Use the spanning-tree backbonefast global configuration command to enable the BackboneFast
feature. Use the no form of this command to return to the default setting.
spanning-tree backbonefast
no spanning-tree backbonefast
Syntax Description This command has no arguments or keywords.
Defaults BackboneFast is disabled.
Command Modes Global configuration
Command History
Usage Guidelines You can configure the BackboneFast feature for rapid PVST+ or for multiple spanning-tree (MST)
mode, but the feature remains disabled (inactive) until you change the spanning-tree mode to PVST+.
BackboneFast is started when a root port or blocked port on a switch receives inferior bridge protocol
data units (BPDUs) from its designated bridge. An inferior BPDU identifies one switch as both the root
bridge and the designated bridge. When a switch receives an inferior BPDU, it means that a link to which
the switch is not directly connected (an indirect link) has failed (that is, the designated bridge has lost
its connection to the root switch). If there are alternate paths to the root switch, BackboneFast causes the
maximum aging time on the ports on which it received the inferior BPDU to expire and allows a blocked
port to move immediately to the listening state. BackboneFast then transitions the interface to the
forwarding state. For more information, see the software configuration guide for this release.
Enable BackboneFast on all supported switches to allow the detection of indirect link failures and to start
the spanning-tree reconfiguration sooner.
Examples This example shows how to enable BackboneFast on the switch:
Switch(config)# spanning-tree backbonefast
You can verify your setting by entering the show spanning-tree summary privileged EXEC command.
Related Commands
Release Modification
12.1(6)EA2 This command was introduced.
Command Description
show spanning-tree summary Displays a summary of the spanning-tree port states.

Cisco Catalyst 2950 Specifications

General

Forwarding Bandwidth	8.8 Gbps
Switching Capacity	13.6 Gbps
Forwarding Rate	6.6 Mpps
Weight	3.6 kg
RAM	16 MB
Flash Memory	8 MB
Operating Humidity	10% to 85% non-condensing
Uplink Ports	2 x 10/100/1000Base-T
Dimensions	4.4 cm x 44.5 cm x 24.2 cm
Remote Management Protocol	SNMP, Telnet, HTTP
Features	Quality of Service (QoS), VLAN support
Compliant Standards	IEEE 802.3, IEEE 802.3u, IEEE 802.1D, IEEE 802.1Q, IEEE 802.1p
Status Indicators	system
Operating Temperature	0 to 45°C
Ports	24 x 10/100 Ethernet ports
MAC Address Table Size	8, 192 entries
Power Supply	Internal 100-240V AC, 50-60Hz