TCPIP tutorial RFC 1180Word文档格式.docx

TCPIP tutorial RFC 1180Word文档格式.docx

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particularlyonthestepsinforwardinganIPdatagramfromsource

hosttodestinationhostthrougharouter.Itdoesnotspecifyan

Internetstandard.Distributionofthismemoisunlimited.

TableofContents

1.Introduction................................................1

2.TCP/IPOverview.............................................2

3.Ethernet....................................................8

4.ARP.........................................................9

5.InternetProtocol...........................................12

6.UserDatagramProtocol......................................22

7.TransmissionControlProtocol...............................24

8.NetworkApplications........................................25

9.OtherInformation...........................................27

10.References..................................................27

11.RelationtootherRFCs......................................27

12.SecurityConsiderations.....................................27

13.Authors'

Addresses..........................................28

1.Introduction

ThistutorialcontainsonlyoneviewofthesalientpointsofTCP/IP,

andthereforeitisthe"

barebones"

ofTCP/IPtechnology.Itomits

thehistoryofdevelopmentandfunding,thebusinesscaseforits

use,anditsfutureascomparedtoISOOSI.Indeed,agreatdealof

technicalinformationisalsoomitted.Whatremainsisaminimumof

informationthatmustbeunderstoodbytheprofessionalworkingina

TCP/IPenvironment.Theseprofessionalsincludethesystems

administrator,thesystemsprogrammer,andthenetworkmanager.

ThistutorialusesexamplesfromtheUNIXTCP/IPenvironment,however

themainpointsapplyacrossallimplementationsofTCP/IP.

Notethatthepurposeofthismemoisexplanation,notdefinition.

Ifanyquestionarisesaboutthecorrectspecificationofaprotocol,

pleaserefertotheactualstandardsdefiningRFC.

Socolofsky&

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RFC1180ATCP/IPTutorialJanuary1991

ThenextsectionisanoverviewofTCP/IP,followedbydetailed

descriptionsofindividualcomponents.

2.TCP/IPOverview

Thegenericterm"

TCP/IP"

usuallymeansanythingandeverything

relatedtothespecificprotocolsofTCPandIP.Itcaninclude

otherprotocols,applications,andeventhenetworkmedium.Asample

oftheseprotocolsare:

UDP,ARP,andICMP.Asampleofthese

applicationsare:

TELNET,FTP,andrcp.Amoreaccuratetermis

"

internettechnology"

.Anetworkthatusesinternettechnologyis

calledan"

internet"

.

2.1BasicStructure

Tounderstandthistechnologyyoumustfirstunderstandthefollowing

logicalstructure:

----------------------------

|networkapplications|

||

|...\|/..\|/...|

|----------|

||TCP||UDP||

|\/|

|--------|

||IP||

|------*------|

||ARP|||

|-----||

|\||

|------|

||ENET||

|---@--|

----------|-----------------

|

----------------------o---------

EthernetCable

Figure1.BasicTCP/IPNetworkNode

Thisisthelogicalstructureofthelayeredprotocolsinsidea

computeronaninternet.Eachcomputerthatcancommunicateusing

internettechnologyhassuchalogicalstructure.Itisthislogical

structurethatdeterminesthebehaviorofthecomputeronthe

internet.Theboxesrepresentprocessingofthedataasitpasses

throughthecomputer,andthelinesconnectingboxesshowthepathof

Kale[Page2]

data.ThehorizontallineatthebottomrepresentstheEthernet

cable;

the"

o"

isthetransceiver.The"

*"

istheIPaddressandthe

@"

istheEthernetaddress.Understandingthislogicalstructureis

essentialtounderstandinginternettechnology;

itisreferredto

throughoutthistutorial.

2.2Terminology

Thenameofaunitofdatathatflowsthroughaninternetis

dependentuponwhereitexistsintheprotocolstack.Insummary:

if

itisonanEthernetitiscalledanEthernetframe;

ifitisbetween

theEthernetdriverandtheIPmoduleitiscalledaIPpacket;

ifit

isbetweentheIPmoduleandtheUDPmoduleitiscalledaUDP

datagram;

ifitisbetweentheIPmoduleandtheTCPmoduleitis

calledaTCPsegment（moregenerally,atransportmessage）;

andifit

isinanetworkapplicationitiscalledaapplicationmessage.

Thesedefinitionsareimperfect.Actualdefinitionsvaryfromone

publicationtothenext.Morespecificdefinitionscanbefoundin

RFC1122,section1.3.3.

