Network Layer: Logical Addressing Study Notes

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  • At the network layer, a global identification system that uniquely identifies every host and router is necessary for delivery of a packet from host to host.
  • An IPv4 address is 32 bits long and uniquely and universally defines a host or router on the Internet.
  • In classful addressing, the portion of the IP address that identifies the network is called the netid.
  • In classful addressing, the portion of the IP address that identifies the host or router on the network is called the hostid.
  • An IP address defines a device’s connection to a network.
  • There are five classes in IPv4 addresses. Classes A, B, and C differ in the number of hosts allowed per network. Class D is for multicasting and Class E is reserved.
  • The class of an address is easily determined by examination of the first byte.
  • Addresses in classes A, B, or C are mostly used for unicast communication.
  • Addresses in class D are used for multicast communication.
  • Subnetting divides one large network into several smaller ones, adding an intermediate level of hierarchy in IP addressing.
  • Supernetting combines several networks into one large one.
  • In classless addressing, we can divide the address space into variable-length blocks.
  • There are three restrictions in classless addressing: a. The number of addresses needs to be a power of 2. b. The mask needs to be included in the address to define the block. c. The starting address must be divisible by the number of addresses in the block.
  • The mask in classless addressing is expressed as the prefix length (In) in CIDR notation.
  • To find the first address in a block, we set the rightmost 32 – n bits to O.
  • To find the number of addresses in the block, we calculate 2^32- n, where n is the prefix length.
  • To find the last address in the block, we set the rightmost 32 – n bits to O.
  • Subnetting increases the value of n.
  • The global authority for address allocation is ICANN. ICANN normally grants large blocks of addresses to ISPs, which in tum grant small subblocks to individual customers.
  • IPv6 addresses use hexadecimal colon notation with abbreviation methods available.
  • There are three types of addresses in IPv6: unicast, anycast, and multicast.
  • In an IPv6 address, the variable type prefix field defines the address type or purpose.

 

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