lecture17-bgp-covid€¦ · telecom lbl a.b.0.0/16 cornell a.c.0.0/16 a.*.*.* is this way foo.com...
TRANSCRIPT
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ComputerNetworks:ArchitectureandProtocols
CS4450
Lecture17BGPrecap
Packetheaderasaninterface
RachitAgarwal
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Whatdoweknowsofar[1]…
• Networkperformancemetrics
• Transmissiondelay,propagationdelay,queueingdelay,bandwidth
• Sharingnetworks• Circuitswitching,packetswitching,andassociatedtradeoffs• WhyisInternetpacketswitched?
• Architecturalprinciplesanddesigngoals• Layeringprinciple,End-to-endprinciple,Fatesharingprinciple• ManyimportantdesigngoalsfromDavidClark’spaper
• Andmanyimportantmissinggoals
• Addressing• LinklayerMACnames,andscalabilitychallengesattheInternet
• NetworklayerIPaddresses:threerequirements,aggregation,CIDR
2
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Whatdoweknowsofar[2]…• LinkLayer
• SharingaBroadcastmedium,associatedchallenges,CSMA/CD
• Linklayeraddressing:MACnames
• WhyFrames?WhySwitchedEthernet?
• TheSpanningTreeProtocol(STP)
• NetworkLayer
• WhyNetworkLayer?WhynotjustuseSTPacrosstheInternet?
• IPAddressing
• RoutingTables:Acollectionofspanningtrees,oneperdestination
• GeneratingValidRoutingtables(withinadomain):
• Globalview(Link-StateProtocol),andlimitations
• Localview(Distance-vectorProtocol)
• GeneratingValidRoutingtables(acrossdomains):
• BorderGatewayProtocol,Internetstructure,routingpolicies3
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GoalsforToday’sLecture
• RecapIPaddressingandBGPquickly
• UnderstandIP(theInternetProtocol)
• PacketHeaderasanetwork“interface”
4
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NetworkLayer
• THEfunctionality:deliveringthedata
• THEprotocol:InternetProtocol(IP)
• Achievesitsfunctionality(deliveringthedata),usingthreeideas:
• Addressing(IPaddressing)
• Routing(usingavarietyofprotocols)
• Packetheaderasaninterface(Encapsulatingdataintopackets)
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Recap:Threerequirementsforaddressing
• Scalablerouting
• Howmuststatemustbestoredtoforwardpackets?
• Howmuchstateneedstobeupdateduponhostarrival/departure?
• Efficientforwarding
• Howquicklycanonelocateitemsinroutingtable?
• Hostmustbeabletorecognizepacketisforthem
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Recap:L2addressingdoesnotenablescalablerouting
• Scalablerouting
• Howmuchstatetoforwardpackets?
• Oneentryperhostperswitch
• Howmuchstateupdatedforeacharrival/departure?
• Oneentryperhostperswitch
• Efficientforwarding
• ExactmatchlookuponMACaddresses(exactmatchiseasy!)
• Hostmustbeabletorecognizethepacketisforthem
• MACaddressdoesthisperfectly
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Recap:Today’sInternetAddressing:CIDR
• ClasslessInter-domainRouting
• Idea:Flexibledivisionbetweennetworkandhostaddresses
• Prefixisnetworkaddress
• Suffixishostaddress
• Example:
• 128.84.139.5/23isa23bitprefixwith:
• First23bitsfornetworkaddress
• Next9bitsforhostaddresses:maximum2^9hosts
• Terminology:“Slash23”
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“InteriorRouters”
“AutonomousSystem(AS)”or“Domain” Regionofanetworkunderasingleadministrativeentity
“BorderRouters”
An“end-to-end”route
Recap:Whatdoesacomputernetworklooklike?
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AT&T a.0.0.0/8
France Telecom
LBL a.b.0.0/16
Cornella.c.0.0/16
a.c.*.* is this way
a.b.*.* is this way
Recap:IPaddressing->ScalableRouting?
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AT&T a.0.0.0/8
France Telecom
LBL a.b.0.0/16
Cornella.c.0.0/16
a.*.*.* is this way
foo.com a.d.0.0/16
Canaddnewhosts/networkswithoutupda^ngtherou^ngentriesatFranceTelecom
Recap:IPaddressing->ScalableRouting?
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AT&T a.0.0.0/8
LBL a.b.0.0/16
Cornella.c.0.0/16
ESNet
ESNetmustmaintainrou^ngentriesforbotha.*.*.*anda.c.*.*
Recap:IPaddressing->ScalableRouting?
