Zone File (DNS)

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Definition of Zone File (DNS) in Network Encyclopedia.

What is Zone File?

Zone File is a file on a name server that contains information that defines the zone that the name server manages. The zone file is a text file consisting of a series of resource records that form the Domain Name System (DNS) database of the name server. These records identify which name server is responsible for a given zone, timing parameters for zone transfers between name servers, IP address to hostname mappings for hosts within the domains over which the zone file is authoritative, and so on.

A typical zone file might look something like this:

; Database file microsoft.com.dns for microsoft.com.
zone.
@          IN   SOA    dns1.microsoft.com. admin.microsoft.com.(
           12    ; serial number
           3600  ; refresh
           600   ; retry
           86400 ; expire
           3600  ) ; minimum TTL
; Zone NS records
@              IN    NS    dns1
@              IN    NS    dns2
; Zone A records
dns1        IN    A    192.250.100.10
dns2        IN    A    192.250.100.11
proxy1        IN    A    192.250.100.101
fred        IN    A    192.250.100.102
wilma        IN    A    192.250.100.103
localhost    IN     A    127.0.0.1
www             IN    CNAME    fred
ftp             IN    CNAME    wilma

NOTE

On Microsoft Windows NT–based and Windows 2000–based servers running the DNS Server services (and hence configured to operate as name servers for the network), the names of the zone files are similar to the names of the domains over which they have authority, but they have the .dns extension appended to them. For example, the zone file for the domain microsoft.com would be microsoft.com.dns and would be located in the directory \%SystemRoot%\System32\Dns.

Zone File example
Zone File example

A typical DNS server has at least three zone files:

  • <root_domain>.dns: The forward lookup zone file that is used to resolve hostnames into IP addresses for TCP/IP hosts over which the name server has authority. In the preceding example, the root domain is microsoft.com, so the zone file is microsoft.com.dns. 
  • z.y.x.w.in-addr.arpa: The reverse lookup zone file for the forward lookup zone, which is used to resolve IP addresses into hostnames for TCP/IP hosts over which the name server has authority. In the preceding example, the network ID is 192.250.100.0, so the reverse lookup zone file is 100.250.192.in-addr.arpa.dns. 
  • cache.dns: A standard file that exists on all name servers and contains the hostnames and IP addresses of name servers on the Internet that maintain the root domain of the entire DNS namespace. 

TIP

Windows 2000 gives you the option of integrating DNS with Active Directory. This results in zone data being stored in Active Directory, which has advantages over traditional implementations of DNS in which zone data is stored in text files:

  • It provides a more efficient mechanism for zone transfers through the domain replication process of Active Directory. This eliminates the chore of manually configuring zone transfers between primary and secondary DNS servers.
  • It provides additional fault tolerance for the DNS information because all Active Directory integrated zones are primary zones and therefore contain a copy of the zone data.

You should generally use the Windows NT administrative tool called DNS Manager to make changes to zone files on a DNS server running on Windows NT rather than modify these files directly by using a text editor such as Notepad. This will prevent errors from finding their way into the DNS database. Similarly, use the DNS console in Windows 2000 to administer the zone files instead of editing them directly.

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