ch-9: name services by srinivasa r. gudipati. to be discussed.. fundamentals of naming services...

Ch-9: NAME SERVICESCh-9: NAME SERVICES

By Srinivasa R. Gudipati

To be discussed..To be discussed..

Fundamentals of Naming ServicesNaming ResolutionThe Domain Name System (DNS)Directory & Discovery ServicesJini Discovery Service

Fundamentals of Naming ServicesFundamentals of Naming Services

What is Naming Service?

It is a distinct service that is used by client processes to obtain attributes such as the addresses of resources or objects when given their names.


A name is said to be “pure” when it can not be interpreted as bit patterns. Where as non-pure names contain information about the object that they name. The association between name and object is called “binding”. Names are bound to “attributes” of the named objects. One key attribute is “address” of that object.


A name service stores a collection of one or more naming contexts – sets of bindings between textual names and attributes for objects such as users, computers..

The major operation that a name service supports is to resolve a name – that is, look up attributes from a given name.


What is Name Space?

A Name Space is the collection of all valid names recognized by a particular service.

-Hierarchic Name Space: Internal structure of a name represents its position in a hierarchic name space. Eg: Internet domain names.

-File Name Space: Names are chosed from a flat set of numeric or symbolic identifiers.

Name Resolution: NavigationName Resolution: Navigation

Resolution is an iterative process whereby a name is repeatedly presented to naming contexts.

The process of locating naming data from among more than one name server in order to resolve a name is called “Navigation”.


Type of Navigations:

1. Iterative Navigations

2. Non-Recursive Navigation

3. Recursive Navigation


Iterative Navigation:

Client

NS2

NS1

NS3

2

1

3


Non-Recursive Navigation:

Client

NS2

NS1

NS3

1

2

34


Recursive Navigation:

Client

NS2

NS1

NS3

1

2

53

4

The Domain Naming System (DNS)The Domain Naming System (DNS)

The DNS is

1) A distributed database implemented in a hierarchy of name servers and

2) an application-layer protocol that allows hosts and name servers to communicate in order to translate hostnames to IP addresses.


Some of the important services provided by DNS are:

1. Host Aliasing: A host with a complicated hostname can have one or more alias names.

2. Mail server aliasing:

3. Load distribution:


The problems with centralized and single server design:

1. A single point of failure

2. Traffic volumes

3. Distant centralized database

4. Maintenance


Domain Names: The inter net DNS name space is partitioned both organizationally and according to geography. The top-level organization domains in use today across the internet are: Com – Commercial OrganizationEdu – Universities and other educational institutionsGov – US governmental agenciesNet – Major network support centersOrg – Organizations not mentioned above


Three types of Name Servers DNS use:

Local Name Severs: Such as a university, an academic department, an employee’s company. When a host issues a DNS query message, the message is first sent to host’s local name server.


Root Name Sever: In the internet there are a dozen or so root name servers most of which are located in North America. When a local name server can not immediately satisfy a query from a host, the local name server behaves a DNS client and queries one of the root name server.


Authoritative Name Sever: Every host is registered with authoritative name server. Typically authoritative name server for a host is a name server in the host’s local ISP. By definition, a name server is authoritative for a host if it always has a DNS record that translates the host’s hostname to that host’s IP address. When authoritative server is queried by root server, the authoritative name server responds with a DNS reply that contains the requested mapping.


Recursive queries to obtain the mapping for gaia.cs.umass.edu

1

2 34

5

6

Requesting Host surf.eurecom.fr

Local Name Server dns.eurocom.fr

Root Name Server

Authoritative Name Server dns.umass.edu

Gaia.cs.umass.edu


Recursive queries with an iterermediate name server between the root and autoritative name server

1

2



Root Name Server

Intermediate Name Server dns.umass.edu

Gaia.cs.umass.edu

3

45

67

8

Authoritative Name Server dns.cs.umass.edu


A query chain with Recursive and iterative quieries

1

2



Root Name Server

Intermediate Name Server dns.umass.edu

Gaia.cs.umass.edu

56

8

Authoritative Name Server dns.cs.umass.edu

3 4

7

Iterated query


DNS Record:

The name servers that together implement the DNS distributed database, store “Resource Records (RR)” for the hostname to IP address mappings.

A resource record is a four-tuple that contains the

following fields: (Name, Value, Type, TTL)

The Domain Naming System (DNS)The Domain Naming System (DNS)DNS Record:

Type Name ValueA Hostname IP Address

NS Domain Hostname of the Authoritative server

CNAME Alias hostname Canonical hostname

MX Alias Hostname Hostname of mailserver


DNS Caching:

DNS extremely exploits caching in order to improve the delay performance and to reduce the number of DNS messages in the network. When a name server receives a DNS mapping for some hostname, it caches the mapping in local memory (disk/RAM) while passing the message along the name server chain.

Directory and Discovery Services:Directory and Discovery Services:

A service that stores collections of bindings between names and attributes and that looks up entries that match attribute-based specifications is called “directory service”.

A directory service returns attributes of any objects found to match some specified attributes.

Directory and Discovery Services:Directory and Discovery Services:

A discovery service is a directory service that registers the services provided is a spontaneous networking environments.

A discovery service provides an interface for automatically registering and de-registering services, an well as an interface for clients to look up the services that they require from those that are currently available.

Jini Discovery ServiceJini Discovery Service

Three main components: Client, Lookup service, Service Provider


Discovery: A Service provider looks for a Lookup service.


Join: The service Provider registers a service Object and its service of attributes with the Lookup service.


Lookup : A Client looks for a service over its Java type and if necessary different service of attributes.A copy is sent to the Client, with which it can communicate with the looked for service:


Finished : With the help of the service Object can interact the Client directly with the service:

ch-9: name services by srinivasa r. gudipati. to be discussed.. fundamentals of naming services...

Documents

recursive navigation

navigation resolution

naming contexts

maintenance slide

gudipati slide

naming data

domain naming system

internet domain names