Port aggregation combines multiple physical switch ports into a single logical channel to increase bandwidth, provide redundancy, and enable load balancing.

Key Concepts

Port aggregation, also known as link aggregation or EtherChannel, allows multiple physical ports to act as a single logical interface. This improves network performance and provides failover if one port fails. Aggregation can be static (manual configuration) or dynamic using LACP (Link Aggregation Control Protocol), which negotiates the aggregation automatically between devices .

Prerequisites for Aggregation

Before configuring aggregation, ensure the following attributes are consistent across all member ports:

• STP settings: Enable/disable status, priority, and cost .
• VLAN configuration: Port VLAN ID (PVID) and permitted VLANs .
• Port attributes: Speed, duplex mode (full duplex only), and link type (trunk, hybrid, or access), .
• Physical connectivity: Ports should not be connected to other devices during initial configuration .

Configuration Steps

1. Enable Privileged EXEC Mode

Access the switch CLI and enter privileged EXEC mode, providing the password if prompted .

2. Create an Aggregation Group

Enter global configuration mode and assign a channel group ID (range 0–5). Example:

interface range GigabitEthernet1/0/1 - 2channel-group 1 mode on

• on: Static aggregation, no LACP required.
• active: LACP active mode, initiates negotiation.
• passive: LACP passive mode, responds to negotiation .

3. Add Ports to the Aggregation Group

Enter interface configuration mode for each port and assign it to the aggregation group using the chosen mode. Ensure all ports share the same VLAN and speed/duplex settings .

4. Configure Load Balancing

Set the load balance policy to distribute traffic across member ports. Common options include source MAC, destination MAC, or IP-based hashing . Example:

port-channel load-balance src-mac

5. Verify Configuration

Check the aggregation status and member ports:

show etherchannel summaryshow running-config

Ensure all ports are active and participating in the aggregation group .

Best Practices

• Configure the downstream switch first, then move upstream to avoid stranded ports .
• Use ports with similar characteristics (speed, duplex, media type) to prevent mismatches .
• For redundancy across switches, consider MC-LAG (Multi-Chassis Link Aggregation) to allow two switches to act as a single logical unit .
• Avoid mixing static and dynamic LACP modes on the same aggregation group .

By following these steps, you can successfully configure an aggregation switch to improve network performance, provide redundancy, and enable efficient load balancing across multiple physical links.