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Description of DNS Reverse Lookups

This article was previously published under Q164213
In a Domain Name System (DNS) environment, it is common for a user or anapplication to request a Reverse Lookup of a host name, given the IPaddress. This article explains this process.
The following is quoted from RFC 1035:
"The Internet uses a special domain to support gateway location and Internet address to host mapping. Other classes may employ a similar strategy in other domains. The intent of this domain is to provide a guaranteed method to perform host address to host name mapping, and to facilitate queries to locate all gateways on a particular network on the Internet.

"The domain begins at IN-ADDR.ARPA and has a substructure which follows the Internet addressing structure.

"Domain names in the IN-ADDR.ARPA domain are defined to have up to four labels in addition to the IN-ADDR.ARPA suffix. Each label represents one octet of an Internet address, and is expressed as a character string for a decimal value in the range 0-255 (with leading zeros omitted except in the case of a zero octet which is represented by a single zero).

"Host addresses are represented by domain names that have all four labels specified."
Reverse Lookup files use the structure specified in RFC 1035. For example,if you have a network which is, then the Reverse Lookup file forthis network would be 10.150.IN-ADDR.ARPA. Any hosts with IP addresses inthe network will have a PTR (or 'Pointer') entry in 10.150.IN-ADDR.ARPA referencing the host name for that IP address. A single IN-ADDR.ARPA file may contain entries for hosts in many domains.

Consider the following scenario. There is a Reverse Lookup file10.150.IN-ADDR.ARPA with the following contents:
   1.20          IN     PTR     WS1.ACME.COM.   2.20          IN     PTR     WS2.ACME.COM.   3.20          IN     PTR     WS3.ACME.COM.   50.100        IN     PTR     FREE.MONEY.COM.   190.50        IN     PTR     J232.MSN.COM.				

If a DNS resolver wanted to find the host name corresponding to IP address150.10.20.1, it would send a query of the form QTYPE=PTR, QCLASS=IN,QNAME=, and would receive:   WS1.ACME.COM.				

The following is a Network Monitor capture of this process:

Frame 1: This frame shows the query for host name resolution of the IPaddress Note that this is consistent with RFC 1035.QTYPE=Question Type, QCLASS=Question Class and QNAME=Question Name.
0x1:Std Qry for of type Dom. name ptr on classINET addr.   DNS: Question Section: of type Dom. name ptr        on class INET addr.      DNS: Question Name:      DNS: Question Type = Domain name pointer      DNS: Question Class = Internet address class				

Frame 2: Here you see the answer section of the response sent back to therequesting client has the host name of the IP address, which isWS1.ACME.COM.
0x1:Std Qry Resp. for of type Dom. name ptr onclass INET addr.   DNS: Answer section: of type Dom. name ptr on         class INET addr.(3 records present)      DNS: Resource Record: of type Dom. name           ptr on class INET addr.         DNS: Resource Name:         DNS: Resource Type = Domain name pointer         DNS: Resource Class = Internet address class         DNS: Time To Live = 3600 (0xE10)         DNS: Resource Data Length = 21 (0x15)         DNS: Pointer: WS1.ACME.COM.				

Microsoft Windows NT 4.0 DNS Server is compliant with RFC 1035'sdescription of DNS Reverse Lookups.

Article ID: 164213 - Last Review: 02/27/2007 20:48:27 - Revision: 1.2

  • Microsoft Windows 2000 Server
  • Microsoft Windows 2000 Advanced Server
  • Microsoft Windows NT Server 4.0 Standard Edition
  • KB164213