Advanced Computer Networks Notes-4

This article contains topics such as Subnet and Supernet Extensions,IP Multicast address,weakness in internet addressing,dotted decimal notation,special address conventions summary.

Subnet and Supernet Extensions

• In the 1980s as Local Area Network technologies became increasingly popular, it became apparent that requiring a unique prefix for each physical network would exhaust the address space quickly.Consequently, anaddressing extension was developed to conserve network prefixes. Known as subnet addressing, the scheme allows multiple physical networks to share a prefix.



• In the 1990s, a second extension was devised that ignored the classful hierarchy and allowed the division between prefix and suffix to occur at an arbitrary point.Called classless addressing or supernetting, the scheme allows more complete utilization of the address space.

IP Multicast Address

• IP addressing scheme supports a special form of multipoint delivery known as Multicasting,in which a packet is delivered to a specific subset of hosts.


• Class D addresses are reserved fro multicasting.

Weakness in Internet Addressing

• Address not refer to individual hosts but their network connections.


• If a host computer moves from one network to another its IP address must change.


• Thus mobility is a complex problem.



• Suppose a network consists of less than 255 hosts thus it follows class C addressing scheme.Suppose number of hosts supported by class C becomes greater than 255.Then it can't follow class C addressing scheme and must change to class B addressing scheme which requires all of its hosts to change its address which is not easy.


• The above problem occurs when number of hosts supported by a network following class B addressing scheme becomes greater than 2¹⁶ hosts then all the hosts must change to class A addressing scheme.


• Consider the example internet shown in figure below. In the figure, two hosts, A and B, both attach to network 1, and usually communicate directly using that network. Thus, users on host A should normally refer to host B using IP address I₃. An alternate path from A to B exists through router R, and is used
  whenever A sends packets to IP address I₅ (B's address on network 2). Now suppose B's connection to network 1 fails, but the machine itself remains running (e.g., a wire breaks between B and network 1). Users on A who specify IP address I₃ cannot reach B, although users who specify address I₅ can.

Dotted Decimal Notation

• IP addresses are written as four decimal integers separated by decimal points, where each integer gives the value of one octet of IP address.


• Thus the 32 bit internet address:
  
  10000000  00001010  00000010  00011110
  
  
  is written as
  
  128.10.2.30
  


• Figure below summarizes the range of value of each class:
  
  
  
  
  
  
  

Loopback Address

• In the above figure it is clear that not all addresses are assigned a class.


• In particular, the network prefix 127.0.0.0, a value from the class A range, is reserved for loopback, and is intended for use in testing TCP/IP and for inter-process communication on the local computer.


• When any program uses the loopback address as a destination, the protocol software in the computer processes the data without sending traffic across any network.

Summary of Special Address conventions