Cisco Systems 4500 Spanning Tree Protocol, Stateful Switchover

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Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 1 Product Overview
Layer 2 Software Features
For information on configuring SmartPort macros, see Chapter 16, “Configuring SmartPort Macros.”
Spanning Tree Protocol
The Spanning Tree Protocol (STP) allows you to create fault-tolerant internetworks that ensure an active,
loop-free data path between all nodes in the network. STP uses an algorithm to calculate the best
loop-free path throughout a switched network.
For information on configuring STP, see Chapter 18, “Configuring STP and MST.”
The Catalyst 4500 series switch supports the following STP enhancements:
• Spanning tree PortFast—PortFast allows a port with a directly attached host to transition to the
forwarding state directly, bypassing the listening and learning states.
• Spanning tree UplinkFast—UplinkFast provides fast convergence after a spanning-tree topology
change and achieves load balancing between redundant links using uplink groups. Uplink groups
provide an alternate path in case the currently forwarding link fails. UplinkFast is designed to
decrease spanning-tree convergence time for switches that experience a direct link failure.
• Spanning tree BackboneFast—BackboneFast reduces the time needed for the spanning tree to
converge after a topology change caused by an indirect link failure. BackboneFast decreases
spanning-tree convergence time for any switch that experiences an indirect link failure.
• Spanning tree root guard—Root guard forces a port to become a designated port so that no switch
on the other end of the link can become a root switch.
For information on the STP enhancements, see Chapter 21, “Configuring Optional STP Features.”
Stateful Switchover
Stateful switchover (SSO) enables you to propagate configuration and state information from the active
to the redundant supervisor engine so that sub-second interruptions in Layer 2 traffic occur when the
active supervisor engine switches over to the redundant supervisor engine.
• Stateful IGMP Snooping
This feature propagates the IGMP data learned by the active supervisor engine to the redundant
supervisor engine so that when a switchover occurs, the newly active supervisor engine is aware of
the multicast group membership, which alleviates a disruption to multicast traffic during a
switchover.
• Stateful DHCP Snooping
This feature propagates the DHCP-snooped data from the active supervisor engine to the redundant
supervisor engine so that when a switchover occurs, the newly active supervisor engine is aware of
the DHCP data that was already snooped, and the security benefits continue uninterrupted.
For information about SSO, see Chapter 9, “Configuring Cisco NSF with SSO Supervisor Engine
Redundancy.”