The Building Blocks of the Internet
Many components are required to create the worldwide network that we know as the Internet. The following are some of the key components and a description of what they do:
IP (Internet Protocol) address
To locate a device on the Internet, it has to have an address. The addressing scheme used on the Internet is defined by the TCP/IP protocol to have four sections, each of which is a number between 0 and 255 and is separated by a period (e.g. 34.221.98.56).
Domain
To get a "presence" on the Internet, you need to register a Domain in your name that you will have exclusive control over. The Universal Resource Locator (URL) that customers use to reach your site is usually just the Domain Name with a “www" added in front of it. If you want your customers to go to another page on your site other than the default page, you would add the directory and name of that page at the end of your Domain Name.
Router
Routers are devices that connect all the nodes of the Internet together and decide where to send each packet of data. They maintain long tables of IP addresses so they can quickly determine the best (shortest) route to get your data to its final destination.
DNS (Domain Name Server)
All devices on the Internet (Web servers etc.) have a unique IP address. Since these numbers are a bit hard to memorize and type, a system was developed to automatically convert a user-friendly name or Universal Resource Locator (URL) into an IP address. The servers that do this are called Domain Name Servers. When you type a Web site URL into your browser, it will first contact your own ISP's DNS server to see if it can find the corresponding IP address there (which it will if any other customers of your ISP has recently gone to that site as well). If it cannot find it there, it will go to the next higher level of DNS servers on the Internet and will continue to do that until it may eventually reach the DNS server of the ISP that is hosting the Web site (the "authoritative" DNS server for that domain).
This also means that the amount of time it takes to do a DNS lookup on your site will depend on how long the various DNS servers keep your address in their cache. You have some control over the maximum time that any DNS server will store your IP address when you configure the DNS settings for your Domain Name, but you cannot determine the minimum time or which one of the thousands of DNS servers around the Internet actually have your IP addresses recorded in their cache.
Firewall
Firewalls were developed to provide some measure of control over who can access each device on your network. There are several types of firewalls (Stateful Packet Inspection, Proxy etc.) but they all serve to restrict access to only those ports that you really use (e.g. 80 for a Web server, 21 for an FTP host etc.) and block everything else. They can also be used to restrict access based on the source address and the destination address or the specific protocols you want to use (HTTP, SMTP etc.).
