DNS lam viec nhu the nao?

DNS (Domain Name System) la mot he co so du lieu phan tan dung de anh xa giua cac ten mien va cac dia chi IP. DNS dua ra mot phuong phap dac biet de duy tri va lien ket cac anh xa nay trong mot the thong nhat.

Trong pham vi lon hon, cac may tinh ket noi voi internet su dung DNS de tao dia chi lien ket dang URL (Universal Resource Locators). Theo phuong phap nay, moi may tinh se khong can su dung dia chi IP cho ket noi ma chi can su dung ten mien (domain name) de truy van den ket noi do. Voi mo hinh phan cap nhu hinh duoi day :

Mo hinh phan cap ten mien

De hieu ro hon ve hoat dong cua DNS chung ta xet vi du va tham khao hinh ve duoi day:

• Dau tien PC A gui mot request hoi server quan ly ten mien vnn hoi thong tin ve www.yahoo.com.
  Server quan ly ten mien vnn gui mot truy van den server top level domain.
   
• Top level domain luu tru thong tin ve moi ten mien tren mang. Do do no se gui lai cho server quan ly ten mien vnn dia chi IP cua server quan ly mien com (goi tat server com).
   
• Khi co dia chi IP cua server quan ly ten mien com thi lap tuc server vnn hoi server com thong tin ve yahoo.com. Server com quan ly toan bo nhung trang web co domain la com, chung gui thong tin ve dia chi IP cua server yahoo.com cho server vnn.
   
• Luc nay server vnn da co dia chi IP cua yahoo.com roi. Nhung PC A yeu cau dich vu www chu khong phai la dich vu ftp hay mot dich vu nao khac. Do do server vnn tiep tuc truy van toi server yahoo.com de yeu cau thong tin ve server quan ly dich vu www cua yahoo.com.
  
• Le duong nhien khi nhan duoc truy van thi server yahoo.com gui lai cho server vnn dia chi IP cua server quan ly http://www.yahoo.com/.
   
• Cuoi cung la server vnn gui lai dia chi IP cua server quan ly www.yahoo.com. cho PC A va PC A ket noi truc tiep den no. Va bay gio thi server vnn da co thong tin ve www.yahoo.com cho nhung lan truy van den sau cua cac client khac.