How to troubleshoot LACP Issues on Direct Connect LAG

Resolution

What is LACP?

LACP (Link Aggregation Control Protocol) is a subcomponent of the IEEE 802.3ad standard, a discovery protocol that allows multiple Ethernet interfaces to be grouped together to form a single link layer interface. In AWS Direct Connect, you can create a LAG (Link Aggregation Group), which is a logical interface that aggregates multiple dedicated connections at a single endpoint and treats them as a single managed connection.

Note: Specific command syntax for each vendor may vary depending on the OS version, so please refer to the vendor's official documentation.

Verify Physical Connectivity

Verify the operational status of the aggregated interface and member links.

Before troubleshooting LACP issues, you should first verify the physical connection status.

CloudWatch Metrics to Monitor:

• ConnectionState - Monitor connection status (0=DOWN, 1=UP)

Expected: Value should be 1

Junos OS:

show interfaces terse | match lag-name

Cisco IOS:

show etherchannel summary

Check Optical Signal Levels

Verify the received signal average optical output and laser output. Optical signals should read normal power levels.

CloudWatch Metrics to Monitor:

• ConnectionLightLevelRx - Receive signal strength (dBm)
• ConnectionLightLevelTx - Transmit signal strength (dBm)

Junos OS:

show interfaces diagnostics optics interface-name | grep dBm | except thre

Cisco IOS:

show interfaces transceiver

Expected output: Optical power levels should be within the acceptable range (-14.4 to 2.50 dBm for 1G and 10G connections).

Check LACP Configuration

Verify the LACP activity mode (active or passive) on both sides of the connection.

LACP roles:

• LACP allows network devices to negotiate automatic bundling of links by sending LACP packets to peers
• LACP activity can be active or passive
• The transmitting link is called the actor, and the receiving link is called the partner Expected configuration: Both sides can be configured as 'Active', but both sides cannot be set to 'Passive'.

Junos OS:

show lacp interfaces interface-name

Cisco IOS:

show lacp neighbor
show etherchannel detail

LACP Timer Mode (Fast/Slow)

Check that both devices have matching LACP periodic timer configuration.

Junos OS:

show lacp interfaces interface-name

Cisco IOS:

show lacp internal
show lacp neighbor detail

Recommendation: AWS Direct Connect recommends Fast mode (1-second interval) for faster detection and recovery during link failures.

Verify Operational State and Events

Verify the minimum number of active links required for the LAG to remain operational.

Console Verification:

1. Direct Connect Console → LAGs
2. Check "Minimum Links" configuration
3. Verify number of "Available" connections meets minimum requirement
4. Review LAG operational status

Junos OS:

show interfaces ae0

Cisco IOS:

show etherchannel summary

Important: If the number of active links falls below the configured minimum-links value, the LAG goes down.

Check AWS Health Dashboard

AWS Direct Connect connections can go down due to planned or emergency maintenance.

Action:

• Check the Events section of the AWS Health Dashboard
• Look for ongoing or recently completed maintenance affecting your Direct Connect connection

Note: During maintenance, BGP connections may transition to idle state, which can last from minutes to hours.

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Related Information

• Link aggregation groups - AWS Direct Connect
• Monitor with Amazon CloudWatch