A host is a location on a network, used to describe where Internet services are located. It is the minimum amount of details needed to show where a service is, such as an IP address in a TCP/IP network. These details are created using an operating system such as Linux.
Hosts are useful when describing a network because they hide the details of what things have been used to build the network. In a TCP/IP network the only description of a host that you can be sure to get is the IP address, such as "18.104.22.168". You usually get a DNS name to go with the IP address, like AmandaHuggenkiss, HughJanus or MikeRotch.
In the early days of the Internet it was a pretty good guess that one host was one real computer and you could use the two names interchangeably, but now the only thing you can be sure of is that a host is a thing that services run on. A company may create a network of a dozen hosts for their Internet customers to use, but this network may actually be built using any combination of hardware and software. It may be:
- one big computer,
- two computers running the Microsoft Windows OS (Operating Sytem) and two running Linux, or
- twelve toasters running FreeBSD.
Technicians working on the Internet often stick to talking about hosts so they can skip all this complicated administration stuff. The host view is all that anyone using an Internet service sees. Anyone using the services on a host has no idea what the underlying layers are. Anyone administering the host has access to the operating system and can find out all about the hardware and software.
A host is built from operating system resources. An operating system turns a collection of computer devices into a set of resources that applications and services can use. A host is also a set of computer resources, but a more abstract set. One is built on top of another, much like a TCP/IP network can be built on an ethernet network. At the bottom is a layer of computer devices and their controlling software. On top of that is the operating system layer. The operating system hides the annoying little differences between one computer and another from the people and programs that use it. Clever operating systems allow a layer of hosts to be created on top of the operating system.
Lots of hosts can run on one system. If an administrator sets up a PC that supports only one host, you can change the word "host" to "computer" and everyone will still know what you are talking about. If the administrator sets up one behemoth mainframe computer that runs lots of hosts on it, people will start to look at you funny when you mix up the terms. This kind of many-hosts-to-one-computer setup is common in web hosting companies.
Each host in the LIC has a name five characters long eg. ics01.
A host is not anything physical, like a rack or hardware.
The host is not the computer or the operating system, but these terms are often used interchangeably.
A host is also referred to as a server but I assiduously (what does that mean?) avoid calling a host a server because I get very confused with overlapping names.
The LIC has a lot of Internet services running on hosts. An Internet service is the software that gives access to Internet resources. Internet resources are data files containing electronic representations of just about everything.
If we take one step away from the abstract picture of the LANS and one step closer to reality we get this illustration which shows the computers in each LAN. The data center has about as much to do with this schematic diagram as a motorcycle's wiring loom has to do with its wiring schematic.
Each of these 37 rectangles is a computer. The dns LANs contain DNS server computers, the firewall LANs contain firewall computers, and so on. Each LAN has at least two computers for the HA (High Availability) reason that if one breaks down, the other still provides the service. Heavily used LANs such as the web LANs contain several computers, each one identical to the next. The biz LAN does not contain identical computers: there are several pairs of computers that provide different business services such as database, directory and application.