This preview shows page 1. Sign up to view the full content.
Unformatted text preview: ave majo r IP v6 ro llo uts
under way. While the transitio n will be slo w, when wide scale deplo yment do es arrive, IP v6 will o f f er o ther benef its, including po tentially impro ving the speed, reliability, and security o f the
Internet. The DNS: The Internet’s Phonebook
Yo u can actually type an IP address o f a Web site into a Web bro wser and that page will sho w up.
But that do esn’t help users much because f o ur sets o f numbers are really hard to remember. This is where the domain name service (DNS) co mes in. The do main name service is a
distributed database that lo o ks up the ho st and do main names that yo u enter and returns the actual
IP address f o r the co mputer that yo u want to co mmunicate with. It’s like a big, hierarchical set o f
pho ne bo o ks capable o f f inding Web servers, e-mail servers, and mo re. These “pho ne bo o ks” are
called nameserv ers—and when they wo rk to gether to create the DNS, they can get yo u anywhere
yo u need to go o nline. Figure 1 2. 3 When your comp ut er needs t o find t he IP addres s for a hos t or domain name, it s ends a mes s age t o a DNS
res olver, which looks up t he IP addres s s t art ing at t he root names erver. Once t he lookup has t aken
p lace, t hat IP addres s can be s aved in a holding s p ace called a cache, t o s p eed fut ure lookup s . To get a sense o f ho w the DNS wo rks, let’s imagine that yo u type www.yaho o .co m into a Web
bro wser. Yo ur co mputer do esn’t kno w where to f ind that address, but when yo ur co mputer
co nnected to the netwo rk, it learned where to f ind a service o n the netwo rk called a DNS reso lver.
The DNS reso lver can lo o k up ho st/ do main name co mbinatio ns to f ind the matching IP address
using the “pho ne bo o k” that is the DNS. The reso lver do esn’t kno w everything, but it do es kno w where to start a lo o kup that will eventually give yo u the address yo u’re lo o king f o r. If this is the
f irst time anyo ne o n that netwo rk has tried to f ind “www.yaho o .co m,” the reso lver will co ntact o ne
o f thirteen identical ro o t nameservers. The ro o t acts as a lo o kup starting place. It do esn’t h...
View Full Document
This document was uploaded on 01/31/2014.
- Winter '14