Cisco Catalyst 4500 Series, Software Configuration Manual

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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 1 Product Overview
Layer 2 Software Features
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 13, “Configuring Cisco NSF with SSO Supervisor Engine
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 Chapter 33, “Configuring UDLD.”
VLANs
A VLAN configures switches and routers according to logical, rather than physical, topologies. Using
VLANs, you can combine any collection of LAN segments within an internetwork into an autonomous
user group, such that the segments appear as a single LAN in the network. VLANs logically segment the
network into different broadcast domains so that packets are switched only between ports within the
VLAN. Typically, a VLAN corresponds to a particular subnet, although not necessarily.
For more information about VLANs, VTP, and Dynamic VLAN Membership, see Chapter 17,
“Configuring VLANs, VTP, and VMPS.”
The following VLAN-related features also are supported:
• VLAN Trunking Protocol (VTP)—VTP maintains VLAN naming consistency and connectivity
between all devices in the VTP management domain. You can have redundancy in a domain by using
multiple VTP servers, through which you can maintain and modify the global VLAN information.
Only a few VTP servers are required in a large network.