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Description Class TTL Type Data
Start of Authority Internet (IN) Default TTL is
60 minutes
SOA Owner Name,
Primary Name Server
DNS Name, Serial
Number,
Refresh Interval,
Retry Interval,
Expire Time,
Minimum TTL
Host Internet (IN) Zone (SOA)
TTL
A Owner Name (Host DNS
Name),
Host IP Address
Name Server Internet (IN) Zone (SOA)
TTL
NS Owner Name,
Name Server DNS Name
Mail Exchanger Internet (IN) Zone (SOA)
TTL
MX Owner Name,
Mail Exchange Server
DNS Name, Preference
Number
Canonical Name
(an alias)
Internet (IN) Zone (SOA)
TTL
CNAME Owner Name (Alias
Name),
Host DNS Name
Distributing the Database: Zone Files and Delegation
A DNS database can be partitioned into multiple zones. A zone is a portion of the
DNS database that contains the resource records with the owner names that belong
to the contiguous portion of the DNS namespace. Zone files are maintained on DNS
servers. A single DNS server can be configured to host zero, one or multiple zones.
Each zone is anchored at a specific domain name referred to as the zone’s root
domain. A zone contains information about all names that end with the zone’s root
domain name. A DNS server is considered authoritative for a name if it loads the
zone containing that name. The first record in any zone file is a Start of Authority
(SOA) RR. The SOA RR identifies a primary DNS name server for the zone as the
best source of information for the data within that zone and as an entity processing
the updates for the zone.
Names within a zone can also be delegated to other zone(s). Delegation is a
process of assigning responsibility for a portion of a DNS namespace to a separate
entity. This separate entity could be another organization, department or workgroup
within your company. In technical terms, delegating means assigning authority over
portions of your DNS namespace to other zones. Such delegation is represented by
the NS record that specifies the delegated zone and the DNS name of the server
authoritative for that zone. Delegating across multiple zones was part of the original
design goal of DNS. Following are the main reasons for the delegation of a DNS
namespace:
Windows 2000 White Paper 6