ccna routing book

ccna routing book.In a given network, the first address is the network address (line number) and is used to uniquely represent the network segment or broadcast domain/VLAN; the last address is called the directed broadcast address and is used to represent all hosts within the segment. Directed broadcasts are similar to local broadcasts, with the main difference being that for local broadcasts, the router does not propagate them to other network segments, but for directed broadcasts, the router does so by default. All addresses between the network address and the broadcast address are host addresses that can be assigned to host devices within the segment, such as PCs, servers, routers, and switches.Each network has two reserved addresses: the network number (the first address) and the directed broadcast address (the last address) All addresses between these two addresses can be assigned to network devices in the segment, and they are called host addresses.1. network address and directed broadcast addressTo obtain a network address, set each bit of the host portion to 0; an address with all host bits at 1 is the last address and is a directed broadcast address; any address with other values in the host portion is a host address.For example, 192.1.1.0 is a Class C address and a network number. The first byte of the C address is 192.223, and the network number is 3 bytes long. Therefore, the 192 intellectual property is the network number. The last byte is the host part; this byte is 0 means the first address in the network, so the network address is 192.1.l.Oo If the last 8 bits (all host bits) are set to 1 (corresponding to the decimal value of 255), will get the network's directed broadcast address (192.1.1.255)2. Host addressAny address between the network address and the directed broadcast address is a host address. In the previous example, any address with the last byte between 0 and 255 is the host address in network 192.1.1.0: 192.1.1.1 ~ 192.1.1.254. One important point to note is that in every network, there are two addresses that are not available: the first address is reserved for the network number, and the last address is reserved for the directed broadcast address of the network. Once you know how many bits the host portion contains, you can use the following formula to calculate how many host addresses are available: 2H-2O This formula begins with the H subscreen of 2, where H is the number of bits in the host portion.For example, the network portion of a Class C network is 24 bits and the host portion is 8 bits, so in a Class C network, the last byte of the first address is 0,and that byte of the last address is 255 (all 8 bits are 1). In a Class C network, 1 to 254 are all host addresses.Using the previous formula, you can easily determine that the Class C network has 254 host addresses: 2 H-2 = 28-2 = 256-2 = 254. The Class B network contains 65534 host addresses: 2H -2 = 216 -2 = 64536 -2 = 65534OA network contains 16777214 host addresses: 2H -2 = 224 -2 = 16777216 -2 = 16777214 16777216 -2 = 16777214O For the curtain on 2, see Chapter 3.Exam Point Please keep in mind that each network has two addresses that cannot be assigned to hosts. Also, keep in mind the formula 2H-2, which is used to determine how many hosts the network can support based on the number of host bits (H).