Network security

• Network security is a set of technologies that

protects the usability and integrity of a
company's infrastructure by preventing the
entry or proliferation within a network of a
wide variety of potential threats.
• What is a firewall?
• A firewall is software or firmware that prevents
unauthorized access to a network. It inspects
incoming and outgoing traffic using a set of rules to
identify and block threats. 
• Firewalls are used in both personal and enterprise
settings, and many devices come with one built-in,
including Mac, Windows, and Linux computers. They
are widely considered an essential component of
network security.
• A firewall is an integrated collection of
security measures designed to prevent
unauthorized electronic access to a networked
computer system.
A network firewall is similar to
firewalls in building construction,
because in both cases they are
intended to isolate one "network" or
"compartment" from another
 Firewall Policies

To protect private networks and individual

machines from the dangers of the greater
Internet, a firewall can be employed to filter
incoming or outgoing traffic based on a
predefined set of rules called firewall policies.
Trusted internal network

Firewall policies

Untrusted
Firewall
Internet
 Policy Actions

• Packets flowing through a firewall can have one of three outcomes:

– Accepted: permitted through the firewall
– Dropped: not allowed through with no indication
of failure
– Rejected: not allowed through, accompanied by
an attempt to inform the source that the packet
was rejected
• Policies used by the firewall to handle packets are based on several
properties of the packets being inspected, including the protocol used,
such as:
– TCP or UDP
– the source and destination IP addresses
– the source and destination ports
– the application-level payload of the packet (e.g.,
whether it contains a virus).
 Blacklists and White Lists

• Two fundamental approaches to creating firewall policies (or rulesets)

• Blacklist approach (default-allow)
– All packets are allowed through except those that
fit the rules defined specifically in a blacklist.
– Pros: flexible in ensuring that service to the
internal network is not disrupted by the firewall
– Cons: unexpected forms of malicious traffic could
go through
• Whitelist approach (default-deny)
– Packets are dropped or rejected unless they are
specifically allowed by the firewall
– Pros: A safer approach to defining a firewall
ruleset
– Cons: must consider all possible legitimate traffic
in rulesets
 Firewall Types

• packet filters (stateless)

– If a packet matches the packet filter's set of rules, the packet filter will
drop or accept it
• "stateful" filters
– it maintains records of all connections passing through it and
can determine if a packet is either the start of a new connection,
a part of an existing connection, or is an invalid packet.
• application layer
– It works like a proxy it can “understand” certain applications and
protocols.
– It may inspect the contents of the traffic, blocking what it views
as inappropriate content (i.e. websites, viruses,
vulnerabilities, ...)
• Local Area networks are of two types − Peer to
Peer network and client server network.
• client server network
 Client/Server Network

• In client-server network relationships, certain

computers act as servers and others act as
clients.
• A server is simply a computer that provides the
network resources and provides service to other
computers when they request it. A client is the
computer running a program that requests the
service from a server. Local area network (LAN)
is based on client server network relationship.
• A client-server network is one on which all
available network resources such as files,
directories, applications and shared devices,
are centrally managed and hosted and then
are accessed by the client.
• Client server networks are defined by the
presence of servers on a network that provide
security and administration of the network.
 The advantages of client server network

• It is very secure.
• Gives better performance.
• It has centralized backup.
• It is very reliable.
 Disadvantages of client server

• It requires professional administration.

• It is more hardware and software intensive.
• It requires expensive dedicated software.
Types of Servers
• File server − These servers provide the services for storing, retrieving
and moving the data. A user can read, write, exchange and manage the
files with the help of file servers.
• Printer server − The printer server is used for controlling and managing
printing on the network. It also offers the fax service to the network
users.
• Application server − The expensive software and additional computing
power can be shared by the computers in a network with the help of
application servers.
• Message server − It is used to co-ordinate the interaction between
users, documents and applications. The data can be used in the form of
audio, video, binary, text or graphics.
• Database server − It is a type of application server.