Caches are perio dically cleared and ref reshed to

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Unformatted text preview: ave o ne big list, but it can po int yo u to a nameserver f o r the next level, which wo uld be o ne o f the “.co m” nameservers in o ur example. The “.co m” nameserver can then f ind o ne o f the yaho o .co m nameservers. The yaho o .co m nameserver can respo nd to the reso lver with the IP address f o r www.yaho o .co m, and the reso lver passes that inf o rmatio n back to yo ur co mputer. Once yo ur co mputer kno ws Yaho o !’s IP address, it’s then ready to co mmunicate directly with www.yaho o .co m. The yaho o .co m nameserver includes IP addresses f o r all Yaho o !’s public sites: www.yaho o .co m, games.yaho o .co m, spo rts.yaho o .co m, f inance.yaho o .co m, and so o n. The system also remembers what it’s do ne so the next time yo u need the IP address o f a ho st yo u’ve already lo o ked up, yo ur co mputer can pull this o ut o f a sto rage space called a cach e, avo iding all tho se nameserver visits. Caches are perio dically cleared and ref reshed to ensure that data ref erenced via the DNS stays accurate. Distributing IP address lo o kups this way makes sense. It avo ids having o ne huge, hard-to -maintain, and ever-changing list. Firms add and remo ve ho sts o n their o wn netwo rks just by updating entries in their nameserver. And it allo ws ho st IP addresses to change easily, to o . Mo ving yo ur Web server o f f -site to a ho sting pro vider? Just update yo ur nameserver with the new IP address at the ho sting pro vider, and the wo rld will invisibly f ind that new IP address o n the new netwo rk by using the same o ld, f amiliar ho st/ do main name co mbinatio n. The DNS is also f ault-to lerant—meaning that if o ne nameserver go es do wn, the rest o f the service can f unctio n. There are exact co pies at each level, and the system is smart eno ugh to mo ve o n to ano ther nameserver if its f irst cho ice isn’t respo nding. But What If the DNS Gets Hacked? A hacked DNS wo uld be a disaster! Think abo ut it. If bad guys co uld change which Web sites lo ad when yo u type in a ho st and do main name, they co u...
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