Cisco Systems WSC4500X16SFP Understanding Port-Channel Interfaces, Understanding How EtherChannels Are Configured

16-2
Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter16 Understanding and Configuring EtherChannel
Overview of EtherChannel
Note The network device to which a Catalyst4500 series switch is connected may impose its own limits on
the number of interfaces in an EtherChannel.
If a segment within an EtherChannel fails, traffic previously carried over the failed link switches to the
remaining segments within the EtherChannel. Once the segment fails, an SNMP trap is sent, identifying
the switch, the EtherChannel, and the failed link. Inbound broadcast and multicast packets on one
segment in an EtherChannel are blocked from returning on any other segment of the EtherChannel.
Note The port channel link failure switchover for the Catalyst 4500 series switch was measured at 50ms,
giving a customer SONET-like link failure switchover time.
Understanding Port-Channel Interfaces
Each EtherChannel has a numbered port-channel interface. A c onfiguration applied to the port-channel
interface affects all physical interfaces assigned to that interface.
Note QoS does not propagate to members. The defaults, QoS cos = 0 and QoS dscp = 0, apply on the
port-channel. Input or output policies applied on individual interfaces will be ignored.
After you configure an EtherChannel, the configuration that you apply to the port-channel interface
affects the EtherChannel; the configuration that you apply to the physical interfaces affects only the
interface where you apply the configuration. To change the parameters of all ports in an EtherChanne l,
apply configuration commands to the port-channel interface (such commands c an be STP commands or
commands to configure a Layer 2 EtherChannel as a trun k).
Understanding How EtherChannels Are Configured
These subsections describe how EtherChannels are configured:
•EtherChannel Configuration Overview, page 16-2
•Understanding Manual EtherChannel Configuration, page 16-3
•Understanding PAgP EtherChannel Configuration, page 16-3
•Understanding IEEE 802.3ad LACP EtherChannel Configuration, page 16-3
EtherChannel Configuration Overview
You can configure EtherChannels manually or you can use the Port Aggregation Control Protocol
(PAgP) or, with Cisco IOS Release 12.2(25)EWA and later, the Link Aggregation Control Protocol
(LACP) to form EtherChannels. The EtherChannel protocols allow ports with similar characteristics to
form an EtherChannel through dynamic negotiation with co nnected network devices. PAgP is a
Cisco-proprietary protocol and LACP is defined in IEEE 802.3ad.
PAgP and LACP do not interoperate with each other. Ports configured to use PAgP cannot form
EtherChannels with ports configured to use LACP and vice versa.
Table16-1 lists the user-configurab le EtherChannel modes.