DNS & BIND - stud.netgroup.uniroma2.itstud.netgroup.uniroma2.it/cgrl/2015/slides/dns.pdf · Before...

DNS&BIND

LorenzoBraccialeMarcoBonola

Whynametransla9on

Needfornametransla9on •  ini9allybecause>y2isbe>erthanport21•  …imagineIPV6!

–  2002:a050:6768:0:e2f8:47ff:fe38:c5cc:(mypc)•  Importantalsofor:

–  loadbalancing–  decouplingIPandname(i.e.whenchanginghos9ng)–  manyotherthings(e.g.an9-spam!)

•  Wheretostudy:–  DnsandBIND(O’reilly)–  ProDNSandBIND(Aitchison)

BeforeDNS…

•  Trytoputin/etc/hosts:–  63.135.91.11facebook.com

•  Inefficiencies:trafficload,namecollisions,consistencies

127.0.0.1localhost

•  EachcomputerhasHOSTS.txt– s9llusedinallopera9ngsystem,checkyourone!

THERE!

Simplesolu9on

Resolvethatname

Here’sthenumber! DB

nameserverhost

OnInternet–  needofascalablesolu9on(today>~284Mdomains1)–  avoidnamecollision–  reliability–  introducehierarchicalnames:www.example.com.–  Keyconcept:authorityanddelega:on

“silentdot”

1h"ps://investor.verisign.com/releasedetail.cfm?releaseid=892548

InternetDomainNameSystem•  DNS'sdistributeddatabaseisindexedbydomainnames•  Eachdomainnameisessen9allyjustapathinalargeinvertedtree,

calledthedomainnamespace•  Eachnodeinthetreehasatextlabel(withoutdots)thatcanbeup

to63characterslong•  Thefulldomainnameofanynodeinthetreeisthesequenceof

labelsonthepathfromthatnodetotheroot•  Anabsolutedomainnameisalsoreferredtoasafullyqualified

domainname,okenabbreviatedFQDN•  DNSrequiresthatsiblingnodes−nodesthatarechildrenofthe

sameparent−havedifferentlabels.Thisrestric9onguaranteesthatadomainnameuniquelyiden9fiesasinglenodeinthetree(easiercollisionavoidance)

•  ScalabilityisreachedthroughDELEGATION

InternetDomainNameSystemRoot

gTLD:.com,.org,.net…

ccTLD:.it,.us,.

SLD:uniroma2.it,google.com,example.com

TLDs

SLDs

ADomainisastringrepresen9ngtherealmofanAuthorityforroot:IANA(departementofICANN—www.icann.org/)for.it:is@Is9tutoperleApplicazioniTelema9chedelCNR,PISA.

FirstexperimentbyPaulMockapetris1983

generic countrycode

Top-LevelDomains

SecondLevelDomains

HigherLevelDomains…

DNSTree•  Theadministra9ve

responsibilityofpartoftheDomainNameSpacecanbedelegated:thisiscalledazone

•  Thezonecansub-delegate

•  Zonearerepresentedusingzonefiles(RFC1034-1035)

“”

it.de.com…

virgilio Im uniroma2…

ingeconomia… le"ere

AZonedelegatedbytheRootAuthoritytothe“IT”Authority

AZonesub-delegatedtouniroma2

ResourceRecords

•  EveryofthetreecouldhavesomeResourceRecordsthatcontaininforma9onaboutthedomainname– RRhavedifferentstandardizedtypes(e.g.A,PTR,MX)

– Forinstance,theIPv4Addressassociatedwithaname(ResourceRecordoftypeA)

Registrar,Registry,Maintainer

•  Registry:databaseofalldomainnamesregisteredinatop-leveldomainorsecond-leveldomainextension

•  Registrar:frontendtothepublic–  accreditedbyagTLDorccTLD:

•  Exampleh>p://www.nic.it/cgi-bin/List/index.cgi– Workswith“webpages”(asynchronous)

•  Maintainer:frontendtothepublic•  accreditedbyagTLDorccTLD•  WorkswithFAX(synchronous)OBSOLETE*

*From1July2010nomoremaintainercontractsfor.itdomains(source:registro.it)

Whoisaquilante:~orazio$whoisuniroma2.itDomain:uniroma2.itCreated:1997-12-0300:00:00LastUpdate:2013-03-0812:19:02ExpireDate:2014-01-14RegistrantName:Universita'degliStudidiRoma"TorVergata"Organiza9on:Universita'degliStudidiRoma"TorVergata"ContactID:UNIV86(….)AdminContact(…)TechnicalContacts(…)RegistrarOrganiza9on:Universita'degliStudidiRoma"TorVergata"Name:UNIROMA2-REGNameserversdns.uniroma2.itdns1.uniroma2.itns1.garr.net

Upda9ngnames:let’sbuya“domain”

•  Aregistrarinteractswithpublic,storedetailedinforma9on,andpassa“digest”toregistryoperator.

