Note: This is a very simplified example of how DNS (Domain Naming System) works. I'm ignoring things like secondary DNS servers, DNS caching, etc.
Note: Computers only use the numeric addresses of computers
(IP address), not the alphanumeric names. The alphanumeric names
(i.e. www.Unixhub.com) are for humans not computers.
- Sue wants to go to www.UnixHub.com. She types "www.Unixhub.com" into her browser. Her computer ask her ISP's DNS server if it knows the address of www.Unixhub.com (the IP address). Her ISP's computer doesn't (it doesn't have the address cached).
- Her ISP's DNS server goes to the Internet's "Root Server A" (The master server of the Internet run by NSI) and ask it which DNS server knows everything about the domain Unixhub.com (the "authoritative" DNS server for that domain).
- Root Server A tells Sue's ISP's DNS server that the DNS server at 216.181.73.179 knows everything about the domain Unixhub.com.
- Sue's ISP's DNS server goes to 216.181.73.179 and ask it what is the address (IP) for www.Unixhub.com.
- 216.181.73.179 (Unixhub.com's authoritative DNS server) tells Sue's ISP's DNS server that the address (IP) for www.Unixhub.com is 216.181.73.180.
- Sue's ISP's DNS server tells Sue's computer that www.Unixhub.com's address is 216.181.73.180 and her computer makes the connection.
Extended Notes:
- DNS and network routing have nothing to do with each other. DNS is simply a naming system. Network routing works at the IP (numeric address) level and couldn't care less what DNS says. (Many people seem to think that DNS controls the routing of the Internet).
- Routing on the Internet is controled by routers (Cisco routers are the most popular. They are OSI level 3 devices in the OSI network model). Routers route via protocols such as RIP (Routing Information Protocol), ASN (Autonomous System Numbers), BGP (Border Gateway Protocol), OSPF (Open Shortest Path First), etc. (see your local router consultant for more details...)
- DNS servers will "cache" (remember) addresses that they look up (this reduces the load on the Root Servers (there are actually 13 of them, they are named Root Server A-M). This can cause prorogation delays when you make changes to your DNS servers (up to 7 days normally).