管理才能考核表 Title.ppt

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1、Lecture on DHCP,DNS&SNMPDebashis SahaDHCP,DNS,SNMPDebashis SahaMIS Group,IIM Calcuttadsiimcal.ac.in1Lecture on DHCP,DNS&SNMPDebashis SahaFirst QuestionHow does your computer know which IP to use?How does your computer know that www.iimcal.ac.in is at IP 202.54.116.3?How can you track your networks h

2、ealth?Thursday,May 17,20072Lecture on DHCP,DNS&SNMPDebashis SahaThe Internet and AddressingAll machines on the Internet are accessed via their IP addressDotted quad:xxx.xxx.xxx.xxxProblem:IP addresses are hard to remember and hard to statically assign on large networksSolution:Need to come up with a

3、 way to automatically assign IP addresses and a text based representation of machine addresses instead of just 4 numbersThursday,May 17,20073Lecture on DHCP,DNS&SNMPDebashis SahaAddressing SolutionsTwo protocols have been developed to solve these problemsDHCP automatic network configuration(includin

4、g IP address)DNS translates textual based names into IP addresses and vice versaThursday,May 17,20074Lecture on DHCP,DNS&SNMPDebashis SahaDHCP Dynamic Host Configuration ProtocolThursday,May 17,20075Lecture on DHCP,DNS&SNMPDebashis SahaDHCPAllows client machines to receive an IP address,DNS informat

5、ion,etc automaticallyBefore DHCP came into use,users had to type in all this information by hand,which is bad:Easy to mistype something when entering by handManually changing network configuration every time you move your laptop is a painBootp resolved some of these issues and DHCP still uses the sa

6、me port as bootpThursday,May 17,20076Lecture on DHCP,DNS&SNMPDebashis SahaPurpose of DHCPFrom RFC-2131(the Internet standard):The Dynamic Host Configuration Protocol(DHCP)provides a framework for passing configuration information to hosts on a TCP/IP network.DHCP consists of two components:a protoco

7、l for delivering host-specific configuration parameters from a DHCP server to a host and a mechanism for allocation of network addresses to hosts.Thursday,May 17,20077Lecture on DHCP,DNS&SNMPDebashis SahaDHCP functional goalsA host without a valid IP address locates and communicates with a DHCP serv

8、erA DHCP server passes configuration parameters,including an IP address,to the hostThe DHCP server may dynamically allocate addresses to hosts and reuse addressesHosts can detect when they require a new IP addressUnavailability of DHCP server has minimal effect on operation of hostsThursday,May 17,2

9、0078Lecture on DHCP,DNS&SNMPDebashis SahaDHCP:BasicsA client leases an IP address from a DHCP server for a given amount of timeWhen lease expires,the client must ask DHCP server for a new address(clients attempt to renew lease after 50%of the lease time has expired)Typical leases may last for from 3

10、0 seconds to 24 hours,or even longer.Thursday,May 17,20079Lecture on DHCP,DNS&SNMPDebashis SahaWhat does DHCP do?Provides protocol stack,application and other configuration parameters to hostsEliminates need for individual,manual configuration for hostsIncludes administrative controls for network ad

11、ministratorsBackward compatible packet format for BOOTP interoperation(RFC 1542)Can coexist with hosts that have pre-assigned IP addresses and hosts that do not participate in DHCPThursday,May 17,200710Lecture on DHCP,DNS&SNMPDebashis SahaDesign GoalsEliminate manual configuration of hostsPrevent us

12、e of any IP address by more than one hostShould not require a server on every subnetAllow for multiple DHCP serversProvide a mechanism,not a policyProvide the same configuration-including IP address-to a host whenever possibleThursday,May 17,200711Lecture on DHCP,DNS&SNMPDebashis SahaWhat can you do

13、 with DHCPPlug-and-playMove desktop PCs between officesRenumberOther restructuring-change subnet masksMobile IP-laptopsMoving equipment-cartableThursday,May 17,200712Lecture on DHCP,DNS&SNMPDebashis SahaWhat DHCP doesnt doSupport multiple addresses per interfaceInform running host that parameters ha

