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1、 Introduction Name services and the Domain Name System Directory and discovery services Case study of the Global Name Service Case study of the X.500 Directory Service SummaryChapter 9: Name Services A distinct service that is used by client to obtain attributes such as the addresses of resources or

2、 objects when given their names Name management is separated from other services Unification IntegrationWhat is Name Service? Name A human readable string Address Bits used by machines to locate an object Bind Association between a name and an address Resolve Translate from a name to an address Exam

3、pleName and Address Value of a property associated with an object DNS IP address X.500 Persons email address and telephone number CORBA Naming Service Remote object referenceAttributes URL (Uniform Resource Location) Addresses of web resources Dangling problems: a resource may be moved URN (Uniform

4、Resource Name) Intend to solve the dangling problems URN lookup service: mapping from URN to URL E.g. urn:ISBN:0-201-62433-8Uniform Resource Identifiers Introduction Name services and the Domain Name System Directory and discovery services Case study of the Global Name Service Case study of the X.50

5、0 Directory Service SummaryChapter 9: Name Services Scalability Arbitrary number of names Arbitrary number of administrative organizations Flexibility A long lifetime Accommodate variations on the organization of the set of namesGeneral name service requirements High availability Most other systems

6、depend upon it Fault isolation Isolate location failures from entire service Tolerance of mistrust Not all clients are trusted by all components of the systemGeneral name service requirements (2) A collection of all valid names recognized by a particular service Require a syntactic definition E.g. d

7、omain name tree of DNS E.g. directory tree of a file systemName spaces Hierarchic structure, e.g. /etc/passwd Resolve relative to a separate context Potentially infinite Different context managed by different people AliasInternal structure of a name A single administrative authority A name space for

8、 which there exists a single authority E.g. Be stored in a separated server Naming domains are in general stored in different name serversNaming domain Homogeneous/heterogeneous name spaces Merging E.g. mount file system in Unix and NFS E.g. create a higher-level root context Heterogeneity DCE name:

9、 /dcs.qmw.ac.uk/principals/Jean.Dollimore /dcs.qmw.ac.uk/files/pub/reports/TR2000-99Combining name spacescellprincipalscellfiles One file with different names E.g. a NFS directory mounted on different machines One name refer to different files E.g. install configuration for multi-platform One name s

10、pace per people E.g. Plan 9Customizing name spaces Name space is partitioned in different name servers Iterative navigation Client controlling E.g., DNS, NFSName resolutionClient123A client iteratively contacts name servers NS1NS3 in order to resolve a nameNS2NS1NS3Nameservers Non-recursive/Recursiv

11、e Recursive type is suitable to environment where there are administrative domain prohibitsServer controlled navigation123512344A name server NS1 communicates with other name servers on behalf of a clientclientclientRecursiveserver-controlledNS2NS1NS3NS2NS1NS3Non-recursiveserver-controlled Enhance r

12、esponse time Eliminate the workload of high-level name servers Isolate the failures of high-level name serversCaching tech. in name resolution Original Internet Naming scheme A central master files Download to all hosts by FTP Domain names 1987 Name space is partitioned both organizationally and acc

13、ording to geographyThe Domain Name SystemThe DNS name spaceCom Commercial organizationsEdu Universities and other educational institutionsGov US governmental agenciesMil US military organizationsNet Major network support centresOrg Organizations not mentioned aboveInt International organizationsUs u

14、nited StatesUk United KingdomCn - China Host name resolution From URL to IP address Mail host location Given a domain name, return a list of domain names of hosts that can accept the mail E.g. tomdcs.rnx.ac.uk Reverse resolution From IP to URLDNS queries Host information E.g. the architecture type o

15、r operating system of a machine Well-known services A list of the services run by a computer Protocol used to obtain them (UDP & TCP)DNS queries continued DNS names are divided into Zones Zone Include names in the domain, less any sub-domains At least two name servers for the zone Hold name serv

16、ers for the sub-domains Each server hold zero or more Zones Zero zone: the caching name serverDNS name servers Servers that a name server holds Lower-level name servers Child name servers high-level name servers One or more root name servers Parent name serverDNS name servers continued Iterative nav

17、igation / recursive navigation Example DNS resource typesDNS name resolution Replication Zone data are replicated on at least two name servers Master server / secondary server Synchronize periodically Cache Any server is free to cache data Time-to-live valueDNS performance Availability & Scalabi

18、lity Achieved by a combination of replication, cache and partition Acceptable inconsistent naming dataDNS performance (2) Introduction Name services and the Domain Name System Directory and discovery services Case study of the Global Name Service Case study of the X.500 Directory Service SummaryChap

19、ter 9: Name Services A special kind of naming service Searching attributes Entries Each entry is concerned with a set of pairs Query Lookup by known attributes Return interested attributes E.g. query ones telephone No. by his nameDirectory services Yellow page / white page Directory service / Conven

