This document discusses firewalls and provides definitions, types, and reasons for using them. Firewalls are used to maintain security of private networks by blocking unauthorized access. There are three main types of firewalls: packet filtering firewalls which allow or block packets based on header information; proxy or application-level firewalls which pass all network traffic through a proxy application to examine data at the application level; and hybrid firewalls which can perform specialized functions of both packet filtering and application-level gateways. Firewalls are important for network security because the internet poses many threats and internal networks are unlikely to be properly secured.

1. Firewalls:
Presented by:
Nikhil E R
USN:1DA17MCA79

2. Definition -
What
does Firewall mean?
• A firewall is software used to maintain
the security of a private network.
• Firewalls block unauthorized access to
or from private networks and are often
employed to prevent unauthorized Web
users or illicit software from gaining
access to private networks connected to
the Internet.
• A firewall may be implemented using
hardware, software, or a combination of
both.
• A firewall is recognized as the first line of
defense in securing sensitive information.
For better safety, the data can be encrypted.

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WHY TO USE
FIREWALLS?
Firewall is considered as an essential element
to achieve network security for the following
reasons:
•Internal network and hosts are unlikely to be
properly secured.
•Internet is a dangerous place with criminals,
users from competing companies, disgruntled
ex-employees, spies from unfriendly
countries, vandals, etc.
•To prevent an attacker from launching denial
of service attacks on network resource.
•To prevent illegal modification/access to
internal data by an outsider attacker.

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Types of Firewalls:
Firewall is categorized into three basic types −
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•Packet filter
•Application-level gateway
•Circuit-level gateway

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PacketFilteringFirewall
○ Allow or block the packets mostly
based on criteria such as source and/or
destination IP addresses, protocol,
source and/or destination port
numbers, and various other parameters
within the IP header.
○ The decision can be based on factors
other than IP header fields such as
ICMP message type, TCP SYN and ACK
bits, etc.
○ Packet filter rule has two parts −
○ Selection criteria − It is a used as a
condition and pattern matching for
decision making.
○ Action field − This part specifies action
to be taken if an IP packet meets the
selection criteria. The action could be
either block (deny) or permit (allow)
the packet across the firewall.
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○ Cost
○ Low resource usage
○ Best suited for small network
Disadvantges:
• Can work only on the network layer
• Do not support complex rule based support
• Vulnerable to spoofing
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Advantges:

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Proxy Firewalls(Applicationlevel Firewalls)
○ The more sophisticated proxy or application layer
firewalls deal with network traffic by passing all
packets through a separate “proxy” application
that examines data at an application level.
○ A proxy firewall doesn’t allow a direct connection
between your network and the Internet. Instead it
accepts requests and executes them on behalf of
the user.
○ This proxy system enables you to set a firewall to
accept or reject packets based on addresses, port
information and application information. For
instance, you can set the firewall to filter out all
incoming packets belonging to EXE files, which are
often infected with viruses and worms. Proxy
firewalls generally keep very detailed logs,
including information on the data portions of
packets.
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• More secure than packet filter firewalls
• Easy to log and audit incoming traffic
Disadvantages:
• Additional processing overhead on each connection
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Advantages:

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HybridFirewall(circuit-levelgateway):
○ This can be a stand – alone system or it can be a
specialized functions performed by an application –
level gateway for certain applications.
○ It does not permit an end – to – end TCP connection;
rather, the gateway sets two TCP connections.
○ A typical use of the circuit – level gateway is a situation
in which the system administrator trusts the internal
users.
○ The gateway can be configured to support application –
level or proxy service on inbound connections and
circuit – level functions for outbound connections.
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○ Comparatively inexpensive and provide Anonymity to the private network.
Disadvantage :
• Do not filter Individual Packets
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Advantages:

11. Thank You
NIKHIL ER