1 Chapter 4 IP Addressing : Classful Addressing Chapter 4 IP Addressing : Classful Addressing Mi-Jung Choi Dept. of Computer Science, KUN

2 4.1 Introduction oFor a host to communicate with any other host Need a universal identification system Need to name each host oInternet address or IP address is a 32-bit address that uniquely defines a host or a router on the internet oThe 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 o Binary notation bit address, or a 4 octet address or a 4-byte address oDecimal point notation

4 4.2 Classful Addressing oOccupation 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) oFinding the address class

6 Classful Addressing (cont’d) oFinding the class in decimal notation

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

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

9 Classes and Blocks oBlocks 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) netid o 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) netid o 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) o Class D addresses are used for multicasting; there is only one block in this class. o Class E addresses are reserved for special purposes; most of the block is wasted.

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

14 Mask o 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. o Masking concept

15 Mask (cont’d) o AND Operation (refer table 4.2) oThe 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 Special Addresses oSome parts of the address space in class A, B, C for special addresses

17 Special Addresses oNetwork address : an address with the hostid all set to 0s

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

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

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

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

22 Special Addresses (cont’d) oLoopback 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 o A number of blocks in each class are assigned for private use. They are not recognized globally. ClassNetidTotal Class A Class B to Class C to

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

25 Unicast, Multicast, and Broadcast Addresses (cont’d) oAssigned Multicast addresses : starting with a prefix

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

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

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

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

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

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

32 Subnetting (cont’d) oFurther division of a network into smaller networks called subnetworks oR1 differentiating subnets

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

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

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

36 Finding the Subnet Mask Address o 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 o Example 15 What is the subnetwork address if the destination address is and the subnet mask is ?

37 Finding the Subnet Mask Address (cont’d) oSolution The subnetwork address is

38 Comparison of a default mask and a subnet mask o

39 Supernetting oA block of class x addresses oFor example, An organization that needs 1,000 addresses can be granted four class C addresses

40 Supernetting (cont’d) o4 class C addresses combine to make one supernetwork

41 Supernet Mask oIn subnetting, we need the first address of the subnet and the subnet mask to define the range of addresses. o 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) oComparison of subnet, default, and supernet masks