Chapter 6 ARP和RARP.ppt

yn@ 网络工程系 电子科大通信学院 Chapter 6 ARP and RARP ARP ARP package RARP Addresses Host identifier IP address Physical address Issues A送往E的分组需封装在Ethernet帧中传送 IP地址：全局性 物理地址：本地性 Address Mapping（地址映射） Logical address ?? Physical address ARP and RARP 6.1 ARP Address Resolution Protocol，RFC 826 地址解析协议：IP address ? MAC address 6.1.1 ARP Operation 用户输入命令“ftp 主机名”时的操作 IP Packet and ARP Packet 6.1.2 ARP Packet Encapsulation of ARP packet The byte order of ARP packet Example：Ethernet frame Example: ARP Request Packet Example: ARP Reply Packet 6.1.3 ARP Process Case 1：A ? B In same IP network Lab 2 Case 2：A ? D In different IP network Case 1：A ? B Case 2：A ? D Example A host with IP address 0 and physical address 0xB23455102210 has a packet to send to another host with IP address 5 and physical address 0xA46EF45983AB. The two hosts are on the same Ethernet network. Show the ARP request and reply packets encapsulated in Ethernet frames. Example: ARP Request 6.1.4 Proxy ARP Answer RFC 925: Multi-LAN Address Resolution Explicit subnets Transparent subnets（Extended ARP） RFC 1027: Using ARP to Implement Transparent Subnet Gateways Routers: Explicit subnets Hosts: Transparent subnets Discussion .3向.35发送IP分组 .3广播请求.35的ARP分组，R不转发广播 .35向.3发送IP分组 .35广播请求.62的ARP分组 6.1.5 Gratuitous ARP Duplicate address test 6.2 ARP Package Cache Table struct arpentry { /* format of entry in ARP cache */ short ae_state; /* state of this entry (see below) */ short ae_hwtype; /* hardware type */ short ae_prtype; /* protocol type */ char ae_hwlen; /* hardware address length */ char ae_prlen; /* protocol address length */ struct netif *ae_pni; /* pointer to interface structure */ int ae_queue; /* queue of packets for this address */ int ae_attempts; /* number of retries so far */ int ae_ttl; /* time to live */ u_char ae_hwa[MAXHWALEN]; /* Hardware address */ u_char ae_pra[MAXPRALEN]; /* Protocol address */ Output Module 睡眠，直到从IP进程收到IP分组 检查高速缓存表，寻找对应这个分组的目的IP地址的项目。 若找到 状态是RESOLVED