What is firewall


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This presentation shows you in brief description about the Firewall which is used in the computers.

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What is firewall

  1. 1. FirewallOfficially invented in early 1990s H.M.H.R.JAYARATHNA 1 E091040028
  2. 2. What is a firewall?• A firewall protects networked computers from intentional hostile intrusion that could compromise confidentiality or result in data corruption or denial of service• It may be a hardware device(fig.1) or a software program(fig.2) running on a secure host computer. H.M.H.R.JAYARATHNA 2 E091040028
  3. 3. • A firewall sits at the junction point or gateway between the two networks, usually a private network and a public network such as the Internet.• The earliest firewalls were simply routers H.M.H.R.JAYARATHNA 3 E091040028
  4. 4. Fig.1 Hardware firewall providing protection to a Local Network. H.M.H.R.JAYARATHNA 4 E091040028
  5. 5. Fig.2 Computer running firewall software to provide protection H.M.H.R.JAYARATHNA 5 E091040028
  6. 6. What does a firewall do?• examines all traffic routed between the two networks to see if it meets certain criteria• firewall filters both inbound and outbound traffic.• can filter packets based on their source and destination addresses and port numbers. known as address filtering. H.M.H.R.JAYARATHNA 6 E091040028
  7. 7. • can also filter specific types of network traffic. known as protocol filtering (Eg: HTTP, ftp or telnet.)• can also filter traffic by packet attribute or state. H.M.H.R.JAYARATHNA 7 E091040028
  8. 8. What cant a firewall do?• cannot prevent individual users with modems from dialling into or out of the network, bypassing the firewall altogether.• Cannot control employee misconduct or carelessness H.M.H.R.JAYARATHNA 8 E091040028
  9. 9. Who needs a firewall?• Anyone who is responsible for a single computer/private network that is connected to Internet via modem/a public network needs firewall H.M.H.R.JAYARATHNA 9 E091040028
  10. 10. How does a firewall work?• There are two access denial methodologies used – firewall may allow all traffic through unless it meets certain criteria – it may deny all traffic unless it meets certain criteria• Firewalls may be concerned with the type of traffic, or with source or destination addresses and ports. H.M.H.R.JAYARATHNA 10 E091040028
  11. 11. Fig.3 Basic Firewall Operation. H.M.H.R.JAYARATHNA 11 E091040028
  12. 12. What different types of firewalls arethere?• four broad categories – packet filters – circuit level gateways – application level gateways – stateful multilayer inspection H.M.H.R.JAYARATHNA 12 E091040028
  13. 13. Packet filtering firewalls• work at the network level of the OSI model, or the IP layer of TCP/IP.• usually part of a router.• each packet is compared to a set of criteria before it is forwarded.• Depending on the packet and the criteria, the firewall can drop the packet, forward it or send a message to the originator. H.M.H.R.JAYARATHNA 13 E091040028
  14. 14. • Rules can include source and destination IP address, source and destination port number and protocol used.• Advantage: their low cost and low impact on network performance.• implementing packet filtering at the router level affords an initial degree of security at a low network layer. H.M.H.R.JAYARATHNA 14 E091040028
  15. 15. • This type of firewall only works at the network layer however and does not support sophisticated rule based models.• Network Address Translation (NAT) routers offer the advantages of packet filtering firewalls but can also hide the IP addresses of computers behind the firewall, and offer a level of circuit-based filtering. H.M.H.R.JAYARATHNA 15 E091040028
  16. 16. Packet Filtering Firewall H.M.H.R.JAYARATHNA 16 E091040028
  17. 17. circuit level gateways• work at the session layer of the OSI model, or the TCP layer of TCP/IP.• monitor TCP handshaking between packets to determine whether a requested session is legitimate.• Information passed to remote computer through a circuit level gateway appears to have originated from the gateway. H.M.H.R.JAYARATHNA 17 E091040028
  18. 18. • useful for hiding information about protected networks.• Circuit level gateways are relatively inexpensive• They do not filter individual packets.• Advantage: hiding information about private protect networks. H.M.H.R.JAYARATHNA 18 E091040028
  19. 19. Circuit level Gateway H.M.H.R.JAYARATHNA 19 E091040028
  20. 20. Application level gateways• also called proxies• similar to circuit-level gateways except that they are application specific.• can filter packets at the application layer of the OSI model.• Incoming or outgoing packets cannot access services for which there is no proxy. H.M.H.R.JAYARATHNA 20 E091040028
  21. 21. • an application level gateway that is configured to be a web proxy will not allow any FTP, gopher, telnet or other traffic through.• can filter application specific commands such as http:post and get, etc.• can also be used to log user activity and logins. H.M.H.R.JAYARATHNA 21 E091040028
  22. 22. • offer a high level of security, but have a significant impact on network performance.• This is because of context switches that slow down network access dramatically.• They are not transparent to end users and require manual configuration of each client computer. H.M.H.R.JAYARATHNA 22 E091040028
  23. 23. Application level Gateway H.M.H.R.JAYARATHNA 23 E091040028
  24. 24. Stateful Multilayer Inspection Firewall• filter packets at the network layer, determine whether session packets are legitimate and evaluate contents of packets at the application layer.• allow direct connection between client and host, alleviating the problem caused by the lack of transparency of application level gateways. H.M.H.R.JAYARATHNA 24 E091040028
  25. 25. • rely on algorithms to recognize and process application layer data instead of running application specific proxies.• offer a high level of security, good performance and transparency to end users.• are expensive• Due to their complexity are potentially less secure than simpler types of firewalls if not administered by highly competent personnel. H.M.H.R.JAYARATHNA 25 E091040028
  26. 26. Stateful Multilayer Inspection Firewall H.M.H.R.JAYARATHNA 26 E091040028
  27. 27. How do I implement a firewall?• Steps of implementing a firewall 1. Determine the access denial methodology to use. 2. Determine inbound access policy. 3. Determine outbound access policy 4. Determine if dial-in or dial-out access is required. 5. Decide whether to buy a complete firewall product, have one implemented by a systems integrator or implement one yourself. H.M.H.R.JAYARATHNA 27 E091040028
  28. 28. Firewall related problems• Firewalls restrict access to certain worthful services because those are not yet identified by firewall H.M.H.R.JAYARATHNA 28 E091040028
  29. 29. Benefits of a firewall• protect private local area networks from hostile intrusion from the Internet.• Firewalls allow network administrators to offer access to specific types of Internet services to selected LAN users.• Can control the access of outsiders(unidentifiers) to our network or a single machine H.M.H.R.JAYARATHNA 29 E091040028
  30. 30. • References – http://www.vicomsoft.com/learning-center/firewalls/ – A definition of Firewall Security from searchSecurity.com. – A definition of Firewalls from the FreeBSD Handbook – Network Security Tutorial from About.com. – Firewall.com - The Complete Security Portal – Security in Computing, 4th Edition, by Pfleeger & Pfleeger H.M.H.R.JAYARATHNA 30 E091040028