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1、2020/7/13,1,6 网络互连,6.1 网络互连设备 6.2 交付、转发与路由 6.3 小结,2020/7/13,2,6.1 网络互连设备,中继器 路由器 交换机,2020/7/13,3,互连设备,2020/7/13,4,互连设备和OSI模型,2020/7/13,5,中继器,中继器仅仅延长网络的距离, 没有过滤能力 中继器是一个再生器, 不是一个放大器,2020/7/13,6,中继器,2020/7/13,7,中继器功能,2020/7/13,8,集线器: 多端口中继器,2020/7/13,9,集线器: 同一个冲突域,所有设备共享相同的带宽 接入设备越多冲突机率越大 用CSMA/CD技术,2
2、020/7/13,10,路由器,工作在OSI模型的物理层、数据链路层和网络层 同时连接两个或更多的网络, 并同时拥有它们的地址 选择出两节点间”最短”的传输路径 “最短”可能意味着许多因素的组合, 包括最短、最便宜、最快、最可靠等 连接不同传输速率并运行于各种环境的局域网和广域网,2020/7/13,11,路由器,2020/7/13,12,General architecture of an IP router,2020/7/13,13,交换机,传统的交换机工作于OSI模型的数据链路层 可作为多点网桥连接LAN中的设备或网段,2020/7/13,14,交换机,2020/7/13,15,两种交换
3、策略,存储转发 发送信息前把整帧数据读入内存并检查其正确性 可以在不同传输速率的网段间传输数据 快捷模式 读取帧头后即决定把数据转发往何处,2020/7/13,16,帧交换策略,直通转发 交换机检测到目标地址后即转发帧 存贮转发 完整地收到帧并检查无错后才转发,Frame,Frame,Frame,Frame,2020/7/13,17,用交换机组建VLAN,2020/7/13,18,第三层交换机与路由器,能够比路由器更快地传输数据 比路由器更容易安装和配置 功能比不上路由器 不能在以太网和令牌环网间传输数据, 不能打包协议, 不能优化数据传输 在广域网中使用需要路由器, 在局域网中尽量使用交换机
4、,2020/7/13,19,例6.1 Cisco Catalyst 2950系列交换机,最廉价的Cisco交换产品 可堆叠 8.8Gbps的交换背板带宽 最大4.4Gbps数据吞吐率,2020/7/13,20,例6.2 Cisco 2600系列路由器,中小型用户首选 端口设计模块化, 与Cisco 1600、1700, 3600和3700系列共享模块化接口 支持QoS、安全和网络集成特性,16端口交换模块,ADSL信道单元模块,VoATM信道模块,2020/7/13,21,例6.3 采用Cisco 2600组建广域网,可长期使用、能适应不断发展的网络要求 带防火墙保护的虚拟专用网(VPN)可降
5、低成本 集成化路由和交换功能 语音、传真、数据多业务集成 安全、高性能模块化平台上的高速企业级DSL连接 支持QoS, 如资源预留协议(RSVP)、加权公平序列(WFQ)和IP优先级,2020/7/13,22,选择合适的产品,汇聚层,核心层,接入层,2020/7/13,23,选择产品要考虑的要素,产品功能与性能 安装与管理 弹性处理能力 投资保护 平滑升级 无缝远程接入,2020/7/13,24,Cisco全线智能路由器系列,CRS1 80Mpps/LC,GSR/C12000 450Mpps/LC,ESR/C10000 6.2Mpps/LC,C7600 32M48Mpps/slot,C7300
6、 1Mpps3.5Mpps,C7200 400K1Mpps,C3800,C2800,C1800,C850/870,SB100,C800,C1700,C2600XM,C3700,C7400,C7500,运营商核心,运营商边缘/ 企业核心,接入,运营商,运营商与大企业,中小规模企业,小企业,性能,SOHO,2020/7/13,25,6.2 交付、转发与路由,交付 (Delivery) 转发 (Forwarding) 路由 (Routing),2020/7/13,26,Delivery,The network layer supervises the handling of the packets
7、by the underlying physical networks. We define this handling as the delivery of a packet.,2020/7/13,27,Direct and indirect delivery,2020/7/13,28,Forwarding,Forwarding means to place the packet in its route to its destination. Forwarding requires a host or a router to have a routing table. When a hos
8、t has a packet to send or when a router has received a packet to be forwarded, it looks at this table to find the route to the final destination.,2020/7/13,29,Route method versus next-hop method,Next-hop method is the first technique to reduce the contents of a routing table.,2020/7/13,30,Host-speci
9、fic versus network-specific method,Network-specific method is the second technique to reduce the routing table and simplify the searching process.,2020/7/13,31,Default method,Default method is another technique to simplify routing.,2020/7/13,32,Simplified forwarding module in classless address,In cl
10、assless addressing, we need at least four columns in a routing table.,ARP 负责将下一跳路由器的 IP 地址转换成硬件地址, 并将此硬件地址放在链路层的 MAC 帧的首部, 然后根据这个硬件地址找到下一跳路由器.,2020/7/13,33,例. 6.4 Configuration example,2020/7/13,34,Forwarding process example,Show the forwarding process if a packet arrives at R1 with the destination
11、address 180.70.65.140. Solution 1. The first mask (/26) is applied to the destination address. The result is 180.70.65.128, which does not match the corresponding network address. 2. The second mask (/25) is applied to the destination address. The result is 180.70.65.128, which matches the correspon
12、ding network address. The next-hop address and the interface number m0 are passed to ARP for further processing.,2020/7/13,35,Forwarding process example, continued,Show the forwarding process if a packet arrives at R1 with the destination address 201.4.22.35. Solution 1. The first mask (/26) is appl
13、ied to the destination address. The result is 201.4.22.0, which does not match the corresponding network address (row 1). 2. The second mask (/25) is applied to the destination address. The result is 201.4.22.0, which does not match the corresponding network address (row 2). 3. The third mask (/24)
14、is applied to the destination address. The result is 201.4.22.0, which matches the corresponding network address. The next-hop address and the interface number m3 are passed to ARP.,2020/7/13,36,Forwarding process example, continued,Show the forwarding process if a packet arrives at R1 with the dest
15、ination address 18.24.32.78. Solution All masks are applied, one by one, to the destination address, but no matching network address is found. When it reaches the end of the table, the module gives the next-hop address 180.70.65.200 and interface number m2 to ARP.,2020/7/13,37,Address aggregation,20
16、20/7/13,38,Longest mask matching,2020/7/13,39,Longest mask matching, continued,Suppose a packet arrives for organization 4 with destination address 140.24.7.200. The first mask at router R2 is applied, which gives the network address 140.24.7.192. The packet is routed correctly from interface m1 and reaches organization 4. If, however, the routing table was not stored with the longest prefix first, applying the /24 mask would result in the incorrect routing of t
