选择一个LAG

每个端口都会被LAG上的membership选择，每个membership是由设备上唯一的LAG ID进行标识的

43.3.7 Selecting a Link Aggregation Group

Each port is selected for membership in the Link Aggregation Group uniquely identified by the LAG ID (composed of operational information, both derived from local administrative parameters and received through the Link Aggregation Control Protocol). Initial determination of the LAG ID is delayed to allow receipt of such information from a peer Link Aggregation Control entity; in the event such information is not received, locally configured administrative defaults are assumed for the remote port’s operational parameters. Where a particular link is known to be Individual, the complete LAG ID is not required to select the Link Aggregation Group since the link will not be aggregated with any other.

• 每个端口会被LAG选作其中的一个成员，每个端口只能够属于一个LAG组
• 一般都要等收到对方的LACP消息获取到对方的一点信息后才能够确认自己的LAGID，为什么？因为LAGID的组成中需要对端的一些信息（系统优先级，系统标示符，关键参数等）
• 如果没有收到对方的信息，那么就会使用本地的一些默认配置信息进行配置

在一个LAG上的协商

43.3.8 Agreeing on a Link Aggregation Group（协商些什么玩意？）

Before frames are distributed and collected from a link, both the local Link Aggregation Control entity and its remote peer (if present) need to agree on the Link Aggregation Group. The Link Aggregation Control Protocol allows each of the communicating entities to check their peer’s current understanding of the LAG ID, and facilitates rapid exchange of operational parameters while that understanding differs from their own. The protocol entities monitor their operation and, if agreement is not reached (perhaps due to an implementation failure), management is alerted. The ability of LACP to signal that a particular link is Individual can accelerate the use of the link since, if both Link Aggregation Control entities know that the link is Individual, full agreement on the LAG ID is not necessary.i

• LAG上的链路在发送和接收数据帧之前，必须将链路上的参数协商一致，本地链路汇聚控制实例和它的远端peer都需要在LAG层面协商一致
• 链路控制协议允许两个通信实例检查它们双方对LAG ID的理解是否一致（两个通信的实体它们的LAGid应该是需要是一致的）
• 协议实例监控它们的操作，如果协商没有达成一致（也许是由于实现失败）管理模块需要告警
• lacp的能力是发现一条特定的链路是独立的能加速链路的使用
• 如果两个链路控制实例都知道某条链路是独立的，那么完全的LAGID协商就是没有必要的