This can lead to damage of important data ,or the whole network. So the solution isn’t to cut off the network from internet, Instead we can build firewalls to protect the network.

A firewall is a software running on  another computer. which inspects the network traffic through it, and denies or permits pasage based on a set of rules. A firewall’s basic task is to regulate some of the flow of traffic between computer networks.

A firewall can be implemented both in hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized internet users from accessing private networks connected to the internet, especially intranets. All messages entering or leaving the intranet pass through the firewall,which examines each message and blocks those that do not meet the specifies security criteria.

There are several types of firewall techniques:

• Packet filter: It looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules.
• Application gateway: It applies security mechanisms to specific applications such as Telnet servers.
• Circuit-level gateway: It applies security mechanisms when a TCP or UDP connection is established.Once the connection is made,packets can flow between the hosts without further checking.
• Proxy server: The proxy server is a application program which services the requests of the clients by forwarding requests to other servers. The proxy server hides the true network address.

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