Firewall:
A firewall is a device that filters all traffic between a protected or “inside” network and a less trustworthy or “outside” network.
Usually, a firewall runs on a dedicated device, because
it is single point through which traffic is channeled,
performance is important, which means non-firewall
functions should not be done on the same machine.
Because a firewall is executable code, the attacker
could compromise that code and execute from the
firewall device.
The purpose of the fIrewall is to keep “bad” things
outside a protected environment. To accomplish that,
firewall implement a security that is specifically
designed to address what bad thing’s might happen.
Packet-Filtering Firewalls
Packet-filtering firewalls or packet-filtering gateway
applies a set of rules to each incoming IP packet and then
forwards or discards the packets.
The router is typically configured to filter packets going in
both directions (from and to the internal networK).
Stateful Inspection Firewalls
Filtering firewall work on packets one at a time,
accepting or rejecting each packet and moving on to
the next. They have no concept of “state” or “context”
from one packet to the next. A stateful inspection
firewall maintains state information from one packet to
another in the input stream.
Proxy Firewalls
A proxy firewall also called an application layer
firewalls, is a firewall that simulates the (proper) effects
of an application, so that the application will receive
only requests to act properly.
Guards
A guard is a sophisticated firewall. Like a proxy
firewall, it receives protocol data units, interprets them,
and passes through the same or different protocol data
units that achieve either the same result or a modified
results.
The guard decides what services to perform on the
user’s behalf in accordance with its available
knowledge.
Personal Firewalls
A personal firewall is an application program that runs
on a workstation to block unwanted traffic, usually
from the network.
The personal firewall is configured to enforce some
policy. For example, the user may decide that certain
sites, such as computers on the company networks, are
highly trustworthy but most other sites are not.
Limitations of Firewalls
1.The firewall cannot protect against attack that
bypass the firewall.
2.The firewall does not protect against internal threats.
3.The firewall can not protect against the transfer of
virus-infected programs or files.
4.The firewall can be “fooled” by source routing or
address spoofing.
