name services. names and addresses file names -------/etc/passwd urls ---- internet domain...

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NAME SERVICES

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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..

• 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

Combining and Customising name spaces

• Merging

• Heterogeneity

• Customization

Name resolution

• Iterative name resolution

• Navigation –Iterative

• Multicast navigation– Nonrecursive– Recursive

Non-Recursive

client NS1

NS2

NS3

Recursive

Client NS1

NS2

NS3

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

DNS Resource Records

• A • NS• CNAME• SOA• WKS• PTR• HINFO• MX• TXT

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