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Recap:AdministrativeStructureShapesInter-domainRouting
● ASeswantfreedomtopickroutesbasedonpolicy● “Mytrafficcan’tbecarriedovermycompetitor’snetwork!”
● “Idon’twanttocarryA’strafficthroughmynetwork!”
● CannotbeexpressedasInternet-wide“leastcost”
● ASeswantautonomy● Wanttochoosetheirowninternalroutingprotocol
● Wanttochoosetheirownpolicy
● ASeswantprivacy● Choiceofnetworktopology,routingpolicies,etc.
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peer peerprovider customerRelationsbetweenASes
•Customerspayprovider•Peersdon’tpayeachother
BusinessImplications
Recap:BusinessRelationships
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● ASesprovide“transit”betweentheircustomers● Peersdonotprovidetransitbetweenotherpeers
trafficallowed trafficnotallowed
A B C
D E F
QPr Cu
Peer Peer
Recap:Inter-domainRoutingFollowstheMoney
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Recap:BGPInspiredbyDistanceVector
● Per-destinationrouteadvertisements
● Noglobalsharingofnetworktopology
● Iterativeanddistributedconvergenceonpaths
● But,fourkeydifferences
● BGPdoesnotpickshortestpaths● Path-vectorratherthandistancevector
▪ Eachannouncementcontainsthepathforeachdestination● Selectiverouteadvertisement
▪ IfIselectapath,Idon’t*haveto*advertiseittoothers● Routeaggregation
▪ Ratherthanstoringa.b.*.*/16anda.c.*.*/16,storea.*.*.*/8
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Recap:BGPOutline
● BGPPolicy● Typicalpoliciesandimplementation
● BGPprotocoldetails
● IssueswithBGP
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Recap:Policy:
Imposedinhowroutesareselectedandexported
Can reach 128.3/16
blah blah
Route selection
A
P
C
B
Q
Route export
● Selection:Whichpathtouse● Controlswhether/howtrafficleavesthenetwork
● Export:Whichpathtoadvertise● Controlswhether/howtrafficentersthenetwork
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Recap:TypicalExportPolicy
Destinationprefixadvertisedby…
Exportrouteto…
CustomerEveryone
(providers,peers,othercustomers)
Peer Customers
Provider Customers
Knownasthe“Gao-Rexford”rulesCapturecommon(butnotrequired!)prac^ce
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Recap:TypicalSelectionPolicy
● Indecreasingorderofpriority:1. Makeorsavemoney(sendtocustomer>peer>provider)
2. Maximizeperformance(smallestASpathlength)
3. Minimizeuseofmynetworkbandwidth(“hotpotato”)
4. …
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Recap:BGPimplicitdecisionmaking
● Exportpolicy● Givesasetof“possible”pathsforeachAS
● Selectionpolicy● Givesarankingoverallthepossiblepaths
GRIFFIN et al.: STABLE PATHS PROBLEM AND INTERDOMAIN ROUTING 235
Fig. 1. Stable paths problems with shortest path solutions.
, then . Therefore, any stable pathassignment implicitly defines a tree rooted at the origin. Note,however, that this is not always a spanning tree.The stable paths problem is solvable if there
is a stable path assignment for . A stable path assignment isalso called a solution for . If no such assignment exists, thenis unsolvable.Fig. 1(a) presents a stable paths problem called SHORTEST 1.
The ranking function for each nonzero node is depicted as avertical list next to the node, with the highest ranked path atthe top going down to the lowest ranked nonempty path at thebottom. The stable path assignment
is illustrated in Fig. 1(b). If we reverse the ranking order of pathsat node we arrive at SHORTEST 2, depicted in Fig. 1(c). Thestable path assignment
is illustrated in Fig. 1(d). In both cases, the ranking functionsprefer shorter paths to longer paths and the solutions are shortestpath trees. Note that the ranking at node 4 breaks ties betweenpaths of equal length. This results in one shortest path tree asthe solution for SHORTEST 1, while another shortest path tree asthe solution for SHORTEST 2.The ranking of paths is not required to prefer shorter paths
to longer paths. For example, Fig. 2(a) presents a stable pathsproblem called GOOD GADGET. Note that both nodes 1 and 2prefer longer paths to shorter paths. The stable path assignment
illustrated in Fig. 2(b) is not a shortest path tree. This is theunique solution to this problem.A modification of GOOD GADGET, called NAUGHTY GADGET,
is shown in Fig. 2(c). NAUGHTY GADGET adds one permitted path
Fig. 2. Stable paths problems that are not shortest path problems.
