网络实验计算机网络.pptx

Computer NetworksLecture 12Wei Liu (刘威)Dept. of Electronics and Information Eng.Huazhong University of Science and TechnologyDec. 2011 Problem in Chapter4:There Is More Than One Network--169.229.131.81routing cost = delayrouting cost = link utili.130.160.4.128The universities can allocate the IP addresses for internal users freely = utilization of address spaceThe ISPs can have different optimal view of routing= Autonomous SystemReal case of Global InternetThe tree structure of the Internet in 1990--Classful AddressingIn the olden days, only fixed allocation sizesClass A: 0*Very large /8 blocks (e.g., MIT has 18.0.0.0/8)Class B: 10*Large /16 blocks (e.g,. Princeton has 128.112.0.0/16)Class C: 110*Small /24 blocks (e.g., ATT Labs has 192.20.225.0/24)Class D: 1110*Multicast groupsClass E: 11110*Reserved for future useThis is why folks use dotted-quad notation!CIDR: Hierarchal Address AllocationPrefixes are key to Internet scalabilityAddress allocated in contiguous chunks (prefixes)Routing protocols and packet forwarding based on prefixesToday, routing tables contain ~200,000 prefixes (vs. 4B)12.0.0.0/16:::12.1.0.0/1612.3.0.0/2412.2.0.0/1612.3.1.0/24::12.3.0.0/16:::12.0.0.0/812.3.254.0/2412.253.0.0/1912.253.32.0/1912.253.64.0/1912.253.96.0/1912.254.0.0/1612.253.128.0/1912.253.160.0/19Lecture 12Chapter 4. InternetworkingProblem: There Is More Than One Network 4.1 Simple Internetworking (IP) 4.2 Routing 4.3 Global Internet 4.3.1 Subnetting 4.3.2 Classless Routing (CIDR) 4.3.3 Interdomain Routing (BGP) 4.3.4 Routing Areas 4.3.5 IP Version 6 (IPv6) --4.3.3 Interdomain Routing (BGP) Internet and Autonomous SystemInterdomain RoutingPath-vector routingBGP--2“d: path (2,1)”“d: path (1)”31data trafficdata trafficdPath-Vector RoutingExtension of distance-vector routingSupport flexible routing policiesAvoid count-to-infinity problemKey idea: advertise the entire pathDistance vector: send distance metric per dest dPath vector: send the entire path for each dest d--2“d: path (2,1)”