FreeBSD已实现GRAND（Gratuitous Neighbour Discovery）机制，用于解决IPv6通信中的首包延迟问题。1该机制由RFC 9131规范定义，通过让主机主动广告其新配置的IPv6地址和链路层地址，使路由器能在实际流量到达前获知这些信息，从而消除了邻居发现过程中的异步性。1
FreeBSD的实现涉及RFC 4861中规则7.2.6、7.2.7和7.2.8所定义的延迟和随机化行为。1为适应多地址场景，该实现添加了邻居通告的队列和延迟传输基础设施，以管理多个地址的公告过程，同时避免产生不必要的多播流量。1在GRAND机制下，新邻居被标记为STALE状态而非REACHABLE状态。1RFC 9898明确将GRAND作为解决IPv6部署中路由器转发延迟的机制。1
FreeBSD has implemented the GRAND (Gratuitous Neighbor Discovery) mechanism to address the first-packet delay problem in IPv6 networks 1. The mechanism, defined in RFC 9131, allows hosts to proactively advertise their newly configured IPv6 addresses and link-layer addresses, enabling routers to learn this information before traffic arrives and thus eliminating the asynchronous nature of neighbor discovery 1.
The implementation incorporates queuing and delayed transmission infrastructure for neighbor advertisements to handle scenarios with multiple addresses while avoiding unnecessary multicast traffic 1. Newly discovered neighbors are marked as STALE rather than REACHABLE, and the system implements delay and randomization behaviors specified in RFC 4861 rules 7.2.6, 7.2.7, and 7.2.8 1. According to RFC 9898, GRAND serves as a targeted solution to address router forwarding delays encountered during IPv6 deployment 1.
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