OSPF 域（也称为 AS）是连接到 OSPF 骨干网的 OSPF 区域的集合。

RFC 2328，OSPF 版本 2定义了术语，路由器 ID：”

    Router ID
        A 32-bit number assigned to each router running the OSPF
        protocol.  This number uniquely identifies the router within
        an Autonomous System.

-和-

Router ID
    A 32-bit number that uniquely identifies this router in the AS.
    One possible implementation strategy would be to use the
    smallest IP interface address belonging to the router. If a
    router's OSPF Router ID is changed, the router's OSPF software
    should be restarted before the new Router ID takes effect.  In
    this case the router should flush its self-originated LSAs from
    the routing domain (see Section 14.1) before restarting, or they
    will persist for up to MaxAge minutes.