Copyright Goodheart-Willcox Co., Inc. 475 Chapter 15 Network Security Chapter 10. A complete list of port numbers can be found at: www.iana.org/ assignments/port-numbers. You can also conduct an Internet search using the phrase IANA.org port numbers. Th ere are several classifi cations of fi rewalls, such as packet fi lter, application gateway, content fi lter, and circuit level gateway. A typical fi rewall consists of two or more fi ltering techniques. Often, network devices are identifi ed as performing fi re- wall functions in addition to their intended purpose. For example, a network gateway can also perform functions associated with a fi rewall by fi ltering packets based on IP address, port number, or MAC address. Packet Filter A packet fi lter inspects each packet as it passes through the fi rewall and then ac- cepts or rejects the packet based on a set of rules. Th e terms stateful and stateless, as applied to fi rewall technology, refer to the way the packets are inspected. When confi gured for stateless packet inspection, a fi rewall inspects individual packet at- tributes, such as IP address, port number, and protocols. It then applies a fi lter based on the individual packet attributes. Th e fi lter is based on static information. It does not take into account packet fl ow. For example, a malicious program can delete a section of packets or alter the sequence. A stateless packet inspection will not detect the missing packets. Stateless packet inspection aligns with layer 3 of the OSI model. A fi rewall confi gured for stateful packet inspection applies a fi lter based on the sequence of packets. A stateful packet inspection can detect missing packets or an altered sequence of packets. For example, a fi rewall confi gured for stateful packet inspection could detect a MITM exploit, but a fi rewall confi gured for stateless packet inspection could not. Stateful packet inspection aligns with layer 3 and 4 of the Figure 15-20 The firewall is configured to allow packets related to Network Discovery NetBIOS Name Resolution through assigned UDP port 137. Goodheart-Willcox Publisher