14、ve changedPropagate new addresses to DNSSupport inter-server communicationProvide authenticated message deliveryConfigure routers and other network equipmentDesign network addressing planDetermine other configuration parametersLocate other serversThursday,May 17,200713Lecture on DHCP,DNS&SNMPDebashi

15、s SahaDHCP:Messages OverviewSeveral messages are sent back and forth between a client and the DHCP server before it can successfully obtain an IP addressThursday,May 17,200714Lecture on DHCP,DNS&SNMPDebashis SahaDHCP:DISCOVERHardcoding the addresses of DHCP servers kind of defeats the purpose of aut

16、omatic configurationSolution:A client using DHCP will broadcast a DISCOVER message to all computers on its subnet(addr 255.255.255.255)to figure out the IP address of any DHCP serversMost routers are configured to pass this request within the campus or enterpriseThursday,May 17,200715Lecture on DHCP

17、,DNS&SNMPDebashis SahaDHCP:OFFER(Optionally)sent from server in response to a DISCOVERContains an IP address,other configuration information as well(subnet mask,DNS servers,default gateway,search domains,etc)Note that all DHCP servers that receive a DISCOVER request may send an OFFER;since a client

18、typically does not need more than one IP address,more messages needed to zero on one IPThursday,May 17,200716Lecture on DHCP,DNS&SNMPDebashis SahaDHCP:REQUESTSent by client to request a certain IP addressUsually the one sent by an OFFER,but also used to renew leases.Also can be sent to try to get sa

19、me address after a rebootThis message is broadcastMost OSs by default will send a REQUEST for the first OFFER they receive this means that if there is a rogue DHCP server on your subnet,most clients will ignore the OFFERs from the campus DHCP servers(since the OFFER from the rogue server gets to the

20、 users PC first)!Thursday,May 17,200717Lecture on DHCP,DNS&SNMPDebashis SahaDHCP:ACK/NACKSent by server in response to a REQUESTACK:Request accepted,client can start using the IP it REQUESTedNACK:Something is wrong with the clients REQUEST(for example they requested an IP address theyre not supposed

21、 to have)Thursday,May 17,200718Lecture on DHCP,DNS&SNMPDebashis SahaDHCP:RELEASESent by client to end a leaseNot strictly required,but is the“polite”thing to do if done with the IP(could just let the lease expire)Some clients may not send RELEASEs in an attempt to keep the same IP address for as lon

22、g as possibleThursday,May 17,200719Lecture on DHCP,DNS&SNMPDebashis SahaDHCP:Big PictureThursday,May 17,200720Lecture on DHCP,DNS&SNMPDebashis SahaSummaryDHCP works today as a tool for automatic configuration of TCP/IP hostsIt is an open Internet standard and interoperable client implementations are

23、 widely availableProvides automation for routine configuration tasks,once network architect has configured network and addressing planOngoing work will extend DHCP with authentication,DHCP-DNS interaction and inter-server communicationThursday,May 17,200721Lecture on DHCP,DNS&SNMPDebashis SahaDHCP:C

24、onclusionEfficient way of assigning computers IP addresses and delivering configuration information to those computersDoes not solve other problem of addressing that IP addresses are hard to rememberThursday,May 17,200722Lecture on DHCP,DNS&SNMPDebashis SahaIETF standardsFormal process for developme

25、nt,review and acceptance of TCP/IP protocol suite standardsInitial specifications published as Internet Drafts(I-Ds)Accepted specifications published as Request for Comments(RFCs)Thursday,May 17,200723Lecture on DHCP,DNS&SNMPDebashis SahaProtocol statusDHCP has been accepted as a Draft Standard;the

26、specifications are published in:RFC 2131:Dynamic Host Configuration ProtocolRFC 2132:DHCP Options and BOOTP Vendor ExtensionsSeveral additional options are in developmentThursday,May 17,200724Lecture on DHCP,DNS&SNMPDebashis SahaImplementation statusDHCP is an open standard,with freely available spe

