DYNAMIC DNS

DNS? What's that???.........

HERE'S ANSWER::-

You got to this Web page by looking up http://www.sahilarora.org/dynamic/. DNS, the Domain Name Service, is responsible for the big part in the middle: www.sahilarora.org. The Internet is divided into literally millions of domains; each one has its own name.To a human, names like that (or ibm.com, or yahoo.com, or any of the other four million domain names registered) make perfect sense. IP addresses consist of four numbers, each between 0 and 255. More or less. (Some blocks of numbers are reserved for a variety of special purposes.) But not to the computer.

The computer doesn't have a clue. Computers work with numbers. Computers use IP addresses ("dotted quad" numbers like 10.20.30.255) to talk with each other on the Internet.

DNS is the middleman, translating domain names into numbers (and, occasionally, the other way around).

DYNAMIC DNS? What's that???.........

HERE'S ANSWER::-

In theory, there are 2³² (about 4.29e9, 4 billion or so) possible numeric addresses for the Internet. In practice, though, many of them were allocated in an inefficient manner a long time ago, in a way that can't easily be undone today. Some groups, like MIT, were given literally millions of addresses, more than they can ever use, but it's not really practical for them to give them back now. Over the next few years, IPv6 will be phased in, increasing the number of addresses to 2¹²⁸ (3.40e38, give or take), enough for everyone and all their major appliances to have an address. But until then...

There's only so many numbers out there, at least as far as the computer is concerned. (Basically, each of the four parts in the "dotted quad" address can only be between 0 and 255.) Silly technical limitations eat up a lot of those addresses; historical design decisions eat up some more; and of course a LOT of them are already in use.

This means that Internet IP addresses are a finite, scarce resource, and have to be treated somewhat carefully.

EXAMPLE::=

Suppose you have a normal, $20 per month, Internet dialup account from "Some Local ISP, Inc." They have three thousand customers, but it's rare that all of them are online at the same time. (In fact, if they follow industry practice, they probably only have 500 or so phone lines anyway.) So that ISP may only have 600 or 700 IP addresses -- enough to provide one for each phone line, a few for internal use, a few for future growth, but nowhere near one for each of those 3000 customers.

Or maybe you have a cable modem, though "Big CableCo Inc." Whenever your cable modem goes online (when you first plug it in and turn it on), it broadcasts a request for an open address, and some computer in their office eventually answers. Cable modem addresses are usually assigned with "leases," which work just like the lease on an apartment - you're guaranteed to have that address for a certain time, but after that all bets are off. Your landlord (the cable company) might evict you, forcing you to move (get a new IP address) at the end of the lease. (These 'leases' usually only last for a few days, and sometimes only a few hours.) At the end of the lease, you may be able to negotiate a new lease, but you can't be sure of it.

So not everyone can have their own IP address. Your ISP, cable company, or whoever, might let you have a dedicated IP, but they'll probably charge you extra for it. It's more likely, though, that they can't or won't help you...

FUNCTION:::-

Dynamic DNS providers provide a software client program that automates the discovery and registration of client's public IP addresses. The client program is executed on a computer or device in the private network. It connects to the service provider's systems and causes those systems to link the discovered public IP address of the home network with a hostname in the domain name system. Depending on the provider, the hostname is registered within a domain owned by the provider or the customer's own domain name. These services canfunction by a number of mechanisms This group of services is commonly also referred to by the term Dynamic DNS, although it is not the standards-based DNS Update method. However, the latter might be involved in the providers systems.