Know How DNS Works – Domain Name
Know How DNS Works
Pawan Bangar
Domain name Servers DNS are an important but invisible part of the internet, and form one of the largest databases on it. Each machine on an internet is assigned a unique address, called an IP address, which is 32 bit number and is expressed as 4 octets. The method user to represent these IP addresses is known as dotted decimal Notation". A typical address looks like this: 199.249.150.4
It is very difficult to keep in mind the IP addresses of all the websites we visit daily, because its not easy to remember strings of numbers. However, we do remember words. This is where domain names come into the picture. If you want to connect to a particular site, you need to know its IP address but do need to know its URL. The DNS gets the mappings of the IP addresses and the corresponding names.
Names and numbers
DNS converts the machine names such as www.xyz.com to IP addresses such as 199.249.150.9. Basically, it translates from a name to an address and from an address to a name.
The mapping from the IP address to the machine name is called reverse mapping .when you type http://www.xyz.com into your browser, the browser first needs to get the IP address of www.xyz.com. The machine uses a directory service to look up IP addresses and this service is called DNS. When you type www.xyz.com your machines firsts contacts a DNS server, asking it to find the IP address for www.xyz.com. This DNS server might then contact other DNS servers on the internet. DNS is therefore is considered as the global network of servers. The great advantage of DNS is that no organization is responsible for updating it. It is what is known as distributed database.
The three letter codes
A DNS server is just a computer thats running the DNS software. The most popular DNS software is BIND Berkeley Internet Name Domain DNS is hierarchical, tree-structured system. The top is donated by.. And is known as the root of the system. Below the root there are seven immediate sub domain nodes and these are com, org, gov, mil, net, edu, Int, etc.
DNS consists of two components
Nameserver
Resolver
Nameserver:
This performs the task of looking up the names. Usually, there is one nameserver for a cluster of machines. If the nameserver does not contain the requested information, it will contact another nameserver. But it is not required for every server to know how to contact every other server. Every nameserver will know how to contact the root nameserver, and this in turn will know the location of every authoritative nameserver for all the second level domains.
Resolver:
This runs on a client machine to initiate DNS lookups. It contains a list of nameservers to use. As we have read, the function of each of these nameservers is to resolve name queries. There are three types of nameservers-primary nameserver, secondary nameserver, and caching nameserver. The secondary nameservers are configured for backup purposes. Caching nameservers only resolve name queries but do not maintain any DNS database files. It is important to note here that any change to primary nameservers needs to be propagated to secondary nameservers. This is because primary nameservers own the database records. The changes are propagated via a zone transfer.
HOW CACHING"WORKS
DNS uses principle of caching for its operation. When a nameservers receives Information about a mapping, it caches this information .further queries for the same mapping will use this cached result, thereby reducing the search cost. The nameservers dont cache forever. The caching has a component called time to live TTL and the TTL determines how long a server will cache a piece of information. So when the nameservers caches receive an IP address, it receives the TTL with it. The nameserver caches the IP address for the period of time then discards it.
When a process needs to determine an IP address given a DNS address, it calls upon the local host to resolve the address. This can be done in variety of ways:
Table look up. On UNIX hosts, the table is /etc/hosts.
The process communicates with a local nameservers. This is named on a UNIX system.
By sending a massage to the remote system that is identified from the information in the file/etc/resolve.conf.
When a nameserver receives a query for a domain that is does not serve, it may send back a referral to the client by specifying better nameservers. Typically operate in the recursive manner wherein any DNS server passes requests it cannot handle to higher level server and so on, until either the request can be handled or until the root of the DNS name space is reached.
The nameservers contain pointers to other nameserver with the help of which it is possible to traverse the entire domain naming hierarchy. A host with the initial nameserver addresses has to be configured. After this, it is able to use DNS protocols to locate the nameserver responsible for any part or the DNS naming hierarchy.
Thus when a nameserver receives a request, it can do one of the following:
It can answer the request with an IP address. This method is called iterative. In this, the client simply asks the server to resolve a domain name. The server accesses its database, finds its IP address and sends that back. If the server does not find the address, it sends back an error ;DNS not found. Contact another nameserver and try to find the IP address for the requested name. Send back a referral to the client specifying the IP address of better nameservers.
A popular user interface, called nslookupis available on the UNIX system. With this, you can perform any DNS function. This program also displays the result to the user. Using is nslookup, you can obtain a listing of all the hosts in a zone. In order to do this, you first need to identify the nameserver for the zone.
The threats that are associated with the DNS are due to the lack of integrity and authenticity checking of the data held within the 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 to the DNS. These are provided through the use of cryptographic
About The Author
Pawan Bangar,
Technical Director,
Birbals, Ebirbals, SeoBirbals, Hbirbals
India.
