Domain and Host Names Mark Andrews

Domain name Characters 0x00 - 0xff 0-63 octets per label + length octet octets wire length Character set ASCII (0x00-0x7f)

Domain Name Presentation ASCII string of printable characters containing no white space Non printable are expressed as \DDD ‘\’ proceeding character means next character is literal ‘.’ separates labels ‘\’ and ‘.’in labels are expressed as ‘\\’ and ‘\.’

Domain Name Uses Host names (http, ftp, telnet) Mail Boxes mark\.andrews.nominum.com Service location (SRV) _ldap._tcp.example.com Mail domains (MX) HESIOD databases (TXT)

Host name A subset of domain names Restricted character set: ‘A’ - ’Z’, ‘a’ - ‘z’, ‘0’ - ‘9’, ‘-’ and ‘.’ Restricted syntax: –hyphen internal to label –periods can only be used to separate labels –name must contain at least one alpha character

Mail Boxes A subset of domain names Used to encode addresses First Label is the local part of the address. Second and subsequent labels form a mail domain.

Mail Domains A subset of domain names. Identical syntax to host names. May or may not correspond to a host name.

Service Location Used to identify which machines provide a service for a given domain. First two labels identify service and protocol. Both of these labels have a leading underscore so as to not collide with a hostname. Third and subsequent labels are normally syntactically identical to a host name.

Embedded Host Names Most uses of domain names either are or contain hostnames (or mail domains). _ldap._tcp.example.com. SOA host.example.com. mark\.andrews.example.com.... example.com. MX … host.example.com. A...

Relationships All Domain Names Mail Boxes Host Names Mail Domains Service Locations

International Domain Names Preserve a restricted character set in host names. Have labels that cannot be in a hostname. Need to be able to mix hostname labels with non hostname labels in the one domain name. i.e. SRV records should work with IDN