Copyright Goodheart-Willcox Co., Inc. 474 Networking Fundamentals with the network location. Most users do not comprehend how a sophisticated fi re- wall system works. Microsoft simply asks the user to pick the type of environment he or she is in, such as Public, Private, or Domain. Th en, Microsoft automatically confi g- ures Windows Firewall for the type of environment selected. Users have the option to confi gure individual software program access and spe- cifi c port access. Notice in Figure 15-19 that every software application and comput- er service is associated with a protocol such as TCP or UDP and a corresponding port number. Th e basic operation of all fi rewalls is based on fi ltering port numbers that are directly correlated to network services. For example, NetBIOS Name Resolution and UDP port 137 as shown in Figure 15-20. Specifi c, well-known port numbers (0–1023) are correlated to specifi c services assigned by the IANA organization. Well-known port numbers are typically assigned to system services. Registered ports (1024–49151) are also assigned by IANA and are typically assigned to specifi c software applications. Dynamic or private ports (49152–65535) are not assigned and can be used for any purpose by any software designer. You may wish to review the list of typical port number assignments in Figure 15-18 A firewall inspects data packets and allows the packet to pass, or it blocks the packet. Authorized Unauthorized Unauthorized Packets from authorized PCs are passed by the firewall. Local network PCs and file servers Packets from unauthorized PCs are blocked by the firewall. Authorized and unauthorized PCs Firewall Internet (workstation icons) RedlineVector/Shutterstock.com (server icons) fullvector/Shutterstock.com Goodheart-Willcox Publisher Figure 15-19 Windows Firewall with Advanced Security has many default firewall settings that are directly coordinated with the network location or environment, such as Public, Private, or Domain. Goodheart-Willcox Publisher