IP Addresses, Host Names, and Domain Names


Every computer connected to the internet is unique. You can look at any machine that connects the internet in both ways.

Its own IP address (four-digit string, such as ""), in which the first section (s) identifies the specific network in which the machine is connected (for example, "18" refers to MIT's main network)
By its host name (Text strings, for example. "Bitsy.mit.edu"), which contains machine names (such as "bitsy") and domain names (such as "mit.edu" referring to the main MIT network).
Internet Domain Name Service (DNS) can translate hostnames into equivalent IP addresses and vice versa as needed by various programs on the Internet.

This document describes these indicators and explains how to find an address. IP and how to find the hostname and domain name of a specific computer.

IP address
All computers connected to the Internet are identified by four unique strings known as the Internet Protocol (IP). The IP address consists of four numbers. (Each between 0 and 255) separated by time. For example, one machine at MIT has an IP address, such as

At MIT, most machines will have IP addresses starting with "18". "18" refers to MIT's main network, while subsequent numbers specify specific machines. (On other sites, for the first time, two pieces of the IP address identify the network, while the last two segments identify the computer within the network.)

While we often think of IP addresses as four numbers separated by the entire string range, actually a single format 32 bit is "decimal dotted". This number is why each part can only reach up to 255: - or "octet" - is the decimal representation of the binary number 8.

Hostname and domain name
Since IP addresses are quite difficult to remember. (And not particularly narrated), the internet also allows you to specify the computer by name rather than the number of strings. For example, a machine at MIT has an IP address. It can also be called: bitsy.mit.edu.

This whole string is known by the host computer name. In this line, the first part ("bitsy") is the name of the machine itself, while everything else ("mit.edu") is the domain name.

The domain name is the name of the network associated with the organization. For websites in the United States, domain names often use the format: org, type .org, type.

Org org is usually one of the following:

com indicates that commercial organizations (such as companies)
Edu indicates that educational organizations
org indicates general (Usually not commercial) organization
Gov indicates that US government agencies
Million shows the site of the US Army.
For example, the hostname www.toyota.com refers to the World Wide Web server "www" in the toyota.com domain. Ftp.stanford.edu hostname refers to an FTP server named "FTP" on the local network of Stanford University (stanford.edu domain).

MIT actually has many separate networks in operation, so many domain names are associated with MIT. In addition, the main domain mit.edu has, for example, the domain associated with artificial intelligence laboratories at MIT, call ai.mit.edu. (Both domain names that MIT will not use instead. "Alias": A machine with the host name www.ai.mit.edu is not on the same device - or even in the same internet domain - is a machine with The host name www.mit.edu is quite www.ai.mit.edu is the name "www" in the ai.mit.edu domain, while www.mit.edu is the machine named "www" in different domains. Mit edu .)


For sites outside of the United States, domain names usually use the format: org, name, country, id (eg CA for Canada, Germany / Deutschland)

Although every machine has only one IP address at any given time, the machine may have multiple hostnames. (Additional hostnames are also known as "aliases".) For example, the official web service of MIT will run on host machines. "Arachnophobia.mit.edu" ( IP address), but the user refers to the machine by the host name alias. "Web.mit.edu"

Using host aliases makes it easier for service providers to migrate services to new machines without interrupting service. For example, if the care of the MIT web service moves to a faster machine, the new hostname "Web.mit.edu" may change to point to a new machine and remove it as an alias for ("arachnophobia.mit.edu". "May still be the hostname of the old machine); The user is not burdened with having to learn a new IP address or host name from the aliasing point to the new machine.

Domain Name Service (DNS)
On the Internet, many communication programs deal exclusively with IP addresses, also allowing users to identify machines in terms of their hostnames. (Or the hostname alias), or a program that already knows that the IP address must specify a domain name for the connected network. The program must somehow convert the hostname into an IP address (or vice versa) behind the scenes. How did they successfully translate this IP address and hostname?

Mapping of hostnames to IP addresses is handled via a service called Domain Name Service (DNS), rather than using individual machines, programs, or users to keep up with the constant changes in hostnames and addresses. The IP address sets a special global DNS server (the so-called "name server"). All computers on the Internet Applications that need to monitor IP addresses from hostnames (or vice versa) "Name Server" to provide this information.

For example, if you use a web browser to monitor a website. "Web.mit.edu" program actually lists the first place your local DNS machine will get the IP address that matches the hostname you provided; Then the program uses the IP address to process your request.

DNS is often used more often than it should be: virtually every activity that migrates data to the network. (Receive web documents, transfer files, send or receive electronic mail) rely on DNS

Find IP address
There are several ways to find out what IP address is assigned to a particular computer at MIT:

Let people have many possibilities:
Local network administrator (Which may be configured machine)
The person in the department who pays (the IP address will appear on the billing & T)
Service counter, 617.253.1101
If you change an existing device to a new device, you may use an old IP address that you may have saved. For example, if you copy your .cfg file to a floppy before installing Windows 95, you will keep your IP address and can find it in the floppy.
If you have access to Athena and you know the host and domain name of the machine, you can use the hostinfo command to determine the corresponding IP address. For example, to find the IP address for machines with "bitsy" hostnames and "mit.edu" domain names, you can enter Athena and in athena% prompt. Enter the following:
athena% hostinfo gator.99progame..com
Preferred hosts: gator.99progame..com
Official name: gator.99progame..com
Host address:
Hosted Information: DEC / DECSTATION-5000.25 / Ultrix
Line with text The "host address" provides an IP address.

Find the hostname and domain name.
If you already know the IP address of a computer connected to MITnet, you can find the host name and domain name of the machine in any of several ways:

SIPB web form filling machine
If you have access to Athena, you can also set a hostname that corresponds to the IP address given by the hostinfo command. For example, to find the domain and domain name for, you can enter Athena and in athena% prompt, enter the following:
Athena% hostinfo
Preferred hosts:
Official name: gator.99progame..com
Host address:

On the line that says "Official name", gator is the hostname. 99progame..com is the domain name.



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