TCPIP协议原理教学课件：Chapter 6 ARP and RARP

1、Chapter 6 ARP and RARPARPARP package（ARP软件包）RARP7/15/20221TCP/IP Protocol Suite两级地址IP分组交付到主机或路由器需要两级地址互连网级：逻辑地址标识主机/路由器全网统一编址，具有全局唯一性全局地址所有与互联网打交道的软件都要使用逻辑地址在Internet中，逻辑地址就是IP地址（32bit）物理网级：物理地址标识主机/路由器本地范围内具有唯一性，但在整个互联网内不一定具有全局唯一性本地地址分组需要通过物理网络才能到达路由器或主机以太网中，物理地址就是MAC地址（48bit）7/15/20222TCP/IP Proto

2、col SuiteMappingLogical address (IP)Physical addressNetworkData LinkPhysicalMappingTo：电子科技大学成都市建设北路2段4号单位名称（逻辑）单位地址（物理）7/15/20223TCP/IP Protocol Suite IssuesA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AA仅知道：IPA，MACA，IPEEthernet Frame：IP Packet？EBCD目的MAC类型FCS源MACMACA7/15/20224TCP/IP Protocol SuiteAddress

3、Mapping（地址映射）Logical address Physical addressStatic mapping映射表固定设置Dynamic mappingStatic TableLogical addressPhysical addressConsider:NIC changedMobile computerCacheLogical addressPhysical addressLook for the target on demanding, using dynamic Address Resolution Protocol 7/15/20225TCP/IP Protocol Sui

4、teARP and RARPARPLogical addressPhysical addressRARPLogical addressPhysical address7/15/20226TCP/IP Protocol SuiteARPAddress Resolution Protocol，RFC 826地址解析协议：IP address MAC addressIPLANsMANsWANsICMPIGMPARPRARPNetworkLayerNetworkAccessLayerTransport LayerApplication Layer7/15/20227TCP/IP Protocol Su

5、iteARP OperationA: E: Im looking for the physical address of a node whose IP address is: I am the node you are looking for, and my physical address is: 0005.5D06.1418RequestRequestRequestReplyRequestBroadcastUnicastB: C: D: IP addressMAC addressAs ARP Cache：0005.5D06.1418bind7/15/20228TCP/IP Protoco

6、l SuiteARP Cache ARP cacheTo maintain the recent mappings from logical addresses (IP) to hardware addresses (MAC)典型存活时间：2 minutesEssential to the efficient operation of ARP 举例：主机 ARP CacheC:arp aInterface: 8 - 0 x50002Internet AddressPhysical AddressType2 00-03-31-b5-50-00 Dynamic7/15/20229TCP/IP Pr

7、otocol Suite用户输入命令“ftp 主机名”时的操作FTPTCPIPARP以太网驱动程序主机名解析器以太网驱动程序以太网驱动程序主机名IP地址（1）（2）（3）（4）（6）ARPARPFTPTCPIP（5）（7）目的源7/15/202210TCP/IP Protocol SuiteARP PacketHardware TypeProtocol TypeHardware address lenProtocol address lenOperation Request 1, Reply 2Sender hardware address（For example，6 bytes for Et

8、hernet）Sender protocol address（For example，4 bytes for IP）Target hardware address（For example，6 bytes for Ethernet）Target protocol address（For example，4 bytes for IP）It is not filled in a request7/15/202211TCP/IP Protocol SuiteEncapsulation of ARP packetThe byte order of ARP packetExample：Ethernet f

9、rameHTypePTypeHLPLOPsMACsIPtMACtIP222116644byteARP Packet目的MAC类型FCS源MACPacket66246 15004pad28 bytes460 x0806byte7/15/202212TCP/IP Protocol SuiteExample: ARP Request Packet7/15/202213TCP/IP Protocol SuiteExample: ARP Reply Packet7/15/202214TCP/IP Protocol SuiteIP Packet and ARP PacketIPIPIPIPARP requ

10、estARP replyIP packetBindingIP packetIP packetIP packetNo binding7/15/202215TCP/IP Protocol SuiteARP ProcessCase 1：A BIn same IP networkCase 2：A DIn different IP networkACBDR1R2IPA，MACAIPB，MACBIPC，MACCIPD，MACDIP1MAC1IP2MAC2IP3MAC3IP4MAC47/15/202216TCP/IP Protocol SuiteCase 1：A BACBDR1R2IPA，MACAIPB，M

11、ACBIPC，MACCIPD，MACDIP1MAC1IP2MAC2IP3MAC3IP4MAC4IP AddressMAC AddressAs ARP Cache：IPBMACBBs ARP Cache：IPAMACAR1s ARP Cache：IPAMACAsIP=IPA，dIP=IPBARPrequestARPrequestARPrequestARPrequestARPreplyIPIPsMAC=MACA，dMAC=MACBsIP=IPA，dIP=IPBdMAC=广播，Target_IP=IPBSender hardware address: MACASender protocol addr

12、ess: IPATarget hardware address: 0 x00000000Target protocol address: IPBSender hardware address: MACBSender protocol address: IPBTarget hardware address: MACATarget protocol address: IPA7/15/202217TCP/IP Protocol SuiteCase 2：A DACBDR1R2IPA，MACAIPB，MACBIPC，MACCIPD，MACDIP1MAC1IP2MAC2IP3MAC3IP4MAC4IP A

