业务支撑网网络技术Lesson7第二层交换机的功能.pptx

Lesson 7 第二层交换机的功能7.1第二层交换机的工作原理7.2生成树协议(STP)7.3高级生成树协议7.4第二层交换机的基本配置7.5交换机的端口安全7.1 第二层交换机的工作原理7.1.1 面板指示灯7.1.2 交换机和网桥的比较7.1.3 交换机的数据转发方式7.1.4 第二层交换机的功能7.1.5 冗余(Redundant)7.1.1 面板指示灯7.1.2 交换机和网桥的比较网桥(Bridge)交换机(Switch)7.1.3 交换机的数据转发方式 Cut-Through（直通转发）Switch checks destination address and immediately begins forwarding frame Store and Forward（存储转发）Complete frame is received and checked before forwarding Fragment-Free（碎片丢弃）Switch checks the first 64 bytes, then immediately begins forwarding frame7.1.4 第二层交换机的功能地址学习 (Address learning)转发/过滤决定 (Forward/filter decision)避免循环 (Loop avoidance)MAC地址表(MAC Address Table)交换机上电初始化期间MAC地址表是空的地址学习(Learning Addresses)Station A sends a frame to station C.The switch caches the MAC address of station A to port E0 by learning the source address of data frames.The frame from station A to station C is flooded out to all ports except port E0 (unknown unicasts are flooded).地址学习(Learning Addresses)Station D sends a frame to station C.The switch caches the MAC address of station D to port E3 by learning the source address of data frames.The frame from station D to station C is flooded out to all ports except port E3 (unknown unicasts are flooded).过滤帧(Filtering Frames)Station A sends a frame to station C.The destination is known; the frame is not flooded.过滤帧(Filtering Frames )Station A sends a frame to station B.The switch has the address for station B in the MAC address table.广播和组播帧(Broadcast and Multicast Frames)Station D sends a broadcast or multicast frame.Broadcast and multicast frames are flooded to all ports other than the originating port.广播MAC地址：FF.FF.FF.FF.FF.FF组播MAC地址范围 ：01:00:5E:00:00:00---01:00:5E:FF:FF:FF7.1.5 冗余(Redundant)优点：冗余能够避免单点故障缺点：交换循环(Switch loop)交换循环的危害广播风暴(Broadcast Storms)多帧复制(Multiple Frame copies) MAC地址表不稳定（ MAC Database Instability） 广播风暴(Broadcast Storms)Host X sends a broadcast. Switches continue to propagate broadcast traffic over and over.多帧复制(Multiple Frame copies)Host X sends a unicast frame to router Y