Chapter 4 IP Addressing : Classful Addressing

1. Chapter 4 IP Addressing : Classful Addressing Mi-Jung Choi Dept. of Computer Science and Engineering mjchoi@postech.ac.kr

2. 4.1 Introduction • For a host to communicate with any other host • Need a universal identification system • Need to name each host • Internet address or IP address is a 32-bit address that uniquely defines a host or a router on the internet • The IP addresses are unique in the sense that two devices can never have the same address. However, a device can have more one address.

3. Notation • Binary notation 01110101 10010101 00011101 11101010 32 bit address, or a 4 octet address or a 4-byte address • Decimal point notation

4. 4.2 Classful Addressing • Occupation of address space • In classful addressing, the address space is divided into five classes: A, B, C, D, and E. • Finding the class in binary notation

5. Classful Addressing (cont’d) • Finding the address class

6. Classful Addressing (cont’d) • Finding the class in decimal notation

7. Netid and Hostid • Each IP address is made of two parts; netid and hostid. • Netid defines a network; hostid identifies a host on that network.

8. Netid and Hostid (cont’d) • IP addresses are divided into five different classes: A, B, C, D, and E

9. Classes and Blocks • Blocks in class A • Class A is divided into 128 blocks with each block having a different netid. • Millions of class A addresses are wasted.

10. Classes and Blocks (cont’d) • Class B is divided into 16,384 blocks with each block having a different netid Many class B addresses are wasted.

11. Classes and Blocks (cont’d) • Class C is divided into 2,097,152 blocks with each block having a different netid. The number of addresses in a class C block is smaller than the needs of most organizations

12. Classes and Blocks (cont’d) • Class D addresses are used for multicasting; there is only one block in this class. • Class E addresses are reserved for special purposes; most of the block is wasted.

13. Network Address • The network address is the first address. • The network address defines the network to the rest of the Internet. • Given the network address, we can find the class of the address, the block, and the range of the addresses in the block • In classful addressing, the network address (the first address in the block) is the one that is assigned to the organization.

14. Mask • A mask is a 32-bit binary number that gives the first address in the block (the network address) when bitwise ANDed with an address in the block. • Masking concept

15. Mask (cont’d) • AND Operation • The network address is the beginning address of each block. It can be found by applying the default mask to any of the addresses in the block (including itself). It retains the netid of the block and sets the hostid to zero.(refer table 4.2)

16. Special Addresses • Some parts of the address space in class A, B, C for special addresses

17. Special Addresses • Network address : an address with the hostid all set to 0s

18. Special Addresses (cont’d) • Direct Broadcast Address : Used by a router to send a packet to all hosts in a specific network

19. Special Addresses (cont’d) • Limited Broadcast Address : all 1s for the netid and hostid (32bits)

20. Special Addresses (cont’d) • This Host on This Network : used by a host at bootstrap time when it does not know its IP address

21. Special Addresses (cont’d) • Specific Host on This Network : used by a host to send a message to another on the same network

22. Special Addresses (cont’d) • Loopback Address : • IP address of the first byte : 127 • Used to test the software on a machine • Used by a client process to send a message to a server process on the same machine • “Ping”

23. Private Addresses • A number of blocks in each class are assigned for private use. They are not recognized globally. Class Netid Total Class A 10.0.0 1 Class B 172.16 to 172.31 16 Class C 192.68.0 to 192.68.255 256

24. Unicast, Multicast, and Broadcast Addresses • Unicast communication is one-to-one. • Multicast communication is one-to-many. • Broadcast communication is one-to-all.

25. Unicast, Multicast, and Broadcast Addresses (cont’d) • Assigned Multicast addresses : starting with a 224.0.0 prefix http://www.iana.org/assignments/multicast-addresses

26. Unicast, Multicast, and Broadcast Addresses (cont’d) • Unicast Addresses : one-to-one • Multicast addresses : one-to-many; class D address • Used as a destination address

27. Unicast, Multicast, and Broadcast Addresses (cont’d) • Multicast address for conferencing : starting with a 224.0.1 prefix

28. Unicast, Multicast, and Broadcast Addresses (cont’d) • Broadcast addresses : one-to-all • Allowed only at the local level • Limited broadcast address (all 1s) • Direct broadcast address (netid: specific, hostid: all 0s) • No broadcasting is allowed at the global level

29. A Sample Internet with Classful Address • Token Ring LAN (Class C), Ethernet LAN (Class B), Ethernet LAN (Class A), Point-to-point WAN, A Switched WAN

30. 4.4 Subnetting and Supernetting • Subnetting • A network is divided into several smaller networks with each subnetwork (or subnet) having its subnetwork address • Supernetting • Combining several class C addresses to create a larger range of addresses • IP Addresses are designed with two levels of hierarchy

31. Subnetting • Classes A, B, C in IP addressing are designed with two levels of hierarchy (not subnetted) • Netid and Hostid

32. Subnetting (cont’d) • Further division of a network into smaller networks called subnetworks • R1 differentiating subnets

33. Subnetting (cont’d) • Three levels of hierarchy : netid, subnetid, and hostid

34. Subnetting (cont’d) • Three steps of the routing for an IP datagram • Delivery to the site, delivery to the subnetwork, and delivery to the host • Hierarchy concept in a telephone number 031

35. Subnet Mask • A process that extracts the address of the physical network (network/subnetwork portion) from an IP address

36. Finding the Subnet Mask Address • Given an IP address, we can find the subnet address the same way we found the network address in the previous chapter. We apply the mask to the address. • we use binary notation for both the address and the mask and then apply the AND operation to find the subnet address. • Example 15 What is the subnetwork address if the destination address is 200.45.34.56 and the subnet mask is 255.255.240.0?

37. Finding the Subnet Mask Address (cont’d) • Solution 11001000 00101101 00100010 00111000 11111111 11111111 1111000000000000 11001000 00101101 0010000000000000 The subnetwork address is 200.45.32.0.

38. Comparison of a default mask and a subnet mask

39. Supernetting • A block of class x addresses • For example, • An organization that needs 1,000 addresses can be granted four class C addresses

40. Supernetting (cont’d) • 4 class C addresses combine to make one supernetwork

41. Supernet Mask • In subnetting, we need the first address of the subnet and the subnet mask to define the range of addresses. • In supernetting, we need the first address of the supernet and the supernet mask to define the range of addresses.

42. Supernet Mask (cont’d) • Comparison of subnet, default, and supernet masks