DNS Details
Before designing a database schema or an XML format to encode DNS information (the topics of the next two chapters), it is first necessary to identify the various elements that make up the data contained within the DNS system. This chapter will describe the contents of the DNS zone files and the BIND configuration file, providing some insight into what is needed to represent that information in the Ganymede database.
DNS Zone Files
Each DNS zone file contains all the information about the systems within a specific zone, listed as a series of resource records. Resource records have the following general syntax:
{<name>} {<ttl>} <class> <type> <rdata>
- Name
- This is the domain name for this record. It is the DNS name with which the data in this record will be associated. If left blank, it defaults to the last specified name.
- TTL
- This is the time-to-live value for this record, or how long it should be stored in a server's cache. If not explicitly listed, it defaults to the minttl value listed in the SOA resource record.
- Class
- This is the network class for this record. The possible values are IN for Internet, CN for ChaosNet, and HS for Hesiod. The most common by far, and the default, is the IN class.
- Type
- This is the type of this record. The various resource record types are discussed below.
- Rdata
- This is the data that is being described in this record. The meaning of the data is dependent on the resource record type.
SOA
The first resource record in every zone file should be the Start of Authority (SOA) resource record. This record indicates the start of a zone, and provides the following information about that zone:
- Name
- Name of the zone.
- Origin
- The domain name of the name server that was the original or primary source of data for this zone.
-
- Person in charge
- The email address for the person responsible for this zone.
- Serial number
- This is the version of the zone's data. It is incremented every time the data in the zone file is updated.
- Refresh
- How often, in seconds, a secondary name server is to check with the primary name server to see if an update is needed.
- Retry
- How long, in seconds, a secondary server should wait before retrying a failed zone transfer.
- Expire
- Upper time limit, in seconds, that a secondary name server is to use the data before it expires for lack of getting a refresh.
- Minimum TTL
- Default number of seconds to be used for the time-to-live field on resource records that do not specify one in the zone file.
Here is an example of an SOA record:
To be continued ...
NS
A
PTR
MX
CNAME
HINFO
TXT
WKS
BIND Configuration File
Much of the information needed to finish this page can be found at the ISC BIND Documentation home page.
Brian O'Mara
Last modified: Mon Sep 18 03:18:23 CDT 2000