Negar Makvandian
Kamyar Niroumand
Department of Information Technology, Uppsala University

• Name Service is used by client processes to obtain attributes of resources or objects when given their names
• The entities named can be:
• users
• computers
• network domains
• services
• remote objects

• Names facilitate communication and resource sharing
• descriptive attributes are another mean of identification
Client doesn't know the name of entity, but knows information that describes it
Client requires a service rather than a particular entity that implements it.

• Any Process that requires access to a specific resource must possess a name or an identifier for it
• file names: /etc/password
• URLs: http://www.cdk3.net
• Internet domain names: dcs.qmw.ac.uk
• Names
• Pure: are simply uninterrupted bit patterns
• Non-Pure: contain information about the object that they name
Location

• Resolve: a name is resolved when it is Translated into data about the named resource or object
• Binding: association between a name and an object
• A key attribute of an entity that is usually relevant in a distributed system is its address.
• DNS maps domain names to the attributes of a host computer which is IP address
• The X500 directory service maps a person's name onto attributes including their email address and telephone number
• The CORBA Naming Service maps the name of a remote object onto its remote object reference

• Name management is separated from other services
Unification: It is often convenient for resources managed by different services to use the same naming scheme
Integeration: It is not always possible to predict the scope of sharing in a distributed system. Without a common name service, the administrative domains may use entirely different naming conventions!
• Name services were originally quite simple!!!
• corresponding to a single LAN or WAN
• extensible and scalable
• Grapevine
• The Global Name Service

• The Internet Domain Name System (DNS)
• it heavily relies on replication and caching of naming data
• Based on the assumption:
• updates are less frequent
• use of an out-of-date copy of a name translation can generally be detected by client softwares

• A name space is the collection of all valid names recognized by a particular service.
Name spaces require a syntactic definition e.g. “…” is not acceptable as a DNS name.
Name space has hierarchical structure
• Advantages of hierarchical name space
•Each part of a name is resolved relative to a separate context e.g. /etc/password
•Different contexts can be managed by different people

• The Domain Name System (DNS) is a distributed database spreading over Internet, translating human-readable computer hostnames to IP addresses, and implementing reverse DNS lookup by mapping IP addresses to canonical hostnames.
• DNS names are called Domain names
• DNS name space has a hierarchical structure
• Domain name is name space with single administrative authority for assigning names within it and consists several components or labels, separated by delimiter
• e.g. Pc1.uu.se

 DNS is a Fully Qualified Domain Name (FQDN)
 FQDN includes Host name and Domain name
 e.g. Pc1.uu.se
 DNS structure has three levels
 Root Domain (.)
 Top Level Domain (se)
 Second Level Domain (uu)

Resolution is an iterative process which a name is repeatedly presented to naming contexts.
 Name Name context
Name servers and navigation
 Navigation: The process of locating naming data from among several name server in order to resolve a name
Caching
 Cache the results of pervious name resolutions ( DNS resolver cache)

Ipconfig/displaydns
Ipconfig/flushdns
Displays the contents of the DNS client cache
Purges the contents of the DNS client cache

• The Internet DNS is primarily used for simple host name resolution and for looking up electronic mail hosts
• DNS to resolve host names into IP addresses
• DNS to resolve domain names into the IP addresses of mail hosts i.e computers that will accept mail for those domains
• The DNS may return more than one
• The DNS returns an integer preference value for each mall host, indicating the order in which the mail hosts should be tried
• other types of queries
• Reverse resolution: Some soft wares require a domain name to be returned given an IP address. It replies only if the IP address is in its own domain.
• Host information: The DNS can store the machine architecture type and operating system against the domain names of hosts. It has been suggested that this option should not be implemented, because it provides useful information for those attempting to gain unauthorized access to computers.

Iterative Query

Recursive Query

Type
A
NS
CNAME
PTR
HINFO
MX
AXFR
ANY
SOA
Description
Host's IP address
Host's or domain's name server(s)
Host's canonical name, host identified by an alias domain name
Host's domain name, host identified by its IP address
Host information
Host's or domain's mail exchanger
Request for zone transfer
Request for all records
Indicates authority for the domain

 The name nslookup means name server lookup
 Nslookup is used for troubleshooting
 Nslookup is a network administrative command-line tool available for many operating systems for querying the domain name system (DNS) to obtain domain name or IP address mapping or for any other specific DNS record.

 nslookup operates in interactive or non-interactive mode.
 The general command syntax is: nslookup [-option] [name | -] [server]