IP ADDRESSES

C ONTENTS Objectives Introduction IP Versions IPv4 Addressing Classful Addressing Class A Class B Class C Other Classes Dotted Decimal Notation Unforeseen Limitations to Classful Addressing Subnetting Classless Inter-Domain Routing (CIDR) Summary and Practical

O bjectives At the end of the presentation to describe what is IP addressing and implications of it.

I NTRODUCTION The internet protocol (IP) is part of the TCP/IP protocol suit and is the most widely used internetworking protocol. IP belongs to internet layer in TCP/IP model and to Network layer (layer3) in OSI model. Main Purpose of Network layer in OSI model is to Deliver packets from sending computer to receiving computer (host-to-host) across a communications network.

I Pv4 Header VersionIHLType of Services Total Length IdentificationFlagsFragment Offset Time to Live ProtocolHeader Checksum Source Address Destination Address Options + Padding Destination Address Source Address BACK

85, Ward Place, Colombo 7 86, Ward Place, Colombo 7 87, Ward Place, Colombo 7 88, Ward Place, Colombo 7 H ome Addresses

I P Addresses

Objectives Introduction IP Versions IPv4 Addressing Classful Addressing Class A Class B Class C Other Classes Dotted Decimal Notation Unforeseen Limitations to Classful Addressing Subnetting Classless Inter-Domain Routing (CIDR) Summary and Practical

I Pv4 Addresses Source and Destination field of IPv4 header contains 32bit address consisting of network identifier and a host identifier.IPv4 header The first part of an Internet address identifies the network on which the host resides, while the second part identifies the particular host on the given network. All hosts on a given network share the same network-prefix but must have a unique host-number. Similarly, any two hosts on different networks must have different network-prefixes but may have the same host-number.

C lassful IP Addressing Primary Address Classes

C lass A Networks (/8 Prefixes) A maximum of 126 (2 7 -2) /8 networks can be defined. network is reserved for use as the default route network is reserved for the "loopback" function. Each /8 supports a maximum of 16,777,214 ( ) hosts per network. all-0s ("this network") and all-1s ("broadcast") Class A Network address Host address

C lass B Networks (/16 Prefixes) maximum of 16,384 (2 14 ) /16 networks can be defined with up to 65,534 ( ) hosts per network Class B Network address Host address

C lass C Networks (/24 Prefixes) A maximum of 2,097,152 (2 21 ) /24 networks can be defined with up to 254 (2 8 -2) hosts per network Class C Network address Host address

O ther Classes In addition to the three most popular classes, there are two additional classes. Class D addresses have their leading four-bits set to and are used to support IP Multicasting. Class E addresses have their leading four-bits set to and are reserved for experimental use.

D otted-Decimal Notation To make Internet addresses easier for human users to read and write, IP addresses are often expressed as four decimal numbers, each separated by a dot. This format is called "dotted-decimal notation."

U nforeseen Limitations to Classful Addressing The original designers never envisioned that the Internet would grow into what it has become today. Many of the problems that the Internet is facing today can be traced back to the early decisions that were made during its formative years –The decision to standardize on a 32-bit address space meant that there were only 2 32 (4,294,967,296) IPv4 addresses available –The classful A, B, and C octet boundaries were easy to understand and implement, but they did not foster the efficient allocation of a finite address space. Problems resulted from the lack of a network class that was designed to support medium-sized organizations. A /24, which supports 254 hosts, is too small while a /16, which supports 65,534 hosts, is too large

S ubnetting In 1985, RFC 950 defined a standard procedure to support the subnetting, or division, of a single Class A, B, or C network number into smaller pieces. Subnetting was introduced to overcome some of the problems that parts of the Internet were beginning to experience with the classful two-level addressing hierarchy: –Internet routing tables were beginning to grow. –Local administrators had to request another network number from the Internet before a new network could be installed at their site

S ubnetting.. Extended-Network-Prefix –Internet routers use only the network-prefix of the destination address to route traffic to a subnetted environment. Routers within the subnetted environment use the extended-network- prefix to route traffic between the individual subnets. The extended-network-prefix is composed of the classful network- prefix and the subnet-number. –The extended-network-prefix has traditionally been identified by the subnet mask

S ubnetting.. Number of Continuous 1 bits

Objectives Introduction IP Versions IPv4 Addressing Classful Addressing Class A Class B Class C Other Classes Dotted Decimal Notation Unforeseen Limitations to Classful Addressing Subnetting Classless Inter-Domain Routing (CIDR) Summary and Practical

C lassless Inter-Domain Routing (CIDR) CIDR eliminates the traditional concept of Class A, Class B, and Class C network addresses and replaces them with the generalized concept of a "network-prefix." Routers use the network-prefix, rather than the first 3 bits of the IP address, to determine the dividing point between the network number and the host number. As a result, CIDR supports the deployment of arbitrarily sized networks rather than the standard 8-bit, 16- bit, or 24-bit network numbers associated with classful addressing In the CIDR model, each piece of routing information is advertised with a bit mask (or prefix-length). The prefix-length is a way of specifying the number of leftmost contiguous bits in the network-portion of each routing table entry. For example, a network with 20 bits of network-number and 12-bits of host-number would be advertised with a 20-bit prefix length (a /20). The clever thing is that the IP address advertised with the /20 prefix could be a former Class A, Class B, or Class C. Routers that support CIDR do not make assumptions based on the first 3-bits of the address, they rely on the prefix-length information provided with the route /20 Prefix

Objectives Introduction IP Versions IPv4 Addressing Classful Addressing Class A Class B Class C Other Classes Dotted Decimal Notation Unforeseen Limitations to Classful Addressing Subnetting Classless Inter-Domain Routing (CIDR) Summary

Source and Destination field of IPv4 header contains 32bit address consisting of network identifier and a host identifierIPv4 header Primary Address Classes

Dotted-Decimal Notation Subnetting

CIDR eliminates the traditional concept of Class A, Class B, and Class C network addresses and replaces them with the generalized concept of a "network-prefix." Routers use the network-prefix, rather than the first 3 bits of the IP address, to determine the dividing point between the network number and the host number. As a result, CIDR supports the deployment of arbitrarily sized networks rather than the standard 8-bit, 16- bit, or 24-bit network numbers associated with classful addressing. CIDR

O bjectives At the end of the presentation to describe what is IP addressing and implications of it.

Private address space

Network with Default Gateway