Describe the operation and necessity of using private and public IP addresses for IPv4 addressing

chapter 3:IP Addresses

    Describe the operation and necessity of using private and public IP addresses for IPv4 addressing

  • Introduction to IP

    IP:

    Internet Protocol - fundamental packet format that computers use to exchange information. Internet Protocol is a set of technical rules that defines how computers communicate over a network. There are currently two versions: IP version 4 (IPv4) and IP version 6 (IPv6).

    IP addressing:

    IP addressing was designed to allow hosts on one network to communicate with a host on a different network regardless of the type of LANs. An IP address consists of 32 bits. Rather than working with 32 bits at a time, it is a convenient to segment the 32 bits of an IP address into four 8-bit fields (or 8-bit bytes) called octets. Each octet is converted to a decimal number (the Base 10 numbering system) in the range 0-255 and separated by a period (a dot). This format is called dotted decimal notation.

    Hierarchical Addressing Scheme

    IPv4 uses hierarchical addressing scheme. An IP address which is 32-bits in length is divided into two or three parts as depicted:
     
     
    A single IP address can contain information about the network and its sub-network and ultimately the host. This scheme enables IP Address to be hierarchical where a network can have many sub-networks which in turn can have many hosts.
     

    Class A:

    The Class A address was designed to support extremely large networks, with more than 16 million host addresses available. Class A IP addresses use only the first octet to indicate the network address. The remaining three octets provide for host addresses. 
    The first bit of a Class A address is always 0. With that first bit a 0, the lowest number that can be represented is 00000000, decimal 0. The highest number that can be represented is 01111111, decimal 127. The numbers 0 and 127 are reserved and cannot be used as network addresses. Any address that starts with a value between 1 and 126 in the first octet is a Class A address.

    Class B:

    Class B addresses is assigned to medium-sized to large-sized networks. The two high-order bits in a class B address are always set to binary 1 0. The next 14 bits (completing the first two octets) complete the network ID. The remaining 16 bits (last two octets) represent the host ID. This allows for 16,384 networks and 65,534 hosts per network. 

    Class C: 

    Class C addresses are used for small networks. The three high-order bits in a class C address are always set to binary 1 1 0. The next 21 bits (completing the first three octets) complete the network ID. The remaining 8 bits (last octet) represent the host ID. This allows for 2,097,152 networks and 254 hosts per network.  This address space was intended to support small networks with a maximum of 254 hosts.

    Class D:

    The Class D address category was created to enable multicasting in an IP address. Multicast address is a unique network address that directs packets with that destination address to predefined groups of IP addresses. a single station can simultaneously transmit a single stream of datagrams to multiple recipients. The Class D address category, much like the other address categories, is mathematically constrained. The first 4 bits of a Class D address must be 1110. The first octet range for Class D addresses is 11100000 to 11101111, or 224 to 239. An IP address that starts with a value in the range of 224 to 239 in the first octet is a Class D address.
     

    Class E

    Class E is an experimental address that is reserved for future use. The high-order bits in a class E address are set to 1 1 1 1.no Class E addresses have been released for use in the Internet. The first 4 bits of a Class E address are always set to 1111. Therefore, the first octet range for Class E addresses is 11110000 to 11111111, or 240 to 255.
     

    Address Class

    First Octet Range

    Number of Possible Networks

    Number of Hosts Per Network

    Class A

    0 to 126

    127 (2 are reserved)

    16,777,214

    Class B

    128 to 191

    16,384

    65,534

    Class C

    192 to 223

    2,097,152

    254

    IPv4 supports three different type of addressing modes: 

    Unicast Addressing Mode:

    In this mode, data is sent only to one destined host. The Destination Address field Contains 32 bit IP address of the destination host. Here client sends data to the targeted server: 

     Unicast Addressing Mode

    Broadcast Addressing Mode:  

    In this mode the packet is addressed to all hosts in a network segment. The Destination Address field contains special broadcast address i.e. 255.255.255.255.When a host sees this packet on the network; it is bound to process it. Here client   sends packet, which is entertained by all the Servers: 
     
    Broadcast Addressing Mode 

    Multicast Addressing Mode:

    This mode is a mix of previous two modes, i.e. the packet sent is neither destined to a single host nor all the host on the segment. In this packet, the Destination Address contains special address which starts with 224.x.x.x and can be entertained by more than one host. 
     
    Multicast Addressing Mode
     

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