Cisco Catalyst 4500 Series Administration Guide

26-16
Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)E
OL_28731-01
Chapter 26 Configuring EtherChannel and Link State Tracking
Displaying EtherChannel to a Virtual Switch System
Switch(config)# no interface port-channel 1
Switch(config)# end
Displaying EtherChannel to a Virtual Switch System
Catalyst 4500 series switches support enhanced PAgP. If a Catalyst 4500 series switch is connected to a
Catalyst 6500 series Virtual Switch System (VSS) by using a PAgP EtherChannel, the Catalyst 4500
series switch automatically serve as a VSS client, using enhanced PAgP on this EtherChannel for
dual-active detection. This VSS client feature has no impact on the performance of Catalyst 4500 series
switch and does not require any user configuration.
This section includes these topics:
• Understanding VSS Client, page 26-16
• Displaying EtherChannel Links to VSS, page 26-18
Understanding VSS Client
This section describes these topics:
• Virtual Switch System, page 26-16
• Dual-Active Scenarios, page 26-16
• Dual-Active Detection Using Enhanced PAgP, page 26-16
Virtual Switch System
The Cisco Catalyst 6500 Series VSS 1440 allows for the combination of two Cisco Catalyst 6500 Series
switches into a single, logical network entity from the network control-plane and management
perspectives. Within the Cisco VSS, one chassis is designated as the active virtual switch, acting as the
single management point of the entire system, and the other is designated as the standby virtual switch.
There two chassis are bound together by a special link, called Virtual Switch Link (VSL), which carries
the internal signaling and control information between them.
Dual-Active Scenarios
One of the failure scenarios in a VSS is called dual-active, which occurs when the VSL fails completely.
Neither virtual switch knows of the other's status. From the perspective of the active virtual switch, the
standby chassis is lost. The standby virtual switch also views the active chassis as failed and transitions
to active state by using an SSO switchover. Two active virtual switches exist in the network with identical
configurations, causing duplicate IP addresses and bridge identifiers. This scenario has adverse effects
on the network topology and traffic if it persists.
Dual-Active Detection Using Enhanced PAgP
One method for detecting a dual-active scenario is based on enhanced PAgP (PAgP+). Specifically, the
VSS sends regularly scheduled PAgP messages with Type-Length-Values (TLVs) containing the ID of
the current active virtual switch (Figure 26-1). When the VSL fails completely, the standby virtual
switch immediately sends asynchronous PAgP messages with TLVs containing its own ID on all port
channels enabled for enhanced PAgP dual-active detection (Figure 26-2). The remote switch

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