What is Hostname?

Hostname is an alias given to a computer on a TCP/IP network to identify it on the network. Hostnames are a friendlier way of identifying TCP/IP hosts than IP addresses, and hostnames can be resolved into IP addresses by host name resolution using a DNS server or hosts files. Hostnames can include the characters a–z, A–Z, 0–9, period, and dash (-). To ensure full compatibility with the Domain Name System (DNS), do not use any other special characters in hostnames.

Internet hostnames

On the Internet, a hostname is a domain name assigned to a host computer. This is usually a combination of the host’s local name with its parent domain’s name. For example, en.wikipedia.org consists of a local hostname (en) and the domain name wikipedia.org. This kind of hostname is translated into an IP address via the local hosts file, or the Domain Name System (DNS) resolver. It is possible for a single host computer to have several hostnames; but generally the operating system of the host prefers to have one hostname that the host uses for itself.

Any domain name can also be a hostname, as long as the restrictions mentioned below are followed. So, for example, both en.wikipedia.org and wikipedia.org are hostnames because they both have IP addresses assigned to them. A hostname may be a domain name if it is properly organized into the domain name system. A domain name may be a hostname if it has been assigned to an Internet host and associated with the host’s IP address.

Hostname Restrictions

Hostnames are composed of a series of labels concatenated with dots. For example, “en.wikipedia.org” is a hostname. Each label must be from 1 to 63 characters long, and the entire hostname including the delimiting dots, but not a trailing dot, has a maximum of 253 ASCII characters.

The Internet standards (Requests for Comments) for protocols mandate that component hostname labels may contain only the ASCII letters ‘a’ through ‘z’ (in a case-insensitive manner), the digits ‘0’ through ‘9’ and the hyphen-minus character (‘-‘). The original specification of hostnames in RFC 952 mandated that labels could not start with a digit or with a hyphen-minus character and could not end with a hyphen-minus. However, a subsequent specification (RFC 1123) permitted hostname labels to start with digits. No other symbols, punctuation characters, or white space are permitted. Internationalized domain names are stored in the Domain Name System as ASCII strings using Punycode transcription.

What is DNS?

(Domain Name System) The Internet's system for converting alphabetic names into numeric IP addresses. For example, when a Web address (URL) is typed into a browser, DNS servers return the IP address of the Web server associated with that name. In this made-up example, the DNS converts the URL www.company.com into the IP address 204.0.8.51. Without DNS, you would have to type the series of four numbers and dots into your browser to retrieve the website, which you actually can do. See IP address.

A Hierarchy of Servers

The DNS system is a hierarchy of duplicated database servers worldwide that begin with the "root servers" for the top-level domains (.com, .net, .org, etc.). The root servers point to the "authoritative" servers located in ISPs, as well as in large companies, that turn the names into IP addresses; the process known as "name resolution." Using our www.company.com example, COMPANY.COM is the domain name, and WWW is the hostname. The domain name is the organization's identity on the Web, and the hostname is the name of the Web server within that domain (see WWW). See DNS records,  zone file, reverse DNS, recursive DNS, DDNS,  HOSTS file, mDNS, ping, root server and  WINS.

What is IP address?

(Internet Protocol address) The address of a connected device in an IP network (TCP/IP network), which is the worldwide standard both in-house and on the Internet. Every desktop and laptop computer, server, scanner, printer, modem, router, smartphone, tablet and smart TV is assigned an IP address, and every packet (Web, email, video, etc.) traversing an IP network contains a source IP address and a destination IP address.

Public and Private Addresses

For homes and small businesses, the entire local network (LAN) is exposed to the Internet via one public IP address. Large companies may have several public IPs.

In contrast, the devices within the local network use private addresses not reachable from the outside world, and the router enforces this standard. The same private address ranges are used in every network. Therefore, every computer in a company is assigned the same private IP address as a computer in thousands of other companies. See private IP address and NAT.

Logical vs. Physical

An IP address is a logical address that is assigned by software residing in the router or server, and that logical address can change from time to time. For example, a laptop is likely to be assigned a new IP when it starts up in a different hotspot (see DHCP). However, there is a physical address built into every unit of hardware, which cannot change (see MAC address). In order to locate a device in an IP network, the logical IP address is converted to a physical address by a resolution protocol (see ARP).

Static and Dynamic IP

Network infrastructure devices such as servers, routers and firewalls are assigned permanent "static" IP addresses. The user's machines can also be assigned non-changing static IPs by a network administrator but most often are set to be automatically assigned (see DHCP). Internet service providers may periodically change the IPs in the modems of their home users, but business users must have consistent "static" IPs for servers that face the public. See dynamic IP address and static IP address.

Version 4 and 6 (IPv4 and IPv6)

The original IP Version 4 addressing scheme defined 32 bits to hold the IP address, and it is still widely used today. However, a larger Version 6 address was subsequently created, and both are in use. It will take some time before the newer IPv6 is the only system in use. See IPv4 addressing.

References:

https://networkencyclopedia.com/hostname/
https://www.pcmag.com/encyclopedia/term/dns
https://www.pcmag.com/encyclopedia/term/ip-address