Fig. 3. DISAGREE and its two solutions.
(3 4 2 0) for node 3, yet it has the same unique solution as GOODGADGET. However, as is explained in Section IV, the protocolSPVP can diverge for this problem. Finally, by reordering theranking of paths at node 4, we produce a specification calledBAD GADGET, presented in Fig. 2(d). This specification has nosolution and the SPVP protocol will always diverge.So far, our examples each has had at most one solution. This
is not always the case. The simplest instance, called DISAGREE,having more than one solution is illustrated in Fig. 3(a). Thestable path assignment
is depicted in Fig. 3(b). An alternative solution
is shown in Fig. 3(c). No other path assignments are stable forthis problem.
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BGPExample(Allgood)GRIFFIN et al.: STABLE PATHS PROBLEM AND INTERDOMAIN ROUTING 235
Fig. 1. Stable paths problems with shortest path solutions.
, then . Therefore, any stable pathassignment implicitly defines a tree rooted at the origin. Note,however, that this is not always a spanning tree.The stable paths problem is solvable if there
is a stable path assignment for . A stable path assignment isalso called a solution for . If no such assignment exists, thenis unsolvable.Fig. 1(a) presents a stable paths problem called SHORTEST 1.
The ranking function for each nonzero node is depicted as avertical list next to the node, with the highest ranked path atthe top going down to the lowest ranked nonempty path at thebottom. The stable path assignment
is illustrated in Fig. 1(b). If we reverse the ranking order of pathsat node we arrive at SHORTEST 2, depicted in Fig. 1(c). Thestable path assignment
is illustrated in Fig. 1(d). In both cases, the ranking functionsprefer shorter paths to longer paths and the solutions are shortestpath trees. Note that the ranking at node 4 breaks ties betweenpaths of equal length. This results in one shortest path tree asthe solution for SHORTEST 1, while another shortest path tree asthe solution for SHORTEST 2.The ranking of paths is not required to prefer shorter paths
to longer paths. For example, Fig. 2(a) presents a stable pathsproblem called GOOD GADGET. Note that both nodes 1 and 2prefer longer paths to shorter paths. The stable path assignment
illustrated in Fig. 2(b) is not a shortest path tree. This is theunique solution to this problem.A modification of GOOD GADGET, called NAUGHTY GADGET,
is shown in Fig. 2(c). NAUGHTY GADGET adds one permitted path
Fig. 2. Stable paths problems that are not shortest path problems.
Fig. 3. DISAGREE and its two solutions.
(3 4 2 0) for node 3, yet it has the same unique solution as GOODGADGET. However, as is explained in Section IV, the protocolSPVP can diverge for this problem. Finally, by reordering theranking of paths at node 4, we produce a specification calledBAD GADGET, presented in Fig. 2(d). This specification has nosolution and the SPVP protocol will always diverge.So far, our examples each has had at most one solution. This
is not always the case. The simplest instance, called DISAGREE,having more than one solution is illustrated in Fig. 3(a). Thestable path assignment
is depicted in Fig. 3(b). An alternative solution
is shown in Fig. 3(c). No other path assignments are stable forthis problem.
1 2 3 4
R1 10 20 30 -
R2 130 20 30 430
AssumesaparticularadvertisementorderingMaylookdifferentwithdifferentordering
Inreal-world:orderingdependsonlatency,processingdelay,etc.
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BGP: Issues
● Reachability
● Security
● Convergence
● Performance
● Anomalies
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1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0
“1” prefers “1 3 0” over “1 0” to reach “0”
Example of Policy Oscillation
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Initially: nodes 1, 2, 3 know only shortest path to 0
1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0
Step-by-step Policy Oscillation
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1 advertises its path 1 0 to 2
1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0adve
rtise
: 1 0
Step-by-step Policy Oscillation
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1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0
Step-by-step Policy Oscillation
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1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0
advertise: 3 0
3 advertises its path 3 0 to 1
Step-by-step Policy Oscillation
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1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0
Step-by-step Policy Oscillation
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1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0withdr
aw: 1
0
1 withdraws its path 1 0 from 2
Step-by-step Policy Oscillation
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1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0
Step-by-step Policy Oscillation
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1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0
advertise: 2 0
2 advertises its path 2 0 to 3
Step-by-step Policy Oscillation
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1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0
Step-by-step Policy Oscillation
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1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0
withdraw: 3 0
3 withdraws its path 3 0 from 1
Step-by-step Policy Oscillation
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1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0
Step-by-step Policy Oscillation
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1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0
1 advertises its path 1 0 to 2ad
verti
se: 1
0
Step-by-step Policy Oscillation
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1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0
Step-by-step Policy Oscillation
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1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0
withdraw: 2 0
2 withdraws its path 2 0 from 3
Step-by-step Policy Oscillation
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1
2 3
1 3 0 1 0
3 2 0 3 0
2 1 0 2 0
0
We are back to where we started!
