name services. names and addresses file names -------/etc/passwd urls ---- internet domain...
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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..
• 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
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
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
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
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
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
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
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 “.”
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
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
Naming domains
• It is a name space for which there exist a single overall administrative authority for assigning names within it
• ukac.ukqmw.ac.ukdcs.qmw.ac.uk
Name resolution
• Iterative name resolution
• Navigation –Iterative
• Multicast navigation– Nonrecursive– Recursive
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
Domain Name System
• Domain names
• Dns queries– Host name resolution– Mail host name resolution– Reverse resolution– Host Information– Well known services
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
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
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