IP子網(wǎng)劃分和VLSM

IPSubnettingandVLSM熊金波

福建師范大學軟件學院教學目標（Objectives

）1.IP地址表示（RepresentationofIPAddress）2.IP地址分類（ClassofIPAddress）3.保留和私有地址（ReservedandPrivateIPAddress）4.網(wǎng)絡(luò)掩碼和子網(wǎng)劃分（NetworkMaskandSubnetting

）5.可變長度子網(wǎng)掩碼（VLSM

）6.使用VLSM設(shè)計自己的網(wǎng)絡(luò)（DesignOurNetworkUsingVLSM）7.路由匯總（Summarization

）8.IP尋址故障診斷（IPAddressingTroublesDiagnosis）1IP地址表示（RepresentationofIPAddress）為了容易使用，采用點分十進制格式來表示IP地址TomaketheIPaddresseasiertouse,theaddressisusuallywrittenasfourdecimalnumbersseparatedbyperiods192.168.123.22IP地址的類別（ClassofIPAddress）3保留地址（ReservedAddress）

保留地址指某些地址不能分配網(wǎng)絡(luò)上的設(shè)備使用

Certainhostaddressesarereservedandcannotbeassignedtodevicesonanetwork.1.主機部分全0表示網(wǎng)絡(luò)地址AnIPaddressthathasbinary0sinallhostbitpositionsisreservedforthenetworkaddress.2.主機部分全1表示廣播地址AnIPaddressthathasbinary1sinallhostbitpositionsisreservedforthebroadcastaddress.

3.全0的IP地址，即0.0.0.0。設(shè)置缺省路由時使用。

AnIPaddressthathasbinary0sinallbitpositionsisreservedfordefaultroute4.全1地址255.255.255.255，表示泛洪廣播

AnIPaddressthathasbinary0sinallbitpositionsisreservedforfloodbroadcast私有地址（PrivateIPAddress）1.私有地址可以節(jié)省IP地址PrivateIPaddressesareanothersolutiontotheproblemoftheimpendingexhaustionofpublicIPaddresses.2.私有地址不能在Internet上被路由PrivateIPaddressesarenotroutedontheInternetbackbone.

Exercise:IPAddressClassesAddressClassNetworkHost10.2.1.1128.63.2.100201.222.5.64192.6.141.2130.113.64.16256.241.201.10IPAddressClassesExerciseAnswersAddressClassNetworkHost10.2.1.1128.63.2.100201.222.5.64192.6.141.2130.113.64.16256.241.201.10ABCCBNonexistent10.0.0.0128.63.0.0201.222.5.0192.6.141.0130.113.0.00.2.1.10.0.2.1000.0.0.640.0.0.20.0.64.16網(wǎng)絡(luò)掩碼的作用（FunctionofNetworkMask）10101100000100000000001010100000172.16.2.16011111111111111110000000000000000255.255.0.010101100000100000000000000000000172.16.0.0NetworkID4網(wǎng)絡(luò)掩碼（NetworkMask）A類：255.0.0.0B類：255.255.0.0C類：255.255.255.0

子網(wǎng)劃分（Subnetting）

為了克服有限的IP地址，所有類別網(wǎng)絡(luò)可以被劃分為更小的子網(wǎng)。ToefficientlymanagealimitedsupplyofIPaddresses,allclassescanbesubdividedintosmallersubnetworks.

劃分子網(wǎng)原因（ReasonsforSubnetting）1.提供靈活的編址ProvidesaddressingflexibilityProvides2.提供廣播抑制BroadcastContainment

3.為LAN提供低水平的安全

Low-levelsecurity

ontheLAN.簡單實例

（SimpleCase）介紹子網(wǎng)劃分（IntroductiontoSubnetting）網(wǎng)絡(luò)號碼主機號碼網(wǎng)絡(luò)號碼主機號碼網(wǎng)絡(luò)號碼主機號碼子網(wǎng)號碼不考慮子網(wǎng)網(wǎng)絡(luò)掩碼子網(wǎng)掩碼擴充的網(wǎng)絡(luò)號碼考慮子網(wǎng)化B類

介紹子網(wǎng)劃分（IntroductiontoSubnetting）劃分子網(wǎng)要從主機位借位Hostbitsmustarereassigned(or“borrowed”)asnetworkbits.

