In this topic, you will learn how to configure and verify EtherChannel (LACP & PAgP) on Cisco devices. Understanding EtherChannel is essential for building scalable, resilient, and high-performance networks.

EtherChannel is a powerful feature used in Cisco networking to increase bandwidth and provide redundancy by combining multiple physical links into one logical link. It enhances both performance and reliability between switches, routers, or servers.

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Introduction

EtherChannel is a technology that allows multiple physical Ethernet links to be combined into one logical link. This helps increase bandwidth, provides redundancy, and simplifies network management. By bundling several interfaces together, EtherChannel ensures efficient load balancing and prevents network failures by allowing traffic to be rerouted through available links if one or more links go down.

EtherChannel supports protocols such as Port Aggregation Protocol (PAgP) and Link Aggregation Control Protocol (LACP), which negotiate the formation of the channel between devices. It is widely used in enterprise networks to improve performance and provide fault tolerance without requiring complex routing protocols or spanning tree adjustments.

EtherChannel Protocols

There are two main EtherChannel protocols used to negotiate and manage multiple Ethernet links:

• Link Aggregation Control Protocol (LACP)
• Port Aggregation Protocol (PAgP)

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LACP EtherChannel

Link Aggregation Control Protocol (LACP) is one of the protocols that is used to create an EtherChannel, which bundles multiple physical links into a single logical link to increase bandwidth and provide redundancy. LACP is part of the IEEE 802.3ad standard and is widely supported across different network devices and vendors, making it suitable for interoperable networks.

With LACP, two devices actively exchange information to negotiate which links should be part of the aggregated channel. This dynamic negotiation ensures that only compatible links are grouped together and that traffic is evenly distributed across the available links. If one link in the EtherChannel fails, LACP automatically removes it from the aggregation and maintains the connection using the remaining links, ensuring network stability.

LACP offers two operational modes:

• Active Mode – The device actively initiates negotiations with the peer device to form an EtherChannel.
• Passive Mode – The device responds to negotiation requests but does not actively start them.

PAgP EtherChannel

Port Aggregation Protocol (PAgP) is a Cisco proprietary protocol used to automatically create an EtherChannel by grouping multiple physical Ethernet links into one logical connection. By combining links, PAgP provides higher bandwidth, load balancing, and redundancy, while simplifying link management and configuration.

PAgP helps ensure that only compatible interfaces are bundled together by exchanging protocol packets between devices. It verifies settings such as speed, duplex, and VLAN configuration before forming the EtherChannel. This dynamic negotiation ensures that all participating links operate efficiently and uniformly.

PAgP operates in two modes:

• Auto Mode – The device waits for the other side to initiate negotiation before forming an EtherChannel.
• Desirable Mode – The device actively initiates negotiation with the peer to form an EtherChannel.

Since PAgP is Cisco proprietary, it is typically used in environments where all participating devices are Cisco switches. Understanding how to configure and verify PAgP-based EtherChannel is essential for managing high-performance and resilient network links within Cisco-based infrastructures.

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Configuring and Verifying Ether channel (LACP & PAgP)

Configuring EtherChannel with LACP

LACP operates in two modes.

• Active Mode – The device actively initiates negotiations with the peer device to form an EtherChannel.
• Passive Mode – The device responds to negotiation requests but does not actively start them.

At least one side must be in Active mode.

Layer 2 Configuration Example (Trunk or Access):

Switch(config)# interface range gi0/1 - 2
Switch(config-if-range)# switchport mode trunk         ! or 'access'
Switch(config-if-range)# channel-group 1 mode active    ! LACP
Switch(config-if-range)# exit

Switch(config)# interface port-channel 1
Switch(config-if)# switchport mode trunk                ! or 'access'

Layer 3 Configuration Example (Routing):

Switch(config)# interface range gi0/1 - 2
Switch(config-if-range)# no switchport
Switch(config-if-range)# channel-group 2 mode active    ! LACP
Switch(config-if-range)# exit

Switch(config)# interface port-channel 2
Switch(config-if)# no switchport
Switch(config-if)# ip address 192.168.10.1 255.255.255.0

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Configuring EtherChannel with PAgP

PAgP operates in two modes:

Desirable Mode – The device actively initiates negotiation with the peer to form an EtherChannel.

Auto Mode – The device waits for the other side to initiate negotiation before forming an EtherChannel.

At least one side must be in Desirable mode.

Layer 2 Configuration Example (Access or Trunk):

Switch(config)# interface range gi0/3 - 4
Switch(config-if-range)# switchport mode trunk          ! or 'access'
Switch(config-if-range)# channel-group 3 mode desirable ! PAgP
Switch(config-if-range)# exit

Switch(config)# interface port-channel 3
Switch(config-if)# switchport mode trunk

Note: PAgP cannot be used for Layer 3 EtherChannel, only Layer 2.

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Verifying EtherChannel (LACP or PAgP)

The following commands are used to verify the configuration and status of EtherChannel.

Command	Description
show etherchannel summary	Summarizes EtherChannel interfaces, protocol, and status
show interfaces port-channel <id>	Shows detailed interface info
show running-config interface port-channel <id>	Displays config on logical port-channel
show interfaces etherchannel	Shows load balancing and hashing methods
show lacp neighbor	Shows LACP neighbor info (LACP only)
show pagp neighbor	Shows PAgP neighbor info (PAgP only)
show spanning-tree interface port-channel <id>	Verifies STP role of EtherChannel

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