If peer-link is down for any reason, MLAG control plane messages cannot be exchanged properly, causing the MLAG system to operate abnormally. To ensure the reliability of peer-link, note the following points when configuring and deploying peer link.

Only one peer link connecting the two peer devices is allowed in an MLAG domain.
When configuring the peer link, only one LAG port can be used as peer link.
Use a LAG port with at least two directly connected physical ports to guarantees reliable communication between the peer devices on the peer link. Use of any intermediate transmission device between the two peer devices on the peer link is not allowed. All of the directly connected physical ports should be added into one LAG port to form the peer-link. We don’t support more than one L2 connection between MLAG peer switches.
10G or 40G speed ports should be used for peer link to enough bandwidth is provided when the network is deployed.
Any manual action to shut down the peer link is strictly forbidden.

For more details, you can refer to the peer link concept in Principle of MLAG.

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