DOMAIN NAME SYSTEM (DNS)
A Domain Name System or Domain Name Service (DNS) is a network protocol whose job
is to map domain names such as “gohacking.com” to its corresponding IP address like
“104.28.6.51”.
is to map domain names such as “gohacking.com” to its corresponding IP address like
“104.28.6.51”.
Since Internet is the mother of millions of computers each having a unique IP address, it
becomes impossible for people to remember the IP address of each and every computer
they want to access. So, in order to make this process simpler the concept of domain
names was introduced. As a result users can easily access any website just by typing their
domain names in the browser’s address bas such as “google.com” or “yahoo.com” without
having to remember their actual IP addresses.
However, since the network protocol understands only the IP address and not the domain
names, it is necessary to translate the domain name back to its corresponding IP address
before establishing a connection with the target server. This is where DNS comes in
handy.
Your Internet Service Provider has a DNS server which maintains a huge record of
existing domain names and their corresponding IP addresses. Each time you type the URL
such as “http://www.google.com” on your browser’s address bar, your computer will use
the DNS server from the ISP and translates the domain name “google.com” to its
corresponding IP address to make a connection with the Google’s server. All this process
will happen in a split second behind the scenes and hence goes unnoticed.
becomes impossible for people to remember the IP address of each and every computer
they want to access. So, in order to make this process simpler the concept of domain
names was introduced. As a result users can easily access any website just by typing their
domain names in the browser’s address bas such as “google.com” or “yahoo.com” without
having to remember their actual IP addresses.
However, since the network protocol understands only the IP address and not the domain
names, it is necessary to translate the domain name back to its corresponding IP address
before establishing a connection with the target server. This is where DNS comes in
handy.
Your Internet Service Provider has a DNS server which maintains a huge record of
existing domain names and their corresponding IP addresses. Each time you type the URL
such as “http://www.google.com” on your browser’s address bar, your computer will use
the DNS server from the ISP and translates the domain name “google.com” to its
corresponding IP address to make a connection with the Google’s server. All this process
will happen in a split second behind the scenes and hence goes unnoticed.
How DNS Works?
Let us understand the working of Domain Name System using the following example:
Whenever you type a URL such as “http://www.gohacking.com” on your browser’s
address bar, your computer will send a request to the local name server (the ISP DNS
server) to resolve the domain name to its corresponding IP address. This request is often
referred to as a DNS query.
The local name server will receive the query to find out whether it contains the matching
name and IP address in its database. If found, the corresponding IP address (response) is
returned. If not, the query is automatically passed on to another DNS server that is in the
next higher level of DNS hierarchy. This process continues until the query reaches the
DNS server that contains the matching name and IP address. The IP address (response)
then flows back the chain in the reverse order to your computer. The following figure 2.4
illustrates the above process.
Whenever you type a URL such as “http://www.gohacking.com” on your browser’s
address bar, your computer will send a request to the local name server (the ISP DNS
server) to resolve the domain name to its corresponding IP address. This request is often
referred to as a DNS query.
The local name server will receive the query to find out whether it contains the matching
name and IP address in its database. If found, the corresponding IP address (response) is
returned. If not, the query is automatically passed on to another DNS server that is in the
next higher level of DNS hierarchy. This process continues until the query reaches the
DNS server that contains the matching name and IP address. The IP address (response)
then flows back the chain in the reverse order to your computer. The following figure 2.4
illustrates the above process.
FIREWALL
Firewalls are basically a barrier between your computer (or a network) and the Internet
(outside world). A firewall can be simply compared to a security guard who stands at the
entrance of your house and filters the visitors coming to your place. He may allow some
visitors to enter while deny others whom he suspects of being intruders. Similarly a
firewall is a software program or a hardware device that filters the information
(packets) coming through the Internet to your personal computer or a computer network.
(outside world). A firewall can be simply compared to a security guard who stands at the
entrance of your house and filters the visitors coming to your place. He may allow some
visitors to enter while deny others whom he suspects of being intruders. Similarly a
firewall is a software program or a hardware device that filters the information
(packets) coming through the Internet to your personal computer or a computer network.
How Firewall Works?
Firewalls may decide to allow or block network traffic between devices based on the rules
that are pre-configured or set by the firewall administrator. Most personal firewalls such as
Windows firewall operate on a set of pre-configured rules which are most suitable under
normal circumstances, so that the user need not worry much about configuring the
firewall.
Personal firewalls are easy to install and use and hence preferred by end-users to secure
their personal computers. However, in order to meet customized needs large networks and
companies prefer those firewalls that have plenty of options to configure.
For example, a company may set up different firewall rules for FTP servers, telnet
servers and web servers. In addition, the company can even control how the employees
connect to the Internet by blocking access to certain websites and restricting the transfer of
files to other networks. Thus, in addition to security, a firewall can give the company a
tremendous control over how people use their network.
