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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  Name Systems and TCP/IP Name Registration and Name Resolution            9  TCP/IP Name Systems: Host Tables and Domain Name System (DNS)                 9  TCP/IP Domain Name System (DNS)                      9  DNS Name Space, Architecture and Terminology

DNS Structural Elements and Terminology: Domains, Subdomains, and Nodes; Roots, Leaves and Branches; Parents, Children and Siblings 1 2 3 Absolute (Fully-Qualified) and Relative (Partially-Qualified) Domain Name Specifications

DNS Name Length Limit

There is a maximum limit of 255 characters for a complete domain name, for implementation purposes. In practice, most domain names are much shorter than this limit, as it would violate the whole purpose of domain names if we let them get so long that nobody could remember them anyway.

In many protocols, it is possible to specify a particular resource within a domain name by providing a directory structure after a name. This is done using the standard TCP/IP uniform resource locator (URL) syntax, where a path is indicated using slashes to separate subdirectories. For example, a specific file at “salt.crystal.rocks” might be located at “salt.crystal.rocks/chem/composition”.

While DNS names are case-insensitive, the labels in a URL path are not. So this example would be different from “salt.crystal.rocks/chem/Composition”. See the topic on URL syntax for more details.

DNS Structural Elements and Terminology: Domains, Subdomains, and Nodes; Roots, Leaves and Branches; Parents, Children and Siblings 1 2 3 Absolute (Fully-Qualified) and Relative (Partially-Qualified) Domain Name Specifications