Network Administration: SOA Records - dummies

Network Administration: SOA Records

Every zone must begin with a Source of Authority (SOA) record, which names the zone and provides default information for the zone. The following table lists the fields that appear in the RDATA section of an SOA record.

These fields are positional, so you should include a value for all of them and list them in the order specified. Because the SOA record has so many RDATA fields, you’ll probably need to use parentheses to continue the SOA record onto multiple lines.

RDATA Fields for an SOA Record
Name Description
MNAME The domain name of the name server that is authoritative for
the zone.
RNAME An e-mail address (specified in domain name format; not regular
e-mail format) of the person responsible for this zone.
SERIAL The serial number of the zone. Secondary zones use this value
to determine whether they need to initiate a zone transfer to
update their copy of the zone.
REFRESH A time interval that specifies how often a secondary server
should check whether the zone needs to be refreshed. A typical
value is 3600 (one hour).
RETRY A time interval that specifies how long a secondary server
should wait after requesting a zone transfer before trying again. A
typical value is 600 (ten minutes).
EXPIRE A time interval that specifies how long a secondary server
should keep the zone data before discarding it. A typical value is
86400 (one day).
MINIMUM A time interval that specifies the TTL value to use for zone
resource records that omit the TTL field. A typical value is 3600
(one hour).

Note two things about the SOA fields:

  • The e-mail address of the person responsible for the zone is given in DNS format, not in normal e-mail format. Thus, you separate the user from the mail domain with a dot rather than an @ symbol. For example, would be listed as

  • The serial number should be incremented every time you change the zone file. If you edit the file via the graphic interface provided by Windows DNS, the serial number is incremented automatically. However, if you edit the zone file via a simple text editor, you have to manually increment the serial number.

Here’s a typical example of an SOA record, with judicious comments to identify each field: IN  SOA (               ; authoritative name server              ; responsible person
    148                              ; version number
    3600                             ; refresh (1 hour)
    600                              ; retry (10 minutes)
    86400                            ; expire (1 day)
    3600 )                           ; minimum TTL (1 hour)