31 Days Before Your CCNA Exam

110 31 Days Before Your CCNA ExamFigure 21-1Bit 0Version (4)IPv4 Header FormatBit 15Bit 16Header Priority & TypeLength (4) of Service (8)Total Length (16)Identification (16)Flags(3)Fragment Offset (13)Bit 31Time To Live (8) Protocol (8) Header Checksum (16)Source IP Address (32)Destination IP Address (32)20BytesIP Options (0 Or 32 If Any)Data (Varies If Any)An IP address consists of two parts:■■The high order, or left-most, bits specify the network address component (network ID) of theaddress.The low order, or right-most, bits specify the host address component (host ID) of the address.Classes of AddressesFrom the beginning, IPv4 was designed with class structure: Class A, B, C, D and E. Class D isused for multicasting addresses and Class E is reserved for experimentation. Classes A, B, and Care assigned to network hosts. To provide a hierarchical structure, these classes are divided intonetwork and host portions, as shown in Figure 21-2. The high-order bits specify the network ID,and the low order bits specify the host ID.Figure 21-2The Network/Host Boundary for Each Class of IPv4 Address8 Bits8 Bits8 Bits8 BitsClass A:NetworkHostHostHostClass B: Network Network Host HostClass C: Network Network Network HostClass D:Class E:MulticastResearch