13、ddressMAC AddressAs ARP Cache：IP1MAC1Bs ARP Cache：IPAMACAR1s ARP Cache：IPAMACAsIP=IPA，dIP=IPDARPrequestARPrequestARPrequestARPrequestARPreplyIPIPsMAC=MACA，dMAC=MAC1sIP=IPA，dIP=IPDdMAC=广播，Target_IP=IP1IPD不在本网内，分组由R1转发sMAC=MAC2，dMAC=MAC3sIP=IPA，dIP=IPDsMAC=MAC4，dMAC=MACDsIP=IPA，dIP=IPDIP1是A的缺省网关（Defau

14、lt Gateway）7/15/202218TCP/IP Protocol Suite关键问题：ARP解析谁的IP地址？7/15/202219TCP/IP Protocol SuiteExampleA host with IP address 0 and physical address 0 xB23455102210 has a packet to send to another host with IP address 5 and physical address 0 xA46EF45983AB. The two hosts are on the same Ethernet network

15、. Show the ARP request and reply packets encapsulated in Ethernet frames.7/15/202220TCP/IP Protocol SuiteExample: ARP Request7/15/202221TCP/IP Protocol SuiteExample: ARP Request7/15/202222TCP/IP Protocol SuiteProxy ARP（代理ARP）Proxy ARP: 产生子网效应代表另一个物理网络中一组主机回答ARP Request，在ARP Reply中通告自己的MAC地址（即将解析的IP与

16、代理ARP的MAC绑定）To fool the sender of the ARP request into thinking that the router is the destination host, when in fact the destination host is on the other side of the router “Honest”HidedQ: In the same IP network or not?7/15/202223TCP/IP Protocol SuiteAnswerRFC 925: Multi-LAN Address ResolutionExpli

17、cit subnetsTransparent subnets（Extended ARP）RFC 1027: Using ARP to Implement Transparent Subnet GatewaysRouters: Explicit subnetsHosts: Transparent subnets“ From the host point of view, there are no subnets, and their physical networks are simply one big IP network. ”7/15/202224TCP/IP Protocol Suite

18、Proxy ARP功能To be used to create a subnetting effect 两个物理网络，具有相同网络地址（即不需要重新划分子网）使用路由器分别连接这两个网络，并执行ARP代理，实现两个逻辑子网方案：路由器上运行Proxy ARP软件 transparent subnet gateway当路由收到对特定主机的ARP请求时，用自己的物理地址（接收端口）进行ARP应答代理ARP应答的条件（同时满足）：与源站点不在同一逻辑子网的主机路由器有到达该节点的路由（非默认路由）且路由表项记录的发送接口接收该ARP请求的接口关键：创建子网，但不需要重新划分子网地址7/15/2022

19、25TCP/IP Protocol SuiteDiscussion.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R/24Main network2/27Hided network.00.201 IP发送失败 IP发送成功 ARP失败 ARP成功设想：R代替.35向.3返回ARP应答 Proxy ARP（RFC 925）7/15/202226TCP/IP Protocol SuiteGratuitous ARP功能：Duplicate address testAB441. ARP re

20、quest: sIP = tIP = 42. ARP reply: sIP = tIP = 43. Disable local interface: 4Startup orChange IP addressW. Stevens, TCP/IP Illustrated Volume 1: The Protocol7/15/202227TCP/IP Protocol SuiteGratuitous ARP PacketThe same sender and target IP address7/15/202228TCP/IP Protocol SuiteChapter 6 ARP and RARP

21、ARPARP package（ARP软件包）RARP7/15/202229TCP/IP Protocol SuiteARP Package7/15/202230TCP/IP Protocol SuiteARP CacheHost（Windows XP）Router（Cisco）C: arp aInterface: 4 - 0 x2 Internet Address Physical Address Type 3 00-90-27-a7-98-41 dynamic 7 00-90-27-1d-d9-94 dynamic 2 00-90-27-1a-67-e7 dynamicRouter# sho

22、w arpProtocol Address Age (min) Hardware Addr Type InterfaceInternet 3 - 0090.27a7.9841 ARPA Ethernet0Internet 4 5 0005.5d06.1418 ARPA Ethernet0Internet - 00e0.7bc0.b205 ARPA Ethernet17/15/202231TCP/IP Protocol Suite思考更新ARP绑定时，发现已有的绑定与新的绑定不一样，是保持已有的还是替换它？封装IP报文的以太帧中的源MAC和IP报文中的源IP可否用于刷新ARP表项？目的MAC和目

23、的IP呢？教材中ARP输入模块描述与RFC 826中的Packet Reception一节有矛盾7/15/202232TCP/IP Protocol SuiteRFC ReferencesRFC 1122: Requirements for Internet Hosts - Communication LayersSection 2.3.2: ARP cache, ARP packet queueRFC 1812: Requirements for IPv4 RoutersSection 3.3.2RFC 1433: Directed ARPARP helper addressRFC 1868: ARP Extension UNARPAnnounce leaving