http://www.Curtis-M-Kularski.info
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The Internet and its structure is very complex. Most people don't know how things actually work, or don't care to know. It is good for people to have a general understanding of DNS hierarchy, so if a problem arises, it will be possible to contact the correct people to fix it. The very base of the Internet is called the Root Zone. The Root Zone consists of 13 servers, A.Root-Servers.net to M.Root-Servers.net. From there, your Internet Service Provider retrieves information from those servers in the form of a DNS ZONE Transfer and places the available data on their DNS servers for retrieval. WEB / WWW When you first request a web-page in your browser, the browser forwards your request to the DNS server at your Internet Service Provider. Your Internet Service Provider had previously retrieved the information from the Root Zone Servers. Most ISPs will update their servers once every 12 hours. The data that is retrieved from the ISP's DNS Server is the list of servers that hold data about the domain name you are trying to access, the servers listed are called Name Servers. Once your computer has the list of servers, it contacts the first one on the list and asks the server for the most recent data available for the domain name your requested. The data that your computer receives is the IP (Internet Protocol) address of the host/server that actually contains the data you requested. That data looks like this to humans: DOMAIN.COM. IN A 192.168.1.115 Once the IP address is received, the computer will connect to it and ask for the page that you want. Within a matter of seconds, all of this takes place and your computer displays the page that you asked for. The information that directs your computer to the right server to get to a website is called a DNS file. All levels of the Internet that require DNS servers to operate are called "DNS ZONES". The Root Zone is ".", and specify sub-domains such as ".com", ".net" and ".org". Commonly, the "Sub-domains" of the Root Zone are called TLDs or Top Level Domains. The Root Zone holds data for the servers that maintain the TLDs and allows their queries to be successfully carried out. After the TLDs are specified by the Root ZONE, the ZONEs of the TLDs then provide data for Domains. Domains such as "Curtis-M-Kularski" exist under the TLDs, in this case it is "INFO", when they are combined you get the address "Curtis-M-Kularski.info". Even farther down, the ZONEs of the domains also can specify other levels. If you type WWW before a domain name, that is called an SLD, or Second Level Domain. As with the other levels contained within a ZONE, an SLD also can contain a ZONE, however it is very uncommon. If you register a domain with the Official United States Domain Registry (http://www.nic.us), your domain will be assigned in the format of Name.City.State.US, all of the levels in that CAN contain ZONE data, however only .US and NAME have to. "Name.City.State" can exist in the DNS/ZONE file for .US by itself, then the data for NAME can exist in the NAME Zone file. That is possible because no other levels contain data. E-mail works in a similar manner to accessing a web site, but a little more is involved. When you send e-mail, you connect to an SMTP Server. If your server uses the name SMTP.YOURNAME.COM, then the e-mail application will communicate with your ISP's DNS Server and get information for YOURNAME.COM, which will lead to a DNS file that contains the record that specifies the sub-domain of SMTP. Your e-mail program will use that data to connect to the IP Address of the server. Once connected, the SMTP server will receive the outgoing e-mail. When the e-mail is transferred to the SMTP server, your e-mail application is out of the picture. If the e-mail is being sent to Somebody@Somewhere.com, the SMTP server will access the DNS record for SOMEWHERE.COM, the data may look something like this: SOMEWHERE.COM. IN MX 10 MAIL1.SOMEWHERE.COM. The data above is an example of the e-mail portion of a DNS file. The first 2 lines are Mail Exchanger (MX) Records. An MX record has something that no other DNS record does, a preference label. In the first line, "10" is the preference; in the second line "20" is the preference. The purpose of the preference is to have multiple servers available to receive e-mail, in the event that the primary e-mail server is down. The lowest number receives the highest preference. A DNS file can contain as many MX records as needed, but you shouldn't be concerned even is only 1 server is listed for your e-mail provider, because as long as ZONE data exists for a domain, a sending server will retry up to 100 times (depending on its software) before returning an error to the sender and deleting the e-mail. The last 2 lines in the set of data specifies the IP addresses of the servers, in the format of a standard A record. Once the SMTP server has obtained the address of the receiving e-mail server, the e-mail is transferred and the other server stores the e-mail for later retrieval by the user. The user on the other end (somebody@somewhere.,com) will then check their e-mail using an e-mail client program. The e-mail client program will connect to either a POP or IMAP based e-mail server, in this case POP.SOMEWHERE.COM. The client will query the ISP's DNS server to get the name server list for SOMEWHERE.COM, then it will use one of the servers on this list to obtain the address of POP residing in the SOMEWHERE.COM domain. Finally, the e-mail client will connect to the IP address and download the e-mail. YOU HAVE MAIL! COMING SOON: a diagram explaining everything above. |
Curtis M. Kularski |
