Objective: Classful Internet Addressing

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.

Need of IP Address

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.

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.

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

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.

Five forms of Internet IP Address

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

The number of networks and computers per network

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.

Dotted Decimal Notation

The first decimal value defines the class of the IP address

The first decimal value defines the class of the IP address

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

Special Purpose IP Address

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

Assigning IP Addresses Assigning Prefix Address Public Private Assigning Suffix Address

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.

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

IP Addresses for Routers

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.

Subnet addressing

Subnet addressing Hierarchical addressing concept Subdivide the 32-bit IP address into (network number, subnet number, and host number). Analogous to telephone system: {+91 484 2748388}

IP Address in original addressing Scheme IP Address in subnetting Scheme

HOST ID

IP Address : 141.14.73.24 Subnet Mask : 255.255.192.0 Network Address : ? 141.14.73.24 AND 255.255.192.0 73 (01001001) AND 192 (11000000) 01000000  64  141.14.64.0

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

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

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

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.

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

Solution Classless Addressing

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

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

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

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