Que: How does Firewall Works? or Explain Working Technique of Firewall.
Ans:
How
do firewalls work?
Ø Firewalls
enforce the established security policies through a variety of security
policies through a variety of mechanisms.
o NAT(network
address translation)
o Basic
packet filtering
o Stateful
packet filtering
o ACLs
o Application
layer proxies
NAT:-
Ø It
allows you to mask significant amounts of information from outside of network.
Ø It
allows an outside entity to communicate with an entity inside the firewall
without truly knowing its address.
Ø It
is technique of IPv4 to bind private IP address to public address.
Ø NAT
can assist in security by preventing direct access to devices from outside the
firm, without first having address change at NAT devices.
Ø Benefit
is that fewer public IP address are needed and from a security point of view
the internal address structure is not known to outside world.
Ø If
a hacker attacks the source address he is simply attacking the NAT device, not
actual sender of packet.
Basic
packet filtering:-
Ø It
involves looking at packets their ports, protocols, source and destination
addresses and checking that information against the rules configured on
firewall.
Ø For
Example, telnet and FTP connections may be prohibited from being established to
mail or dB server but they may be allowed for respective service servers.
Ø It
is simple method of filtering based on information in each packet header such
as IP address and TCP/UDP ports.
Ø It
will not detect and catch all undesired packets but it is fast and efficient.
Stateful
packet filtering:-
Ø It
means that firewall maintains context on conversation.
Ø Means
it will look all packets.
Ø Traffic
from an outside server to an inside server may be allowed if it is requested
but blocked if it is not.
Ø Example,
request for a web page.
Ø Advance
firewalls employ stateful packet filtering to prevent several types of undesired
communication.
Ø Disadvantage
is that it takes significant resources and processing to perform this type of
monitoring and reduces efficiency and requires more robust and expensive
hardware.
Application
layer proxies:-
Ø Here
packets are not allowed to traverse the firewall but data instead flows up to
an application that in turn decides what to do with it.
Ø Example,
SMTP proxy may accept inbound mail from the internet and forward it to the
internal corporate mail server.
Ø While
proxies provide a high level of security by making it very difficult for an
attacker to manipulate the actual packets arriving at the destination.
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