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1、Chapter 9 交换机原理及配置,地址（MAC）学习 转发/筛选 环路避免,Switch 的三个功能,Switches 地址学习,初始 MAC 地址表为空 学习源地址,MAC address table,0260.8c01.1111,0260.8c01.2222,0260.8c01.3333,0260.8c01.4444,E0,E1,E2,E3,A,B,C,D,Switches地址学习,Station A sends a frame to Station C Switch caches station A MAC address to port E0 by learning the sou
2、rce 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),MAC address table,0260.8c01.1111,0260.8c01.2222,0260.8c01.3333,0260.8c01.4444,E0: 0260.8c01.1111,E0,E1,E2,E3,D,C,B,A,Switches地址学习,Station D sends a frame to stat
3、ion C Switch caches station D MAC address 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),MAC address table,0260.8c01.1111,0260.8c01.2222,0260.8c01.3333,0260.8c01.4444,E0: 0260.8c
4、01.1111,E3: 0260.8c01.4444,E0,E1,E2,E3,D,C,A,B,Switches 转发/过滤,Station A sends a frame to station C Destination is known, frame is not flooded,E0: 0260.8c01.1111,E2: 0260.8c01.2222,E1: 0260.8c01.3333,E3: 0260.8c01.4444,0260.8c01.1111,0260.8c01.2222,0260.8c01.3333,0260.8c01.4444,E0,E1,E2,E3,X,X,D,C,A,
5、B,MAC address table,Station D sends a broadcast or multicast frame Broadcast and multicast frames are flooded to all ports other than the originating port,0260.8c01.1111,0260.8c01.2222,0260.8c01.3333,0260.8c01.4444,E0,E1,E2,E3,D,C,A,B,E0: 0260.8c01.1111,E2: 0260.8c01.2222,E1: 0260.8c01.3333,E3: 0260
6、.8c01.4444,MAC address table,广播与多播Frame,冗余路径,冗余路径消除了单故障点 冗余路径的不利后果： 广播风暴, 多个Frame副本, MAC地址表不稳定,Segment 1,Segment 2,Server/host X,Router Y,Segment 1,Segment 2,Server/host X,Router Y,Broadcast,Switch A,Switch B,Host X sends a Broadcast,广播风暴,Segment 1,Segment 2,Server/host X,Router Y,Broadcast,Switch A
7、,Switch B,Host X sends a Broadcast,广播风暴,Segment 1,Segment 2,Server/host X,Router Y,Broadcast,Switches continue to propagate broadcast traffic over and over,Switch A,Switch B,广播风暴,多个Frame副本,Segment 1,Segment 2,Server/host X,Router Y,Unicast,Switch A,Switch B,Host X sends an unicast frame to router Y
8、Router Y MAC address has not been learned by either switch yet,Segment 1,Segment 2,Server/host X,Router Y,Switch A,Switch B,Host X sends an unicast frame to Router Y Router Y MAC Address has not been learned by either Switch yet Router Y will receive two copies of the same frame,多个Frame副本,Segment 1,
9、Segment 2,Server/host X,Router Y,Unicast,Unicast,Switch A,Switch B,Host X sends an unicast frame to Router Y Router Y MAC Address has not been learned by either Switch yet Switch A and B learn Host X MAC address on port 0,Port 0,Port 1,Port 0,Port 1,多个Frame副本,Segment 1,Segment 2,Server/host X,Router
10、 Y,Unicast,Unicast,Switch A,Switch B,Host X sends an unicast frame to Router Y Router Y MAC Address has not been learned by either Switch yet Switch A and B learn Host X MAC address on port 0 Frame to Router Y is flooded Switch A and B incorrectly learn Host X MAC address on port 1,Port 0,Port 1,Por
11、t 0,Port 1,多个Frame副本,Complex topology can cause multiple loops to occur Layer 2 has no mechanism to stop the loop,Server/host,Workstations,Loop,Loop,Loop,多个环路问题,解决办法: Spanning-Tree Protocol,将一些Port置为Block状态，避免环路的产生,Block,x,One root bridge per network One root port per nonroot bridge One designated p
12、ort per segment,x,Designated port (F),Root port (F),Designated port (F),Nondesignated port (B),Root bridge,Nonroot bridge,SW X,SW Y,100baseT,10baseT,生成树协议 STP Spanning-Tree Operations,Switch Y Default priority 32768 (8000 hex) MAC 0c0022222222,Switch X Default priority 32768 (8000 hex) MAC 0c0011111
13、111,BPDU,BPDU = Bridge protocol data unit 桥协议数据单元(2 秒) Root bridge ： bridge ID 最小的桥 Non Root bridge： 其它的桥 Bridge ID = Bridge priority + bridge MAC address,生成树协议根桥选择,Switch Y Default priority 32768 MAC 0c0022222222,Switch X Default priority 32768 MAC 0c0011111111,Root bridge,x,Port 0,Port 1,Port 0,Po
14、rt 1,100baseT,10baseT,Designated port (F),Root port (F),Nondesignated port (B),Designated port (F),生成树协议端口选择,非根桥root port：非根桥上到根桥cost最小的端口 designated port：每一Segment上到根桥cost最小端口 根桥的所有端口都是designated port nondesignated port：剩余的所有端口,生成树协议端口最终状态,最终状态 根桥的所有端口： Forwarding 非根桥root port： Forwarding designate
15、d port： Forwarding nondesignated port： Blocking,注意：Blocking状态不能转发数据， 但可收发BPDU消息,Link Speed Cost (reratify IEEE spec) Cost (previous IEEE spec) - 10 Gbps 2 1 1 Gbps 4 1 100 Mbps 19 10 10 Mbps 100 100,生成树协议路径成本,Switch Y MAC 0c0022222222 Default priority 32768,Switch X MAC 0c0011111111 Default priority 32768,Port 0,Port 1,Port 0,Port 1,Switch Z Mac 0c0011110000 Default priority 32768,Port 0,Can you figure out: What is the root bridge? What are the designated, nondesignat
