Firewall

FIREWALL

 A firewall is a system designed to prevent unauthorized 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.

Three basic types of firewalls 

• packet filtering
•  application, 
• packet inspection

• Packet filtering: The system examines each packet entering or leaving the network and accepts or rejects it based on user-defined rules. Packet filtering is fairly effective and transparent to users, but it is difficult to configure. In addition, it is susceptible to IP spoofing.
  
  
  Three basic actions regarding the packet consist of a silent discard, with Internet Control  Message Protocol or TCP  response to the sender, and forward to the next hop. Packets may be filtered by source and destination IP  addresses, protocol, source and destination ports. 
• Application: This process applies security mechanisms when a TCP or UDP connection is established. Once the connection has been made, packets can flow between the hosts without further checking.Different techniques are used to surface such security vulnerabilities at different stages of an applications life cycle such as design, development, deployment.
• Packet inspection: A proxy server is a type of gateway that hides the true network address of the computer(s) connecting through it. A proxy server connects to the internet, makes the requests for pages, connections to servers, etc.

• Endpoint specific: Endpoint based application firewalls function by determining whether a process should accept any given connection. Application firewalls filter connections by examining the process ID of data packets against a rule set for the local process involved in the data transmission. Application firewalls accomplish their function by hooking into socket calls to filter the connections between the application layer and the lower layers. Application firewalls that hook into socket calls are also referred to as socket filters.