1-The DNS domain namespace, as shown in the following
figure, is based on the concept of a tree of named domains.
Each level of the tree can represent either a branch or a
leaf of the tree. A branch is a level where more than one
name is used to identify a collection of named resources. A
leaf represents a single name used once at that level to
indicate a specific resource.
DNS Domain namespace
The previous figure shows how Microsoft is assigned
authority by the Internet root servers for its own part of
the DNS domain namespace tree on the Internet. DNS clients
and servers use queries as the fundamental method of
resolving names in the tree to specific types of resource
information. This information is provided by DNS servers in
query responses to DNS clients, who then extract the
information and pass it to a requesting program for
resolving the queried name.
In the process of resolving a name, keep in mind that DNS
servers often function as DNS clients, querying other
servers in order to fully resolve a queried name. For more
information, see How DNS query works.
The creation of host tables to map computer names to
addresses greatly improved the usability of the early
Internet and the TCP/IP protocol suite that implemented it.
Unfortunately, while the host table name system worked well
when the internetwork was small, it did not scale
particularly well as the Internet started to grow in size
and complexity. The name system had to stay but the use of
host tables had to be dispensed with in favor of a newer,
more capable system.
Over the period of several years, many engineers worked to
create a system that would meet not just the needs of TCP/IP
internetworks of the time, but also of the future. The new
name system was based on a hierarchical division of the
network into groups and subgroups, with names reflecting
this structure. It was designed to store data in a
distributed fashion to facilitate decentralized control and
efficient operation, and included flexible and extensible
mechanisms for name registration and resolution. This new
name system for TCP/IP was called the Domain Name System (DNS).
In this section I describe the concepts behind TCP's Domain
Name System, as well as its operation. The section is
divided into four subsections. The first provides and
overview of DNS, including a description of its
characteristics and components. The next three subsections
describe how DNS implements each of the three primary name
system functions: the DNS name space and architecture; the
DNS name registration process, including hierarchical
authorities and administration; and the DNS name resolution
process, focusing on how name servers and resolvers work.
Finally, I have a topic that briefly highlights the changes
made to DNS to support the new version 6 of the Internet
Protocol, and its much longer addresses.
. With the help of above table EMP, perform the following
operation is sql.
a) Add the new column “DEPTNO”
b) Rename the table
c) Update table
d) Modify the table if column ‘SAL’ whose data type is
number (10) and you want to enter varchar2 (15) . For
example $USD 20 etc.