•  Registryoperatorbuilda“zonefile”(i.e.Datadescribingthedomain)andpassittointerestedTLD

•  Periodically,ICANNdistributea“TLDmasterfile”toeachRootServer.

Me Registrar

buyuniroma4.com

registryoperator

toTLDDNS

toTLDDNS

zonefile

www.example.com

•  Thedomainnameexample.comwasdelegatedfromagTLDauthority,whichinturnwasdelegatedfromICANN(authorityforDNSRootZone)

•  Theownerofthedomainchoosesthewwwpart(calledhostname)

•  ThisisaFullyQualifiedDomainName(FQDN)– specifiesanexactloca9onintheDNStreehierarchy

DNSImplementa9on

•  Exactlymapsthedomainnamedelega9onstructure

RootDNS

TLDDNS

DomainDNS

13root-servers(froma.root-servers.nettom)

Rootservers(anycast)

ADNScomprehends:

1.  Zonefiles–  translatesthedomainnamesintoopera9onalen99es,suchashosts,mailservers,servicesforusebyDNSsokware.

– standardwithResourceRecords(RFC1035,soportable!)

2.  DNSprogram3.  Resolverlibrary(asktheques9ons)

DNSQueries:itera9vevsrecursiveQuerywww.uniroma2.it

referralto.itccTLDDNS

rootserver

Querywww.uniroma2.it

referraltouniroma2.itDNS

TLDDNS

Querywww.uniroma2.it

Authorita9veanswer

DomainDNS

RootServers:responsetoonlyitera9vequeries

DNSQueries:itera9vevsrecursivei.e.findananswer

Clients:emitsrecursivequeries

DNSQueriestraceinh>p://stud.netgroup.uniroma2.it/cgrl/2012/traces/dns.pcap

DnsResponse

DNSResolver

•  Theclient-sideoftheDNSisusuallycalledaDNSresolver.

•  OnPC,weusuallyhavesimpleresolvers(called"stubresolvers")thatcannotfollowreferrals– NeedarecursiveDNS

•  Browserusegethostbynameorgethostbyaddrmethodstoinvokename/ipresolu9on–  func9onsprovidedbythestubresolver

Dig

debianpackage:dnsu:lsroot@ale:~#digwww.uniroma2.it;<<>>DiG9.7.3<<>>www.uniroma2.it;;globalop9ons:+cmd;;Gotanswer:;;->>HEADER<<-opcode:QUERY,status:NOERROR,id:31347;;flags:qrrdra;QUERY:1,ANSWER:2,AUTHORITY:2,ADDITIONAL:0;;QUESTIONSECTION:;www.uniroma2.it. IN A;;ANSWERSECTION:www.uniroma2.it. 3600 IN CNAME webhouse01.ccd.uniroma2.it.webhouse01.ccd.uniroma2.it.3600IN A 160.80.2.46;;AUTHORITYSECTION:ccd.uniroma2.it. 3600 IN NS dns1.uniroma2.it.ccd.uniroma2.it. 3600 IN NS dns.uniroma2.it.;;Query9me:53msec;;SERVER:213.133.99.99#53(213.133.99.99);;WHEN:ThuMar2218:35:152012;;MSGSIZErcvd:115

Dig

Examples:•  [email protected]

–  resolvewiththe8.8.8.8DNS•  [email protected]+trace

–  recursivelydoallthequeries•  dig.ns+short

–  showinshortformallthensfieldsofrootservers•  dig-x204.152.184.167+short

–  reverselookup

tcpdumpfordns

tcpdump–n–tportdomain–iany–s0IP192.168.0.111.3072>192.168.0.11.53:

34896+A?www.uniroma2.it.(36)

Fields:QueryID(+=recursionpreferred)Querytype(findArecord)Queryvalue(for?www.uniroma2.it.)Lenghtofpkt

