DSL Network Guide Chapter 16: DNS and IP Addresses
Whenever you visit a website you do so by entering in it's domain name. To get to the Yahoo! website you do so by entering in www.yahoo.com. So how does your ISP know where to get this information? It does so by finding out it's IP address. An IP address is like a phone number. If you want to call your friend you would look in a phone book and find his phone number and call that number. Likewise whenever you want to access a website your computer access a DNS (Domain Name Server) to find out the websites IP address. Using an IP address the internet can find the website just like the phone network can find someone's house with a phone number. You can diminstrate this by typing http://126.96.36.199. This will take you to yahoo.com because 188.8.131.52 is yahoo's IP address.
Every time your computer connects to the internet your ISP assigns your computer an IP address. Your ISP has a certain "pool" of IP addresses that it can hand out. Whenever your computer makes a request to access a certain IP address your ISP finds out which ISP's IP pool that address belongs to. It then contacts that ISP and that ISP find out exactly who's computer that certain IP address belongs to. Now the two computer can talk to each other. When you visit a website your IP address is given to the other computer so the computer knows who requested the information and where to send that information to.
When you connect to the internet your computer is also assigned a DNS server. SBC customers in Connecticut might be assigned 184.108.40.206 and 220.127.116.11. The first server assigned is the primary server and the second is the secondary server. The secondary is used only if the primary fails to respond. These values can also be manually assigned by you in your computer or on your router. This is usually done if your computer is having trouble resolving domain names. Using these servers your computer can now resolved domain names.
The basic option sold by most ISPs is a dynamic IP address. This means that everytime you connect to the internet you are assigned a different IP address. If you plan on running a VPN or a hosting a server you may need to keep the same IP address. To do this you would need to purchase a static IP address from your ISP. With a static IP address you get assigned the same IP address everytime you connect.
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