D-Link DFL-2500 User Guide - Page 58

8 CHAPTER Logical Objects Logical objects are basic network elements defined in the firewall, referring to the entities needed to be protected and also the untrusted resources and applications that should be monitored by the security policies. 8.1 Address Book Like the contacts book which records people's name with one's phone number and email address, the address book in a Firewall is a list of symbolic names associated with various types of addresses, including IP addresses and ethernet MAC addresses. These items are fundamental elements heavily used in the firewall's configuration, such as specifying filtering fields for security policies. Therefore, choosing a descriptive and easily remembered name for each address item will greatly ease administration work. The administrator can use the names in each configuration task instead of filling in addresses every time, and in case of any modification to an address, only one point in the address book need to be changed. 8.1.1 IP address To enable every entity receiving and sending data from or to a TCP/IP network, a network layer (OSI layer 3) IP address is required to associate with each point between the network entity and the physical link, that is an interface. In other words, each interface has a unique IP address in the 39