MasterSlaveconfigura9on

•  redundancyforloadbalancingandfaultresilience

•  zonesarepassedfrommastertoslave–  fullorpar9alzonetransfer

•  9ming?

master slave

SOArequest

SOAresponse

AXFRrequest

En9reZone

ZoneFile:Example$ORIGINexample.com.;changesthe'zonename'whichisaddedtoany'unqualified'name$TTL1h;defaultexpira9on9meTTLvalueexample.com.INSOAns.example.com.myemail.example.com.(2007120710;serialnumberofthiszonefile1d;slaverefresh(1day)2h;slaveretry9meincaseofaproblem(2hours)4w;slaveexpira9on9me(4weeks)1h;maximumcaching9meincaseoffailedlookups(1hour))example.com.NSns;ns.example.comisanameserverforexample.comexample.com.NSns.somewhere.example.;abackupnameserverforexample.comexample.com.MX10mail.example.com.;[email protected].;equivalenttoaboveline,"@"representszoneorigin@MX50mail3;equivalenttoaboveline,butusingarela9vehostnameexample.com.A192.0.2.1;IPv4addressforexample.com AAAA2001:db8:10::1;IPv6addressforexample.comnsA192.0.2.2;IPv4addressforns.example.comAAAA2001:db8:10::2;IPv6addressforns.example.commailA192.0.2.3;IPv4addressformail.example.com,

mail2A192.0.2.4;IPv4addressformail2.example.commail3A192.0.2.5;IPv4addressformail3.example.comwwwCNAMEexample.com.;www.example.comisanaliasforexample.com

direc9ves

RFC1035

SOARR

NSRR

MXRR

AandAAAARR

CNAMERR

ResourceRecords(RR)

•  AStartofAuthority(SOA)RR:–  describesglobalcharacteris9csofthezonedomain–  oneandonlyoneforeachzonefile(firstRRinazonefile)

•  NameServer(NS)RR:Definesnameserversthatareauthorita9veforthezoneordomain.TheremustbetwoormoreNSResourceRecordsinazonefile.NSRRsmayreferenceserversinthisdomainorinaforeignorexternaldomain.TheseRRsaremandatory.

•  MailExchanger(MX)RR:Definesthemailserversforthezone(op9onal)•  Address(A)RR:DefinetheIPv4addressofallthehosts(orservices)that

existinthiszoneandwhicharerequiredtobepubliclyvisible.IPv6entriesaredefinedusingAAAA(calledQuadA)RRs(op9onal)

•  CanonicalName(CNAME)RR:DefinesanAliasRR,whichallowsonehost(orservice)bedefinedasthealiasnameforanotherhost(op9onal)

•  And:PTR,TXT,AAAA,SRVandNSEC,RRSIG,DS,DNSKEY,KEY(DNSSEC)

Syntax:SOARR•  Specifiesauthorita9veinforma9onaboutaDNSzone

•  Severalparameters–  serial:date(conven9on:YYYYMMDDSS)–  refresh:telltoslavehowokencheckforchanges(default3600)

–  retry:intervalbetweentwosubsequenta>empttocontactthemasterincaseofproblems(default600)

–  expire:ifslavefailstocontactmasterakerexpire9me,itstopstoresolvethatzone(default86400)

– >lTheminimum9me-to-livevalueappliestoallresourcerecordsinthezonefile(default3600)

ZoneDomain Class RR NS emaildnsmaster

example.com. IN SOA ns.example.com. email.example.com.

Syntax:NSRR•  DelegatesaDNSzonetousethegivenauthorita9vename

servers

•  Thenamefieldcanbeanyof:–  AFullyQualifiedDomainName(FQDN)e.g.example.com.(endswithadot)

–  Anunqualifiedname(doesnotendwithadot)–  An'@'(subs9tutesthecurrentvalueof$ORIGIN)–  a'space'or'blank'(tab)-thisisreplacedwiththepreviousvalueofthenamefield.Ifnonamehasbeenpreviouslydefinedthismayresultinthevalueof$ORIGIN.

ZoneName TTL class rr dnsname

example.com. IN NS ns1.example.com.

Syntax:ARR

•  ResolveanametoaIPv4addressName TTL class rr Address

example.com. IN A 93.184.216.119

ReverseMapping

•  Howtofindthenamecorrespondingto1.2.3.4?– Andmoregenerally,howtobuildatreetokeepthestructurescalable(asinthecaseofname)?

