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Hack Attacks Revealed A Complete Reference with Custom Security Hacking Toolkit phần 3

Khi các số thập phân được nhập vào máy tính, hệ thống chuyển đổi các thành định dạng nhị phân 0 và 1, về cơ bản liên quan đến điện phí tính phí so với hiện trạng. Địa chỉ IP, ví dụ, mạng cấp dưới và tính toán với ký hiệu nhị phân. | First Octet NIC Assigned Class C 206 0.125 0 Network Host Figure 6.3 IP address example. Binary When decimal numbers are entered into the computer the system converts these into binary format 0s and 1s which basically correlate to electrical charges charged versus uncharged. IP addresses for example are subnetted and calculated with binary notation. An example of an IP address with 24 bits in the mask is shown in Figure 6.3. The first octet 206 indicates a Class C Internet-assigned IP address range with the format network.network.network.host with a standard mask binary indicating 255.255.255.0. This means that we have 8 bits in the last octet for hosts. The 8 bits that make up the last or fourth octet are understood by infrastructure equipment such as routers and software in the following manner Bit 1 2 3 4 5 6 7 8 Value 128 64 32 16 8 4 2 1 255 254 usable hosts In this example of a full Class C we only have 254 usable IP addresses for hosts 0 and 255 cannot be used as host addresses since the network number is 0 and the broadcast address is 255. Note that when a bit is used we indicate it with a 1 3 Bits 1 1 1 Value 128 64 32 16 8 4 2 1 When a bit is not used we indicate this with a 0 3 Bits 0 0 0 0 0 Value 128 64 32 16 8 4 2 1 As a result 3 Bits 1 1 1 0 0 0 0 0 Value 128 64 32 16 8 4 2 1 We add the decimal value of the used bits 128 64 32 224. This means that the binary value 11100000 equates to the decimal value 224. DECIMAL BINARY 224 11100000 153 Hex The hexadecimal system is a form of binary shorthand. Internetworking equipment such as routers use this format while formulating headers to easily indicate Token Ring numbers bridge numbers networks and so on to reduce header sizes and transmission congestion. Typically hex is derived from the binary format which is derived from decimal. Hex was designed so that the 8 bits in the binary 11100000 Decimal 224 will equate to only two hex characters each representing 4 bits. To clarify take a look at the binary .