ARP protocol Routing in the Internet a knows b's IP address, wants to learn physical address of B The Global Internet consists of autonomous A broadcasts ARP query pkt, containing Bs Systems(AS)interconnected with each other IP address Stub As: small ce all machines on LAN receive ARP query Multihomed AS: large corporation(no transit) B receives ARP packet, replies to a with its Transit AS: provider (Bs) physical layer address A caches(saves)IP-to-physical address pairs Two-level rou until information becomes old (times out) Intra-AS istrator is responsible for choice soft state: information that times out (goes away) unless refresh Internet As Hierarchy Intra-AS Routing Inter-AS border (exterior gateway) routers Also known as Interior Gateway Protocols a Most common IGPs RIP: Routing Information Protocol OSPF: Open Shortest Path First IGRP: Interior Gateway Routing Protocol ntra-AS interior(gateway)routers RIP(Routing Information Protocol) RIP( Routing Information Protocol Distance vector algorithm Included in BSD-UNIX Distribution in 1982 Distance metric: of hops(max= 15 hops Network Next Router Num, of hops to dest Distance vectors: exchanged every 30 sec via Response Message(also called advertisement a Each advertisement: route to up to 25 destination nets20 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 115 ARP protocol „ A knows B's IP address, wants to learn physical address of B „ A broadcasts ARP query pkt, containing B's IP address „ all machines on LAN receive ARP query „ B receives ARP packet, replies to A with its (B's) physical layer address „ A caches (saves) IP-to-physical address pairs until information becomes old (times out) „ soft state: information that times out (goes away) unless refreshed 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 116 Routing in the Internet „ The Global Internet consists of Autonomous Systems (AS) interconnected with each other: „ Stub AS: small corporation „ Multihomed AS: large corporation (no transit) „ Transit AS: provider „ Two-level routing: „ Intra-AS: administrator is responsible for choice „ Inter-AS: unique standard 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 117 Internet AS Hierarchy Inter-AS border (exterior gateway) routers Intra-AS interior (gateway) routers 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 118 Intra-AS Routing „ Also known as Interior Gateway Protocols (IGP) „ Most common IGPs: „ RIP: Routing Information Protocol „ OSPF: Open Shortest Path First „ IGRP: Interior Gateway Routing Protocol (Cisco propr.) 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 119 RIP ( Routing Information Protocol) „ Distance vector algorithm „ Included in BSD-UNIX Distribution in 1982 „ Distance metric: # of hops (max = 15 hops) „ Can you guess why? „ Distance vectors: exchanged every 30 sec via Response Message (also called advertisement) „ Each advertisement: route to up to 25 destination nets 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 120 RIP (Routing Information Protocol) Destination Network Next Router Num. of hops to dest. w A 2 y B 2 z B 7 x -- 1 …. …. .... w x y z A C D B Routing table in D