Firewalls use one or more of the following methods to control the incoming and outgoing
traffic in a network:
1. Packet Filtering: In this method, packets (small chunks of data) are analyzed against
a set of filters. Packet filters has a set of rules that come with accept and deny actions
which are pre-configured or can be configured manually by the firewall
administrator. If the packet manages to make it through these filters then it is allowed
to reach the destination; otherwise it is discarded.
2. Stateful Inspection: This is a newer method that doesn’t analyze the contents of the
packets. Instead, it compares certain key aspects of each packet to a database of
trusted source. Both incoming and outgoing packets are compared against this
database and if the comparison yields a reasonable match, then the packets are
allowed to travel further. Otherwise they are discarded. Firewall Configuration:
traffic in a network:
1. Packet Filtering: In this method, packets (small chunks of data) are analyzed against
a set of filters. Packet filters has a set of rules that come with accept and deny actions
which are pre-configured or can be configured manually by the firewall
administrator. If the packet manages to make it through these filters then it is allowed
to reach the destination; otherwise it is discarded.
2. Stateful Inspection: This is a newer method that doesn’t analyze the contents of the
packets. Instead, it compares certain key aspects of each packet to a database of
trusted source. Both incoming and outgoing packets are compared against this
database and if the comparison yields a reasonable match, then the packets are
allowed to travel further. Otherwise they are discarded. Firewall Configuration:
Firewalls can be configured by adding one or more filters based on several conditions as
mentioned below:
1. IP addresses: In any case, if an IP address outside the network is said to be
unfavourable, then it is possible to set filter to block all the traffic to and from
that IP address. For example, if a certain IP address is found to be making too
many connections to a server, the administrator may decide to block
traffic from this IP using the firewall.
2. Domain names: Since it is difficult to remember the IP addresses, it is an
easier and smarter way to configure the firewalls by adding filters based on
domain names. By setting up a domain filter, a company may decide to block all
access to certain domain names, or may provide access only to a list of
selected domain names.
3. Ports/Protocols: If the services running on a given port is intended for the
public or network users, they are usually kept open. Otherwise they are blocked
using the firewall so as to prevent intruders from using the open ports for
making unauthorized connections.
4. Specific words or phrases: A firewall can be configured to filter one or more
specific words or phrases so that both the incoming and outgoing packets are
scanned for the words in the filter.
For example, you may set up a firewall rule to filter any packet that
contains an offensive term or a phrase that you may decide to block from
entering or leaving your network.
Hardware vs. Software Firewall:
Hardware firewalls provide higher level of security and hence preferred for servers where
security has the top most priority. The software firewalls on the other hand are less
expensive and hence preferred in home computers and laptops.
Hardware firewalls usually come as an in-built unit of a router and provide maximum
security as it filters each packet at the hardware level itself even before it manages to enter
your computer. A good example is the Linksys Cable/DSL router.
PROXY SERVER
In a computer network, a proxy server is any computer system offering a service that acts
as an intermediary between the two communicating parties, the client and the server.
In the presence of a proxy server, there is no direct communication between the client and
the server. Instead, the client connects to the proxy server and sends requests for resources
such as a document, web page or a file that resides on a remote server. The proxy server
handles this request by fetching the required resources from the remote server and
forwarding the same to the client.
as an intermediary between the two communicating parties, the client and the server.
In the presence of a proxy server, there is no direct communication between the client and
the server. Instead, the client connects to the proxy server and sends requests for resources
such as a document, web page or a file that resides on a remote server. The proxy server
handles this request by fetching the required resources from the remote server and
forwarding the same to the client.
How Proxy Server Works?
An illustration of how a proxy server works is shown in the --
As shown in the below example, whenever the client connects to a web proxy server and
makes a request for the resources (in this case, “Sample.html”) that reside on a remote
server (in this case, xyz.com), the proxy server forwards this request to the target server on
behalf of the client so as to fetch the requested resource and deliver it back to the client.
A proxy server is most widely used to conceal the IP address or the origin of the Internet
users during their activity. Since it the proxy server which handles the requests between
the client and the target, only the IP address of the proxy server is exposed to the outside
world and not the actual one. Therefore, most hackers use a proxy server during the
attacks on their target so that it would be hard to trace back to them.
As shown in the below example, whenever the client connects to a web proxy server and
makes a request for the resources (in this case, “Sample.html”) that reside on a remote
server (in this case, xyz.com), the proxy server forwards this request to the target server on
behalf of the client so as to fetch the requested resource and deliver it back to the client.
A proxy server is most widely used to conceal the IP address or the origin of the Internet
users during their activity. Since it the proxy server which handles the requests between
the client and the target, only the IP address of the proxy server is exposed to the outside
world and not the actual one. Therefore, most hackers use a proxy server during the
attacks on their target so that it would be hard to trace back to them.
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