ApplicationLayer -1- Network Tools...Summary: Application Layer (1) • Domain Name System –Mapping host names to IP addresses • Host configuration –Obtaining an IP address •

Application Layer-1-

NetworkTools

2015,Lecture 08Kaan Bür

EITF25– Internet:TechnologyandApplications

PreviouslyonEITF25

• AddressingaboveIP– Ports, sockets

• Process-to-processdelivery• Transportlayerprotocols– TCP– UDP

• QualityofService2015-11-30 2EITF25– Internet:TechnologyandApplications

TransportLayer

Application layer

• Principlesofdigitalcommunications– Fromelectricalsignals tobitstopackets

• Usingthephysicalinfrastructure– Networkaccess

• Findingyourway– Addressing, routing

• Makinguseofitall– Applications

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Today:ApplicationLayer (1)

• DomainNameSystem,DNS[S24.2][F26.6]

• HostConfiguration,DHCP[S21.5][F18.4.4]

• DebuggingTools,ICMP[S14.3][F19.2]

• World-WideWeb,HTTP[S24.3][F26.1]

*[Kihl&Andersson:7.5,7.7,7.9,12.4]2015-11-30 4EITF25– Internet:TechnologyandApplications

MappinghostnametoIPaddress

• Applicationprotocolsusehostnames• TCP/IPprotocolsuiteusesIPaddresses• MappingfromhostnametoIPaddresses

• DomainNameSystem(DNS)– Domainnamespace– Domainnameresolution

• www.lth.se ≡130.235.209.2202015-11-30 EITF25– Internet:TechnologyandApplications 5

DomainNameSystem(DNS)

• Internet’stelephonebook:Address↔name– Oneofthemost important systemson theInternet

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Domainnamespace

• Namesmustbeunique– Completecontrolneeded

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Domainnamesandlabels

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Internetdomains

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Genericdomains

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se

lth

eit

eit.lth.se

…

Countrydomains

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Hierarchyofdomainnameservers

• 13logicalrootnameservers– implemented by376physicalservers

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Domains,subdomains,zones

Domain

• SubtreeofDNS

Zone

• Servers’controlarea

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Domainnameresolution

• Actionofaddressmapping– Client=resolver– Server=DNS

• Oneservercannothavealltheanswers!– Howtoaskothers?–Whattodowiththeanswer?

• Caching– Rememberwhatyou’ve learned!

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Recursiveresolution

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Iterativeresolution

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DomainnametoIPaddress (1)

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magi.magicnet.setroll.trollnet.se

1. magi.magicnet.se ?

ns.trollnet.se2015-11-30 EITF25– Internet:TechnologyandApplications

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DomainnametoIPaddress (2)

troll.trollnet.semagi.magicnet.se

ns.trollnet.se x.ns.se

2. magicnet.se ?

3. Ask ns.magicnet.se

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DomainnametoIPaddress (3)

troll.trollnet.semagi.magicnet.se

ns.trollnet.se ns.magicnet.se

4. magi.magicnet.se ?

5. IP = 194.52.54.47

6. IP = 194.52.54.47

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DomainnametoIPaddress (4)

troll.trollnet.semagi.magicnet.se

7. IP = 194.52.54.47

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Exercise: Breakthisviciouscycle!

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IPaddr.

DNS

TCPUDP

IP

DHCP

ObtaininganIPaddress

• DynamicHostConfigurationProtocol– Application layer

• DHCP– IPaddress• Allocationfrompoolorstatic

– Networkmask– Defaultgateway– DNSserver(s)

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DHCPoperation

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DHCPstates

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75%

Seeyouin15’:)

• Afterthebreak– Networkdebugging– ICMP–World-wide web

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DebuggingTools

• Applicationsusedfordebugging• Twoexamples– Ping– Traceroute

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Ping

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Traceroute

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InternetControlMessageProtocol

• ICMP• SupportprotocolforIP– Errorreporting– Query

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Encapsulation

• ICMPmessagesencapsulatedinIPpackets

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ICMPmessageformats

• Errorreporting

• Querymessages

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ICMPv4messagetypes

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• Routingupdateforhosts–Moreefficientwhen toomanyhosts

Redirection(errorreportingtype)

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DEFAULT ROUTER

Exercise: ICMPinaction

Q: Inwhatkindofnetworkcanahostneverreceivearedirectionmessage?

A: Inanetworkwithonlyonerouter

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Echorequestandreply (querytype)

• Ismydestinationalive?

• Networkdiagnostics– IPlayer

• Debuggingtools– Ping– Traceroute

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Traceroute

• Usedtotraceapacket’sroutefromsourcetodestination

• UsesthreeICMPmessages– EchoRequest (query)

– TimeExceeded (error)

– DestinationUnreachable (error)

• ManipulatesTTLfieldinIPheader• Uses‘wrong’ portnumber

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Traceroute

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Echo request

Applicationlayerparadigms

• Client-serverparadigm–WWW,Onlinegames,WebTV,Facebook

• Peer-to-peerparadigm– BitTorrent, Voddler, Skype

• Someapplicationsusebothparadigms– Spotify

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Client-serverparadigm

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Peer-to-peerparadigm

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Application:WWW

• TheideaoftheWorld-WideWeb(WWW)wasfirstproposedbyTimBerners-Lee in1989atCERN,theEuropeanOrganizationforNuclearResearch

• ThepurposewastoallowallCERNresearchersatdifferentlocationsthroughoutEuropetoaccesseachothers’ results

• ThecommercialWebstartedin1993.

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ComponentsofWWW

• Webdocuments(pages)– HyperTextMarkup Language (HTML) forstaticwebpages

– Script languages (PHP,ASP, JSP,CGIetc.)fordynamic

• UniversalResourceLocator(URL)– Standardwaytoidentify locationofwebdocuments

• HyperTextTransferProtocol(HTTP)– Protocol toaccessdocuments onawebserver

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UniversalResourceLocator(URL)

• Awebdocumenthasfouridentifiers– Protocol, Host,PortandPath.

• AURLisdefinedas– protocol://host:port/path

• StandardHTTPport80isisomitted– http://www.eit.lth.se/course/eitf25

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HypertextTransferProtocol(HTTP)

• Text-basedprotocol• Twobasictypesofmessages– RequestsandResponses

• SetsupandusesaTCPconnection

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Documentretrieval

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OperationofHTTP1.1

• Persistentconnection– OnlyoneTCPsession forallrequestsfromthesameserver.

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HTTPrequestandresponseformat

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HTTPmethodsinrequests

• Usingthese’methods’,clientsmayrequestcorrespondingactionsfromserver.

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Examplerequestandresponse

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Cookies

• OriginalWWWwasstateless– Eachrequest/response treatedseparately– Nohistoryofpreviousmessages

• Cookies– storeinformation aboutclient– introduce conceptofauser session

• Implementation(creationandstorage)ofcookiescanbedifferent,butsameconcept

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Cookies

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Summary: ApplicationLayer (1)

• DomainNameSystem–Mapping hostnamestoIPaddresses

• Hostconfiguration– Obtaining anIPaddress

• Debuggingtools– Ping, traceroute,ICMP

• Client-servervs.P2Papplications– www,http, cookies

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