cisco ccna security 9tut

cisco ccna security 9tut.Class E 240.0.0.0.255.255.255.255 ReservedClass A, B, and C IP addresses can be assigned to a host's NIC or router interface for regular IP unicast communications; Class D IP addresses are generally used as multicast addresses; and Class E are all reserved and cannot be used for IP routing. The network number length and host address number length of IP addresses vary by class.The first 8 bits of a Class A IP address are the network number, and the last 24 bits are the host address number. This means that a Class A IP address contains 256 (28) different networks, each of which can hold 16,777,216 (224) hosts. For example, IP addresses 1.1.1.1 and 2.2.2.2 belong to two different Class A networks, while addresses 1.1.1.1 and 1.4.1.1 belong to the same Class A network l.x.x.xoThe first 16 bits of a Class B IP address are the network number and the last 16 bits are the host address number. Class B IP addresses include 65,536 (216) different networks, each of which can hold and 65,536 (216) hosts.The first 24 bits of a Class C IP address are the network number and the last 8 bits are the host address number. Class C IP addresses include 16,777,216 (224) distinct networks, each capable of holding 256 (28) hosts.Figure 1-46 shows the network numbering portion and the host numbering portion of a Class 3 IP address.In general, each network has the following two special IP addresses that cannot be assigned to a single host. /iffiNetwork (numbered) address: an IP address with the host number portion all set to 0. This address is used to identify the entire Ning network. Broadcast address: An IP address with the host number portion all set to 1 (binary, corresponding to the decimal number 255). Each IP address can be followed by a network mask that specifies the number of bits in the network number portion and the host number portion of the IP address. /The network mask is a binary number that is 32 bits in length, like the IP address. The next digit of the network number portion of the network mask is represented by all 1's and the host number portion is represented by all 0's. The network mask can also be expressed in dotted decimal format like the IP address S-sui. For example, the network mask for a Class A network is 11111111000000000000000000000000 or 255.0.0.0. The network mask can sometimes be abbreviated to a backslash (/) followed by the number of digits of the network number of the IP address. For example, a Class A network mask can be abbreviated to /8. This representation is commonly known as a classless inter-domain routing (CIDR) representation. The network mask may seem unnecessary because the class of the IP address already reflects the information that the network mask is intended to reflect (for example, the number of bits in the network number for the Class A IP address 3.3.3.3 must be 8 bits). However, the network mask is important to the concept of subnetting, which will be introduced in the next section. The default network masks for Class A, B, and C IP addresses are shown in Table 1.9. Class D and E IP addresses do not have any predefined network masks because neither of these addresses is used for unicast communication.Second Disc . Table 1.9 Default Network Masks for Class A, B, and C IPv4 AddressesNo. Class Number of networks Number of hosts per network Network maskClass A 128-2 16,777,216-2 255.0.0.0 or /8