<P> A domain name consists of one or more parts, technically called labels, that are conventionally concatenated, and delimited by dots, such as example.com . </P> <Ul> <Li> The right-most label conveys the top - level domain; for example, the domain name www.example.com belongs to the top - level domain com . </Li> <Li> 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 . The empty label is reserved for the root node . The full domain name may not exceed a total length of 253 ASCII characters in its textual representation . Thus, when using a single character per label, the limit is 127 levels: 127 characters plus 126 dots have a total length of 253 . In practice, some domain registries may have shorter limits . </Li> <Li> A hostname is a domain name that has at least one associated IP address . For example, the domain names www.example.com and example.com are also hostnames, whereas the com domain is not . However, other top - level domains, particularly country code top - level domains, may indeed have an IP address, and if so, they are also hostnames . </Li> <Li> Hostnames impose restrictions on the characters allowed in the corresponding domain name . A valid hostname is also a valid domain name, but a valid domain name may not necessarily be valid as a hostname . </Li> </Ul> <Li> The right-most label conveys the top - level domain; for example, the domain name www.example.com belongs to the top - level domain com . </Li> <Li> 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 . The empty label is reserved for the root node . The full domain name may not exceed a total length of 253 ASCII characters in its textual representation . Thus, when using a single character per label, the limit is 127 levels: 127 characters plus 126 dots have a total length of 253 . In practice, some domain registries may have shorter limits . </Li>

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