1. Objective: Classful Internet Addressing

2. Internet Protocol (IP):
A protocol used in the internet layer.
IP makes use of the existing networks to deliver information,
where these networks may use a variety of protocols.

3. Need of IP Address

4. Each computer / router is assigned a unique protocol address.
Different networks may adopt different hardware addresses with different sizes and different formats.
E.g, Ethernet address: 48 bits
Need a uniform addressing scheme to interconnect
Each computer / router is assigned a unique protocol address.

5. IP Addressing Scheme
Each computer / router is assigned a unique IP address having 32 bits.
Each IP address is a pair (netid, hostid)
The prefix (netid) specifies the network to which the computer is attached.
The suffix (hostid) specifies a particular computer on a network.

6. IP address : 32 bits.
Given only 32 bits, how many bits should be allocated to the prefix and the suffix?

7. The Classful Addressing Scheme
The IP addressing scheme defines three primary classes, where each class has a distinct prefix/suffix size.
The internet can accommodate large networks, medium networks, and small networks.

8. Five forms of Internet IP Address

9. Five forms of Internet IP Address
Classes A, B, C are the primary classes.
The IP addresses of computers and routers belong to these classes.
Class D is used for multicasting.
Class E reserved for future use

10. The number of networks and computers per network

11. Dotted Decimal Notation
Use to represent the 32-bit IP address.
not convenient for human to manipulate
Each octet (8-bit) is expressed as a decimal value, and adjacent decimal values are separated by a dot.

12. Dotted Decimal Notation

13. The first decimal value defines the class of the IP address

14. The first decimal value defines the class of the IP address

15. The range of dotted decimal values that correspond to each of the original IPv4 address classes.

16. Special Purpose IP Address

17. 127.x.x.x localhost Loopback address
Intended for use in testing TCP/IP and for inter-process communication on the local computer
127.x.x.x
localhost

18. Assigning IP Addresses
Assigning Prefix Address
Public
Private
Assigning Suffix Address

19. The ISP coordinates with a central organization
(the Internet Assigned Number Authority (IANA, on or before 1998);
the Internet Corporation for Assigned Names and Numbers (ICANN, after 1998))
to ensure the uniqueness of the prefix.

20. IP Addresses for Routers
A router is connected to multiple networks.
It belongs to multiple networks.
It is assigned multiple IP addresses where every IP address corresponds to one network

21. IP Addresses for Routers

22. Subnet addressing Also called subnet routing, or subnetting
One IP network address, but with two or more physical networks
Only local routers know that there are multiple physical networks and how to route traffic among them.

23. Subnet addressing

24. Subnet addressing Hierarchical addressing concept
Subdivide the 32-bit IP address into (network number, subnet number, and host number).
Analogous to telephone system:
{ }

25. IP Address in original addressing Scheme
IP Address in subnetting Scheme

27. HOST ID

30. IP Address :
Subnet Mask :
Network Address : ?
AND
73 ( ) AND 192 ( )
 

31. The number of subnets must be a power of 2.
Note
The number of subnets must be a power of 2.

32. Classful Addressing Address is pair of (netid, hostid)
In practice (netid, hostid) is not uniform through out network
Each address is self identifing
Class of address can be determined from 3 higher order bits

33. Advantage of classful addressing scheme
small routing table for routers
one routing entry per network

34. Weaknesses in classful addressing scheme
Addresses refer to network connections
If a host computer (notebook) moves from one network to another, its IP address must change because the network id has changed.

35. Weaknesses in classful addressing scheme
When any class C network grows to more than 255 hosts, it must have its address changed to a class B address.
The change must be done for all machines.
difficult to debug individual machines
Insufficient number of network addresses

36. Solution
Classless Addressing

37. Classless addressing
uses a variable number of bits for the network and host portions of the address.

38. Subnet and Classless Addressing
Subnet addressing was initially used within large organizations
Classless addressing extended the approach to all Internet

39. Means 199 of the 254 possible suffixes would never be assigned
Consider an ISP that hands out prefixes. A customer of the ISP requests a prefix for a network that contains 55 hosts
classful addressing requires a complete class C prefix
only 6 bits of suffix are needed to represent all possible host values
Means 199 of the 254 possible suffixes would never be assigned

40. Classless Addressing
classless addressing allows the ISP to assign
a prefix that is 26 bits long
a suffix that is 6 bits long