The group of computers that belong to the same company/organisation and share the part of the IP address is called domain. It can be identified by the domain name, that is usually representing type of the company/organisation.
In networking term Fully Qualified Domain Name (FQDN) is referring to a local host name together with its domain name.
Domain name consists of characters or labels separated by dots. The closer label is to the right, the higher level domain it is. As an example lets use this website where the article is located fiberbit.com.tw. The .tw is top level domain (TLD), .com is the second level domain, and fiberbit is the third level domain.
Table 1. Some well-known top-level domains.
Domain suffix
Type of organisation
ARPA
Reverse lookup domain (special Internet function)
COM
Commercial
EDU
Educational
GOV
Government
ORG
Noncommercial organisation
NET
Network
INT
International Treaty Organisation
MIL
US military organisation
BIZ
Businesses
INFO
Unrestricted use
AERO
Air-transport industry
COOP
Cooperatives
Domain names are registered in the ICANN, by the authority. Table 1 shows most important TLDs that are used in the world. On top of that there are also TLPs for every country/territory in the world (for example .tw means Taiwan).
When the domain is registered, the name is being reserved. The global database is being updated, so no other person/organisation can use the same domain. Domain name is limited by 253 characters, which include letters, numbers, and special characters.
