CHAPTER
21-1
Catalyst 3550 Multilayer Switch Software Configuration Guide
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21
Configuring EtherChannel
This chapter describes how to configure EtherChannel on La ye r 2 and Layer 3 interfaces. To configure
Layer 3 interfaces, you must have the enhanced multilayer software image (EMI) installed on your
switch. All Catalyst 3550 Gigabit Ethernet switches ship with the E MI i nsta lled. Cata lyst 3550 Fa st
Ethernet switches can be shipped with either the standard multilayer software image (SMI) or EMI
pre-installed. You can order the Enhanced Multilayer Software Image Upgrade kit to upgrade
Catalyst 3550 Fast Ethernet switches from the SMI to the EMI.
Note For complete syntax and usage information for the commands used in this chapter, refer to the
Catalyst 3550 Multilayer Switch Command Reference for this release.
This chapter consists of these sections:
Understanding Port-Channel Interfaces, page 21-2
Configuring EtherChannel, page 21-7
Displaying EtherChannel and PAgP Status, page 21-16

Understanding EtherChannel

EtherChannel consists of individual Fast Ethernet or Gigabit Ethern et links bundled into a single logical
link as shown in Figure21-1. The EtherChanne l p rov id es f ul l-dup lex band wid th up to 800 Mbps (Fast
EtherChannel) or 8 Gbps (Gigabit EtherChannel) between you r s witc h and a noth er sw it ch or h ost.
Each EtherChannel can consist of up to eight compatibly configured Ethernet interfaces. All interfaces
in each EtherChannel must be the same speed, and all mu st b e c onf igure d as ei ther L ayer 2 or Layer 3
interfaces.
Note The network device to which your switch is connected can impose its own limits on the number of
interfaces in the EtherChannel. For Catalyst 3550 switches, the number of EtherChannels is limited
to the number of ports of the same type.
If a link within an EtherChannel fails, traffic previously carried over that failed link changes to the
remaining links within the EtherChannel. A trap is sent for a failure, identifying the switch, the
EtherChannel, and the failed link. Inbound broadcast and multicast packets on one link in an
EtherChannel are blocked from returning on any other link of t he E the rCh ann el.