– but…why?example:theanI-spamcase

•  InverttheIPandsearchintheIN-ADDR.ARPAdomain

ReverseMapping:zonefile

…$ORIGIN254.168.192.IN-ADDR.ARPA.…17INPTRwww.example.org

192.168.254.17

Trywith:dig-x204.152.184.167+short

PTRRR

ReverseMapping

•  IPv4addressesareallocatedinnetblocksbytheRIRs….

RIRs•  RegionalInternetRegistry•  ManageIPaddressesandASnumbers

ReverseMapping•  IPv4addressesareallocatedinnetblocksbytheRIRsto

eitheraLocalInternetRegistry,LIR(typicallyISP,orNa9onalInternetRegistry(NIR),whichinturnwillallocatetoanLIR.)

•  EachInternetRegistrylevelisdelegatedtheresponsibilityforreversemappingtheaddressesithasbeenassigned.

•  TheLIRmaydelegatetheresponsibilityforreversemappingtotheenduser

h>ps://www.ripe.net/membership/indices/IT.htmlItalianLIRs

Interested?SearchforInternetGovernancehNp://en.wikipedia.org/wiki/Internet_governance

Thingsarege�ngserious!

BIND

Firstsimpleexample:cgrl.edu

DNS10.0.0.1

PC210.0.0.101

PC110.0.0.100LANA

10.0.0.0/24

DNS(ns.cgrl.edu.)istheauthorita9venameserverforthezonecgrl.edu. edu

cgrl

pc1 pc2 alias ns10.0.0.1CNAMEpc110.0.0.100 10.0.0.101

Bind•  bindexecutable:/usr/sbin/named•  rndc:commandlineadministra9onofthenameddaemon

•  Likemanydaemonsgotitsstart/stopscriptin/etc/init.d–  /etc/init.d/bind[startstoprestartstatusreload]

•  Goodnews!Onlyone(usuallyshort)conffile:/etc/bind/named.conf

•  Badnews!itincludesseveralotherfiles!!suchas:•  Zonefiles:in/etc/bind/.Example:db.edu.cgrl•  op9ons:/etc/bind/named.conf.op9ons•  otherfiles

/etc/bind/named.conf

FIRSTSTEP:Addazoneforcgrl.eduto/etc/bind/db.edu.cgrl

BINDconfigura9on/etc/bind/named.conf!

/etc/bind/db.edu.cgrl!

NOTE: we are not using wildcards and special characters… more later on

CheckBINDconfigura9on

•  Tocheckzonefiles:–  named-checkzone$ZONE_NAME$ZONE_FILE

•  Tocheckconffiles:–  named-checkconf

•  Viewinsyslog(or,ifinanotherlogfileifyouchangedit)

Andforreverseaddressmapping?Wesimplymakens.cgrl.eduauthorita9veforthezone:0.0.10.IN-ADDR.ARPA

/etc/bind/named.conf!

/etc/bind/db.0.0.10!

Resolverconfigura9on/etc/resolv.conf!

/etc/resolv.confnameserver8.8.8.8nameserver8.8.4.4domainmydomain.comsearchmysearch.comd2.com

primaryDNSsecondaryDNSsearchdirec:veforshortnames

•  Whentrytoresolv“test”itresolvetest.mydomain.com(usinggethostnameordomainifpresent)

•  Ifyouwantthattestwillberesolvedastest.Aandtest.BspecifysearchAB.(incasetest.Afails,resolverwillgofortest.B)

•  Thedomainandsearchkeywordsaremutuallyexclusive.Ifmorethanoneinstanceofthesekeywordsispresent,thelastinstancewins.

•  Let’sput127.0.0.1totestournewdnsserver!!

