In essence, DNS is simply a database that links meaningful names (known as host names), such as microsoft.com, to a specific IP address, such as 192.168.124.1. Simply linking addresses to names is just the beginning, though, because DNS has many more features in addition to host-name-to-address mapping.
The key features of host name to IP mapping are as follows:
In addition to the basic IP-address-to-host-name mapping records stored by the DNS database, records are also maintained by DNS for other purposes. DNS contains a number of record types that facilitate other applications. The Mail Exchanger (MX) record, for example, provides mail servers with the information required to forward e-mail messages to the recipient's e-mail server. Another type of record, the service (SVC) record, is used by Microsoft Active Directory to locate network services.
Seeing the DNS difference
By itself, DNS doesn't appear to do much, and on top of that, DNS can seem a bit intimidating because it has number of different features and record types. One key to understanding the importance of DNS is realizing how other processes and applications depend on the services DNS provides. By understanding how DNS provides the underlying services used by various applications, you can get a clearer picture of why DNS exists and how it works.
Many common applications use DNS services, including
Serving the e-mail connection
E-mail is one of the more popular applications that use DNS. Although the Web simply uses DNS for linking names to IP addresses for Web sites, e-mail servers also require some specialized records above and beyond what is required for basic host name to IP addresses. For example, when an e-mail message is sent from your e-mail client (such as Microsoft Outlook or Netscape Messenger), it can be sent either directly to the target domain (Microsoft.com if the note was sent to user @ microsoft.com) or to another e-mail server that is providing a relay service. If your e-mail application specifies an outgoing (SMTP) mail server that is not the final destination server for the message, you're making use of the relay process.
An e-mail address is made up of two parts: a recipient and a host. In the address [email protected], postmaster is the recipient, the user who will receive the message. This is irrelevant to the SMTP process, though, because the mail transfer agent (MTA) is responsible for making sure that the message gets into the mailbox of the recipient.
The host, domain.tld, is of much more interest. In this case, domain.tld refers not to a host in the traditional sense of an A record but rather to a mail server known as a mail exchanger (MX). This server is responsible for accepting all mail for domain.tld, denoted by a special record — an MX record — in DNS.
Beyond the Web and e-mail are many applications that either rely on or can use DNS services. These applications can include databases, multi-tier Web applications built by using middleware or an application server, peer-to-peer sharing programs, instant messaging, and multiplayer games.
In quite a practical sense, any application that uses the Internet to connect two or more hosts to share information, or otherwise communicate, is probably relying on DNS services in one form or another.
The key features of host name to IP mapping are as follows:
- Mappings of addresses to names and vice versa (known as records) are stored in a database.
- The DNS database is distributed.
- A DNS database also stores additional records.
In addition to the basic IP-address-to-host-name mapping records stored by the DNS database, records are also maintained by DNS for other purposes. DNS contains a number of record types that facilitate other applications. The Mail Exchanger (MX) record, for example, provides mail servers with the information required to forward e-mail messages to the recipient's e-mail server. Another type of record, the service (SVC) record, is used by Microsoft Active Directory to locate network services.
Seeing the DNS difference
By itself, DNS doesn't appear to do much, and on top of that, DNS can seem a bit intimidating because it has number of different features and record types. One key to understanding the importance of DNS is realizing how other processes and applications depend on the services DNS provides. By understanding how DNS provides the underlying services used by various applications, you can get a clearer picture of why DNS exists and how it works.
Many common applications use DNS services, including
- World Wide Web (WWW)
- Other applications, such as instant messaging
Serving the e-mail connection
E-mail is one of the more popular applications that use DNS. Although the Web simply uses DNS for linking names to IP addresses for Web sites, e-mail servers also require some specialized records above and beyond what is required for basic host name to IP addresses. For example, when an e-mail message is sent from your e-mail client (such as Microsoft Outlook or Netscape Messenger), it can be sent either directly to the target domain (Microsoft.com if the note was sent to user @ microsoft.com) or to another e-mail server that is providing a relay service. If your e-mail application specifies an outgoing (SMTP) mail server that is not the final destination server for the message, you're making use of the relay process.
An e-mail address is made up of two parts: a recipient and a host. In the address [email protected], postmaster is the recipient, the user who will receive the message. This is irrelevant to the SMTP process, though, because the mail transfer agent (MTA) is responsible for making sure that the message gets into the mailbox of the recipient.
The host, domain.tld, is of much more interest. In this case, domain.tld refers not to a host in the traditional sense of an A record but rather to a mail server known as a mail exchanger (MX). This server is responsible for accepting all mail for domain.tld, denoted by a special record — an MX record — in DNS.
Beyond the Web and e-mail are many applications that either rely on or can use DNS services. These applications can include databases, multi-tier Web applications built by using middleware or an application server, peer-to-peer sharing programs, instant messaging, and multiplayer games.
In quite a practical sense, any application that uses the Internet to connect two or more hosts to share information, or otherwise communicate, is probably relying on DNS services in one form or another.