The legal characters available for tcp host names are:
a-z
A-Z
0-9
- (hyphen,the underscore is illegal)
. (dot)
Each protocol has naming conventions. The machine name / domain name combination configured at install follows NetBIOS conventions. When you install tcp/ip, the default tcp protocol machine name will default to the NetBIOS machine name. It can be left the same or changed. Each protocol can have a different machine name. If the NetBIOS machine name has illegal characters (for ip, legal for NetBIOS) such as the underscore, they will be converted to hyphens.