Editing Domain name (section)

===Second-level and lower level domains===
Below the top-level domains in the domain name hierarchy are the [[second-level domain]] (SLD) names. These are the names directly to the left of .com, .net, and the other top-level domains. As an example, in the domain ''example.co.uk'', ''co'' is the second-level domain.

Next are third-level domains, which are written immediately to the left of a second-level domain. There can be fourth- and fifth-level domains, and so on, with virtually no limitation. Each label is separated by a [[full stop]] (dot). An example of an operational domain name with four levels of domain labels is ''sos.state.oh.us''. 'sos' is said to be a sub-domain of 'state.oh.us', and 'state' a sub-domain of 'oh.us', etc. In general, [[subdomain]]s are domains subordinate to their parent domain. An example of very deep levels of subdomain ordering are the [[IPv6]] reverse resolution [[DNS zone]]s, e.g., 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa, which is the reverse DNS resolution domain name for the IP address of a [[loopback]] interface, or the [[localhost]] name.

Second-level (or lower-level, depending on the established parent hierarchy) domain names are often created based on the name of a company (e.g., ''bbc''.co.uk), product or service (e.g. ''hotmail''.com). Below these levels, the next domain name component has been used to designate a particular host server. Therefore, ''ftp.example.com'' might be an FTP server, ''www.example.com'' would be a [[World Wide Web]] server, and ''mail.example.com'' could be an email server, each intended to perform only the implied function. Modern technology allows multiple physical servers with either different (cf. [[Load balancing (computing)|load balancing]]) or even identical addresses (cf. [[anycast]]) to serve a single hostname or domain name, or multiple domain names to be served by a single computer. The latter is very popular in [[Web hosting service]] centers, where service providers host the websites of many organizations on just a few servers.

The hierarchical [[DNS label]]s or components of domain names are separated in a fully qualified name by the [[full stop]] (dot, ''.'').