what is firewall in networking


COMPUTER NETWORK

DATE: 3-FEB-2019

BY ABHAY MISHRA


hello friends today we discuss about computer security .yes you think right i told firewall for what help in our network .

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Firewall -

A firewall is a system designed to prevent
unauthorised access to or from a private network. You can
implement a firewall in either hardware or software form, or
a combination of both. Firewalls prevent unauthorized
Internet users from accessing private networks connected to
the Internet, especially intranets. All messages entering or
leaving the intranet (i.e., the local network to which you are
connected) must pass through the firewall, which examines
each message and blocks those that do not meet the
specified security criteria. Software or combination of
software and hardware, used to protect users’ data from
unintended recipients on the network/internet.



Several types of firewalls exist:

1. Packet-filtering firewalls: Packet-filtering firewalls operate at the router and compare each packet received to a set of established criteria (such as allowed IP addresses, packet type, port number, etc.) before being either dropped or forwarded.

2. Circuit-level gateways: Circuit-level gateways monitor the TCP handshaking going on between the local and remote hosts to determine whether the session being initiated is legitimate -- whether the remote system is considered "trusted." They don't inspect the packets themselves, however.

3. Stateful inspection firewalls: Stateful inspection firewalls on the other hand, not only examine each packet, but also keep track of whether or not that packet is part of an established TCP session. This offers more security than either packet filtering or circuit monitoring alone, but exacts a greater toll on network
performance.

4. Application-level gateways: Application-level gateways (proxies) combine some of the attributes of packet filtering firewalls with those of circuit-level gateways. They filter packets not only according to the service for which they are intended (as specified by the destination port), but also by certain other characteristics such as HTTP request string. While application-level gateways provide considerable data security, they can dramatically impact network performance.

5. Multi layer inspection firewalls: Multi-layer inspection firewalls combine packet filtering with circuit monitoring, while still enabling direct connections between the local and remote hosts, which are transparent to the network. Multi layer firewalls work by retaining the status (state) assigned to a packet by each firewall component through which it passes on the way up the protocol stack. This gives the user maximum control over which packets are allowed to reach their final destination, but again affects network performance, although generally not so dramatically as proxies do.






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so that is called firewall ....
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