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  1. 1. Firewalls Supervised By : Dr. Lo’ai Tawalbeh Done by : SHADI SAMARA ALA` AL_SAYYED The Arab Academy for Banking and Financial Sciences Security Technologies
  2. 2. Aims and Objectives <ul><li>Understand what a Firewall is and why </li></ul><ul><li>it is needed </li></ul><ul><li>Advantages and Disadvantages of a </li></ul><ul><li>Firewall </li></ul><ul><li>Different types of Firewall </li></ul><ul><li>Authentication techniques used by </li></ul><ul><li>Firewalls </li></ul><ul><li>Different Configurations of Firewalls </li></ul>
  3. 3. What is Security? <ul><li>The quality or state of being secure—to be free from danger” </li></ul><ul><li>A successful organization should have multiple layers of security in place: </li></ul><ul><ul><li>Physical security </li></ul></ul><ul><ul><li>Personal security </li></ul></ul><ul><ul><li>Operations security </li></ul></ul><ul><ul><li>Communications security </li></ul></ul><ul><ul><li>Network security </li></ul></ul><ul><ul><li>Information security </li></ul></ul>
  4. 4. Characteristics of Information <ul><li>The value of information comes from the characteristics it possesses: </li></ul><ul><ul><li>Availability </li></ul></ul><ul><ul><li>Accuracy </li></ul></ul><ul><ul><li>Authenticity </li></ul></ul><ul><ul><li>Confidentiality </li></ul></ul><ul><ul><li>Integrity </li></ul></ul><ul><ul><li>Utility </li></ul></ul><ul><ul><li>Possession </li></ul></ul>
  5. 5. <ul><li>Physical Design </li></ul><ul><li>Physical design of an information security program is made up of two parts : </li></ul><ul><li>Security technologies </li></ul><ul><li>Physical security </li></ul><ul><li>  Physical design process: </li></ul><ul><li>select specific technologies. </li></ul><ul><li>- Identifies complete technical solutions based on these technologies (deployment, operations and maintenance elements) </li></ul><ul><li>- Design physical security measures to support the technical solution. </li></ul>
  6. 6. <ul><li>Firewalls </li></ul><ul><li>A software or hardware component that restricts network communication between two computers or networks. </li></ul><ul><li>In buildings, a firewall is a fireproof wall that restricts the spread of a fire. </li></ul><ul><ul><li>Network firewall prevents threats from spreading from one network to another </li></ul></ul><ul><li>Prevent specific types of information from moving between the outside world (untrusted networks) and the inside world (trusted networks) </li></ul><ul><li>The firewall may be a separate computer system, a software service running on an existing router all server, or a separate network containing a number of supporting devices. </li></ul>
  7. 7. Internet Firewalls
  8. 8. The Internet Protocol Stack
  9. 9. What Firewalls do <ul><li>Protects the resources of an internal network. </li></ul><ul><li>- Restrict external access. </li></ul><ul><li>- Log Network activities. </li></ul><ul><li>-Intrusion detection </li></ul><ul><li>-DoS </li></ul><ul><li>- Act as intermediary </li></ul><ul><li>- Centralized Security Management </li></ul><ul><ul><ul><li>Carefully administer one firewall to control internet traffic of many machines. </li></ul></ul></ul><ul><ul><ul><li>Internal machines can be administered with less care. </li></ul></ul></ul>
  10. 10. Types of Firewalls (General) <ul><li>Firewalls types can be categorized depending on: </li></ul><ul><ul><li>The Function or methodology the firewall use </li></ul></ul><ul><ul><li>Whether the communication is being done between a single node and the network, or between two or more networks. </li></ul></ul><ul><ul><li>Whether the communication state is being tracked at the firewall or not. </li></ul></ul>
  11. 11. Types of Firewalls <ul><li>2. With regard to the scope of filtered communications the done between a single node and the network, or between two or more networks there exist : </li></ul><ul><ul><li>Personal Firewalls, a software application which normally filters traffic entering or leaving a single computer. </li></ul></ul><ul><ul><li>Network firewalls, normally running on a dedicated network device or computer positioned on the boundary of two or more networks. </li></ul></ul>
  12. 12. <ul><li>Firewall categorization methods </li></ul><ul><ul><li>1-The Function or methodology the firewall use </li></ul></ul><ul><li>Five processing modes that firewalls can be categorized by are : </li></ul><ul><li>1.  packet filtering </li></ul><ul><li>2.  application gateways </li></ul><ul><li>3.  circuit gateways </li></ul><ul><li>4.  MAC layer firewalls </li></ul><ul><li>5.  hybrids </li></ul>
