ICMP:因特网控制报文协议(工 nternet Control Message Protocol) 口用于主机、路由器、网关之间交 换网络层信息 Type Code description O报告错误: unreachab|e 0 echo reply(ping host, network, port, dest network unreachable protoco 1 dest host unreachable o进行 request/epy应答 dest protocol unreachable ping命令) dest port unreachable 口同处于网络层但“凌驾”于IP 2367 dest network unknown 之上: dest host un known O ICMP报文需要IP分组来传 source quench(congestion 输 0333333489 control -not used echo request(ping 口ICMP报文:type, code plus route advertisement first 8 bytes of ip datagram 10 router dIscovery causing error 11 000000 TTL expired bad ip header 主讲人:西安交通大学程向前 第5讲网络层之二5b-4主讲人：西安交通大学 程向前 第5讲 网络层之二 5b-4 ICMP: 因特网控制报文协议(Internet Control Message Protocol)  用于主机、路由器、网关之间交 换网络层信息  报告错误: unreachable host, network, port, protocol  进行request/reply 应答 (ping命令)  同处于网络层但“凌驾”于 IP 之上:  ICMP报文需要 IP分组来传 输  ICMP 报文: 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