tcpipchapter7internetprotocol

1、internet protocol（ip）lrfc 791iplansmanswansicmpigmparprarpnetworknetworklayerlayernetworknetworkaccessaccesslayerlayerthe features of ip communicationlfeatureschapter 7 internet protocolldatagramlfragmentationloptionslchecksumlip packagedatagram（數(shù)據(jù)報）（數(shù)據(jù)報）ip headerversion fieldlver（version）: 4 bitshe

2、ader length fieldlhlen（header length）: 4 bitsdifferentiated services (type of service field)ltos（服務(wù)類型）：（服務(wù)類型）：8 bits早期早期differentiated services differentiated services code pointcode point，區(qū)分服務(wù)編碼點，區(qū)分服務(wù)編碼點type of service field（tos）ltostotal length fieldltotal length（總長度字段）：（總長度字段）：16 bitslincludes th

3、e headerl以字節(jié)單位以字節(jié)單位l總長度首部長度（即總長度首部長度（即4hlen）+ 數(shù)據(jù)長度數(shù)據(jù)長度fragmentation fieldslidentification（標識字段）：（標識字段）：16 bitsl源站每發(fā)送一個分組，標識值源站每發(fā)送一個分組，標識值1l（源（源ip地址，標識）地址，標識） 全網(wǎng)唯一全網(wǎng)唯一分組標識分組標識time to live fieldlttl（生存時間）：（生存時間）：8 bits，指明數(shù)據(jù)報生存時間，指明數(shù)據(jù)報生存時間protocol fieldl協(xié)議：協(xié)議：8 bitschecksum fieldl校驗和：校驗和：16 bitsl差錯檢測差錯

4、檢測option fieldl選項：選項：0 40 bytescopycopy 0 copy only in first fragment0 copy only in first fragment1 copy into all fragments1 copy into all fragmentsclassclass00 datagram control00 datagram control01 reserved01 reserved1010 debugging and management debugging and management1111 reserved reservednumber

5、number00000 end of option00000 end of option00001 no option00001 no option00011 loose source route00011 loose source route00111 record route00111 record route01001 strict source route01001 strict source routechapter 7 internet protocolldatagramlfragmentationloptionslchecksumlip package數(shù)據(jù)報的封裝（數(shù)據(jù)報的封裝（

6、encapsulation ）ethernet frame headerethernet frame headerip dataip dataip datagram example數(shù)據(jù)報大小與網(wǎng)絡(luò)數(shù)據(jù)報大小與網(wǎng)絡(luò)mtulmtu: maximum length of data that can be encapsulated in a frame mtu is dependent mtu is dependent on the on the physical physical networknetworkphysical networkmtuhyperchannel65535token ring

7、 (16 mbps)17914token ring (4 mbps)4464fddi4352ethernet1500數(shù)據(jù)報大小與網(wǎng)絡(luò)數(shù)據(jù)報大小與網(wǎng)絡(luò)mtul每個每個ip分組分組都封裝在都封裝在幀幀中傳輸中傳輸fragmentation (分片分片)lfragmentation: 在在mtu較小較小的網(wǎng)絡(luò)上，的網(wǎng)絡(luò)上，ip將較長的數(shù)據(jù)報將較長的數(shù)據(jù)報劃分成更小的部分（劃分成更小的部分（fragment）hdata 1600 bytesdata 2600 bytesdata 3200 bytes0 060060012001200offsetoffset = 0 = 0offset offset =

8、 600/8 = 75= 600/8 = 75offsetoffset = 1200/8 =150 = 1200/8 =150fragmentation operationlto be fragmented by and a la datagram can be fragmented more than oncelan ip header must be included in each fragmentfragmentation examplereassembly（重組操作（重組操作 ）lonly by lconnectionless 各分片的傳輸路徑可不同各分片的傳輸路徑可不同l有重組時限

9、有重組時限 reassembly timerl若丟失分片，則無法重組若丟失分片，則無法重組ip分組分組a ab b如何重組如何重組重組表重組表l重組表的功能：重組表的功能：分片長度分片長度=400offset=0m=1分片長度分片長度=400offset=50m=1分片長度分片長度=100offset=100m=0to process an ip packetl合法性檢查合法性檢查l分片與重組分片與重組l選項處理（自學(xué)）選項處理（自學(xué)）chapter 7 internet protocolldatagramlfragmentationloptionslchecksumlip packageop

10、tions（自學(xué)）（自學(xué)）ltypesstrict source route (嚴格源路由嚴格源路由)lformat 作用作用l嚴格按給定的嚴格按給定的ip地址逐跳轉(zhuǎn)發(fā)，中間不允地址逐跳轉(zhuǎn)發(fā)，中間不允許經(jīng)過其它許經(jīng)過其它ip地址地址fragmentation with optionsl哪些選項會復(fù)制到所有分片中？哪些只在第一哪些選項會復(fù)制到所有分片中？哪些只在第一個分片中出現(xiàn)？為什么？個分片中出現(xiàn)？為什么？l哪些選項用于數(shù)據(jù)報控制？哪些選項用于調(diào)試哪些選項用于數(shù)據(jù)報控制？哪些選項用于調(diào)試管理？管理？chapter 7 internet protocolldatagramlfragmentati

11、onloptionslchecksumlip packagechecksumlrfc 1071（rfc 1141，1624，1936），附錄），附錄clip分組的校驗和只包括分組的校驗和只包括分組首部分組首部，而不包括數(shù)據(jù)而不包括數(shù)據(jù)examplec code algorithm（frc1071）unsigned short cksum (char *addr, unsigned short count) register long sum = 0;while (count1) sum + = *(unsigned short *) addr+;count - = 2;if (count0)sum + = *(unsigned char *) addr;while (sum 16)sum = (su