  13. 13. <ul><li>1- packet filtering : </li></ul><ul><li>examine the header information of data packets that come into a network. </li></ul><ul><li>a packet filtering firewall installed on TCP/IP based network and determine wether to drop a packet or forward it to the next network connection based on the rules programmed in the firewall. </li></ul><ul><li>Packet filtering firewalls scan network data packets looking for violation of the rules of the firewalls database. </li></ul><ul><li>Filtering firewall inspect packets on at the network layers. </li></ul><ul><li>If the device finds a packet that matches a restriction it stops the packet from traveling from network to another. </li></ul>
  14. 14. Packet Filtering (cont) <ul><li>filters packet-by-packet, decides to Accept/Deny/Discard packet based on certain/configurable criteria – Filter Rule sets . </li></ul><ul><li>Typically stateless: do not keep a table of the connection state of the various traffic that flows through them </li></ul><ul><ul><li>Not dynamic enough to be considered true firewalls. </li></ul></ul><ul><ul><li>Usually located at the boundary of a network. </li></ul></ul><ul><ul><li>Their main strength points: Speed and Flexibility . </li></ul></ul>
  15. 15. <ul><li>* There are three subsets of packet filtering firewalls: </li></ul><ul><li>- static filtering </li></ul><ul><li>-dynamic filtering </li></ul><ul><li>-stateful inspection </li></ul><ul><li>  static filtering: </li></ul><ul><li>- requires that the filtering rules coverning how the firewall decides which packets are allowed and which are denied. </li></ul><ul><li>-This type of filtering is common in network routers and gateways. </li></ul>
  16. 16. <ul><li>Dynamic filtering </li></ul><ul><li>- allows the firewall to create rules to deal with event. </li></ul><ul><li>-This reaction could be positive as in allowing an internal user to engage in a specific activity upon request or negative as in dropping all packets from a particular address </li></ul><ul><li>  Stateful inspection </li></ul><ul><li>-keep track of each network connection between internal and external systems using a state table. </li></ul><ul><li>-A state table tracks the state and context of each packet in the conversation by recording which station send , what packet and when. </li></ul><ul><li>-More complex than their constituent component firewalls </li></ul><ul><li>-Nearly all modern firewalls in the market today are staful </li></ul>
  17. 17. Stateful Inspection Firewalls
  18. 18. Basic Weaknesses Associated with Packet Filters Statful <ul><ul><li>They cannot prevent attacks that employ application-specific vulnerabilities or functions. </li></ul></ul><ul><ul><li>Logging functionality present in packet filter firewalls is limited </li></ul></ul><ul><ul><li>Most packet filter firewalls do not support advanced user authentication schemes. </li></ul></ul><ul><ul><li>Vulnerable to attacks and exploits that take advantage of problems within the TCP/IP specification and protocol stack, such as network layer address spoofing. </li></ul></ul><ul><ul><li>Susceptible to security breaches caused by improper configurations. </li></ul></ul>
  19. 19. Packet Filtering Summary <ul><li>Advantages : </li></ul><ul><ul><li>One packet filter can protect an entire network </li></ul></ul><ul><ul><li>Efficient (requires little CPU) </li></ul></ul><ul><ul><li>Supported by most routers </li></ul></ul><ul><li>Disadvantages : </li></ul><ul><ul><li>Difficult to configure correctly </li></ul></ul><ul><ul><ul><li>Must consider rule set in its entirety </li></ul></ul></ul><ul><ul><li>Difficult to test completely </li></ul></ul><ul><ul><li>Performance penalty for complex rulesets </li></ul></ul><ul><ul><ul><li>Stateful packet filtering much more expensive </li></ul></ul></ul><ul><ul><li>Enforces ACLs at layer 3 + 4, without knowing any application details </li></ul></ul>
  20. 20. Packet Filtering Firewalls <ul><li>The original firewall </li></ul><ul><li>Works at the network level of the OSI </li></ul><ul><li>model </li></ul><ul><li>Applies packet filters based on access </li></ul><ul><li>Rules: </li></ul><ul><li>– Source IP address </li></ul><ul><li>– Destination IP address </li></ul><ul><li>– Application or protocol </li></ul><ul><li>– Source port number </li></ul><ul><li>– Destination port number </li></ul>
  21. 21. Packet Filtering Firewalls Firewalls
