By J in Cisco — 23 Dec 2024

EtherChannel Configuration on Cisco Switches

Introduction

In this lesson, I will explain how to configure, verify, and troubleshoot EtherChannel on Cisco switches. EtherChannel technology combines multiple physical interfaces into a single logical interface, providing increased bandwidth and redundancy for inter-switch connections.

Lesson Objectives

After completing this lesson, you will be able to:

Understand the different EtherChannel protocols (PAgP and LACP)
Configure Layer 2 EtherChannel using both static and dynamic methods
Verify EtherChannel operation and troubleshoot common issues
Implement best practices for EtherChannel deployment

Prerequisites

Basic understanding of Cisco IOS command-line interface
Knowledge of switch port configuration and VLANs
CCNA-level networking knowledge
Access to two Cisco switches supporting EtherChannel (2960, 3750, or similar)
Console cables and Ethernet cables for connectivity

Core Lesson Content

Part 1: Understanding EtherChannel Fundamentals

Protocol Options

EtherChannel can be configured using three methods:

Static configuration (manual)
Port Aggregation Protocol (PAgP) – Cisco proprietary
Link Aggregation Control Protocol (LACP) – IEEE 802.3ad standard

Key Configuration Requirements

All ports must have:
Identical speed and duplex settings
Same native VLAN and allowed VLAN list
Consistent port mode (access or trunk)
Matching EtherChannel protocol settings

Part 2: Basic EtherChannel Configuration

Static EtherChannel Configuration

! Switch 1 Configuration
Switch1(config)# interface range gigabitethernet 1/0/1-2
Switch1(config-if-range)# channel-group 1 mode on
Switch1(config-if-range)# no shutdown

! Switch 2 Configuration
Switch2(config)# interface range gigabitethernet 1/0/1-2
Switch2(config-if-range)# channel-group 1 mode on
Switch2(config-if-range)# no shutdown

Understanding the Output:

channel-group 1: Creates channel-group number 1
mode on: Configures static EtherChannel without any protocol
The port-channel interface is automatically created

What to Look For:

Both switches should show the port-channel interface as “up/up”
Member interfaces should be bundled
No error messages in the logs

LACP Configuration

! Switch 1 Configuration
Switch1(config)# interface range gigabitethernet 1/0/3-4
Switch1(config-if-range)# channel-group 2 mode active
Switch1(config-if-range)# no shutdown

! Switch 2 Configuration
Switch2(config)# interface range gigabitethernet 1/0/3-4
Switch2(config-if-range)# channel-group 2 mode passive
Switch2(config-if-range)# no shutdown

Understanding LACP Modes:

active: Initiates LACP negotiation
passive: Responds to LACP negotiation
At least one side must be active

Part 3: Verification and Troubleshooting

Essential Verification Commands

Switch# show etherchannel summary
Switch# show etherchannel port-channel
Switch# show running-config interface port-channel 1
Switch# show interfaces port-channel 1

Sample Output Analysis:

Switch# show etherchannel summary
Group  Port-channel  Protocol    Ports
------+-------------+-----------+--------------------------------
1      Po1(SU)         -        Gi1/0/1(P) Gi1/0/2(P)
2      Po2(SU)        LACP      Gi1/0/3(P) Gi1/0/4(P)

Understanding the Output:

(SU) = Port-channel is up and in use
(P) = Port is bundled in port-channel
(I) = Port is stand-alone (not bundled)

Common Issues and Solutions

Mismatched Configuration

Problem: Ports won’t bundle
Solution: Verify speed, duplex, VLANs match on all ports

Protocol Mismatch

Problem: One side using LACP, other using PAgP
Solution: Ensure both switches use the same protocol

Load Balancing Issues

Problem: Uneven traffic distribution
Solution: Configure appropriate load-balancing method

   Switch(config)# port-channel load-balance src-dst-mac

Practical Exercise

Lab Scenario

Configure a 4-port EtherChannel between two switches using LACP:

Connect four physical links between switches
Configure LACP EtherChannel
Verify the configuration
Test failover by disconnecting one link
Monitor traffic distribution

Exercise Steps

! Switch 1
Switch1(config)# interface range gi1/0/1-4
Switch1(config-if-range)# switchport mode trunk
Switch1(config-if-range)# channel-group 1 mode active
Switch1(config-if-range)# no shutdown

! Switch 2
Switch2(config)# interface range gi1/0/1-4
Switch2(config-if-range)# switchport mode trunk
Switch2(config-if-range)# channel-group 1 mode active
Switch2(config-if-range)# no shutdown

Key Takeaways

EtherChannel provides bandwidth aggregation and redundancy
Always verify configuration requirements before implementation
Use dynamic protocols (LACP/PAgP) when possible for automatic negotiation
Regular verification ensures optimal performance

Next Steps

Learn about Layer 3 EtherChannel configuration
Explore advanced load-balancing methods
Study Multi-chassis EtherChannel (MEC) concepts
Practice different failure scenarios

Quick Reference Commands

! Configuration Commands
channel-group <number> mode {on | active | passive | auto | desirable}
port-channel load-balance {src-mac | dst-mac | src-dst-mac}

! Verification Commands
show etherchannel summary
show etherchannel port-channel
show spanning-tree

Verification Checklist

All ports show the correct channel-group assignment
Port-channel interface is up/up
Load balancing configuration is appropriate
Spanning-tree shows port-channel as a single logical interface
No error messages in the system logs