Know How Domain Name Servers Work

Written by Pawan Bangar

Continued from page 1


DNS uses principle of ‘caching' for its operation. When a nameservers receives Information about a mapping, it caches this information .further queries forrepparttar same mapping will use this cached result, thereby reducingrepparttar 107787 search cost. The nameservers don't cache forever. The caching has a component called time to live (TTL) andrepparttar 107788 TTL determines how long a server will cache a piece of information. So whenrepparttar 107789 nameservers caches receive an IP address, it receivesrepparttar 107790 TTL with it. The nameserver cachesrepparttar 107791 IP address forrepparttar 107792 period of time then discards it.

When a process needs to determine an IP address given a DNS address, it calls uponrepparttar 107793 local host to resolverepparttar 107794 address. This can be done in variety of ways:

•Table look up. On UNIX hosts,repparttar 107795 table is /etc/hosts.

•The process communicates with a local nameservers. This is named on a UNIX system.

•By sending a massage torepparttar 107796 remote system that is identified fromrepparttar 107797 information inrepparttar 107798 file/etc/resolve.conf.

When a nameserver receives a query for a domain that is does not serve, it may send back a referral torepparttar 107799 client by specifying better nameservers. Typically operate inrepparttar 107800 recursive manner wherein any DNS server passes requests it cannot handle to higher level server and so on, until eitherrepparttar 107801 request can be handled or untilrepparttar 107802 root ofrepparttar 107803 DNS name space is reached.

The nameservers contain pointers to other nameserver withrepparttar 107804 help of which it is possible to traverserepparttar 107805 entire domain naming hierarchy. A host withrepparttar 107806 initial nameserver addresses has to be configured. After this, it is able to use DNS protocols to locaterepparttar 107807 nameserver responsible for any part orrepparttar 107808 DNS naming hierarchy.

Thus when a nameserver receives a request, it can do one ofrepparttar 107809 following:

•It can answerrepparttar 107810 request with an IP address. This method is called iterative. In this,repparttar 107811 client simply asksrepparttar 107812 server to resolve a domain name. The server accesses its database, finds its IP address and sends that back. Ifrepparttar 107813 server does not findrepparttar 107814 address, it sends back an error (‘DNS not found'). •Contact another nameserver and try to findrepparttar 107815 IP address forrepparttar 107816 requested name. •Send back a referral torepparttar 107817 client specifyingrepparttar 107818 IP address of better nameservers.

DNS transaction occurs widely overrepparttar 107819 internet. The two most common types of transaction are DNS zone transfers and DNS queries/responses.

A popular user interface, called ‘nslookup'is available onrepparttar 107820 UNIX system. With this, you can perform any DNS function. This program also displaysrepparttar 107821 result torepparttar 107822 user. Using is nslookup, you can obtain a listing of allrepparttar 107823 hosts in a zone. In order to do this, you first need to identifyrepparttar 107824 nameserver forrepparttar 107825 zone.

The threats that are associated withrepparttar 107826 DNS are due torepparttar 107827 lack of integrity and authenticity checking ofrepparttar 107828 data held withinrepparttar 107829 DNS. Also, other protocols can use host names as an access control mechanism. The internet engineering task force (IETF) has come up with DNS security (DNSSEC) extensions to DNS protocol. The main objective to DNSSEC is to provide authentication and integrity torepparttar 107830 DNS. These are provided throughrepparttar 107831 use of cryptographic `

Pawan Bangar Technical Director, Birbals,India. Reach Pawan visit,,,

Why to Adopt .Net

Written by Pawan Bangar

Continued from page 1
•New opportunities: with .Net software and services, corporate IT departments will share inrepparttar ability to create new and novel revenue streams. By exposing key business processes that were typically locked in internal systems,repparttar 107786 enterprise can create a number of new and exciting opportunities to make money. •Empowering Employees: .Net offersrepparttar 107787 promise of allowing employees to act onrepparttar 107788 appropriate information where and when they need it. A contact or appointment added to a pocket PC by a project manager while at a job site can instantly be accessible to members ofrepparttar 107789 same team scattered throughrepparttar 107790 world.

Pawan Bangar Director birbals group India

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