Basic Address Types ICMP: Internet Control Message rOToco unicast: Type Code descnption -level information est. network unreachable error reporti multicast. communication ICMP msgs carried in IP anycast: for one-to-nearest ICMP Message Formats ARP: Address Resolution Protocol s Each uestion: how to determine MAC address of B ARP module given B's IP address? ARP Table: IP/MAC ome Lan nodes e IP address: MAC address. typically 20 How do devices use arp tables ARP Table to send data? (1) 旦翻画 1616 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 91 Basic Address Types unicast: for one-to-one communication multicast: for one-to-many communication anycast: for one-to-nearest communication M M M A A A U 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 92 ICMP: Internet Control Message Protocol „ used by hosts, routers, gateways to communication network-level information „ error reporting: unreachable host, network, port, protocol „ echo request/reply (used by ping) „ network-layer “above” IP: „ ICMP msgs carried in IP datagrams „ ICMP message: type, code plus first 8 bytes of IP datagram causing error Type Code description 0 0 echo reply (ping) 3 0 dest. network unreachable 3 1 dest host unreachable 3 2 dest protocol unreachable 3 3 dest port unreachable 3 6 dest network unknown 3 7 dest host unknown 4 0 source quench (congestion control - not used) 8 0 echo request (ping) 9 0 route advertisement 10 0 router discovery 11 0 TTL expired 12 0 bad IP header 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 93 ICMP Message Formats 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 94 ARP: Address Resolution Protocol „ Each IP node (Host, Router) on LAN has ARP module, table „ ARP Table: IP/MAC address mappings for some LAN nodes < IP address; MAC address; TTL> < ………………………….. > „ TTL (Time To Live): time after which address mapping will be forgotten (typically 20 min) Question: how to determine MAC address of B given B’s IP address? 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 95 ARP Table 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 96 How do devices use ARP tables to send data?(1)