27、cificationsCan be(and has been)implemented entirely from the specificationCommercial implementations are widely availableNon-commerical implementations are also availableThursday,May 17,200725Lecture on DHCP,DNS&SNMPDebashis SahaDHCP ResourcesCompilation of DHCP-related WWW links and other informati

28、on:http:/www.dhcp.orgDHCP FAQ(maintained by John Wobus)dhcp-v4bucknell.edu mailing list(admin requests to listservbucknell.edu)IETF information can be retrieved from:http:/ri.reston.va.usI-Ds and RFCs can also be retrieved from:http:/www.rfc-editor.orgThursday,May 17,200726Lecture on DHCP,DNS&SNMPDe

29、bashis SahaDNS Domain Name SystemThursday,May 17,200727Lecture on DHCP,DNS&SNMPDebashis SahaSecond QuestionHow does your computer know which IP to use?How does your computer know that www.iimcal.ac.in is at IP 202.54.116.3?How can you track your networks health?Thursday,May 17,200728Lecture on DHCP,

30、DNS&SNMPDebashis SahaDomain Name System(DNS)The first IP networks distributed host files on a regular basisThis became a burden and an automated distributed solution was neededIP Addresses are great for computersIP address includes information used for routing.IP addresses are tough for humans to re

31、member.IP addresses are impossible to guess.ever guessed at the name of a WWW site?Thursday,May 17,200729Lecture on DHCP,DNS&SNMPDebashis SahaHostnamesDNS is bornDomain names comprise a hierarchy so that names are unique,yet easy to remember.The domain name system is usually used to translate a host

32、 name into an IP address.Ex:www.xxx.org IP 212.87.7.181(which one would you rather remember?)Thursday,May 17,200730Lecture on DHCP,DNS&SNMPDebashis SahaDNS:BasicsHierarchical namespaceDistributed system very few core serversStores other information than simple hostname IP mappingsRequest/response pr

33、otocolThursday,May 17,200731Lecture on DHCP,DNS&SNMPDebashis SahaDNS Hierarchyeducomorginrpi albanyaciimcalThursday,May 17,200732Lecture on DHCP,DNS&SNMPDebashis SahaHost name structureEach host name is made up of a sequence of labels separated by periods.Each label can be up to 63 charactersThe tot

34、al name can be at most 255 characters.Examples:monica.cs.rpi.eduThursday,May 17,200733Lecture on DHCP,DNS&SNMPDebashis SahaDomain NameThe domain name for a host is the sequence of labels that lead from the host(leaf node in the naming tree)to the top of the worldwide naming tree.A domain is a subtre

35、e of the worldwide naming tree.Thursday,May 17,200734Lecture on DHCP,DNS&SNMPDebashis SahaHierarchical Namingcomedugovmilnetorgusarpacolordaocsfoobarfoobar.cs.colorado.eduThursday,May 17,200735Lecture on DHCP,DNS&SNMPDebashis SahaTop level domainsedu,gov,com,net,org,mil,Countries each have a top lev

36、el domain(2 letter domain name).Such as.in,.uk,.it,etc.New top level domains include:.aero .biz .coop .info .name .proThursday,May 17,200736Lecture on DHCP,DNS&SNMPDebashis SahaDomain Naming Systemeducomharvard mithbseewwwphysicscisco yahoonasa nsf arpa navy acm ieeegovmilorgnetukfrThursday,May 17,2

37、00737Lecture on DHCP,DNS&SNMPDebashis SahaDNS:ArchitectureDNS servers are responsible for one or more domains of any level“Root servers”are maintained throughout the world(one is in Palo Alto)and are responsible for all of the top-level domainsWhen you register a domain,an entry for that domain is a

38、dded to the appropriate root serverOwners of each regular domain or subdomain maintain(or outsource)their own DNS servers containing the correct informationThursday,May 17,200738Lecture on DHCP,DNS&SNMPDebashis SahaName ServersPartition hierarchy into zoneseducomprinceton mitcseeux01 ux04physicscisc

