True or False: When configured as an MLAG domain, the Arista switches use the same MLAG System ID.

The fundamental principle of Multi-Chassis Link Aggregation (MLAG) is to make two separate physical switches appear as a single logical switch to a connected device. To achieve this, both switches in the MLAG domain must present a unified identity during LACP (Link Aggregation Control Protocol) negotiations. They do this by sharing a common MLAG System ID, which is a unique MAC address configured to be identical on both MLAG peers. This shared System ID ensures that any downstream device sees a single LACP partner, allowing it to form a port-channel across the two physically distinct Arista switches.

The statement "False" would be incorrect. If the two switches in an MLAG domain used different System IDs, a downstream LACP-enabled device would identify them as two separate and distinct switches. Consequently, the downstream device would not be able to form a single Link Aggregation Group (LAG) with ports spanning both upstream switches, defeating the primary purpose of MLAG.

1. Arista Networks EOS Configuration Guide: In the section describing MLAG concepts, the documentation states, "The two switches in an MLAG domain are the MLAG peers... A single LACP system ID is created for both peers." This confirms that a shared System ID is a core component of the MLAG domain.

Source: Arista EOS 4.31.2F - Configuration Guide, Section: "MLAG Concepts".

2. Arista Networks MLAG - Best Practices White Paper: This document explains the operational details and recommended configurations. It emphasizes the need for a unique system MAC address for the MLAG domain. "The MLAG system-id is a 48-bit MAC address that is unique to the MLAG domain... This MAC address is used as the system-id for LACP."

Source: Arista White Paper, "MLAG - Best Practices", Section: "MLAG Configuration", Subsection: "MLAG System-ID".

3. Arista Networks EOS Configuration Guide (Command Reference): The configuration command itself highlights this requirement. When configuring MLAG, the system-id command is used. The guide notes, "The system ID must be identical on both MLAG peers."

Source: Arista EOS 4.31.2F - Configuration Guide, Section: "MLAG Configuration Commands", Command: system-id.