3bitsborrowedallows23-2or6subnets5bitsborrowedallows25-2or30subnets12bitsborrowedallows212-2or4094subnetsComparisonbetweendecimalandbinaryClasslessInter-DomainRouting(CIDR)

CIDR值:1.掩碼255.0.0.0:/8(A類地址默認掩碼)2.掩碼255.128.0.0:/93.掩碼255.192.0.0:/104.掩碼255.224.0.0:/115.掩碼255.240.0.0:/126.掩碼255.248.0.0:/137.掩碼255.252.0.0:/148.掩碼255.254.0.0:/159.掩碼255.255.0.0:/16(B類地址默認掩碼)10.掩碼255.255.128.0:/1711.掩碼255.255.192.0:/1812.掩碼255.255.224.0:/1913.掩碼255.255.240.0:/2014.掩碼255.255.248.0:/2115.掩碼255.255.252.0:/2216.掩碼255.255.254.0:/2317.掩碼255.255.255.0:/24(C類地址默認掩碼)18.掩碼255.255.255.128:/2519.掩碼255.255.255.192:/2620.掩碼255.255.255.224:/2721.掩碼255.255.255.240:/2822.掩碼255.255.255.248:/2923.掩碼255.255.255.252:/30ClasslessInter-DomainRouting(CIDR)

劃分子網(wǎng)的幾個捷徑

(ShortcutsofSubnetting)1、你所選擇的子網(wǎng)掩碼將會產(chǎn)生多少個子網(wǎng)?----2的x次方-2(x代表掩碼位，即2進制為1的部分)2、每個子網(wǎng)能有多少主機?----2的y次方-2(y代表主機位，即2進制為0的部分)3、合法子網(wǎng)是多少?----塊大小=256-10進制的子網(wǎng)掩碼(結(jié)果叫做blocksize或basenumber)，從0開始以塊大小遞增，即可得到合法子網(wǎng)。4、每個子網(wǎng)的廣播地址是?----廣播地址=下個子網(wǎng)號-15、每個子網(wǎng)的有效主機范圍分別是?----忽略子網(wǎng)內(nèi)全為0和全為1的地址剩下的就是有效主機地址。最后有效1個主機地址=下個子網(wǎng)號-2(即廣播地址-1)實例1：C類地址2位子網(wǎng)化

（

E.g1TwoBits

SubnettingforClassC

）子網(wǎng)號（Subnet）地址范圍（range）00000000000000001~001111111~62

其中:0為網(wǎng)絡(luò)地址，63為廣播地址010000006401000001~0111111165~127

其中:64為網(wǎng)絡(luò)地址，127為廣播地址1000000012810000001~10111111129~191

其中:128為網(wǎng)絡(luò)地址，191為廣播地址11000000~11111111193~255

其中:192為網(wǎng)絡(luò)地址，255為廣播地址實例2：C類地址4位子網(wǎng)化

（

E.g24Bits

SubnettingforClassC

）組合子網(wǎng)號地址范圍00000000000000001~000011111~15其中：15為廣播地址000100001600010001~0001111117~31其中：31為廣播地址001000003200100001~0010111133~47其中：47為廣播地址001100004800110001~0011111149~63其中：63為廣播地址010000006401000001~0100111165~79其中：79為廣播地址010100008001010001~0101111181~95其中：95為廣播地址011000009601100001~0110111197~111其中：111為廣播地址0111000011201110001~01111111113~127其中：127為廣播地址1000000012810000001~10001111129~143其中：143為廣播地址10010000~10011111145~159其中：159為廣播地址10100000~10101111161~175其中：175為廣播地址10110000~10111111177~191其中：191為廣播地址11000000~11001111193~207其中：207為廣播地址1101000020811010001~11011111209~223其中：223為廣播地址1110000022411100001~11101111225~239其中：239為廣播地址1111000024011110001~11111111241~255其中：255為廣播地址可用的子網(wǎng)和主機數(shù)

（NumberofUsableSubnetsandHosts

）usablesubnets＝(2powerofborrowedbits)–2usablehosts=(2powerofremaininghostbits)–2C類地址劃分子網(wǎng)情況匯總

（SummaryofClassCSubnetting）WrittenExercise:SubnetMasksAddressSubnetMaskClassSubnet172.16.2.1010.6.24.20201.222.10.60255.255.255.0255.255.240.0255.255.255.248SubnetMaskExerciseAnswersAddressSubnetMaskClassSubnet172.16.2.1010.6.24.20201.222.10.60255.255.255.0255.255.240.0255.255.255.248BAC172.16.2.010.6.16.0201.222.10.565可變長度子網(wǎng)掩碼（Variable-LengthSubnetMask）HQ172.16.0.0/16

