Stateful Switchover - Cisco Catalyst 4500 Series Configuration Manual

Chapter 1 Product Overview
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For information on the STP enhancements, see

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.
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For information about SSO, see
Redundancy."
SVI Autostate
When an SVI has multiple ports on a VLAN, normally the SVI will go down when all the ports in the
VLAN go down. You can design your network so that some ports are not counted in the calculation of
SVI "going up or down." SVI Autostate provides a knob to mark a port so that it is not counted in the
SVI "going up and down" calculation and applies to all VLANs that are enabled on that port.
Unidirectional Link Detection
The Unidirectional Link Detection (UDLD) protocol allows devices connected through fiber-optic or
copper Ethernet cables to monitor the physical configuration of the cables and detect a unidirectional
link.
With standard UDLD, the time to detect a unidirectional link can vary from a few seconds to several
minutes depending on how the timers are configured. Link status messages are exchanged every couple
of seconds. With Fast UDLD, you can detect unidirectional links in under one second (this also depends
on how the timers are configured). Link status messages are exchanged every couple of hundred
milliseconds.
For information about UDLD and Fast UDLD, see
OL-25340-01
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.
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.
Chapter 23, "Configuring Optional STP Features."
Chapter 11, "Configuring Cisco NSF with SSO Supervisor Engine
Chapter 30, "Configuring UDLD."
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
Layer 2 Software Features
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