Configuring Arista MLAG Step by Step

Configuring Arista MLAG Step by Step

In the world of network engineering, theoretical knowledge is important, but hands-on configuration experience is invaluable. This guide walks through a real-world example of configuring Multi-Chassis Link Aggregation (MLAG) on Arista switches. Each step of the process is explained clearly, with verification steps included along the way.

Essential Show Commands for Troubleshooting

Before configuring, familiarize yourself with these key commands for verification:

• show mlag: Basic MLAG status
• show mlag interfaces: MLAG interface details
• show interfaces status: Port-Channel and L2 forwarding status
• show mlag detail: Comprehensive MLAG information
• show mlag config-sanity: Configuration consistency check
• show po: Port-channel information

Pro Tip: The show mlag detail command is particularly valuable as it provides insights into primary/secondary roles and reload delay values. Understanding these roles ensures you can predict which device will take over in case of failure, while reload delays help avoid flapping during maintenance windows, minimizing disruption to the network.

Step-by-Step Configuration Guide

1. Configuring the MLAG Communication VLAN

First, set up the Layer 2 VLAN for MLAG peer communication:

configure
vlan 4094
trunk group MLAG
no spanning-tree vlan-id 4094

Important Note: While VLAN 4094 is used here, you can choose any VLAN number that doesn’t overlap with production VLANs. This VLAN is local to the MLAG peer group.

2. Setting Up the MLAG Peer-Link Port-Channel

Next, configure the physical connection between MLAG peers:

configure
interface Port-Channel47
description MLAG_Peer_leaf-3b_Po47
switchport mode trunk
switchport trunk group MLAG
!
interface Ethernet 47/48
description MLAG_PEER_leaf-3b_Ethernet47/48
channel-group 47 mode active
no shutdown

Verification Commands:

show interfaces status
show interfaces trunk

3. Establishing the Layer 3 Peering Network

Set up peer-to-peer communication:

configure
interface vlan4094
description MLAG_PEER
mtu 1500
no autostate
ip address 10.1.255.10/31

Pro Tip: The IP addressing here is used solely for communication between these peers. It doesn’t need to be unique across your network, but it can be if required by your design.

4. Defining MLAG Domain Parameters

Bring everything together:

configure
mlag configuration
domain-id Access_Pod3_AGG
local-interface Vlan4094
peer-address 10.1.255.11
peer-link Port-Channel47
reload-delay mlag 300
reload-delay non-mlag 330
exit

Key Verification Commands:

show mlag
show mlag interfaces

5. Adding Member Devices

Add additional devices to the MLAG setup:

configure
interface Port-Channel51
description MEMBER-LEAF-3C_Po49
no shutdown
switchport
switchport trunk allowed vlan 10,310,320,330
switchport mode trunk
mlag 51
!
interface Ethernet51
description MEMBER-LEAF-3C_Ethernet49
channel-group 51 mode active
no shutdown

Critical Note: Ensure the MLAG number matches on both peers for proper operation.

Troubleshooting Tips

Peer Link

• Check physical connections.
• Verify port-channel configuration.
• Ensure VLAN configurations match.

Configuration Inconsistencies

• Use show mlag config-sanity.
• Compare VLAN configurations.
• Verify port-channel settings.

Keepalive

• Verify peer IP connectivity.
• Check VLAN 4094 configuration.
• Ensure no autostate is configured.

Best Practices for Success

Always Verify After Configuration

• Use show commands after each major step.
• Do not proceed until the current step is verified.
• Document any unexpected behavior.

Maintain Configuration Symmetry

• Keep VLAN configurations identical.
• Use consistent naming conventions.
• Match port-channel configurations.

Change Management

• Make changes during maintenance windows.
• Have a rollback plan ready.
• Test configurations in a lab when possible.

Conclusion

Whether setting up a new network or maintaining an existing one, these steps serve as a reliable guide for MLAG configuration. Key takeaways include ensuring configuration symmetry, leveraging verification commands at each stage, and maintaining robust change management practices for smooth deployments. Verify your work at each step for a smooth implementation.

Happy networking!