  22. 22. <ul><li>2- application gateways : </li></ul><ul><li>is also known as proxy server since it runs special software that acts as a proxy for a service request. </li></ul><ul><li>One common example of proxy server is a firewall that blocks or requests for and responses to request for web pages and services from the internal computers of an organization. </li></ul><ul><li>The primary disadvantage of application level firewalls is that they are designed for a specific protocols and cannot easily be reconfigured to protect against attacks in other protocols. </li></ul><ul><li>Application firewalls work at the application layer. </li></ul>
  23. 23. Application/Proxy Servers…cont <ul><li>Filters packets on application data as well as on IP/TCP/UDP fields. </li></ul><ul><li>The interaction is controlled at the application layer </li></ul><ul><li>A proxy server is an application that mediates traffic between two network segments. </li></ul><ul><li>With the proxy acting as mediator, the source and destination systems never actually “connect”. </li></ul><ul><li>Filtering Hostile Code: Proxies can analyze the payload of a packet of data and make decision as to whether this packet should be passed or dropped. </li></ul><ul><li>. </li></ul>
  24. 24. Application/Proxy Servers…cont
  25. 25. Application/Proxy Servers…cont <ul><li>No proxy, no Internet application </li></ul><ul><li>Typical proxies include: </li></ul><ul><li>• FTP </li></ul><ul><li>• SMTP, POP3 </li></ul><ul><li>• Telnet </li></ul><ul><li>• DNS </li></ul><ul><li>• Http </li></ul>
  26. 26. Application/Proxy Servers…cont <ul><li>Advantages : </li></ul><ul><li>Extensive logging capability </li></ul><ul><li>Allow security enforcement </li></ul><ul><li>of user authentication . </li></ul><ul><li>less vulnerable to address </li></ul><ul><li>spoofing attacks. </li></ul><ul><li>Disadvantages: </li></ul><ul><li>Complex Configuration . </li></ul><ul><li>limited in terms of support for new </li></ul><ul><li>network applications and protocols. </li></ul><ul><li>Speed !!. </li></ul>
  27. 27. <ul><li>3- circuit gateways: </li></ul><ul><li>operates at the transport layer. </li></ul><ul><li>Connections are authorized based on addresses , they prevent direct connections between network and another. </li></ul><ul><li>They accomplish this prevention by creating channels connecting specific systems on each side of the firewall and then allow only authorized traffic. </li></ul>
  28. 28. circuit gateways ..cont <ul><li>relays two TCP connections (session layer) </li></ul><ul><li>imposes security by limiting which such connections are allowed </li></ul><ul><li>once created usually relays traffic without examining contents </li></ul><ul><li>Monitor handshaking between packets to decide whether the traffic is legitimate </li></ul><ul><li>typically used when trust internal users by allowing general outbound connections </li></ul><ul><li>SOCKS commonly used for this </li></ul>
  29. 29. Circuit Level Firewalls Example
  30. 30. circuit gateways ..cont <ul><li>Individual packets are not filtered. </li></ul><ul><li>• Access control mechanisms are needed, since </li></ul><ul><li>logs cant catch all the abuses. </li></ul><ul><li>– Time limit on how long ports will last. </li></ul><ul><li>– List of permissible outside called to the port. </li></ul><ul><li>• The other big problem is need to provide new </li></ul><ul><li>client program. </li></ul><ul><li>• Code changes issues include availability of </li></ul><ul><li>application source code for various platforms, </li></ul><ul><li>version control, distribution and more. </li></ul>Disadvantages
  31. 31. <ul><li>4- MAC layer firewalls: </li></ul><ul><li>design to operate at the media access control layer. </li></ul><ul><li>Using this approach the MAC addresses of specific host computers are linked to ACL entries that identify the specific types of packets that can be send to each host and all other traffic is blocked. </li></ul>
  32. 32. <ul><li>5- Hybrids firewalls : </li></ul><ul><li>companied the elements of other types of firewalls , example the elements of packet filtering and proxy services, or a packet filtering and circuit gateways. </li></ul><ul><li>That means a hybrids firewalls may actually of two separate firewall devices; each is a separate firewall system, but they are connected so that they work together. </li></ul>
  33. 33. General Performance
  34. 34. Types of Firewalls <ul><li>3. Finally, Types depending on whether the firewalls keeps track of the state of network connections or treats each packet in isolation, two additional categories of firewalls exist : </li></ul><ul><ul><li>Stateful firewall </li></ul></ul><ul><ul><li>Stateless firewall </li></ul></ul>
