NBMA

OSPF通信协议中网络类型之一

条目

历史版本

非广播-多路访问网络（Non-Broadcast Multiple Access，NBMA）是OSPF通信协议中定义的四种网络类型的其中一种。 NBMA用来描述如X.25和帧中继这类本身并不具有支持广播和多播能力的多路访问网络。其他OSPF定义的网络类型有：广播网络、点对点网络和点对多点网络。OSPF邻居状态关系表示，只有Attempt会出现在NBMA协议中。

基本介绍

在配置NBMA的情况下，OSPF在同一时刻向每一个路由器只会发送一个Hello包（Hello包周期性发送，用于建立和确定路由间的邻居关系）而不是进行多播。Hello包的发送周期间隔的范围为10s~30s，而判断邻居失效(dead)的时间范围为40s~120s（4倍于Hello包发送间隔）。

NBMA (non-broadcast multiple access)is one of four network types in the OSPF (Open Shortest Path First) communications protocol. NBMA is used to accurately model X.25 and frame relay environments in multiple-access networks where there are no intrinsic broadcast and multicast capabilities. The other OSPF network types are: broadcast, point-to-point, and point-to-multipoint. In an NBMA configuration, OSPF sends HELLO packets (packets sent periodically to establish and confirm neighbor relationships between routers) to each router one at a time rather than multicasting them. The HELLO timer (which tells the router how often to send HELLO packets) is extended from 10 to 30 seconds and the dead router timer (which tells the router how long to wait before it decides that a neighboring router is not functioning) is extended from 40 to 120 seconds.