Host names may contain up to 24 characters. Letters, numbers, the dash (-) and underscore (_) characters are allowed in host names. Host names are not case sensitive (that is, upper and lower case letters are treated as the same). The first character of a host name must be a letter of the alphabet. Blank spaces are not permitted in host names.
Dots (.) are not permitted in host names. For example, a host name such as myco.2 is not permitted. Dots are not allowed in host names even if they are enclosed in quotes. For example, `myco.2' is not permitted. Dots are only used as part of a fully qualified host name to identify the domain components. For example, myco-2.sales.doc.com. is a correct fully qualified host name.
Domains and hosts should not have the same name. For example, if you have a sales domain you should not have a machine named sales. Similarly, if you have a machine named home, you do not want to create a domain named home. This caution applies to subdomains, for example if you have a machine named west you don't want to create a sales.west.myco.com subdomain.