Network Firewalls
Network Firewalls are devices that designed to block unauthorized access in network connections.these devices can be software or hardware for example windows firewall is a software firewall and cisco firewall router is a hardware firewall. even it can be combination of both.It means all single data in networks are pass through the firewall,which it examines all of them and blocks those that do not meet the the specified security criteria,simply those that break the security laws.
History:
Firewall originally means a wall to confine a fire,firewall construction (cf).Later uses refer to another structures like,the metal sheet separating aircraft from passengers.
this technology is made in 1980s when the internet was a new technology that made a global connectivity between all global users.in 1980s this technology designed for network security as a router to separate networks from one another.
Packet filters:
this is the first generation of firewalls technology that designed by DEC(Digital Equipment Corporation) engineers in 1980.they named it Packet filter firewalls,and then At AT&T Bell Labs, Bill Cheswick and Steve Bellovin were continuing the researches in this subject and developed this generation working models.
Packet filters act by examines the packs which represent the basic unit of data transfer on networks or in this case on internet,if the packet does not match by filter's rules it passed and if it match by the packet filter rules it blocks or rejected and send a error responses to user.
This model is commonly use in PTC and UDP protocols and mostly using combination of packet's source and destination address.
Packet filtering firewalls work on the first three layers of the OSI,, which means all the work is done between the network and physical layers.
When a packet through a firewall, firewall checks for matches to any of the packet filtering rules that rejects the packet accordingly,For example if a rule in the firewall exists to block telnet access, then the firewall will block the IP protocol for port number 23.
Application layer:
It's the second generation of firewalls which it can understand the applications and protocols(such as web browsing)and it can detect any useless
protocols that through on a non-standard port or any unwanted protocols.
It's much more secure than packet filtering because it acts on all 7 layers of OSI.
For example,ISA (Internet Security and Acceleration)server.
This type of firewall technology can block higher-layer protocols such as FTP, Telnet, DNS, DHCP, HTTP, TCP, UDP and TFTP.
Stateful Filters:
In 1989-1990 three colleagues(Dave Presetto, Janardan Sharma, and Kshitij Nigam)designed the third generation of firewall technology that they named it "circuit level firewalls".
It's a development by combining the the packet filtering and Application layer and it keeps track of the state of network connections(such as TCP or UPD)traveling on it.nly packets matching a known connection state will be allowed by the firewall; others will be rejected.
At last simply it's a technology that make the networks secure.many of users use Microsoft Windows that have a firewall service on it that was known as Internet Connection Firewall.we have many other firewall software,such as PC Tools Firewall Plus,PeerBlock,PeerGuardian,PF,pfSense,ProtoWall,Sentry Firewall ,Shorewall,SmoothWall,Sunbelt Personal Firewall,Tiny Personal Firewall,Untangle ,Vyatta,Windows Firewall,Windows Live OneCare,WinGate,WinRoute,Zeroshell ,ZoneAlarm ,ZoneAlarm Z100G,Zorp firewall and....which these softwares have different services that make our computers and networks much more secure.