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Assume that "host1.mydomain.dom" has an IP address of Which of the following options would be most appropriate as a subsequence of steps in performing the reverse lookup of In the following options "NS" is an abbreviation of "nameserver".

  1. Query a NS for the root domain and then NS for the "dom" domains
  2. Directly query a NS for "dom" and then a NS for "mydomain.dom" domains
  3. Query a NS for in-addr.arpa and then a NS for 128.145.in-addr.arpa domains
  4. Directly query a NS for 145.in-addr.arpa and then a NS for 128.145.in-addr.arpa domains
asked in Computer Networks by (21.2k points) 125 160 160
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3 Answers

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Best answer

Answer is C)

A & B are clearly wrong as we are doing Reverse lookup.

C is most closest answer to process given in RFC 1033. We need to get NS for  in-addr.arpa before doing query to

D is not correct, it is not close to process.


Relevant stuff From https://tools.ietf.org/html/rfc1033 ==>


   The structure of names in the domain system is set up in a
   hierarchical way such that the address of a name can be found by
   tracing down the domain tree contacting a server for each label of
   the name.  Because of this 'indexing' based on name, there is no easy
   way to translate a host address back into its host name.

   In order to do the reverse translation easily, a domain was created
   that uses hosts' addresses as part of a name that then points to the
   data for that host.  In this way, there is now an 'index' to hosts'
   RRs based on their address.  This address mapping domain is called
   IN-ADDR.ARPA.  Within that domain are subdomains for each network,
   based on network number.  Also, for consistency and natural
   groupings, the 4 octets of a host number are reversed.

   For example, the ARPANET is net 10.  That means there is a domain
   called 10.IN-ADDR.ARPA.  Within this domain there is a PTR RR at that points to the RRs for the host SRI-NIC.ARPA
   (who's address is  Since the NIC is also on the MILNET
   (Net 26, address, there is also a PTR RR at
   ADDR.ARPA that points to the same RR's for SRI-NIC.ARPA.  The format
   of these special pointers is defined below along with the examples
   for the NIC.
 The PTR record is used to let special names point to some other
   location in the domain tree.  They are mainly used in the IN-
   ADDR.ARPA records for translation of addresses to names.  PTR's
   should use official names and not aliases.

   For example, host SRI-NIC.ARPA with addresses and
   would have the following records in the respective zone files for net
   10 and net 26:

answered by (45.7k points) 3 12
selected by
+9 votes
answer - C

we are performing reverse lookup of IP address to its hostname

first we need to locate in-addr.apra

then perform reverse lookup of which will point to host1.mydomain.com
answered by (9.3k points)
+4 votes

In Reverse DNS look up from IP address we will get Domain name.For example, one IP address of Google.com is If you were to type this IP address in the Reverse DNS Lookup Tool, it will return the host name of Google as listed in the database of ARPA, the Address and Routing Parameter Area (arpa) top-level domain of the Internet. to do a reverse lookup of the IP address the PTR record for the domain name would be looked up.So first it will check top level domain addr.arpa then ip address part.

So according to the above theory we can conclude C is the answer

answered by (6.5k points) 1 1

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