CCNA Routing & Switching: Rules to assign ip address for router

IP Address Components:
Like other network layer protocols, the IP addressing scheme is integral to the process of routing IP data through an internetwork.

Each host on a TCP/IP network is assigned a unique 32-bit logical address. The IP address is divided into two main parts; the Network Number and the Host Number.

The network number identifies the network and must be assigned by the Internet Network Information Center (InterNIC) if the network is to be part of the Internet.

The host number identifies a host in the network and is assigned by the local network administrator.

IP Address Format:

The 32-bit IP address is grouped 8 bits at a time, each group of 8 bits is an octet. Each of the four octets are separated by a dot, and represented in decimal format, this is known as dotted decimal notation. Each bit in an octet has a binary weight (128, 64, 32, 16, 8, 4, 2, 1). The minimum value for an octet is 0 (all bits set to 0), and the maximum value for an octet is 255 (all bits set to 1).

The following figure shows the basic format of a typical IP address:

IP Address Classes:

IP addressing supports three different commercial address classes; Class A, Class B, and Class C.

In a class A address, the first octet is the network portion, so the class A address of, 10.1.25.1, has a major network address of 10. Octets 2, 3, and 4 (the next 24 bits) are for the hosts. Class A addresses are used for networks that have more than 65,536 hosts (actually, up to 16,581,375 hosts!).

In a class B address, the first two octets are the network portion, so the class B address of, 172.16.122.204, has a major network address of 172.16. Octets 3 and 4 (the next 16 bits) are for the hosts. Class B addresses are used for networks that have between 256 and 65,536 hosts.

In a class C address, the first three octets are the network portion. The class C address of, 193.18.9.45, has a major network address of 193.18.9. Octet 4 (the last 8 bits) is for hosts. Class C addresses are used for networks with less than 254 hosts.

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