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Transcript
Chapter 14-16a Internet Routing Review 1 Introduction Motivation: Router performance is critical to overall performance and QoS in the Internet and private internetworks. Consider: – selecting best routes (optimize delay, load) – maintaining routing tables (router overhead) – router-generated management traffic Topics: – Overview of Graph Theory – Interior Routing Protocols – Exterior Routing Protocols Chapter 14-16: Internet Routing Review 2 Graph Theory and Networks Network Links Network Nodes Size of G: |E| = 10 Order of G: |V| = 6 Chapter 14-16: Internet Routing Review 3 Graph Theory and Networks Weighted Digraph to Represent Link Costs Chapter 14-16: Internet Routing Review 4 Spanning Trees Chapter 14-16: Internet Routing Review 5 Dijkstra’s Link-State Algorithm Based on breadth-first search Running time order of |V|2 Chapter 14-16: Internet Routing Review 8 Bellman-Ford Distance Vector Algorithm Running time order of |V| x |E| Chapter 14-16: Internet Routing Review 9 Ex: Dijkstra vs. Bellman-Ford Least-cost routing algorithms Chapter 14-16: Internet Routing Review 10 Interior/Exterior Routing Protocols C.b a Host h1 C A.a b Exterior routing between networks A and B A.c d A a b c Interior routing within network (AS) A Chapter 14-16: Internet Routing Review B.a a c B Host h2 b Interior routing within network (AS) B 11 Chapter 15 Interior Routing Protocols 12 Internet Routing Example Chapter 14-16: Internet Routing Review 13 Routing Table Fixed vs. Adaptive Routing? Chapter 14-16: Internet Routing Review 14 Routing Information Protocol (RIP) Distance Vector Algorithm Small networks Adaptive Uses UDP transport (port 520) – typically uses simple link delay count metric – fast and simple – max hop count = 15 (RIPv1) – updates sent approximately every 30 seconds – links are invalidated if no update in 180 seconds Chapter 14-16: Internet Routing Review 15 RIP Messages Command – 1 for request – 2 for reply Version – 1: RIPv1, RFC 1058 – 2: RIP-2, RFC 1723 Address Family ID – always 2 for IP addresses IP address – non-zero network portion – zero host portion Cost Metric – typically 1 (i.e. hop count) Chapter 14-16: Internet Routing Review 16 Open Shortest Path First Protocol (OSPF) Link-State Algorithm Preferred for TCP/IP-based internets Adaptive Sent as payload in IP datagram – Dijkstra’s Algorithm – uses flooding to advertise, request info – scale, TOS, hierarchy of areas, etc. – multiple metrics… monetary cost, reliability, throughput, delay, arbitrary – routers flood with new data when a significant change occurs Chapter 14-16: Internet Routing Review 17 Open Shortest Path First Protocol (Scale, Hierarchy) Chapter 14-16: Internet Routing Review 18 OSPF Messages OSPF Header Chapter 14-16: Internet Routing Review Version – 2: current version Type – 1: “Hello”, for discovery – 2: database structure – 3: request link-state – 4: update link-state – 5: acknowledge update Length of message Router ID – unique in a single area Area ID – unique to an AS Internet checksum Authentication Info – Type of authentication – 64 bit authentication value 19 Chapter 16a Exterior Routing Protocols 20 Exterior Routing BGP OSPF RIP Chapter 14-16: Internet Routing Review 21 Border Gateway Protocol (BGP-4) Path Vector Algorithm – cost metrics not used or advertised – each router specifies a complete path to all other nodes (e.g., from node A to node Z = ADFHKXZ) Facilitates routing based on policy instead of cost metrics – use preferred routes, providers (based on policy) – avoid competitors, poor performers, etc. Adaptive Uses TCP transport (port 179) – peers exchange updates on demand – nodes may choose not to participate Chapter 14-16: Internet Routing Review 22 Border Gateway Protocol Example B W X A C Y legend: provider network customer network (Stub AS) W, X, Y, A, B and C are networks Paths are specified as, for example: Path (w, y) = wACy Path (x, y) = xCy BGP routers advertise (update) only those routes that are specified by administrative policy would A advertise …ABx… or …ACx… ? Chapter 14-16: Internet Routing Review 23 BGP Messages Common Attributes Marker – synchronization and authentication mechanism Chapter 14-16: Internet Routing Review Length of message Type – open: establish a neighbor relationship – update: send/withdraw route information – keepalive: acknowledge or confirm relationship – notification: error detected 24