IP Addresses: Classful Addressing IP Addresses

INTRODUCTION 4.1

IP address address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for.communication address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for.communicationcomputer networkInternet Protocolcomputer networkInternet Protocol

An IP address is a 32-bit address. What is an IP Address? The IP addresses are unique.

Address space rule addr15 addr1 addr2 addr41 addr31 addr226 ………….. The address space in a protocol That uses N-bits to define an Address is: 2 N

The address space of IPv4 is 2 32 or 4,294,967,296. IPv4 address space

 IP addresses consist of four sections  Each section is 8 bits long  Each section can range from 0 to 255  Written, for example,

Peter Smith8 Converting to Decimal (Cont.) Now, for double the money, what is its equivalent decimal value? The binary number converts into the decimal number: = 255

Binary Notation

Figure 4-1 Dotted-decimal notation

Example 1 Change the following IP address from binary notation to dotted-decimal notation Solution

Example 2 Change the following IP address from dotted-decimal notation to binary notation: Solution

Example 3 Solution Find the error in the following IP Address There are no leading zeroes in Dotted-decimal notation (045)

Example 3 (continued) Solution Find the error in the following IP Address In decimal notation each number <= is out of the range

The network prefix identifies a network and the host number identifies a specific host (actually, interface on the network). Network prefix and host number host numbernetwork prefix

CLASSFUL ADDRESSING

In classful addressing the address space is divided into 5 classes: A, B, C, D, and E.

18 Are You the Host or the Network? The 32 bits of the IP address are divided into Network & Host portions, with the octets assigned as a part of one or the other. Network & Host Representation By IP Address Class ClassOctet1Octet2Octet3Octet4 Class ANetworkHost Class BNetwork Host Class CNetwork Host

Figure 4-3 Finding the class in binary notation

Figure 4-4 Finding the address class

A Show that Class A has 2 31 = 2,147,483,648 addresses Example 5

Example 6 Solution Find the class of the following IP addresses st is 0, hence it is Class A st and 2 nd bits are 1, and 3 rd bit is 0 hence, Class C

Figure 4-5 Finding the class in decimal notation

Example 7 Solution Find the class of the following addresses st byte = 158 (128<158<191) class B st byte = 227 (224<227<239) class D

Peter Smith25 Are You the Host or the Network? (Cont.) Each Network is assigned a network address & every device or interface (such as a router port) on the network is assigned a host address. There are only 2 specific rules that govern the value of the address.

Peter Smith26 Are You the Host or the Network? (Cont.) A host address cannot be designated by all zeros or all ones. These are special addresses that are reserved for special purposes.

Peter Smith27 Class A Addresses (Cont.) There are 16,777,214 Host addresses available in a Class A address. Rather than remembering this number exactly, you can use the following formula to compute the number of hosts available in any of the class addresses, where “ n ” represents the number of bits in the host portion: (2 n – 2) = Number of available hosts

Peter Smith28 Class A Addresses (Cont.) For a Class A network, there are: 2 24 – 2 or 16,777,214 hosts. Half of all IP addresses are Class A addresses. You can use the same formula to determine the number of Networks in an address class. Eg., a Class A address uses 7 bits to designate the network, so (2 7 – 2) = 126 or there can be 126 Class A Networks.

Peter Smith29 Class B IP Addresses Class B addresses use the 1 st 16 bits (two octets) for the Network address. The last 2 octets are used for the Host address. The 1 st 2 bit, which are always 10, designate the address as a Class B address & 14 bits are used to designate the Network. This leaves 16 bits (two octets) to designate the Hosts.

Peter Smith30 Class B IP Addresses (Cont.) So how many Class B Networks can there be? Using our formula, (2 14 – 2), there can be 16,382 Class B Networks & each Network can have (2 16 – 2) Hosts, or 65,534 Hosts.

Peter Smith31 Class C IP Addresses Class C addresses use the 1 st 24 bits (three octets) for the Network address & only the last octet for Host addresses.the 1 st 3 bits of all class C addresses are set to 110, leaving 21 bits for the Network address, which means there can be 2,097,150 (2 21 – 2) Class C Networks, but only 254 (2 8 – 2) Hosts per Network.

Peter Smith32 Special Addresses (Cont.) Within each address class is a set of addresses that are set aside for use in local networks sitting behind a firewall or NAT (Network Address Translation) device or Networks not connected to the Internet.

Network Addresses 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.

Example 8 Solution Given the network address , find the class, the block, and the range of the addresses The 1 st byte is between 128 and 191. Hence, Class B The block has a netid of The addresses range from to

Default Mak Class A default mask is Class B default mask is Class C Default mask

Peter Smith37 A Trial Separation Subnet masks apply only to Class A, B or C IP addresses. The subnet mask is like a filter that is applied to a message’s destination IP address. Its objective is to determine if the local network is the destination network.

Mask A mask is a 32-bit binary number. The mask is ANDeD with IP address to get The bloc address (Network address) Mask And IP address = Block Address

Figure 4-10 Masking concept

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.

Example: ellington.cs.virginia.edu Network address is: (or ) Host number is: Netmask is: (or ffff0000) Prefix or CIDR notation: /16 Network prefix is 16 bits long Example

IP address of a network – Host number is set to all zeros, e.g., Broadcast address – Host number is all ones, e.g., – Broadcast goes to all hosts on the network – Often ignored due to security concerns