Master Zone File Syntax

A DNS zone file contains the list of all Resource Records in the DNS zone. Format is defined in RFC1035 page 33 with an addendum in RFC2308. A unique SOA RR and at least one NS RR for the zone name are required. A complete RR is a quintuplet {FQDN_NAME, TTL, CLASS, TYPE, RDATA} which can be in abbreviated form in some cases.

• Comments start with a semicolon ";" and go to the end of line.
• Empty lines are allowed; any combination of tabs and spaces acts as a delimiter.
• RR are defined line by line as :
  [Name] [TTL] [CLASS] TYPE RDATA
  • if no Name, the name is taken from the last stated RR
  • if Name exists, it starts at the first character of the line
  • if Name is not dot-terminated (non FQDN), the default domain name defined by $ORIGIN directives is concatenated to Name
  • if no TTL, the TTL is defined by $TTL directives.
  • if no CLASS, the CLASS is taken from the last stated RR
  • TTL and CLASS can be exchanged.
• $TTL integer_value sets the default value of TTL for following RRs in file (RFC2308, bind>8.1)
• $ORIGIN fqdn_name sets the default value of domain name for following RRs in file. Initially, in BIND, the value is set to the current zone name.
• $INCLUDE filename inserts the named file into the current file. NB: be careful about value of $TTL or $ORIGIN after a $INCLUDE
• "@" is used to denote the current default domain name.
• "(" and ")" are used to group data that crosses a line boundary. Line terminations are not recognized within parentheses
• "\" is used to quote special characters. Ex : "\." can be used to place a dot character in a label; "\223" is the 8-bit character corresponding to decimal value 223.

Stylistic hints

• Organize RR : Start with SOA, NS and MX of the zone, continue with delegation (NS) and glue. Group RR by names.
• Comments are useful
• Use spaces or tabulations for vertical alignment
• Start file with a $ORIGIN and a $TTL
• Try to avoid writing of the zone name in the file
• Generate serial number in SOA as : year/month/day/version 4+2+2+2.
• BE CAREFUL: Modify the serial number each time the master file is modified