39、o yahoo nasa nsfarpa navyacm ieeegovmilorgnetukfrRootname serverPrincetonname serverCisconame serverCSname serverEEname serverEach zone implements two or more name servers 1.Primary2.secondaryThursday,May 17,200739Lecture on DHCP,DNS&SNMPDebashis SahaHierarchical Administration-“Zones”arpacomingovmi

40、lnetorgusarpaaciimcalwwwwww.iimcal.ac.inThursday,May 17,200740Lecture on DHCP,DNS&SNMPDebashis SahaAdministration-ZonesA zone is a subtree of the DNS tree that is independently managedSecond-level domains(“ac.in”)are usually an independent zoneMost sub-domains(“iimcal.ac.in”)are also independent.A z

41、one must provide multiple name servers.This server records the members in the domain.You typically need a primary name server and one or more secondary name servers.Secondary retrieves information from primary using a zone transfer.Thursday,May 17,200741Lecture on DHCP,DNS&SNMPDebashis SahaResolving

42、 an addressA.C.D wants to know about F.E.DACDEGBFHHost“A.C.D”asks“B.C.D”(the local name server)to resolve“F.E.D”Name serversThursday,May 17,200742Lecture on DHCP,DNS&SNMPDebashis SahaResolving an addressB.C.D doesnt know the answer.It wants to ask the primary domain server for the“E.D”domain,so it a

43、sks the parent of the“B.C”domain(“D”in this example)to resolve“E.D”.D asks H,the root server.H doesnt know the answer,but its the top-level domain and knows that“G.E.D”is the primary domain server for the“E.D”domainB.C.D now knows the primary domain server for the E.D domain,and can now ask“G.E.D”ab

44、out“F.E.D”Thursday,May 17,200743Lecture on DHCP,DNS&SNMPDebashis SahaDomain serversWhat kind of records can be requested for a given domain?Address translationCaching informationMail server informationAuthoritative nameserver informationHow is this data requested?Each record has a type and certain d

45、ata associated with it clients request records of a certain type from a serverThursday,May 17,200744Lecture on DHCP,DNS&SNMPDebashis SahaDNS OrganizationDistributed DatabaseThe organization that owns a domain name is responsible for running a DNS server that can provide the mapping between hostnames

46、 within the domain to IP addresses.So-some machine run by RPI is responsible for everything within the rpi.edu domain.Thursday,May 17,200745Lecture on DHCP,DNS&SNMPDebashis Saharpi.eduDNS DBrpi.eduDNS DBDNS Distributed DatabaseThere is one primary server for a domain,and typically a number of second

47、ary servers containing replicated databases.rpi.eduDNS DBAuthoritativerpi.eduDNS DBReplicasrpi.edu DNS serverThursday,May 17,200746Lecture on DHCP,DNS&SNMPDebashis SahaDNS ClientsA DNS client is called a resolver.A call to gethostbyname()is handled by a resolver(typically part of the client).Most Un

48、ix workstations have the file/etc/resolv.conf that contains the local domain and the addresses of DNS servers for that domain.Thursday,May 17,200747Lecture on DHCP,DNS&SNMPDebashis Saha/etc/resolv.confdomain rpi.edu128.113.1.5128.113.1.3Thursday,May 17,200748Lecture on DHCP,DNS&SNMPDebashis Sahanslo

49、okupnslookup is an interactive resolver that allows the user to communicate directly with a DNS server.nslookup is usually available on Unix workstations.(dig and host are also DNS clients).Thursday,May 17,200749Lecture on DHCP,DNS&SNMPDebashis SahaDNS ServersServers handle requests for their domain

50、 directly.Servers handle requests for other domains by contacting remote DNS server(s).Servers cache external mappings.Thursday,May 17,200750Lecture on DHCP,DNS&SNMPDebashis SahaServer-Server CommunicationIf a server is asked to provide the mapping for a host outside its domain(and the mapping is no