Most of the parameters used in link aggregation messages were borrowed from the Spanning Tree Protocol. Recall that a Spanning Tree bridge system identifier consists of the following components:
A 2-byte priority number.
A unique MAC address assigned to the system. The system's smallest MAC address normally is used.
Systems other than bridges (for example, routers or servers) that need to aggregate links can be assigned unique system identifiers in exactly the same way.
Similarly, the ports of any participating system can be assigned identifiers with the same structure as the Spanning Tree Protocol port identifiers. That is, asystem port ID consists of the following components:
A port priority value
The port number ...