Hostname Restriction/Limitations For Database Server

All host names should conform to the RFC 952 standard, which permits alphanumeric characters. Host names using underscores ("_") are not allowed. The Internet standards (Request for Comments) for protocols mandate that component hostname labels may contain only the ASCII letters 'a' through 'z' (in a case-insensitive manner), the digits '0' through '9', and the hyphen (-). The original specification of hostnames in RFC 952, mandated that labels could not start with a digit or with a hyphen, and must not end with a hyphen. This what Oracle recommends for host name for RAC, and it apply also on non-RAC instances. REFERENCES