Omar Bennett
A fully qualified domain name (FQDN) is a complete domain name that specifies the exact location of a resource in the domain name system (DNS). It is the complete address of an internet host or computer and provides its exact location within the DNS by specifying the hostname, domain name, and top-level domain (TLD). For example, in the FQDN www.shop.example.com, www is the hostname, shop.example is the second-level domain name, and com is the TLD. Each label in an FQDN is separated by a period, and the entire FQDN has a maximum length of 255 characters. FQDNs are essential for accessing domain services, such as email or File Transfer Protocol (FTP), and each device on the internet has its own FQDN.
| Characteristics | Values |
|---|---|
| Length | 255 characters maximum |
| Format | hostname.domain.TLD |
| Characters | Letters, numbers and hyphens |
| First position on each label | Number or letter |
| Hierarchy | Read from right to left |
| Top-level domain | .com, .net, .us, .co.uk |
| Second-level domain | Chosen name below the top-level domain |
| Third-level domain | Defines sub-address |
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What You'll Learn
- FQDNs are essential for accessing domain services, protocols and remote servers
- Each FQDN has a max length of 255 characters
- FQDNs are conventionally written as a list of domain labels separated by dots
- A FQDN is a complete domain name that specifies the exact location of a resource in the DNS
- Each device on the internet has an Internet Protocol (IP) address and a corresponding FQDN
FQDNs are essential for accessing domain services, protocols and remote servers
A fully qualified domain name (FQDN) is a complete address that specifies its exact location in the internet's domain name system. It includes the hostname and the domain name, which together identify a specific computer or server on the internet. Each device on the internet has an Internet Protocol (IP) address and a corresponding FQDN.
FQDNs are essential for accessing domain services, protocols, and remote servers. They are used to locate and access resources online or within a private network, ensuring accurate communication and routing between devices and servers. When trying to connect to a remote server, the DNS server performs a lookup in its DNS table to resolve the FQDN to its corresponding IP address. Sometimes, using an FQDN is essential to reach a remote server, especially if it doesn't share the same internet service provider.
FQDNs are also crucial for network communications, such as File Transfer Protocol (FTP) or email services. They ensure that DNS directs traffic to the correct server. For example, the FQDN of a mail server is needed to connect a domain name's email to an email application on a phone. Additionally, FQDNs are used in various internet interactions as they are easier to remember than IP addresses.
FQDNs are also beneficial when migrating services to a different server. Using an FQDN instead of an IP address quickly changes the DNS records and prevents communication issues and outages that can occur when changing an IP address. Furthermore, FQDNs can improve a website's SEO rankings in web browsers. They provide a standardised and human-readable means of addressing remote hosts, making it easier for users and applications to establish connections and interact with resources on different networks.
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Each FQDN has a max length of 255 characters
A fully qualified domain name (FQDN) is the complete address of an internet host or computer. It provides its exact location within the domain name system (DNS) by specifying the hostname, domain name, and top-level domain (TLD). An FQDN is always labelled in the format of hostname.domain.TLD. For example, a mail server on the yahoo.com domain might use the FQDN mail.yahoo.com.
Each FQDN has a maximum length limit of 255 characters. This limit ensures that the domain name structure remains manageable and consistent with internet standards set by organisations like ICANN (the Internet Corporation for Assigned Names and Numbers). The length of each label within the FQDN must be between 1 and 63 characters, and the full domain name is limited to 255 characters, including full stops. Each label is separated by a period and ends with a trailing period, although most systems imply the period even if one is not provided.
The FQDN must only use letters, numbers, and hyphens. A number or letter must take the first position on each label. For example, an FQDN might be 'www.example.com', which consists of the host 'www', the domain 'example', and the TLD '.com'. Each part of this FQDN contributes to the total character count, which must not exceed 255 characters.
The maximum length of 255 characters for an FQDN is a standard that helps maintain consistency and compatibility across different systems and networks. It ensures that domain names remain within a manageable length, facilitating efficient processing and communication between various network components. This standard is essential for maintaining the overall functionality and reliability of the internet and its associated systems.
It is worth noting that while the maximum length for an FQDN is 255 characters, it is advisable to keep domain names relatively short. Shorter domain names are generally easier to remember, type, and share. They can also help prevent issues with character limits in certain contexts, such as URL length restrictions in web browsers or display limitations on mobile devices.
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FQDNs are conventionally written as a list of domain labels separated by dots
A fully qualified domain name (FQDN) is a domain name that specifies its exact location in the tree hierarchy of the Domain Name System (DNS). It is conventionally written as a list of domain labels separated by dots. Each label is formed from the set of ASCII letters, digits, and hyphens, but not starting or ending with a hyphen. The labels are case-insensitive. For example, in the FQDN somehost.example.com, "com" is a label directly under the root zone, "example" is nested under "com", and finally, "somehost" is nested under "example.com". The topmost layer of every domain name is the DNS root zone, which is expressed as an empty label and can be represented in an FQDN with a trailing dot, such as somehost.example.com.
