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NAME SERVICES

NAME SERVICES. Names and addresses. File names -------/etc/passwd URLS ----http://www.yahoo.com Internet domain names—dcs.qmw.ac.uk Identifiers- ROR, NFS File Handles Pure Name Impure Name. Names and addresses contd.

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NAME SERVICES

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  1. NAME SERVICES

  2. Names and addresses • File names -------/etc/passwd • URLS ----http://www.yahoo.com • Internet domain names—dcs.qmw.ac.uk • Identifiers- ROR, NFS File Handles • Pure Name • Impure Name

  3. Names and addresses contd.. • A name is resolved when it is translated into data about the named resource or object • Name  Object is binding • Names are bound to attributes of named object

  4. Names and Services • Names in DS-> specific to some service • A client uses such a name when requesting a service to perform an operation upon a named service • A filename -> FS • A process identifier ->PMS

  5. Name Services examples • DNS maps domain name to the attributes of a host Computer • X500 DS maps a person’s name into attributes including their email address and telephone no • CORBA NS maps a RO -> ROR

  6. Composed naming domains used to access a resource from a URL http://www.angelfire.com/WebExamples/earth.html 55.55.55.55 1234 WebExamples/earth.html 2:60:8c:2:b0:5a file

  7. URL and URN • URL-> A DNS computer name and path name • Dangling link • URN’s to solve dangling link • Owner of a resource registers its name , along with its current URL with a URN look up service • The owner registers the new URL if resource moves

  8. URC • URC – Uniform Resource Characteristic or Uniform Resource Citations are a subset of URNS • An URC is a description of a Web Service consisting of attributes of the resource

  9. Name Service Requirements • To handle an arbitrary no of names and to serve an arbitrary no of administrative organizations • A long lifetime • High availability • Fault Isolation

  10. Name spaces • A collection of all valid names recognized by a particular service • Heirarchical name spaces • Flat name spaces • DNS names are called domain names • DNS – Heirarchical • Consists of one or more name components or labels seperated by deleimiter “.”

  11. DNS Namespace contd • The root is referred to as “.” • Client software keeps a list of domain names that are appended automatically to any single component name before resolution

  12. Naming Aliases • Allowing a convenient name to be substituted for a more complicated one • One domain name is defined to stand for another • www.dcs.qmw.ac.uk -> copper.dcs.qmw.ac.uk

  13. Naming domains • It is a name space for which there exist a single overall administrative authority for assigning names within it • ukac.ukqmw.ac.ukdcs.qmw.ac.uk

  14. Combining and Customising name spaces • Merging • Heterogeneity • Customization

  15. Name resolution • Iterative name resolution • Navigation –Iterative • Multicast navigation • Nonrecursive • Recursive

  16. Non-Recursive NS2 client NS1 NS3

  17. NS2 Recursive NS1 Client NS3

  18. Caching • Client name resolution software and servers maintain a cache of the results of previous name resolutions • Request is checked in the cache first • Performance • Availability

  19. Domain Name System • Domain names • Dns queries • Host name resolution • Mail host name resolution • Reverse resolution • Host Information • Well known services

  20. DNS Name Servers • DNS naming data are divided into zones • A zone contains the following data • Attribute data for names in domain • The name and addresses of at least two name servers ->authoritative data for the zone • The names of NS -> Sub domain • Zone management parameters

  21. DNS name servers contd.. • SA enter the data for a zone into a master file , which is source of authoritative data for the zone • Two types of servers • Master server • Secondary server • TTL

  22. DNS Resource Records • A • NS • CNAME • SOA • WKS • PTR • HINFO • MX • TXT

  23. Format Domainname ttl class type value 1D IN NS dnso 1D IN MX mail1.qmw.ac.uk www 1D IN CNAME copper copper 1D IN A 167.34.24.25 dcs 1D IN NS dnso.dcs dnso.dcs 1D IN A 123.453.45

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