Step-by-step Policy Oscillation
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NetworkLayer
• THEfunctionality:deliveringthedata
• THEprotocol:InternetProtocol(IP)
• Achievesitsfunctionality(deliveringthedata),usingthreeideas:
• Addressing(IPaddressing)
• Routing(usingavarietyofprotocols)
• Packetheaderasaninterface(Encapsulatingdataintopackets)
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WhatisDesigningIP?
• Syntax:formatofpacket
• Nontrivialpart:packet“header”
• Restisopaquepayload(whyopaque?)
• Semantics:meaningofheaderfields
• Requiredprocessing
Opaque PayloadHeader
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PacketHeaderasInterface
• Thinkofpacketheaderasinterface
• Onlywayofpassinginformationfrompackettoswitch
• Designinginterfaces:
• Whattaskareyoutryingtoperform?
• Whatinformationdoyouneedtoaccomplishit?
• Headerreflectsinformationneededforbasictasks
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WhatTasksDoWeNeedtoDo?
• Readpacketcorrectly
• Getthepackettothedestination
• Getresponsestothepacketbacktosource
• Carrydata
• Tellhostwhattodowiththepacketoncearrived
• Specifyanyspecialnetworkhandlingofthepacket
• Dealwithproblemsthatarisealongthepath
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ReadingPacketCorrectly
• Wheredoestheheaderend?
• Wherethethepacketend?
• Whatprotocolareweusing?
• Whyisthissoimportant?
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GettingtotheDestination
• Providedestinationaddress
• Shouldthisbelocationoridentifier(name)?
• Andwhat’sthedifference?
• Ifahostmovesshoulditsaddresschange?
• Ifnot,howcanyoubuildscalableInternet?
• Ifso,thenwhatgoodisanaddressforidentification?
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GettingResponseBacktoSource
• Sourceaddress
• Necessaryforrouterstorespondtosource
• Whenwouldtheyneedtorespondback?
• Failures!
• Dotheyreallyneedtorespondback?
• Howwouldthesourceknowifthepackethasreachedthedestination?
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CarryData
• Payload!
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Questions?
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ListofTasks
• Readpacketcorrectly
• Getthepackettothedestination
• Getresponsestothepacketbacktosource
• Carrydata
• Tellhostwhattodowithpacketoncearrived
• Specifyanyspecialnetworkhandlingofthepacket
• Dealwithproblemsthatarisealongthepath
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TellingDestinationHowtoProcessPacket
• Indicatewhichprotocolsshouldhandlepacket
• Whatlayersshouldthisprotocolbein?
• Whataresomeoptionsforthistoday?
• Howdoesthesourceknowwhattoenterhere?
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SpecialHandling
• Typeofservice,priority,etc.
• Options:discusslater
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DealingWithProblems
• Ispacketcaughtinloop?
• TTL
• Headercorrupted:
• DetectwithChecksum
• Whataboutpayloadchecksum?
• Packettoolarge?
• Dealwithfragmentation
• Splitpacketapart
• Keeptrackofhowtoputtogether
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AreWeMissingAnything?