Secondsimpleexample:delega9onofstuden9.cgrl.edu

DNS10.0.0.2

PC210.0.0.101

PC110.0.0.100

LANA10.0.0.0/24

www192.168.1.200

LANB192.168.1.0/24

DNS2192.168.1.2

Secondsimpleexample:delega9onofstuden9.cgrl.edu

edu

cgrl

pc1 pc2 alias ns10.0.0.1CNAMEpc110.0.0.100 10.0.0.101

studen9

www192.168.1.200

ns192.168.1.2

cgrl.edudomain

cgrl.eduzone

studen9.cgrl.eduzone

cgrl.edudelegatedtons.cgrl.edustuden9.cgrl.edudelegatedtons.studen9.cgrl.edu

BINDconfigura9on–dnsdns#/etc/bind/db.edu.cgrl!

delega:on

@subs9tutesthecurrentvalueof$ORIGIN

Rela9venamesappendedtocurrentzone

Gluerecord

•  Howwecanresolvens.studen9.cgrl.edu?–  ifthatwasexactlythednsresponsibletoresolve*.studen9.cgrl.edu!!

•  AgluerecordisanArecordforthenameserverthatisauthorita9veforthedelegatedzone– ns.studen9.cgrl.eduINA192.168.1.2

BINDconfigura9on–dns2

dns2#/etc/bind/db.studenti.cgrl.edu!

Add to dns2#/etc/bind/named.conf!

MXrecordsandloadBalancing•  inmostusedMTAclients,ifequalDNSpreferencesàRoundrobin!

INMX10mail.example.comINMX10mail2.example.comINMX10mail3.example.commailINA192.168.0.4mail2INA192.168.0.5mail3INA192.168.0.6

LoadBalancing•  ThenameserverwilldeliveralltheIPaddressesdefinedforthegivennameinanswertoaqueryfortheARRs;

•  theorderofIPaddressesinthereturnedlistisdefinedbytherrset-orderstatementinBIND’snamed.conffile.–  rrset-order{typeMXname"example.com"orderrandom;ordercyclic};

•  Cachingcansignificantlydistorttheeffec9venessofanyDNSIPaddressalloca9onalgorithm.ATTLvalueof0maybeusedtoinhibit

Mailserverfailover

;zonefilefragmentINMX10mail.example.com.INMX20mail.example.net.....mailINA 192.168.0.4....

•  Ifthemostpreferredmailserver,theonewiththelowestnumber(10),isnotavailable,mailwillbesenttothesecondmostpreferredserver

SenderPolicyFramework(SPF)•  ThedesignintentoftheSPFrecordistoallowareceiving

MessageTransferAgent(MTA)toverifythattheorigina9ngIP(thesource-ip)ofane-mailfromasenderisauthorizedtosendmailforthesender’sdomain.

•  TXTRR(BINDreleasesfrom9.4.0supporttheSPFRRtype)

•  v=spf1[pre]type[[pre]type]...[mod]”where:–  pre:+=pass(default),-=fail,~=sokfail(indeterminateresult),?=neutral

–  type:Thisdefinesthemechanismtypetouseforverifica9onofthesender.

SPF:SMTPConversa9onExample==>220teamits105.teamITS.netESMTPSendmail8.13.6.20060614/8.13.6;Wed,6Dec200714:27:47-0600(CST)<--HELOteamits104.teamITS.net==>250teamits105.teamITS.netHellopy-in-f99.google.com[64.233.167.99],pleasedtomeetyou<--mailfrom:[email protected]==>[email protected]<--rcptto:[email protected]==>[email protected]<--Data==>354Pleasestartmailinput.<--From:[email protected]<--To:[email protected]<--Subject:Wanttobuyawidget?<--<--Bodytextofmessage.<--.==>250Mailqueuedfordelivery.<--Quit==>221Closingconnec9on.Goodbye.

SPFExamples

•  mail.acme.example.net.TXT"v=spf1a–all”– Theonlyhostthatcanannounceitselfasmail.acme.example.netismail.acme.example.net(indicatedbythe"a")

•  @INTXT"v=spf1a:mail.example.com/27-all”–  or:@INSPF"v=spf1a:mail.example.com/27–all– Wecanuseslashnota9ontospecifyaCIDRrange

Exerciseinclass

DNS10.0.0.2

PC210.0.0.101

PC110.0.0.100

LANA10.0.0.0/24

www192.168.1.200

LANB192.168.1.0/24

DNS2192.168.1.2

www2192.168.1.201

Addwww2VMandloadbalancewww.studen9.cgrl.edubetweenwwwandwww2

LoadBalancingofwwwserveronlanB

•  SimplyaddanotherARRin/etc/bind/db.studen9.cgrl.edu•  BINDwillautoma9callyroundrobinthrooguhthen

addressesboundtothesamename

Ques9on

Whywwwcan’tresolve,forexample,pc1.cgrl.edu?Solu9on?

