Chapter 6 - Chapter 6 ITS 1 Chapter 6 Firewalls Prevent...

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Chapter 6 ITS 1 Chapter 6 Firewalls Prevent specific types of information from moving between the outside world (untrusted network) and the inside world (trusted network) May be separate computer system; a software service running on existing router or server; or a separate network containing supporting devices Processing Modes of Firewalls Five processing modes that firewalls can be categorized by are: Packet filtering Application gateways Circuit gateways MAC layer firewalls Hybrids Packet Filtering Packet filtering firewalls examine header information of data packets Most often based on combination of: Internet Protocol (IP) source and destination address Direction (inbound or outbound) Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) source and destination port requests Simple firewall models enforce rules designed to prohibit packets with certain addresses or partial addresses Three subsets of packet filtering firewalls: Static filtering: requires that filtering rules governing how the firewall decides which packets are allowed and which are denied are developed and installed Dynamic filtering: allows firewall to react to emergent event and update or create rules to deal with event Stateful inspection: firewalls that keep track of each network connection between internal and external systems using a state table
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Chapter 6 ITS 2 Application Gateways Frequently installed on a dedicated computer; also known as a proxy server Since proxy server is often placed in unsecured area of the network (e.g., DMZ), it is exposed to higher levels of risk from less trusted networks
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Chapter 6 ITS 3 Additional filtering routers can be implemented behind the proxy server, further protecting internal systems Circuit Gateways Circuit gateway firewall operates at transport layer Like filtering firewalls, do not usually look at data traffic flowing between two networks, but prevent direct connections between one network and another Accomplished by creating tunnels connecting specific processes or systems on each side of the firewall, and allow only authorized traffic in the tunnels MAC Layer Firewalls Designed to operate at the media access control layer of OSI network model Able to consider specific host computer’s identity in its filtering decisions MAC addresses of specific host computers are linked to access control list (ACL) entries that identify specific types of packets that can be sent to each host; all other traffic is blocked Hybrid Firewalls Combine elements of other types of firewalls; i.e., elements of packet filtering and proxy services, or of packet filtering and circuit gateways Alternately, may consist of two separate firewall devices; each a separate firewall system, but connected to work in tandem Firewalls Categorized by Generation First generation: static packet filtering firewalls Second generation: application-level firewalls or proxy servers
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This note was uploaded on 05/27/2011 for the course ITS 375 taught by Professor Thomas during the Fall '10 term at N.C. State.

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Chapter 6 - Chapter 6 ITS 1 Chapter 6 Firewalls Prevent...

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