CS 118 Spring 2014 Chpt 4 Section 4C Transport Layer 3 1 Chapter 4 Network Layer 4 1 Introduction 4 2 Virtual circuit and datagram networks 4 3 What s inside a router 4 4 IP Internet Protocol Datagram format IPv4 addressing ICMP IPv6 4 5 Routing algorithms Link state Distance Vector Hierarchical routing 4 6 Routing in the Internet RIP OSPF BGP 4 7 Broadcast and multicast routing Network Layer 4 2 Internet Routing is hierarchical two levels aggregate routers into regions autonomous systems AS routers in same AS run same routing protocol Gateway router Direct link to router in another AS intra AS routing protocol routers in different AS may run different intra AS routing protocol Network Layer 4 4 Interconnected ASes 3c 3a 3b AS3 2a 1c 1a 1d 2c AS2 1b AS1 Intra AS Routing algorithm Inter AS Routing algorithm Forwarding table 2b forwarding table configured by both intra and inter AS routing algorithm intra AS sets entries for internal dests inter AS Intra As sets entries for external dests Network Layer 4 5 Inter AS tasks suppose router in AS1 receives datagram dest outside of AS1 router should forward packet to gateway router but which one AS1 must 1 learn which dests reachable through AS2 which through AS3 2 propagate this reachability info to all routers in AS1 Job of inter AS routing 3c 3a 3b AS3 2a 1c 1a 1d 2c AS2 2b 1b AS1 Network Layer 4 6 Example Setting forwarding table in router 1d suppose AS1 learns via inter AS protocol that subnet x reachable via AS3 gateway 1c but not via AS2 inter AS protocol propagates reachability info to all internal routers router 1d determines from intra AS routing info that its interface I is on the least cost path to 1c installs forwarding table entry x I x 3c 3a 3b AS3 2a 1c 1a 1d 2c 2b AS2 1b AS1 Network Layer 4 7 Example Choosing among multiple ASes now suppose AS1 learns from inter AS protocol that subnet x is reachable from AS3 and from AS2 to configure forwarding table router 1d must determine towards which gateway it should forward packets for dest x this is also job of inter AS routing protocol 3c 3b 3a AS3 x 2a 1c 1a 1d 2c AS2 2b 1b AS1 Network Layer 4 8 Chapter 4 Network Layer 4 1 Introduction 4 2 Virtual circuit and datagram networks 4 3 What s inside a router 4 4 IP Internet Protocol Datagram format IPv4 addressing ICMP IPv6 4 5 Routing algorithms Link state Distance Vector Hierarchical routing 4 6 Routing in the Internet RIP OSPF BGP 4 7 Broadcast and multicast routing Network Layer 4 10 Intra AS Routing also known as Interior Gateway Protocols IGP most common Intra AS routing protocols RIP Routing Information Protocol OSPF Open Shortest Path First IGRP Interior Gateway Routing Protocol Cisco proprietary Network Layer 4 11 Chapter 4 Network Layer 4 1 Introduction 4 2 Virtual circuit and datagram networks 4 3 What s inside a router 4 4 IP Internet Protocol Datagram format IPv4 addressing ICMP IPv6 4 5 Routing algorithms Link state Distance Vector Hierarchical routing 4 6 Routing in the Internet RIP OSPF BGP 4 7 Broadcast and multicast routing Network Layer 4 12 RIP Routing Information Protocol distance vector algorithm included in BSD UNIX Distribution in 1982 distance metric of hops max 15 hops From router A to subnets u v A z C B w x D destination hops u 1 v 2 w 2 x 3 y 3 z 2 y Network Layer 4 13 RIP advertisements distance vectors exchanged among neighbors every 30 sec via Response Message also called advertisement each advertisement list of up to 25 destination nets within AS Network Layer 4 14 RIP Example z w A x y D B C Destination Network to dest w y z x Next Router Num of hops A B B 2 2 7 1 Routing table in D Network Layer 4 15 RIP Example Dest w x z Next hops 1 1 C 4 w A Advertisement from A to D z x y D B C Destination Network to dest w y z x Next Router A B BA Routing table in D Num of hops 2 2 75 1 Network Layer 4 16 RIP Link Failure and Recovery If no advertisement heard after 180 sec neighbor link declared dead routes via neighbor invalidated new advertisements sent to neighbors neighbors in turn send out new advertisements if tables changed link failure info quickly propagates to entire net poison reverse used to prevent ping pong loops infinite distance 16 hops Network Layer 4 17 RIP Table processing RIP routing tables managed by application level process called route d daemon advertisements sent in UDP packets periodically repeated routed routed Transprt UDP network forwarding IP link physical Transprt UDP table forwarding table network IP link physical Network Layer 4 18 Chapter 4 Network Layer 4 1 Introduction 4 2 Virtual circuit and datagram networks 4 3 What s inside a router 4 4 IP Internet Protocol Datagram format IPv4 addressing ICMP IPv6 4 5 Routing algorithms Link state Distance Vector Hierarchical routing 4 6 Routing in the Internet RIP OSPF BGP 4 7 Broadcast and multicast routing Network Layer 4 19 OSPF Open Shortest Path First open publicly available uses Link State algorithm LS packet dissemination topology map at each node route computation using Dijkstra s algorithm OSPF advertisement carries one entry per neighbor router advertisements disseminated to entire AS via flooding carried in OSPF messages directly over IP rather than TCP or UDP Network Layer 4 20 OSPF advanced features not in RIP security all OSPF messages authenticated to prevent malicious intrusion multiple same cost paths allowed only one path in RIP For each link multiple cost metrics for different TOS e g satellite link cost set low for best effort high for real time integrated uni and multicast support Multicast OSPF MOSPF uses same topology data base as OSPF hierarchical OSPF in large domains Network Layer 4 21 Chapter 4 Network Layer 4 1 Introduction 4 2 Virtual circuit and datagram networks 4 3 What s inside a router 4 4 IP Internet Protocol Datagram format IPv4 addressing ICMP IPv6 4 5 Routing algorithms Link state Distance Vector Hierarchical routing 4 6 Routing in the Internet RIP OSPF BGP 4 7 Broadcast and multicast routing Network Layer 4 24 Internet inter AS routing BGP BGP Border Gateway Protocol the de facto standard BGP provides each AS a means to 1 2 3 Obtain subnet reachability information from neighboring ASs Propagate reachability information to all ASinternal routers Determine good routes to subnets based on reachability information and policy allows subnet to advertise its existence to rest of Internet I am here Network Layer 4 25 BGP basics pairs of routers BGP peers exchange routing info over semi permanent TCP
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