For each link configured as bundle member, the following information is exchanged between the systems that host each end of the link bundle:
A globally unique local system identifier
An identifier (operational key) for the bundle of which the link is a member
An identifier (port ID) for the link
The current aggregation status of the link
This information is used to form the link aggregation group identifier (LAG ID). Links that share a common LAG ID can be aggregated. Individual links have unique LAG IDs.
The system identifier distinguishes one router from another, and its uniqueness is guaranteed through the use of a MAC address from the system. The bundle and link identifiers have significance only to the router assigning them, which must guarantee that no two links have the same identifier, and that no two bundles have the same identifier.