Cisco Catalyst 2950 Software Guide

9-9
Catalyst 2950 Desktop Switch Software Configuration Guide
78-11380-03
Chapter 9 Configuring STP
Understanding Advanced STP Features
Figure 9-3 STP and Redundant Connectivity
You can also create redundant links between switches by using EtherChannel groups. For more
information, see the Chapter 10, “Configuring the Switch Ports.”
Accelerated Aging to Retain Connectivity
The default for aging dynamic addresses is 5 minutes, the default setting of the mac-address-table
aging-time global configuration command. However, an STP reconfiguration can cause many station
locations to change. Because these stations could be unreachable for 5 minutes or more during a
reconfiguration, the address-aging time is accelerated so that station addresses can be dropped from the
address table and then relearned. The accelerated aging is the same as the forward-delay parameter value
(spanning-tree vlan vlan-id forward-time seconds global configuration command) when STP
reconfigures.
Because each VLAN is a separate spanning-tree instance, the switch accelerates aging on a per-VLAN
basis. An STP reconfiguration on one VLAN can cause the dynamic addresses learned on that VLAN to
be subject to accelerated aging. Dynamic addresses on other VLANs can be unaffected and remain
subject to the aging interval entered for the switch.
Understanding Advanced STP Features
This section describes how advanced STP features work. It includes this information:
• Understanding Port Fast, page 9-10
• Understanding BPDU Guard, page 9-10
• Understanding UplinkFast, page 9-11
• Understanding Cross-Stack UplinkFast, page 9-12
• Understanding BackboneFast, page 9-17
• Understanding Root Guard, page 9-19
For configuration information, see the “Configuring Advanced STP Features” sectiononpage9-30.
Catalyst 2950
switch
Workstations
Catalyst 2950
switch
Catalyst 2950
switch
Switch A
Switch B
Active link
Blocked link
Switch C
65024

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