• Readpacketcorrectly
• Getthepackettothedestination
• Getresponsestothepacketbacktosource
• Carrydata
• Tellhostwhattodowithpacketoncearrived
• Specifyanyspecialnetworkhandlingofthepacket
• Dealwithproblemsthatarisealongthepath
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FromSemanticstoSyntax
• Thepastfewslidesdiscussedtheinformationtheheadermustprovide
• Willnowshowthesyntax(layout)ofIPv4header,anddiscussthe
semanticsinmoredetail
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IPPacketStructure
4-bit Version4-bit Header
Length8-bit Type of
Service (TOS)
16-bit Total Length (Bytes)
16-bit Identification 3-bit Flags 13-bit Fragment Offset
8-bit Time to Live (TTL)
8-bit Protocol 16-bit Header Checksum
32-bit Source IP Address
32-bit Destination IP Address
Options (if any)
Payload
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20BytesofStandardHeader,thenOptions
4-bit Version4-bit Header
Length8-bit Type of
Service (TOS)
16-bit Total Length (Bytes)
16-bit Identification 3-bit Flags 13-bit Fragment Offset
8-bit Time to Live (TTL)
8-bit Protocol 16-bit Header Checksum
32-bit Source IP Address
32-bit Destination IP Address
Options (if any)
Payload
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NextSetofSlides
• Mappingbetweentasksandheaderfields
• Eachofthesefieldsisdevotedtoatask
• Let’sfindoutwhichonesandwhy…
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GoThroughTasksOne-by-One
• Readpacketcorrectly
• Getthepackettothedestination
• Getresponsestothepacketbacktosource
• Carrydata
• Tellhostwhattodowithpacketoncearrived
• Specifyanyspecialnetworkhandlingofthepacket
• Dealwithproblemsthatarisealongthepath
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ReadPacketCorrectly
• Versionnumber(4bits)
• IndicatestheversionoftheIPprotocol
• Necessarytoknowwhatotherfieldstoexpect
• Typically“4”(forIPv4),andsometimes“6”(forIPv6)
• Headerlength(4bits)
• Numberof32-bitwordsintheheader
• Typically“5”(fora20-byteIPv4header)
• CanbemorewhenIPoptionsareused
• Totallength(16bits)
• Numberofbytesinthepacket
• Maximumsizeis65,535bytes(2^16-1)
• …thoughunderlyinglinksmayimposesmallerlimits
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FieldsforReadingPacketCorrectly
4-bit Version4-bit Header
Length8-bit Type of
Service (TOS)
16-bit Total Length (Bytes)
16-bit Identification 3-bit Flags 13-bit Fragment Offset
8-bit Time to Live (TTL)
8-bit Protocol 16-bit Header Checksum
32-bit Source IP Address
32-bit Destination IP Address
Options (if any)
Payload
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GettingPackettoDestinationandBack
• TwoIPaddresses
• SourceIPaddress(32bits)
• DestinationIPaddress(32bits)
• DestinationAddress
• Uniquelocatorforthereceivinghost
• Allowseachnodetomakeforwardingdecisions
• SourceAddress
• Uniquelocatorforthesendinghost
• Recipientcandecidewhethertoacceptpacket
• Enablesrecipienttosendareplybacktothesource
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FieldsforReadingPacketCorrectly
4-bit Version4-bit Header
Length8-bit Type of
Service (TOS)
16-bit Total Length (Bytes)
16-bit Identification 3-bit Flags 13-bit Fragment Offset
8-bit Time to Live (TTL)
8-bit Protocol 16-bit Header Checksum
32-bit Source IP Address
32-bit Destination IP Address
Options (if any)
Payload
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Questions?
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ListofTasks
• Readpacketcorrectly
• Getthepackettothedestination
• Getresponsestothepacketbacktosource
• Carrydata
• Tellhostwhattodowithpacketoncearrived
• Specifyanyspecialnetworkhandlingofthepacket
• Dealwithproblemsthatarisealongthepath
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TellingHostHowtoHandlePacket
• Protocol(8bits)
• Identifiesthehigherlevelprotocol
• Importantfordemultiplexingatreceivinghost
• Mostcommonexamples
• E.g.,“6”fortheTransmissionControlProtocol(TCP)
• E.g.,“17”fortheUserDatagramProtocol
IP HeaderTCP Header
IP HeaderTCP Header
Protocol = 6 Protocol = 17
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FieldsforReadingPacketCorrectly
4-bit Version4-bit Header
Length8-bit Type of
Service (TOS)
16-bit Total Length (Bytes)
16-bit Identification 3-bit Flags 13-bit Fragment Offset
8-bit Time to Live (TTL)
8-bit Protocol 16-bit Header Checksum
32-bit Source IP Address
32-bit Destination IP Address
Options (if any)
Payload
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SpecialHandling
• Type-of-Service(8-bits)
• Allowpacketstobetreateddifferentlybasedonneeds
• E.g.,lowdelayforaudio,highbandwidthforbulktransfer
• Hasbeenredefinedseveraltimes,nogeneraluse
• Options
• Abilitytospecifyotherfunctionality
• Extensibleformat
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ExamplesofOptions
• RecordRoute
• StrictSourceRoute
• LooseSourceRoute
• Timestamp
• Traceroute
• RouterAlert
• …
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PotentialProblems
• HeaderCorrupted:Checksum
• Loop:TTL
• Packettoolarge:Fragmentation
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PreventingLoops
• Forwardingloopscausepacketstocycleforever
• Astheseaccumulate,eventuallyconsumeallcapacity
• Time-to-live(TTL)Field(8-bits)
• Decrementedateachhop,packetdiscardedifreaches0
• …and“timeexceeded”messageissenttothesource
• Using“ICMP”controlmessage;basisfortraceroute
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TTLField
4-bit Version4-bit Header
Length8-bit Type of
Service (TOS)
16-bit Total Length (Bytes)
16-bit Identification 3-bit Flags 13-bit Fragment Offset
8-bit Time to Live (TTL)
8-bit Protocol 16-bit Header Checksum
32-bit Source IP Address
32-bit Destination IP Address
Options (if any)
Payload
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HeaderCorruption
• Checksum(16bits)
• Particularformofchecksumoverpacketheader
• Ifnotcorrect,routerdiscardspackets
• Soitdoesn’tactinbogusinformation
• Checksumrecalculatedateveryrouter
• Why?
