• Default Route: we represent the IPv4 default route as The default route is used as a "catch all" route when a more specific route is not available. The use of this address also reserves all addresses in the - ( /8) address
  • Network and Broadcast Addresses: As explained earlier, within each network the first and last addresses cannot be assigned to hosts. These are the network address and the broadcast address, respectively.
  • Loopback: One such reserved address is the IPv4 loopback address The loopback is a special address that hosts use to direct traffic to them. Although only the single 0.0.1 address is used, addresses to are reserved. Any address within this block will loop back within the local host. No address within this block should ever appear on any network.
  • Link-Local Addresses: IPv4 addresses in the address block 254.0.0 to ( /16) are designated as link-local addresses. These addresses can be automatically assigned to the local host by the operating system in environments where no IP configuration is available. These might be 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.
  • TEST-NET Addresses: The address block to ( /24) is set aside for teaching and learning These addresses can be used in documentation and network examples.
  • Network Prefixes: An important question is: How do we know how many bits represent the network portion and how many bits represent the host portion? When we express an IPv4 network address, we add a prefix length to the network address. The prefix length is the number of bits in the address that gives us the network portion. For example, in /24, the /24 is the prefix length - it tells us that the first 24 bits are the network address. This leaves the remaining 8 bits, the last octet, as the host portion.

Private and Public IP addresses

  • Public IP addresses: Public IP addresses are assigned by the InterNIC (Internet's Network Information Centre) and consists of class based network Ids or   blocks of CIDR based addresses (called CIDR blocks) that are globally rout-able to the Internet and are unique.
  • Private IP address: An address that is used for internal networks. These addresses are not rout-able to the Internet.

          The private address blocks are:

 to ( /8)

 to ( /12)

 to ( /16)