Problems with Classful Addressing

The problem with this classful addressing method is that millions of class A addresses are wasted, many of the class B addresses are wasted, whereas, the number of addresses available in class C is so small that it cannot cater to the needs of organizations. Class D addresses are used for multicast routing and are therefore available as a single block only. Class E addresses are reserved.

Since there are these problems, Classful networking was replaced by Classless Inter-Domain Routing (CIDR) in 1993. We will be discussing Classless addressing in the next post.

• The network ID is 24 bits long.
• The host ID is 8 bits long.
• 2^21 = 2097152 network address
• 2^8 – 2 = 254 host address
• Within any network, the host ID must be unique to that network.
• Host ID in which all bits are set to 0 cannot be assigned because this host ID is used to represent the network ID of the IP address.
• Host ID in which all bits are set to 1 cannot be assigned because this host ID is reserved as a broadcast address to send packets to all the hosts present on that particular network.
• The network ID cannot start with 127 because 127 belongs to the class A address and is reserved for internal loopback functions.
• All bits of network ID set to 1 are reserved for use as an IP broadcast address and therefore, cannot be used.
• All bits of network ID set to 0 are used to denote a specific host on the local network and are not routed and therefore, aren’t used.

An IP address is an address having information about how to reach a specific host, especially outside the LAN. An IP address is a 32-bit unique address having an address space of 2³². Generally, there are two notations in which the IP address is written, dotted decimal notation and hexadecimal notation.

Dotted Decimal Notation

Hexadecimal Notation
 

Some points to be noted about dotted decimal notation: 

1. The value of any segment (byte) is between 0 and 255 (both included).
2. No zeroes are preceding the value in any segment (054 is wrong, 54 is correct).