Visit us at:
www.birbals.com
www.ebirbals.com
www.hbirbals.com
How to Create A Homepage That Works – Site
How to Create A Homepage That Works
Mike Cheney
Want to know what the worst thing to say on a homepage is " Welcome to our homepage." And yet, time after time, we all come across such homepages on the Internet. The reason that this is such a poor opening gambit is the fact that the visitor already knows he / she is looking at your homepage, whats the point in teaching them to suck eggs
Your websites homepage needs to contain much more important messages than a simple welcome statement or brief history to your company. Why has someone landed on your website in the first place What problem are they looking to solve What type of information do they seek If your homepage doesnt convey that your website has the answers to these questions in the visitors minds then its game over - they will leave, never to return.
3 Seconds To Make The Right Impression
So how you can retain visitors and grab them as soon as they view the homepage of your website Well, try condensing the key selling points of your business. Why are you different Why should they do business with you as opposed to anyone else
A lot of businesses also lose sight of the fact that their homepage should not only convey what the business is about but also what the website is about. What can visitors do on the website What types of information can they find here What are the best things about the website If you dont convey all these vital messages quickly via the homepage people will not stick around trying to find the answers themselves deeper within the site.
Put Yourself In The Shoes Of Your Customer
As with many marketing approaches the key here is to take a step back and imagine yourself as a customer viewing the homepage for the first time. What would you want to see Perhaps client comments to instil a sense of trust. Or maybe press clippings that illustrate the profile and respectability of the company
Whatever you decide to place on the homepage keep it snappy. Less is more. Its a clich
How Your Cars Suspension Works – Auto
How Your Cars Suspension Works
Kevin Schappell
"Suspension," when discussing cars, refers to the use of front and rear springs to suspend a vehicles "sprung" weight. The springs used on todays cars and trucks are constructed in a variety of types, shapes, sizes, rates, and capacities. Types include leaf springs, coil springs, air springs, and torsion bars. These are used in sets of four for each vehicle, or they may be paired off in various combinations and are attached by several different mounting techniques. The suspension system also includes shocks and/or struts, and sway bars.
Back in the earliest days of automobile development, when most of the cars weight including the engine was on the rear axle, steering was a simple matter of turning a tiller that pivoted the entire front axle. When the engine was moved to the front of the car, complex steering systems had to evolve. The modern automobile has come a long way since the days when "being self-propelled" was enough to satisfy the car owner. Improvements in suspension and steering, increased strength and durability of components, and advances in tire design and construction have made large contributions to riding comfort and to safe driving.
Cadillac allegedly produced the first American car to use a steering wheel instead of a tiller.
Two of the most common steering mechanisms are the "rack and pinion" and the standard or recirculating-ball systems that can be either manual or assisted by power. The rack and pinion was designed for sports cars and requires too much driver muscle at low speeds to be very useful in larger, heavier cars. However, power steering makes a heavy car respond easily to the steering wheel, whether at highway speeds or inching into a narrow parking place, and it is normal equipment for large automobiles.
The suspension system has two basic functions, to keep the cars wheels in firm contact with the road and to provide a comfortable ride for the passengers. A lot of the systems work is done by the springs. Under normal conditions, the springs support the body of the car evenly by compressing and rebounding with every up-and-down movement. This up-and-down movement, however, causes bouncing and swaying after each bump and is very uncomfortable to the passenger. These undesirable effects are reduced by the shock absorbers.
The above information is directly from the Auto Insight program, which you can buy online from AutoEducation.com.
Common Problems:
Shocks and struts can wear out and affect handling. If you car bounces excessively over bumps and leans hard in corners, your shocks could be warn. Look behind the wheel for the shock or strut and look for leaking oil. This is a sure sign of a worn shock or strut.
Ball joints. Ball joints wear and can cause your car to wander while driving down the road. This is dangerous as they can separate and cause you to lose control.
Preventive maintenance:
Check your shocks or struts for leakage frequently. Also pay attention to how your car handles. If you notice the ride deteriorating take your car in to have the struts checked.
Ball joints should be checked when your car is inspected, if not, have your mechanic check them at least twice a year.
At each oil change make sure you or your mechanic lubricates the ball joints and any other suspension components. Some components cannot be lubricated as they are sealed from the factory.
About The Author
Kevin Schappell maintains http://www.carbuyersclub.com where he gives advice on buying, selling, insurance, and financing. A mechanical engineer and car guy, Kevin has decided to spend his online time helping others learn about automobiles. To learn more about how your car works, Kevin has created http://www.mycarwizard.com.
kevin@schappell.com