Domain Name System (DNS) servers maintain a distributed database used to translate
computer names to Internet Protocol (IP) addresses on
Transmission Control Protocol/Internet Protocol (TCP/IP)
networks which includes the internet.
[NOTES FROM THE FIELD] - Being able to install DNS is not a requirement for the
70-270 exam. Understanding the functionality of DNS and how
it affects Windows XP Professional clients in workgroups and
within domains is.
In the next few weeks in my Learn Active Directory in 15 Minutes a
Week series of articles I will cover DNS in more depth,
including a more in depth view of installing DNS.
The Microsoft Domain Name System (DNS) is the name resolution
service that resolves Uniform Resource Locator names (URLs)
and other DNS names into their “true” dotted decimal format.
http://www.zandri.net
translates into a specific Internet Protocol (IP) address
and it is that address resolution that allows you to reach
the server destination you are looking for.
Lookup Queries and Lookup Types
There are two different types of DNS lookup, forward and reverse.
A forward lookup query resolves a DNS name to an IP address
and is the most common DNS query. A reverse lookup query
resolves an IP address to a name.
A DNS name server can resolve a query only for a zone for which it
has authority. When DNS servers receive a resolution request, they attempt to locate
the requested information in their own database.
There are two types of queries that can be performed in DNS: Iterative
and Recursive.
A DNS resolution query made from a client to a DNS server where
the server returns the best answer that it can provide based
on its local cache or stored zone data is called an
Iterative query. If the server performing the Iterative
query does not have an exact match for the name request, it
provides a pointer to an authoritative server in another
level of the domain namespace. The client system will then
query that server and so on and will continue this process
until it locates a server that is authoritative for the
requested name or until an error is returned such as name
not found or a time-out condition is met.
A DNS resolution query made from a client to a DNS server in which
the server assumes the full workload and responsibility for
providing a complete answer to the query is called a
recursive query.
The server, if it cannot resolve the resolution from it's own database
will then perform separate iterative queries to other
servers (on behalf of the client) to assist in returning an
answer to the recursive query and will continue this process
until it locates a server that is authoritative for the
requested name or until an error is returned such as name
not found or a time-out condition is met.
Client computers send recursive queries to DNS servers in most
cases and usually the DNS server is set up to make iterative
queries to provide an answer to the client.
The following is an example of the query process of a client
computer making a request to a DNS server to resolve the
address web address of
www.zandri.net.
First the client computer generates a request for the IP address of
www.zandri.net by
sending a recursive query to the DNS server that it is
configured to use in its network configuration. (We'll call
this server LOCALCFG)
The second step is for LOCALCFG DNS server that has received a
recursive query to look it its local database. If it does
find that answer locally it is returned. If it is unable to
locate an entry for
www.zandri.net in its own database, it sends an
iterative query to a DNS server that is authoritative for
the root of the local domain. (We'll call this server
LOCALROOT)
If the LOCALROOT DNS server, which is authoritative for the root
domain, has the answer in its local database it sends a
response to LOCALCFG. If the LOCALROOT DNS server is unable
to locate an entry for
www.zandri.net in its database, it sends a reply to the
querying DNS server (LOCALCFG) with the IP addresses of DNS
servers that are authoritative for the .net domain. (If it
were .com you would be sent the IP addresses of DNS servers
that are authoritative for the COM domain. If it were .org
you would be sent the IP addresses of DNS servers that are
authoritative for the ORG domain and so on.) We'll call this
server DNSNET.
The DNS server that received the client recursive query (LOCALCFG)
sends an iterative query to a server that is authoritative
for the .net domain (DNSNET).
If the DNS server that is authoritative for the .net domain (DNSNET)
has an entry for
www.zandri.net in its local cache it will return it to
LOCALCFG. If DNSNET is unable to locate an entry for
www.zandri.net in its
database, it sends a reply to the querying DNS server (LOCALCFG)
with the IP addresses of DNS servers that are authoritative
for the zandri.net domain. (We'll call this server ZANDRIDNS).
The DNS server that received the client recursive query (LOCALCFG)
sends an iterative query to a server that is authoritative
for the zandri.net domain. (ZANDRIDNS)
The DNS server that is authoritative for the zandri.net domain (ZANDRIDNS)
locates an entry for
www.zandri.net in its database and sends a reply to the
querying DNS server (LOCALCFG) with the IP address of
www.zandri.net.
The DNS server (LOCALCFG) that received the recursive query sends a
reply to the client computer with the IP address of
www.zandri.net.
If you have any questions, comments or
even constructive criticism, please feel free to drop me a
note.
I want to write solid technical
articles that appeal to a large range of readers and skill
levels and I can only be sure of that through your feedback.
Until next time, best of luck in your
studies and remember,