The hierarchy of domains descends from the right to the left label in the name. Each label to the left specifies a subdivision, or subdomain, of the domain to the right. For example, the label "example" specifies a node example.com as a subdomain of the com domain, and "www" is a label to create www.example.com, a subdomain of example.com. Each label may contain from 1 to 63 octets, and the full domain name is limited to 255 octets, full stops included. The empty label is reserved for the root node and when fully qualified is expressed as the empty label terminated by a dot.
The FQDN serves to show the exact location of a computing resource inside the Domain Name System (DNS) hierarchy. An FQDN is traditionally written as a list of domain labels: the top-level domain, the second-level domain name, a subdomain (if used), and the host domain, each separated by dots or periods. The label hierarchy is read from right to left. As an example of FQDN syntax, in the address www.shop.example.com, “.com” is the top-level domain, “example” is the second-level domain name, “shop” is the subdomain, and “www” is the host name.
FQDNs are useful in connecting to domain services, such as email or File Transfer Protocol. For example, the FQDN of a mail server is needed to connect a domain name's email to an email application on a phone, such as Gmail or Apple Mail. Each device on the internet has an Internet Protocol (IP) address and a corresponding FQDN.
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A FQDN is a complete domain name that specifies the exact location of a resource in the DNS
A fully qualified domain name (FQDN) is a complete domain name that specifies the exact location of a resource in the domain name system (DNS). It is the full address of an internet host or computer, providing its exact location within the DNS.
An FQDN is typically written as a list of domain labels, separated by dots or periods, with the top-level domain on the rightmost side. For example, in the FQDN "somehost.example.com", "com" is the top-level domain, "example" is the second-level domain, and "somehost" is the host domain. Each label in an FQDN can contain a maximum of 63 octets, and the full domain name is limited to 255 octets, including full stops.
The FQDN is essential for identifying and accessing network resources, such as servers, websites, and services on the Internet. It is also used in email addressing, where the domain name is represented by the site's FQDN, and in web server hosting to identify and access web servers. Additionally, FQDNs are used in accessing FTP (File Transfer Protocol) servers and configuring email services.
To ensure interoperability across diverse networked environments, FQDNs facilitate the organisation, identification, and access of online resources. They are crucial for precise locating and communication, as each resource can be assigned a distinct FQDN.
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Each device on the internet has an Internet Protocol (IP) address and a corresponding FQDN
Every device connected to the internet has a unique Internet Protocol (IP) address. IP addresses are used to transfer data between two connected devices, allowing machines on different networks to communicate with each other. The Internet Protocol has two versions: IPv4 and IPv6. IPv4 is the older version, with space for up to 4 billion IP addresses, while IPv6 has space for trillions of IP addresses.
Each device on the internet also has a corresponding Fully Qualified Domain Name (FQDN). An FQDN is the complete address of an internet host or computer and provides its exact location within the domain name system (DNS) by specifying the hostname, domain name, and top-level domain (TLD). For example, in the FQDN "www.whatis.com", "www" is the hostname, "whatis" is the domain name, and ".com" is the top-level domain. Each label, including the hostname, domain name, and TLD, is usually separated by a period.
FQDNs are useful for connecting to domain services such as email or File Transfer Protocol (FTP). For instance, the FQDN of a mail server is required to link a domain name's email to an email application on a phone. Additionally, FQDNs can be beneficial when migrating services to a different server, as they can prevent communication issues and outages that may occur when changing an IP address.
It is important to note that while FQDNs and URLs are sometimes used interchangeably, they are not the same. An FQDN is a part of a URL and does not carry the TCP/IP protocol information, such as Hypertext Transfer Protocol (HTTP) or Hypertext Transfer Protocol Secure (HTTPS), which is always present at the beginning of a URL.
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Frequently asked questions
A fully qualified domain name (FQDN) is the complete address of an internet host or computer. It provides its exact location within the domain name system (DNS) by specifying the hostname, domain name, and top-level domain (TLD).
PQDNs are typically used for convenience and are applicable when the full name isn't required to resolve the host, as the domain may already be known. In these cases, only the hostname is required. To understand the difference, think of a phone number: the PQDN is the three-digit area code, and the FQDN is the full 10-digit phone number.
The entire FQDN has a maximum length of 255 characters, including full stops. Each label within the FQDN must be between 1 and 63 characters long.
An FQDN is always formatted as hostname.domain.TLD, with each label separated by a period. For example, in the FQDN "www.shop.example.com", "www" is the hostname, "shop.example" is the domain name, and ".com" is the top-level domain.
