The document discusses link aggregation, which combines multiple network connections to increase throughput beyond a single connection and provide redundancy if one link fails. It defines etherchannel as a form of link aggregation that uses either the Cisco proprietary PAgP protocol or the IEEE standard LACP protocol to negotiate the aggregated link. The benefits of link aggregation are outlined as configuring one logical port channel interface instead of multiple links, single STP calculation, load balancing between links, and the ability to achieve bandwidths over 8Gbps. Steps for configuring etherchannel are provided, including ensuring matching settings on ports and choosing the appropriate channel mode.

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3- Link Aggregation
3.1 Link Aggregation Overview
3.2 Link Aggregation Configuration

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3.1 Link Aggregation Overview

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LINKAGGREGATIONBASICS
• Combining (aggregating) multiple
network connections in parallel in
order to increase throughput beyond
what a single connection could
sustain, and to provide redundancy
in case one of the links should fail
• Etherchannel is a form of LAG
• Interface types must be same on
both sides
SW1 SW2
SW1 SW2
Four 1 Gbps Links (Physical Interface)
One 4 Gbps Etherchannel Link
Gig 1/0/1
Gig 1/0/2
Gig 1/0/3
Gig 1/0/4
Po1

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LINKAGGREGATIONBENEFITS
• Configure just a Po (Port
Channel) interface instead of
configuring 4 seperate links
• One logical link for STP (i.e. If
gig1/0/1 is down, STP
recalculation is not made again
• Load-balancing
• Up to 8Gbps BW
SW1 SW2
SW1 SW2
Four 1 Gbps Links (Physical Interface)
One 4 Gbps Etherchannel Link
Gig 1/0/1
Gig 1/0/2
Gig 1/0/3
Gig 1/0/4
Po1

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PAGP
• Cisco Systems proprietary networking
protocol, which is used for etherchannel
• Can be configured to operate in three
different modes :
 Auto : Passive negotiation of the channel
 Desirable : Active negotiation of the channel
 On : No protocols are used, it assumes the
other side has enabled link aggregation
Channel
Mode
Auto Desirable On
Auto NO YES NO
Desirable YES YES NO
On NO NO YES

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LACP
• IEEE specification which is used for
creating etherchannel
• Can be configured to operate in three
different modes :
 On : Channel member without protocol
 Active : Enables LACP unconditionally
 Passive : Enables LACP only when an
LACP device is detected
Channel
Mode
On Active Passive
On YES NO NO
Active NO YES YES
Passive NO YES NO

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3.1 Link Aggregation Configuration

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ETHERCHANNELCONFIGURATIONSTEPS
• Check If your chassis supports etherchanel
• Make sure that ;
 Duplex modes
 Port speeds
 VLANs
match on ports at both sides
• Choose the right channel mode
SW1 SW2
Gig 1/0/1
Full Duplex
VLAN 20
Gig 1/0/2
Full Duplex
VLAN 20
Gig 1/0/3
Full Duplex
VLAN 20
Gig 1/0/4
Full Duplex
VLAN 20

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ETHERCHANNELCONFIGURATION
SW1 SW2
Fa0/1 Fa0/1
Fa0/2 Fa0/2

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VERIFYINGETHERCHANNELCONFIGURATION
SW1
SW1 SW2
Fa0/1 Fa0/1
Fa0/2 Fa0/2

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