Every computer connected to the network is assigned a number known as an "IP address." An IP address is a number composed of four integers ranging from 0 to 255 (in computer terms, a 32-bit binary number), for example:

145.216.0.108

To specify a server machine for access from client programs, this IP address can be used. To access a server machine with the above IP address, specify in the URL as follows:

http://145.216.0.108:50000/…​…​ (The bold part is the IP address. The '50000' following the colon ':' is an example of a "port number")

However, there are cases where this method cannot be used. This happens when the computer intended to be used as a server is subject to "dynamic IP address assignment".

Computers that are subject to dynamic IP address assignment do not have a fixed IP address. Instead, an IP address is automatically assigned when the computer is connected to the network. Assigned IP addresses have an expiration period, after which they are reclaimed. Upon reconnection to the network, an IP address is reassigned, but there is no guarantee that it will be the same as before.

In the early days of network proliferation, the only way to assign an IP address to individual computers was to give them a fixed IP address, which was cumbersome to manage. To avoid this, dynamic assignment technology was devised and has become widely adopted.

However, if a server machine’s IP address changes frequently, it is inconvenient to specify the IP address in the URL. That is, if you are using the IP address as a means of identifying the server machine, you need to fix the server machine’s IP address. The IP address can be fixed from the server machine’s control panel. Note that fixing an IP address is usually a system administrator’s authority, so please consult your system administrator.

A name that identifies a computer on the network. To access a server machine using a hostname, specify in the URL as follows:

http://fusionplace.fusions.co.jp:50000/…​…​ (The bold part is an example of a hostname. The '50000' following the colon ':' is an example of a "port number")

Compared to a fixed IP address, hostnames are easier to understand for users and offer several administrative benefits. On the other hand, assigning a hostname to a computer requires a "Domain Name Server (DNS)" that performs the conversion from hostnames to IP addresses. Therefore, if a DNS is not operated within the company, it may require effort to set one up.

Assigning hostnames is also typically an authority of the system administrator.