EtherChannel and Link Aggregation

Learning objectives

• Explain the purpose and scope of EtherChannel and Link Aggregation.
• Identify important protocols, roles, fields, and terminology.
• Apply the concept to a practical network scenario.
• Use IOS XE commands to verify operational behavior.

1. Core concepts

EtherChannel combines compatible physical Ethernet links into one logical Port-Channel. It increases aggregate bandwidth across multiple flows and provides redundancy. STP treats the bundle as one logical link. A single flow is usually assigned to one member by a hash, so it does not automatically receive the sum of all member bandwidth.

2. How it works

LACP is the IEEE link aggregation protocol. LACP active initiates negotiation and passive responds but does not initiate. Active-active or active-passive can form a channel. Passive-passive does not. Cisco PAgP is proprietary. Static mode on does not negotiate. Member ports need compatible speed, duplex, VLAN, and trunk settings.

Visual walkthrough

3. Worked example

On both switches, configure matching interfaces in channel-group 1 mode active, then configure Port-channel1 as a trunk with matching allowed and native VLANs. Confirm all expected members are bundled, not suspended or individual.

IOS XE commands and verification

Syntax and feature availability can vary by device family and software release. Confirm platform support before applying configuration.

interface range gi1/0/1-2
 channel-group 1 mode active
interface port-channel 1
 switchport mode trunk
 switchport trunk allowed vlan 10,20,30
show etherchannel summary
show lacp neighbor

Common mistakes and troubleshooting

• Check physical and interface state before changing higher-layer settings.
• Verify both ends agree on addressing, VLAN, encapsulation, and protocol parameters.
• Use operational show commands; configured text alone does not prove a feature is working.
• Change one variable at a time and verify the result.

Knowledge check

Choose one answer per question. Submit to see why the correct choice is right and why every other option is wrong. These are original practice questions, not Cisco exam questions.