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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  Name Systems and TCP/IP Name Registration and Name Resolution            9  TCP/IP Name Systems: Host Tables and Domain Name System (DNS)                 9  TCP/IP Domain Name System (DNS)                      9  DNS Name Servers and Name Resolution                           9  DNS Resolution Concepts and Resolver Operations

DNS Name Resolution Process 1 2 3 4 DNS Electronic Mail Support and Mail Exchange (MX) Resource Records

Resource Record Setup for Reverse Resolution

With the IN-ADDR.ARPA structure in place, we can now associate one entry in this name space with each entry in the “real” DNS name space. We do this using the “PTR” (pointer) resource record type. For example, if “www.xyzindustries.com” has the IP address 191.27.203.8, then the DNS server for its zone will have an address resource record indicating this. In master file text format, it will say something like this:

www.xyzindustries.com. A 191.27.203.8

However, there will also be the following entry for it within the IN-ADDR.ARPA domain:

8.203.27.191.IN-ADDR.ARPA PTR www.xyzindustries.com

(Remember that DNS names are case-insensitive, so the “IN-ADDR.ARPA” could also be given as “in-addr.arpa”).

Once this is done, reverse name resolution can be easily performed by doing a name resolution on “8.203.27.191.in-addr.arpa”. If we do this, a server for the “IN-ADDR.ARPA” domain will return to us the name “www.xyzindustries.com”. This is also shown in Figure 246.

DNS Name Resolution Process 1 2 3 4 DNS Electronic Mail Support and Mail Exchange (MX) Resource Records