20、tional naming service Directory servers and navigation Similar to name service Example Active Directory Service X.500 LDAPDirectory services (2) A special kind of directory service Register the services provided in a spontaneous network General operations Register / lookup / de-register E.g. a regis

21、tered printerDiscovery servicesResourceClass=printer, type=laser, colour=yes, resolution=600dpi,Location=room101, url= A lookup service A service registers an object with a set of attributes Clients query the lookup service Clients download service object that matches query Leases A limited period o

22、f time during which the service can be usedJini A priori Multicast to a well-know IP multicast address Lookup services listen on the receiving socket Lookup services announce their existence ExampleHow to locate lookup service in Jini? Introduction Name services and the Domain Name System Directory

23、and discovery services Case study of the Global Name Service Case study of the X.500 Directory Service SummaryChapter 9: Name Services Designed by DEC lab lampson 1986 Design objectives Millions of computer names Billions of email addresses for users Long life time: accommodate changesIntroduction t

24、o GNS Directory tree / value tree Directory identifier (DI) Unique identifier of a directory Name of an entry E.g. Architecture of GNS Multiple name servers Directory tree is partitioned and stored in many servers Replication Each partition is replicated in several servers Cache Inconsistency cache

25、data is acceptableArchitecture of GNS (2) Merge two name space by a super-root How to it transparent to client applications? E.g. how to locate /uk/ac/qmw ?How does GNS accommodate changes?ECUKFRDI: 599DI: 574DI: 543NORTH AMERICAUSDI: 642DI: 457DI: 732#599 = #633/EC#642 = #633/NORTH AMERICAWell-know

26、n directories:CANADADI: 633 (WORLD) Client agent Store the DI of working root by client agent E.g., for , client agent stores #599 which is the DI of “/”, i.e. EC Resolve name Working root DI + relative path Uniquely refer to a name in the merged tree E.g. Working root DI A table of well-know direct

27、ories Mapping between working root DI to new absolute path Replication Well-know directories are replicated at each nodes Bottleneck of consistency ExamplesWell-known directories Introduction Name services and the Domain Name System Directory and discovery services Case study of the Global Name Serv

28、ice Case study of the X.500 Directory Service SummaryChapter 9: Name Services General purpose directory service Directory information tree (DIT) Partitioned and stored in different servers Organized according to distinguished name Service architecture Directory user agent (DUA) Directory service age

29、nt (DSA)X.500 Architecture DIB entry Consist of a name and a set of attributes Attribute definition language Search Query by “a base name + a filter expression” Return a list of entriesSearch in X.500 A distributed object naming service based on LDAPLight Directory Access Protocol (LDAP)c=Chinast=Be

30、ijingst=Hubeil=Beijingou=Tsinghual=Wuhanou=Beidadc=Deandc=Deandc=Teacherdc=Coursedc=Teacherdc=Courseou=Wudadc=Deandc=Teacherdc=CourseAB2B1C Introduction Name services and the Domain Name System Directory and discovery services Case study of the Global Name Service Case study of the X.500 Directory S

31、ervice SummaryChapter 9: Name Services Basics of naming service Map between name and attributes of objects binding, resolve Name space Syntactic rules Multiple name servers Cache & replication Cases DNS GNS: accommodating changes X.500: directory serviceSummaryComposed naming domains used to acc

32、ess a resource from a URL URLResource ID (IP number, port number, pathname)Network address2:60:8c:2:b0:5a fileWeb server5WebExamples/earth.html8888DNS lookupSocketDNS name serversa.root-(root)(ac.uk)dns0.dcs.qmw.ac.uk(dcs.qmw.ac.uk)alpha.qmw.ac.uk(qmw.ac.uk)dns0-doc.ic.ac.uk(ic.ac.uk)ns.pu

33、()ic.ac.ukqmw.ac.ukdcs.qmw.ac.uk*.qmw.ac.uk*.ic.ac.uk*.dcs.qmw.ac.uk* .ns1.nic.uk(uk)DNS resource recordsRecord typeMeaningMain contentsAA computer addressIP numberNSAn authoritative name serverDomain name for serverCNAMEThe canonical name for an aliasDomain n

34、ame for aliasSOAMarks the start of data for a zone Parameters governing the zoneWKSA well-known service description List of service names and protocolsPTRDomain name pointer (reverselookups)Domain nameHINFOHost informationMachine architecture and operatingsystemMXMail exchangeList of pairsTXTText st

35、ringArbitrary textService discovery in JiniPrinting service serviceLookup serviceLookupPrinting serviceadminadminadmin, financefinanceClientClientCorporate infoservice1. finance lookup service?2. Here I am: .3. Request printing4. Use printing serviceNetworkGNS directory tree and value tree for user Peter.SmithUKFRACQMWDI: 322Peter.SmithpasswordmailboxesDI: 599 (EC)DI: 574DI: 543DI: 437AlphaGammaBetaMerging trees under a new rootECUKFRDI: 599DI: 574DI: 543NORTH AMERICAUSDI: 642DI: 457