Transcript ppt - Department of Information Technology

Name Services
Negar Makvandian
Kamyar Niroumand
Department of Information Technology, Uppsala University
Introduction
• 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
Introduction
• 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.
Names, Addresses and other
attributes
• 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
Names, Addresses and other
attributes
• 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 services and the Domain
Name System
• 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
Name services and the Domain
Name System
• 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• use of an out-of-date copy of a name translation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
Name Space
• 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
Domain Name System(DNS)
•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 Structure
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)
Name Resolution
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)
Name Resolution
Ipconfig/displaydns
Ipconfig/flushdns
Displays the contents of the DNS client cache
Purges the contents of the DNS client cache
EXAMPLE OF Domain Name
System
DNS queries
• 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
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•
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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.
DNS queries
Iterative Query
DNS queries
Recursive Query
Resource Records
Type
Description
A
Host's IP address
NS
Host's or domain's name server(s)
CNAME
Host's canonical name, host identified by an
alias domain name
PTR
Host's domain name, host identified by its IP
address
HINFO
Host information
MX
Host's or domain's mail exchanger
AXFR
Request for zone transfer
ANY
Request for all records
SOA
Indicates authority for the domain
Nslookup command
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 command
nslookup operates in interactive or non-interactive
mode.
The general command syntax is:
nslookup [-option] [name | -] [server]
Any Question?
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