  35. 35. Types of Firewalls ..cont <ul><ul><li>Stateful firewall </li></ul></ul><ul><ul><li>keeps track of the state of network connections (such as TCP streams) traveling across it. </li></ul></ul><ul><ul><li>Stateful firewall is able to hold in memory significant attributes of each connection, from start to finish. These attributes, which are collectively known as the state of the connection, may include such details as the IP addresses and ports involved in the connection and the sequence numbers of the packets traversing the connection. </li></ul></ul>
  36. 36. Types of Firewalls ..cont <ul><ul><li>Stateless firewall </li></ul></ul><ul><ul><li>Treats each network frame (Packet) in isolation. Such a firewall has no way of knowing if any given packet is part of an existing connection, is trying to establish a new connection, or is just a rogue packet. </li></ul></ul><ul><ul><li>The classic example is the File Transfer Protocol, because by design it opens new connections to random ports. </li></ul></ul>
  37. 37. Network Address Translation (NAT) <ul><li>- Existed for a short period of time; now NAT is part of every firewall </li></ul><ul><li>-Developed in response to two major issues in network engineering and security : </li></ul><ul><li>First , network address translation is an effective tool for hiding the network-addressing schema present behind a firewall environment. </li></ul><ul><li>Second , the depletion of the IP address space has caused some organizations to use NAT for mapping non-routable IP addresses to a smaller set of legal addresses. </li></ul>
  38. 38. Network Address Translation ..cont <ul><ul><li>NAT goals </li></ul></ul><ul><ul><li>– Allow use of internal IP-addresses </li></ul></ul><ul><ul><li>– Hide internal network structure </li></ul></ul><ul><ul><li>– Disable direct internet connections </li></ul></ul><ul><ul><li>NAT-types </li></ul></ul><ul><ul><li>– Dynamic </li></ul></ul><ul><ul><li>• For connections from inside to outside </li></ul></ul><ul><ul><ul><li>• There may be fewer outside addresses than internal addresses </li></ul></ul></ul><ul><ul><li>– Static </li></ul></ul><ul><ul><li>• For connections from outside to specific servers inside </li></ul></ul><ul><ul><li>• One-to-one address mapping (fixed) </li></ul></ul>
  39. 39. Network Address Translation ..cont
  40. 40. Firewall Configurations or ( Architecture) <ul><li>Packet Filtering Router </li></ul><ul><li>Dual Homed Gateway </li></ul><ul><li>Screened Host Gateway ( bastion host ) </li></ul><ul><li>Screened Subnet Gateway or Demilitarized Zone (DMZ) </li></ul><ul><li>Firewall Appliance </li></ul>
  41. 41. Packet Filtering Router <ul><li>A packet filtering router is a router configured to screen packets between two networks. It routes traffic between the two networks and uses packet filtering rules to permit or deny traffic. Implementing security with a router is usually not that easy. Most routers were designed to route traffic, not to provide firewall functionality, so the command interface used for configuring rules and filters is neither simple nor intuitive. </li></ul>
  42. 42. Dual Homed Gateway <ul><li>This is a secure firewall design comprising an application gateway and a packet </li></ul><ul><li>filtering router. It is called “dual homed” because the gateway has two network </li></ul><ul><li>interfaces, one attached to the Internet, the other to the organization's network. Only </li></ul><ul><li>applications with proxy services on the application gateway are able to operate </li></ul><ul><li>through the firewall. Since IP forwarding is disabled in the host, IP packets must be </li></ul><ul><li>directed to one of the proxy servers on the host, or be rejected. Some manufacturers </li></ul><ul><li>build the packet filtering capability and the application proxies into one box, </li></ul><ul><li>thereby simplifying the design (but removing the possibility of having an optional </li></ul><ul><li>info server and modems attached to the screened subnet, </li></ul><ul><li>disadvantage s of the dual homed gateway are that it may be a bottleneck to </li></ul><ul><li>performance, and it may be too secure for some sites (!) since it is not possible to let </li></ul><ul><li>trusted applications bypass the firewall and communicate directly with peers on the </li></ul><ul><li>Internet. They must have a proxy service in the firewall. </li></ul>
  43. 43. Dual Homed Gateway ..cont <ul><li>A dual-homed gateway typically sits behind the gateway (usually a router) to the untrusted network and most often is a host system with two network interfaces. Traffic forwarding on this system is disabled, thereby forcing all traffic between the two networks to pass through some kind of application gateway or proxy. Only gateways or proxies for the services that are considered essential are installed on the system. This particular architecture will usually require user authentication before access to the gateway/proxy is allowed. Each proxy is independent of all other proxies on the host system. </li></ul>
