Introduction to Multi-Chassis Link Aggregation

Today I am going to talk about another technology named as Multi-Chassis Link Aggregation which is generally used is many of the vendors like Juniper, Arista Networks and so on. Here in this article I am going to have discussion with respect to Arista Networks.

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Now the question is what is Multi-Chassis Link Aggregation ?
A multi-chassis link aggregation group (MLAG) is a pair of links that terminate on two cooperating switches and appear as an ordinary link aggregation group (LAG). The cooperating switches are MLAG peer switches and communicate through an interface called a peer link. 

While the peer link’s primary purpose is exchanging MLAG control information between peer switches, it also carries data traffic from devices that are attached to only one MLAG peer and have no alternative path. An MLAG domain consists of the peer switches and the control links that connect the switches 

Note: Multi-Chassis Link Aggregation is nothing but the same Cisco uses Multi-Chassis Ether-Channel. If you would like to understand the MEC, please go through the below link for your reference


Connecting two switches as MLAG peers requires the establishment of the peer link and an SVI that defines local and peer IP addresses on each switch. 

Fig 1.1- Multi-Chassis LAG

The peer link is composed of a LAG between the switches. When all devices that connect to the MLAG domain are dually connected to the switches through an MLAG, a peer link of two Ethernet interfaces is sufficient to handle MLAG control data and provide N+1 redundancy. 

When the domain connects to devices through only one MLAG peer, the peer link may require additional Ethernet interfaces to manage data traffic. Disruptions to peer link connectivity due to forwarding agent restarts may cause an extended MLAG outage. 

I will not talk about the configuration here as i already share the same type of configuration on Cisco devices in my earlier article. Hope this article helps you to understand the concept of the Multi-Chassis Link Aggregation.