Adriverissoftwarethatcommunicatesdirectlywiththenetwork

interfacehardware.Amoduleissoftwarethatcommunicateswitha

driver,withnetworkapplications,orwithanothermodule.

Thetermsdriver,module,Ethernetframe,IPpacket,UDPdatagram,

TCPmessage,andapplicationmessageareusedwhereappropriate

2.3FlowofData

Let'

sfollowthedataasitflowsdownthroughtheprotocolstack

showninFigure1.ForanapplicationthatusesTCP（Transmission

ControlProtocol）,datapassesbetweentheapplicationandtheTCP

module.ForapplicationsthatuseUDP（UserDatagramProtocol）,data

passesbetweentheapplicationandtheUDPmodule.FTP（File

TransferProtocol）isatypicalapplicationthatusesTCP.Its

protocolstackinthisexampleisFTP/TCP/IP/ENET.SNMP（Simple

NetworkManagementProtocol）isanapplicationthatusesUDP.Its

protocolstackinthisexampleisSNMP/UDP/IP/ENET.

TheTCPmodule,UDPmodule,andtheEthernetdriveraren-to-1

multiplexers.Asmultiplexerstheyswitchmanyinputstooneoutput.

Theyarealso1-to-nde-multiplexers.Asde-multiplexerstheyswitch

oneinputtomanyoutputsaccordingtothetypefieldintheprotocol

header.

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123...n123...n

\|/|\||/^

\||/|\||/|

-------------flow----------------flow

|multiplexer|of|de-multiplexer|of

-------------data----------------data

||||

|v||

11

Figure2.n-to-1multiplexerand1-to-nde-multiplexer

IfanEthernetframecomesupintotheEthernetdriveroffthe

network,thepacketcanbepassedupwardstoeithertheARP（Address

ResolutionProtocol）moduleortotheIP（InternetProtocol）module.

ThevalueofthetypefieldintheEthernetframedetermineswhether

theEthernetframeispassedtotheARPortheIPmodule.

IfanIPpacketcomesupintoIP,theunitofdataispassedupwards

toeitherTCPorUDP,asdeterminedbythevalueoftheprotocol

fieldintheIPheader.

IftheUDPdatagramcomesupintoUDP,theapplicationmessageis

passedupwardstothenetworkapplicationbasedonthevalueofthe

portfieldintheUDPheader.IftheTCPmessagecomesupintoTCP,

theapplicationmessageispassedupwardstothenetworkapplication

basedonthevalueoftheportfieldintheTCPheader.

Thedownwardsmultiplexingissimpletoperformbecausefromeach

startingpointthereisonlytheonedownwardpath;

eachprotocol

moduleaddsitsheaderinformationsothepacketcanbede-

multiplexedatthedestinationcomputer.

DatapassingoutfromtheapplicationsthrougheitherTCPorUDP

convergesontheIPmoduleandissentdownwardsthroughthelower

networkinterfacedriver.

Althoughinternettechnologysupportsmanydifferentnetworkmedia,

Ethernetisusedforallexamplesinthistutorialbecauseitisthe

mostcommonphysicalnetworkusedunderIP.ThecomputerinFigure1

hasasingleEthernetconnection.The6-byteEthernetaddressis

uniqueforeachinterfaceonanEthernetandislocatedatthelower

interfaceoftheEthernetdriver.

Thecomputeralsohasa4-byteIPaddress.Thisaddressislocated

atthelowerinterfacetotheIPmodule.TheIPaddressmustbe

uniqueforaninternet.

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ArunningcomputeralwaysknowsitsownIPaddressandEthernet

address.

2.4TwoNetworkInterfaces

Ifacomputerisconnectedto2separateEthernetsitisasinFigure

3.

|------*----*------|

||ARP||||ARP||

|-----||-----|

|\||/|

|------------|

||ENET||ENET||

|---@-----@--|

----------|-------|---------

|---o---------------------------

|EthernetCable2

---------------o----------

EthernetCable1

Figure3.TCP/IPNetworkNodeon2Ethernets

Pleasenotethatthiscomputerhas2Ethernetaddressesand2IP

addresses.

Itisseenfromthisstructurethatforcomputerswithmorethanone

physicalnetworkinterface,theIPmoduleisbothan-to-m

multiplexerandanm-to-nde-multiplexer.

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\||/|\||/^

/||\|/||\|

/||\v/||\|

123...m123...m

Figure4.n-to-mmultiplexerandm-to-nde-multiplexer

Itperformsth