可變長度子網(wǎng)掩碼（Variable-LengthSubnetMask）HQ172.16.1.0/24172.16.2.0/24HQ172.16.0.0/16

172.16.14.32/27

172.16.14.64/27

172.16.14.96/27

可變長度子網(wǎng)掩碼（Variable-LengthSubnetMask）CBA將子網(wǎng)172.16.14.0/24劃分為更小的子網(wǎng)，首先掩碼長度為27Subnet172.16.14.0/24isdividedintosmallersubnets:Subnetwithonemaskatfirst(/27)HQ172.16.1.0/24172.16.2.0/24HQ172.16.0.0/16

172.16.14.32/27

172.16.14.64/27

172.16.14.96/27

將沒有使用的掩碼長度為27的子網(wǎng)進一步劃分為掩碼長度為30Subnetwithonemaskatfirst(/27)Furthersubnetoneofthesesubnetsnotusedelsewhere(/30)CBAHQ172.16.1.0/24172.16.2.0/24HQ172.16.0.0/16

172.16.14.136/30172.16.14.132/30172.16.14.140/30可變長度子網(wǎng)掩碼（Variable-LengthSubnetMask）主機30臺以內(nèi)

計算VLSM（CalculatingVLSMs）SubnettedAddress:172.16.32.0/20

InBinary10101100.00010000.00100000.00000000計算VLSM（CalculatingVLSMs）VLSMAddress:172.16.32.0/26

InBinary10101100.00010000.00100000.00000000SubnettedAddress:172.16.32.0/20

InBinary10101100.00010000.00100000.00000000計算VLSM（CalculatingVLSMs）NetworkSubnetVLSMsubnetHost10101100.00010000.00100000.00000000=172.16.32.0/261stsubnet:VLSMAddress:172.16.32.0/26

InBinary10101100.00010000.00100000.00000000SubnettedAddress:172.16.32.0/20

InBinary10101100.00010000.00100000.00000000SubnettedAddress:172.16.32.0/20

InBinary10101100.00010000.00100000.00000000VLSMAddress:172.16.32.0/26

InBinary10101100.00010000.00100000.00000000

1stsubnet:10101100.00010000.00100000.00000000=172.16.32.0/26172.16.00100000.01000000=172.16.32.64/26172.16.00100000.10000000=172.16.32.128/26172.16.00100000.1000000=172.16.32.192/26172.16.00100001.00000000=172.16.33.0/26NetworkSubnetVLSMSubnetHost12ndsubnet:3rdsubnet:4thsubnet:5thsubnet:計算VLSM（CalculatingVLSMs）6練習：使用VLSM規(guī)劃自己的網(wǎng)路

（Exercise:DesignOurNetworkUsingVLSM）Derivedfromthe172.16.32.0/20Subnet(62Hosts)(62Hosts)(62Hosts)(62Hosts)Derivedfromthe172.16.33.0/26Subnet練習答案（ExerciseAnswer）172.16.33.0/30172.16.33.4/30172.16.33.8/30172.16.33.12/30Derivedfromthe172.16.33.0/26Subnet30-BitMask(2Hosts)172.16.32.0/26172.16.32.64/26172.16.32.128/26172.16.32.192/2626-BitMask(62Hosts)Derivedfromthe172.16.32.0/20Subnet7路由匯總（RouteSummarization）Routingtable172.16.25.0/24172.16.26.0/24172.16.27.0/24172.16.27.0/24172.16.26.0/24172.16.25.0/24A路由匯總（RouteSummarization）

路由協(xié)議能夠?qū)讞l路由條目匯總成一條RoutingprotocolscansummarizeaddressesofseveralnetworksintooneaddressIcanroutetothe

172.16.0.0/16network.

RoutingTable172.16.0.0/16BRoutingTable172.16.25.0/24172.16.26.0/24172.16.27.0/24172.16.27.0/24172.16.26.0/24172.16.25.0/24ARoutingTable172.16.16.0/20在一個位組內(nèi)匯總

（SummarizingwithinanOctet）172.16.168.0/24=10101100.00010000.10101000.00000000相同的位數(shù)為21（NumberofCommonBits=21）

不同位數(shù)11位（monBits=11）匯總：172.16.168.0/21（Summary:172.16.168.0/21）172.16.169.0/24=172 .16.10101001.0172.16.170.0/24=172 .16.10101010.0172.16.171.0/24=172 .16.10101011.0172.16.172