  44. 44. Screened Host Gateway ( bastion host ) <ul><li>The screened host gateway is similar to the above, but more flexible and less secure, </li></ul><ul><li>since trusted traffic may pass directly from the Internet into the private network, </li></ul><ul><li>thereby bypassing the application gateway. In this design the application gateway </li></ul><ul><li>only needs a single network connection. </li></ul><ul><li>The IP router will normally be configured to pass Internet traffic to the application </li></ul><ul><li>gateway or to reject it. Traffic from the corporate network to the Internet will also </li></ul><ul><li>be rejected, unless it originates from the application gateway. The only exception to </li></ul><ul><li>these rules will be for trusted traffic that will be allowed straight through. </li></ul>
  45. 45. Screened Host Gateway ..cont <ul><li>The screened host, or bastion host, is typically located on the trusted network, protected from the untrusted network by a packet filtering router. All traffic coming in through the packet filtering router is directed to the screened host. Outbound traffic may or may not be directed to the screened host. This type of firewall is most often software based and runs on a general-purpose computer that is running a secure version of the operating system. Security is usually implemented at the application level. </li></ul>
  46. 46. Screened Host Gateway ..cont <ul><li>highly secure host system </li></ul><ul><li>potentially exposed to &quot;hostile&quot; elements </li></ul><ul><li>hence is secured to withstand this </li></ul><ul><li>may support 2 or more net connections </li></ul><ul><li>may be trusted to enforce trusted separation between network connections </li></ul><ul><li>runs circuit / application level gateways </li></ul><ul><li>or provides externally accessible services </li></ul>
  47. 47. Screened Subnet Gateway <ul><li>This configuration creates a small isolated network between the Internet and the </li></ul><ul><li>corporate network, which is sometimes referred to as the demilitarised zone (DMZ), </li></ul><ul><li>The advantages of this configuration is that multiple hosts and </li></ul><ul><li>gateways can be stationed in the DMZ, thereby achieving a much greater throughput </li></ul><ul><li>to the Internet than the other configurations; plus the configuration is very secure as </li></ul><ul><li>two packet filtering routers are there to protect the corporate network. </li></ul><ul><li>The IP router on the Internet side will only let through Internet traffic that is </li></ul><ul><li>destined for a host in the DMZ (and vice versa). The IP router on the corporate </li></ul><ul><li>network side will only let site traffic pass to a host in the DMZ (and vice versa). </li></ul><ul><li>This system is as secure as the dual homed gateway, but it is also possible to allow </li></ul><ul><li>trusted traffic to pass straight through the DMZ if required. This configuration is of </li></ul><ul><li>course more expensive to implement! </li></ul>
  48. 48. Screened Subnet Gateway ..cont <ul><li>A screened subnet or DMZ is typically created between two packet filtering routers. When using this architecture, the firewall solution is housed on this screened subnet segment along with any other services available to the untrusted network. Conceptually, this architecture is similar to that of a screened host, except that an entire network rather than a single host is reachable from the outside </li></ul>
  49. 49. Firewall Appliance <ul><li>A firewall appliance typically sits behind the gateway (usually a router) to the untrusted network. This architecture resembles the packet filtering router and dual-homed Gateway architectures in that all traffic must pass through the appliance. In most instances these appliances come pre-configured on their own box. They may also have other services built in, such as Web servers and e-mail servers. Because they usually don't need the extensive configuration that other firewalls often require, they are touted as being much simpler and faster to use. Some manufacturers market them as &quot;plug-and-play&quot; firewall solutions </li></ul>
  50. 50. Firewall Appliance ..cont <ul><li>For some networks, implementing more than one firewall solution may be a more effective option. For example, implement a packet filtering router at the entrance to the network for perimeter security and then configure an application gateway for a specific department or building. This type of solution would not only protect the trusted network from the outside, but would also protect a specific department or building from unauthorized users on the trusted network </li></ul>
