Interface ConfigDomain 5.0

channel-group [number] mode [protocol]

Bundles multiple physical interfaces into a single logical "Port-Channel." This multiplies your total bandwidth (e.g., four 1Gbps links become one 4Gbps pipe) and treats the bundled links as a single interface, preventing Spanning Tree Protocol (STP) from blocking the redundant cables.

Quick Reference

Execution ModeSwitch(config-if-range)#

Maximum Bundled LinksUp to 8 active links per channel.

Open Standard (802.3ad)LACP (Active / Passive)

Cisco ProprietaryPAgP (Desirable / Auto)

Syntax & Protocol Modes

channel-group [1-6] mode [active | passive | desirable | auto | on]

Mode Keyword	Protocol & Behavior
active	LACP (Open Standard). The switch actively sends LACP negotiation packets to form a bundle. Works with non-Cisco equipment.
passive	LACP (Open Standard). The switch passively waits for LACP packets. It will only form a bundle if the other side is set to `active`.
desirable	PAgP (Cisco Proprietary). The switch actively sends PAgP negotiation packets. Only works with other Cisco switches.
auto	PAgP (Cisco Proprietary). The switch passively waits for PAgP packets. It will only form a bundle if the other side is set to `desirable`.
on	Static / No Protocol. Forces the ports into a bundle without sending any negotiation packets. Highly dangerous as it can cause massive loops if the other side is misconfigured.

CLI Deployment Scenarios

Scenario 1: Creating an LACP EtherChannel

You are connecting a Catalyst switch to a Dell PowerEdge server with four NICs. You must use the open-standard LACP protocol to bundle them.

Switch(config)# interface range g1/0/1 - 4

Switch(config-if-range)# channel-group 1 mode active

Creating a port-channel interface Port-channel 1

! A new logical interface named "interface port-channel 1" is automatically created.

Scenario 2: Applying Trunk Configurations to the Bundle

Once an EtherChannel is formed, you must apply all configuration changes to the logical Port-Channel interface, not the physical gigabit ports.

Switch(config)# interface port-channel 1

Switch(config-if)# switchport mode trunk

Switch(config-if)# switchport trunk allowed vlan 10,20

! The logical port-channel pushes this config down to physical ports g1/0/1 - 4 simultaneously.

CCNA Exam Gotchas

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The Passive-Passive Mismatch

If Switch A is set to mode passive and Switch B is set to mode passive, the EtherChannel will never form. Both sides are waiting for the other to initiate. The same applies to auto - auto in PAgP. At least one side of the link must be an initiator (active or desirable).

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The Consistency Rule (Err-Disable)

To bundle physical ports together, they must be perfectly identical. If Port 1 is running at 1Gbps full-duplex on VLAN 10, and Port 2 is running at 100Mbps half-duplex on VLAN 20, the switch will reject the bundle and throw the ports into an err-disable suspended state. Speed, duplex, and allowed VLANs must match exactly before you execute the channel-group command.