R

10.0.0.2

10.0.1.2

10.0.2.2

10.0.1.3

pc1

dns-stud

dns-dip

router(dhcpserver)

dns-sld

10.0.0.1

10.0.2.110.0.1.1

pc2

10.0.2.3

stud.cgrl.edu dip.cgrl.edu

cgrl.eduserver1server2

dhcp dhcp

AsmallInternet… Netkitlab:lab4-dns.tar.gz

Statements:BIND

•  many!–  h>p://www.zytrax.com/books/dns/ch7/statements.html

•  allow-transfer{192.168.1.2;};(defaultyes)•  orselec9ve:

zone"example.com"in{....allow-transfer{192.168.1.2;};....};

•  Theallow-no9fy{192.168.254.2;};statementdisablesNOTIFYmessagesfromanyhostexceptthezonemastertominimizepossiblemaliciousac9on.

Viewclause

view"goodguys"{match-clients{192.168.254.0/24;};//theexample.comnetworkrecursionyes;//requiredzoneforrecursivequerieszone"."{

typehint;file"root.servers";

};

•  Toofferdifferentservicestodifferentclients(e.g.insideandoutsideourcompany)

•  Theviewstatementcantakeaseriousnumberofstatements

MasterSlaveconfigura9on:AXFR

FullZoneTransfer•  Master:thezonefilewillbereadfromthelocalfilestore

•  Slave:obtainsthezonerecordsusingzonetransfer•  EverythingdoneusingTCP,zonetransferarealwaysstartedbyclients

master slave

SOArequest

SOAresponse

AXFRrequest

En9reZone

MasterSlaveconfigura9on:IXFR

Incrementalzonetransfer•  Requestsazonetransferofthegivenzonebutonlydifferences

fromapreviousserialnumber.•  AXFRcanbesentiftheauthorita9veserverisunabletofulfillthe

requestduetoconfigura9onorlackofrequireddeltas.

master slave

SOArequest

SOAresponse

IXFRrequest

Changesinzoneinfo

MasterSlaveconfigura9on:No9fy

serverscansendaNOTIFYmessagetoclientstosignalchangesNo9fydecreaselatencyandpropaga9on9meofzonechanges

master slave

SOArequest

SOAresponse

IXFRorAXFRrequest

Changesinzoneinfo

No9fy

Example:delega9onandredundancy

Masterforsubdomain:us.example.com

Masterfor:example.comSlaveforus.example.com

Delega9onofsubdomain:us.example.com

Bind:DelegateaSubdomain(Subzone)

zone"example.com"in{typemaster;file"master.example.com";

};"us.example.com"IN{

typeslave;file"slave.us.example.com";masters{10.10.0.24;};

};Delega9onwithredundancy

Virtualsubdomaindon’trequireanyaddi9onalnameservers!

Reversedelega9on

•  Example:howtoreversedelegatesubnet</24:– RFC2317

•  64/26.199.168.192.IN-ARDDR.ARPA.INNSns2.example.com.

Assignee

(End-user)ZoneFile

•  Simple!

65INPTRfred.example.com.66INPTRjoe.example.com.67INPTRbill.example.com.

Assignor

Out-of-SequenceSerialNumbers

•  SN=4byteintandsetasadate(conven9on)– biggerSN,newerthedata

•  whatifwemakeamistakeandputadatainthefuture?– what9llthefuturewillcometocorrecttheerror–  incrementby2^31thevalue,pushtoalltheslaves,andthenputtherightvalue(wrappedthroughzero)

Wildcard

@INMX10mail.example.com.* INMX10mail.example.com.

•  anMXqueryeverythingelse.example.comwillreturnthehostmail.example.com.

R

10.0.0.2

10.0.1.2

10.0.2.2

10.0.1.3

pc1

dns-stud

dns-dip

router(dhcpserver)

dns-sld

10.0.0.1

10.0.2.110.0.1.1

pc2

10.0.2.3

stud.cgrl.edu dip.cgrl.edu

cgrl.eduserver1server2

dhcp dhcp

10.0.3.1

YOU.stud.cgrl.edu

www/mailmydns

10.0.3.2 10.0.3.3

Exercise

DNS & BIND - stud.netgroup.uniroma2.itstud.netgroup.uniroma2.it/cgrl/2015/slides/dns.pdf · Before...

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