INTERNET PROTOCOL VERSION 4 (IPv4) | M Tech PhD Thesis Guidance

INTERNET PROTOCOL VERSION 4 (IPv4)

IPv4 provides hierarchical addressing for the packet that carries out data. It can provide a maximum of 232 possible address spaces, out of which there  are  about  18  million  private  addresses  and  270  million  multicast addresses.

The Anatomy of IPv4 Address

Each   device   on   the   network   must   be   uniquely   defined   and identified. At the network layer, the packets that are to be communicated need to be identified with the source and destination addresses.  IPv4 address is represented by 32 bits consisting of 4 octets of 8 bits each. With IPv4, each packet  has  a  32-bit  source  address  and  has  32-bit  destination  address  in  the layer 3 header. The network address representations are shown in Figure 1.

                                                       Figure 1. Network Address Representations

These addresses are used in the data network in the form of binary patterns.  Within  the  device,  digital  logic  is  applied  for  interpretation.  For  a human to  understand the  network,  a string of  32-bits is  difficult to  interpret and   remember.   Therefore,   IPv4   addresses   are   represented   using   dotted decimal format. There are three types of address in an IPv4 network which are host address, network address and broadcast address as shown in Figure 2.

                                                        Figure 2. Types of Address in an IPv4 Network

The address by which a network is commonly referred to is known as the network address. A special address that is used to send data to all hosts in the network is known as the broadcast address and the address, assigned to the end devices in the network is known as the host address.

Network Classes

Five  address  classes  were  defined  by  the  Internet  community  to accommodate networks of  varying sizes. (Hasan Alkhatib & Bruce Wootton 2003) grouped the network address ranges into specific  sizes that  are called class A, class B and class C, class D and class E addresses. The classification of network address is shown in Figure 3.

                                                                           Figure 3 Network Classes

Special and Reserved IPv4 Address Ranges

The special addresses are assigned to hosts with restrictions on how these hosts interact within the network. The special address and the reserved address  are  shown  in  Table  1.2.  Loopback  addresses,  Link-Local  addresses and  TEST-NET  addresses  are  known  as  the  special  addresses.  127.0.0.1 Address is denoted as loop back address. It is the address used by the host to direct  traffic  to  themselves.  The  loopback  address  generates  a  shortcut  way for   TCP/IP   applications   and   services   that   run   on   the   same   device   to communicate with  each other.  By using the loopback address  instead of  the assigned IPv4 host address, two services on the same host can be avoided on the lower layers of the TCP/IP stack. The loopback address can also be pinged to test the configuration of TCP/IP on the local host.

                                               Table 1 Special Addresses and Reserved Addresses

IPv4  addresses  169.254.0.0  to  169.254.255.255  (169.254.0.0  /16) are designated as  link-local addresses.  These addresses can be automatically allocated to the local host by the available operating system in environments where no IP configuration is available (Fall Kevin & Richard Stevens 2011). The  link-local  address  is  used  in  a  small  peer-to-peer  network  or  for  a  host that   could   not   automatically   obtain   an   address   from   a   Dynamic   Host Configuration Protocol (DHCP) server.

The  address  block  192.0.2.0  to  192.0.2.255  (192.0.2.0  /24)  is  set apart   for   teaching   and   learning   purposes.   They   can   also   be   used   for documentation   purpose.   Unlike   the   experimental   addresses,   the   network devices  will  accept  these  addresses  in  their  configurations.  These  addresses should  not  appear  on  the  Internet.  The  reserved  IPv4  addresses  include experimental addresses, multicast addresses and host addresses. The multicast addresses  include  link-local  address,  globally  scoped  addresses  and  limited scope   addresses.   IPv4   experimental   addresses   range   from   240.0.0.0   to 255.255.255.254. They are reserved for future use. Major block of addresses are reserved for special  purposes and  these are  the IPv4 multicast addresses that range from 224.0.0.0 to  239.255.255.255. The  IPv4  multicast addresses 224.0.0.0  to  224.0.0.255  are  reserved  link-local  addresses.  These  addresses are  to  be  used  for  multicast  groups  on  a  local  network.  Packets  to  these destinations are always transmitted with a time-to-live (TTL) value of 1. The     globally     scoped     addresses     are     from     224.0.1.0     to 238.255.255.255 that may be used to multicast data across the Internet. After accounting for the ranges reserved for  experimental addresses and  multicast addresses,  they  leave  an  address  range  of  0.0.0.0  to  223.255.255.255  that could  be  used  for  IPv4  hosts.  However,  within  this  range  many  of  the addresses are already reserved as special addresses.

Public and Private Addresses

Though  most of the  IPv4 host addresses  are  public addresses that are  accessible  to  the  Internet,  there  are  blocks  of  addresses  that  are  used  in networks  that  require  limited  or  no  Internet  access.  These  addresses  are  the private addresses. These addresses are set aside for private networks. The use of the private addresses need not be unique outside the networks. Numerous hosts  in  different  networks  may  use  the  identical  private  space  addresses (Wegner  &  Rockwell  2000).  Packets  using  these  addresses  as  the  source  or destination address must not appear on the public Internet.

The  router  or  firewall  device  at  the  perimeter  of  these  private networks must block or translate these addresses. Even if these packets were to make their way to the Internet, the routers would not have routes to forward them   to   the   suitable   private   network.   The   private   address   blocks   are from10.0.0.0  to  10.255.255.255  (10.0.0.0/8),  172.16.0.0  to  173.31.255.255 (172.16.0.0/12) and 192.168.0.0 to 192.168.255.255 (192.168.0.0/16).

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