Chapter 4 IP Addressing : Classful Addressing

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.

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

Notation (cont’d) Hexadecimal Notation - 8 hexadecimal digits - Used in network programming 0111 0101 1001 0101 0001 1101 1110 1010 75 95 1D EA 0x75951DEA

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

Classful Addressing (cont’d) Finding the address class

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

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.

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

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.

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.

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

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.

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.

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

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)

4.3 Others Issues Multihomed devices (computers, or routers) A computer that is connected to different networks Having more than one address

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

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

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

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

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

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

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”

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

Unicast, Multicast, and Broadcast Addresses Unicast communication is one-to-one. Multicast communication is one-to-many. Broadcast communication is one-to-all. Multicast delivery will be discussed in depth in Chapter 14.

Unicast, Multicast, and Broadcast Addresses (cont’d) Assigned Multicast addresses : starting with a 224.0.0 prefix

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

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

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

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

4.4 Subnetting and Supernetting 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

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

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

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

031 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

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

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 can do this in two ways: straight or short-cut. Straight Method In the straight method, 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?

Finding the Subnet Mask Address (cont’d) Solution 11001000 00101101 00100010 00111000 11111111 11111111 11110000 00000000 11001000 00101101 00100000 00000000 The subnetwork address is 200.45.32.0.

Comparison of a default mask and a subnet mask

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

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

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.

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