DNS Message

There are  the only  two kinds  of DNS message DNS query and reply messages. Further mote both query  and reply message have  the same  format  as shown in figure. The  semantics of the  various fields in a DNS message  are as follows.

 

                                                            Figure  DNS message  format

The first 12 bytes is the header section which  has a number of fields. The first  field is a 16 bit numbers  that identifies the query. This identifier is copied into the reply message to a query allowing the client  to match received replies with sent  queries. There are a  number of flags in the flag field. A 1 bit query reply flag indicates whether the message  is a query or a reply a 1 bit  authoritative flag is set in a reply message  when  a DNS server is  an authoritative server for a queried name. A 1 bit  recursion desired flag  is set  when  a client  host  or DNS  server desired that the DNs  server perform recursion  when it doesn't have  the records. A 1 bit  recursion available field  is set in a reply  if the  DNS  server  supports  recursion. In  the header there are also   four number of fields. These fields  indicate  the number  of occurrences of the four  type  of the  data section that  follow the header.

a.The question  section  carries  one or more  question that is  queries for information  being  sent to a DNS  name  server. This  section  includes a name field  that containing the name  that is  being queried and a type field that indicates the type  of question being  asked  about  the name  for example   a host  address  associated with  a name  or the mail server for a name .

b.Answer carries  one or more  resources records  that answer  the questions  indicated in the question  section above.

c.Recall that  in each  resource  records there is  the type  ( for example A , NS, MNAME, and MX), the  value  and the TTL. A reply can return multiple RRS in  the answer since  a hostname   can have multiple  IP address.

d.The authority  contains  one  more  resource  records that paid  to authoritative name  servers  that can  be used  to continue the resolution process.

e.The additional  section  conveys one or more  resource records that contain additional information  related to the query that is not  strictly necessary to answer  the queries.

 

 

Posted Date: 3/9/2013 4:33:31 AM | Location : United States

Ask an Expert

Related Discussions:- Dns message - application layer, Assignment Help, Ask Question on Dns message - application layer, Get Answer, Expert's Help, Dns message - application layer Discussions

Write discussion on Dns message - application layer
Your posts are moderated

Write your message here..

Related Questions

Set up to use pvm run and complie, PVM uses two environment variables when ... PVM uses two environment variables when starting and running. Every PVM user needs to set these two variables to use PVM. The initial variable is PVM_ROOT, which is set to the loca

Overview of the transport layer protocols, Overview of the Transport  Laye... Overview of the Transport  Layer Protocols Transport layer  can be  available  more than  protocols  to the  network  applications. For  example the network  applications. For

Explain about the intranet hardware and software, Explain about the Intrane... Explain about the Intranet hardware and software Intranets not only provide a secure environment for companies but also provide an excellent working environment that is full of

Layer 2 switch, A typical layer 2 switch has a number of features. Identify... A typical layer 2 switch has a number of features. Identify and explain 5 features that you think are important that you would consider in your evaluation of L2 switches offered b

What are instance variables, What are instance variables? Instance vari... What are instance variables? Instance variables are those which are explained at the class level. Instance variables require not be initialized before using them as they are au

Why do we require a subnet mask? , If the host has the subnet ID why do we ... If the host has the subnet ID why do we require a subnet mask?

What are the bridges, Bridges - Operate in both physical and data link ... Bridges - Operate in both physical and data link layers - Utilized to divide a network into smaller segments - May as well relay frames between separate LANs - Keeps t

Explain the building blocks of client and server, Explain the building bloc... Explain the building blocks of Client/Server? The client side building block runs the client side of the application. The server side building block runs the server side of

Define ike phases, Can you define IKE phases? Can you define IKE phases?

Define decoder, Define Decoder? A device or program that translates enc... Define Decoder? A device or program that translates encoded data into its original format (e.g. it decodes the data). The term is often used in reference to MPEG-2 video and so