Cisco Catalyst 4500 Series Software Configuration Guide

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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 26 Configuring Optional STP Features
About UplinkFast
About UplinkFast
Note UplinkFast is most useful in wiring-closet switches. This feature might not be useful for other types of
applications.
Spanning Tree UplinkFast provides fast convergence after a direct link failure and uses uplink groups to
achieve load balancing between redundant Layer 2 links. Convergence is the speed and ability of a group
of internetworking devices running a specific routing protocol to agree on the topology of an
internetwork after a change in that topology. An uplink group is a set of Layer 2 interfaces (per VLAN),
only one of which is forwarding at any given time. Specifically, an uplink group consists of the root port
(which is forwarding) and a set of blocked ports, except for self-looping ports. The uplink group provides
an alternate path in case the currently forwarding link fails.
Figure 26-6 shows an example of a topology with no link failures. Switch A, the root switch, is
connected directly to Switch B over link L1 and to Switch C over link L2. The Layer 2 interface on
Switch C that is connected directly to Switch B is in the blocking state.
Figure 26-6 UplinkFast Before Direct Link Failure
If Switch C detects a link failure on the currently active link L2 on the root port (a direct link failure),
UplinkFast unblocks the blocked port on Switch C and transitions it to the forwarding state without
going through the listening and learning states, as shown in Figure 26-7. This switchover takes
approximately one to five seconds.
Figure 26-7 UplinkFast After Direct Link Failure
L1
L2 L3
Switch C
Switch A
(Root)
Switch B
Blocked port
11241
L1
L2 L3
Switch C
Switch A
(Root)
Switch B
UplinkFast transitions port
directly to forwarding state
Link failure
11242

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