• WhyincludeTTL?
• Whyonlyheader?
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ChecksumField
4-bit Version4-bit Header
Length8-bit Type of
Service (TOS)
16-bit Total Length (Bytes)
16-bit Identification 3-bit Flags 13-bit Fragment Offset
8-bit Time to Live (TTL)
8-bit Protocol 16-bit Header Checksum
32-bit Source IP Address
32-bit Destination IP Address
Options (if any)
Payload
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PacketHeaderasaninterface
• Uselesstolearntheheaderformatbyheart
• Ifyourememberthetasksthatneedtobeperformed…
• Understandingwhyheaderformatiswhatitis…
• Ingeneral:ifyouunderstandtheproblem,solutioniseasy
• Astheproblemevolves,youwillknowwheretolookforasolution
• TransitionfromIPv4toIPv6
• Graduallyhappening…
• Ifyouwanttolearnabit,seebackupslides
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Thisisitfortoday!
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IPv6
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IPv6
• Motivated(prematurely)byaddressexhaustion
• Addressfourtimesasbig
• SteveDeeringfocusedonsimplifyingIP
• Gotridofallfieldsthatwerenotabsolutelynecessary
• “SpringCleaning”forIP
• Resultisanelegant,ifunambitious,protocol
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IPv4andIPv6HeaderComparison
Version IHLType of Service (TOS)
Total Length
Identification Flags Fragment Offset
Time to Live (TTL) Protocol Header Checksum
Source Address
Destination Address
Options
Version Traffic Class Flow Label
Payload Length Next Header Hop Limit
Source Address
Destination Address
Field name kept from IPv4 to IPv6
Fields not kept in IPv6
Name and position changed in IPv6
New field in IPv6
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SummaryofChanges
• EliminatedFragmentation
• Eliminatedheaderlength
• EliminatedChecksum
• Newoptionsmechanism(nextheader)
• Expandedaddress
• AddedFlowLabel
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IPv4andIPv6HeaderComparison
Version IHLType of Service (TOS)
Total Length
Identification Flags Fragment Offset
Time to Live (TTL) Protocol Header Checksum
Source Address
Destination Address
Options
Version Traffic Class Flow Label
Payload Length Next Header Hop Limit
Source Address
Destination Address
Field name kept from IPv4 to IPv6
Fields not kept in IPv6
Name and position changed in IPv6
New field in IPv6
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PhilosophyofChanges
• Don’tdealwithproblems:leavetoends
• Eliminatedfragmentation
• Eliminatedchecksum
• WhyretainTTL?
• Simplifyhandling
• Newoptionsmechanism(usesnextheaderapproach)
• Eliminatedheaderlength
• Whycouldn’tIPv4dothis?
• Providegeneralflowlabelforpacket
• Nottiedtosemantics
• Providesgreatflexibility
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Traffic Class
IPv4andIPv6HeaderComparison
IHLType of Service (TOS)
Total Length
Identification Flags Fragment Offset
Time to Live (TTL) Protocol Header Checksum
Source Address
Destination Address
Options
Version Flow Label
Payload Length Next Header Hop Limit
Source Address
Destination Address
To Destination and Back (expanded)
Deal with Problems (greatly reduced)
Read Correctly (reduced)
Special Handling (Similar)
Version