ICND1 break down — DNS Basic

Posted on July 16, 2009. Filed under: CCNA, ICND1 break down | Tags: , , , , |


DNS stands for Domain Name System. DNS provides a name for a domain’s one or more IP addresses. For instance, the domain name abc.example.com might translate to 158.12.104.18. This makes it much easier to remember URLs and email addresses.

The benefits of DNS includes: convenience ,consistancy and simplicity.

Key Components of DNS

Domain Name

The data stored in the DNS is identified by domain names that are organized as a tree according to organizational or administrative boundaries. Each node of the tree, called a domain, is given a label. The domain name of the node is the concatenation of all the labels on the path from the node to the root node.

For example: webserver1.train.microsoft.com 

  • train.microsoft.com is the domain name.
  • . is the root domain
  • com is the top level domain
  • microsoft is the second-level domain
  • train is a subdomain of microsoft
  • webserver1 is the hostname

Zones

For administrative purpose, domain name space is divided into DNS zones, each starting at a node and extending down to the leaf node or to nodes where other zones start. A DNS zone is a portion of the global DNS name space for which administrative responsibility has been delegated. The data for each zone is stored in a name server, which answers queries about the zone using the DNS protocol.

It is import to understand the difference between a zone and a domain.

A zone consists of discrete or contiguous portion of the domain tree, which can map exactly to a sigle domain or include only part of a domain.. On the other hand, every node in the DNS tree is a domain, even if it has no subdomains.

Name server

Any computer registered to join the Domian Name System can act as  a DNS server. A DNS server contains a database of network names and address for other Internet hosts. DNS servers are organized in a hierarchy structure. At its top level, the root zone or root domain “.” is administered by a set of 13 root nameserver clusters distributed throughout the world.

Name Resolution Process

The Name Resolution process is simple:

  1. Upon receiving query from client, the local nameserver will check if it has the authority for the required domain name. If it has, the local nameserver returns the IP address sought. Otherwise, go to step 2.
  2. query one of the root nameservers to find the server authoritative for the next level down.
  3. querying this second nameserver for the address of a DNS server with detailed knowledge of the second-level domain.
  4. repeating the previous step to progress down the name, until the final step which would, rather than generating the address of the next DNS server, return the final address sought.

Note, DNS protocol use both TCP and UDP ports — port 53/tcp and port 53/udp.

DNS — a distributed database with a hierarchical structure that can serve foundation for name resolution in a TCP/IP network.

ICND1 and ICND2 break down

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