  51. 51. Network Configuration Examples <ul><li>Protected Private Network </li></ul><ul><li>Semi-Militarised Zone </li></ul><ul><li>Private LAN stays secure </li></ul>
  52. 52. Protected Private Network <ul><li>Allow all access from private network to the </li></ul><ul><li>Internet. </li></ul><ul><li>Deny all access from the Internet to the private </li></ul><ul><li>network. </li></ul>
  53. 53. Semi-Militarised Zone
  54. 54. Private LAN stays secure
  55. 55. Advantages of a Firewall <ul><li>Stop incoming calls to insecure services </li></ul><ul><li>such as rlogin and NFS </li></ul><ul><li>Control access to other services </li></ul><ul><li>Control the spread of viruses </li></ul><ul><li>Cost Effective </li></ul><ul><li>More secure than securing every </li></ul><ul><li>system </li></ul>
  56. 56. Disadvantages of a Firewall <ul><li>Central point of attack </li></ul><ul><li>Restrict legitimate use of the Internet </li></ul><ul><li>Bottleneck for performance </li></ul><ul><li>Does not protect the ‘back door’ </li></ul><ul><li>Cannot always protect against </li></ul><ul><li>smuggling </li></ul><ul><li>Cannot prevent insider attacks </li></ul>
  57. 57. Firewalls have weaknesses <ul><li>Some security hackers boast there is </li></ul><ul><li>not a single firewall that they cannot </li></ul><ul><li>Penetrate </li></ul><ul><li>They cannot keep out data carried inside </li></ul><ul><li>applications, such as viruses within email </li></ul><ul><li>Messages </li></ul><ul><li>Although firewalls provide a high level of security </li></ul><ul><li>in today's private networks to the outside world </li></ul><ul><li>we still need the assistance of other related </li></ul><ul><li>security components in order to guarantee </li></ul><ul><li>proper network security. </li></ul>
  58. 58. <ul><li>Firewalls categorized by development generation : </li></ul><ul><li>First generation firewalls: are static packet filtering firewalls. </li></ul><ul><li>Second generation firewalls: are application-level firewalls or proxy service. </li></ul><ul><li>Third generation firewalls: are stateful inspection firewalls. </li></ul><ul><li>Fourth generation firewalls: dynamic packets filtering firewalls, allow only a particular packet with a particular source, destination, and port address to enter. </li></ul><ul><li>Fifth generation firewalls: is the kernel proxy . </li></ul>
  59. 59. <ul><li>Selecting the right firewall </li></ul><ul><li>Most important of these is the extend to which the firewall design provides the desired protection.  </li></ul><ul><li>what type of firewall technology offers the right balance between protection and cost for the needs of the organization? </li></ul><ul><li>how easy is it to set up and configure the firewall. </li></ul><ul><li>  The second most important issue is cost. </li></ul>
  60. 60. Selecting Firewall Solution <ul><li>In order to pick the best architecture and packet screening method for a firewall solution, the following questions should be considered: </li></ul><ul><li>What does the firewall need to do? </li></ul><ul><li>What additional services would be desirable? </li></ul><ul><li>How will it fit in the existing network? </li></ul><ul><li>How will it effect existing services and users? </li></ul>
  61. 61. Firewall Products Classification <ul><li>H/W – Platform </li></ul><ul><li>-Linux, Solaris, Windows,….system. </li></ul><ul><li>-Proprietary (Nokia-Box, Cisco PIX) </li></ul><ul><li>Software </li></ul><ul><li>-Checkpoint FireWall 1 (FW-1) </li></ul><ul><li>-NetGuard Guardian </li></ul><ul><li>Perimeter Firwall </li></ul><ul><li>-Checkpoint </li></ul><ul><li>-PIX </li></ul><ul><li>-Sun SPF </li></ul><ul><li>Stand Alone Box (Appliance) </li></ul><ul><li>- Satic Wall </li></ul><ul><li>- Watch Guard FireBox </li></ul><ul><li>- Netscreen </li></ul><ul><li>Personal FireWall </li></ul><ul><ul><li>BlackICE </li></ul></ul><ul><ul><li>Zone Alarm </li></ul></ul>
  62. 62. References <ul><li>Steven Bellovin, “Security Problems in the TCP/IP Protocol Suite ”, Computer Communication Review, Vol. 19, No. 2, pp. 32-48, April 1989. </li></ul><ul><li>Matt Bishop, Introduction to Computer Security , Addison-Wesley, 2005. </li></ul><ul><li>William Cheswick, Steven Bellovin, and Avriel Rubin, Firewalls and Internet Security, 2 nd edition , 2003. </li></ul><ul><li>Fyodor, “The Art of Port Scanning,” </li></ul><ul><li>Fyodor, NMAP man page, </li></ul>