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Brief history

In May 1974, the Institute of Electrical and Electronic Engineers (IEEE) published a paper entitled "A Protocol for Packet Network Intercommunication".
The paper's authors, Vint Cerf and Bob Kahn, described an internetworking protocol for sharing resources using packet switching among network nodes.
A central control component of this model was the "Transmission Control Program" that incorporated both connection-oriented links and connectionless datagram services between hosts.
The monolithic Transmission Control Program was later divided into a modular architecture consisting of the Transmission Control Protocol at the transport layer and the Internet Protocol at the network layer.
The model became known as the Department of Defense (DoD) Internet Model and Internet Protocol Suite, and informally as TCP/IP.

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Brief history

The Internet Protocol is one of the elements that define the Internet. The dominant internetworking protocol in the Internet Layer in use today is IPv4; the number 4 is the protocol version number carried in every IP datagram.

IPv4 is described in RFC (Request for Comments) 791 (1981).

A Request for Comments (RFC) is a formal document from the Internet Engineering Task Force (IETF) that is the result of committee drafting and subsequent review by interested parties. Some RFCs are informational in nature. Of those that are intended to become Internet standards, the final version of the RFC becomes the standard and no further comments or changes are permitted. Change can occur, however, through subsequent RFCs that supersede or elaborate on all or parts of previous RFCs.

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Brief history

The IETF (Internet Engineering Task Force) is the body that defines standard Internet operating protocols such as TCP/IP. The IETF is supervised by the Internet Society Internet Architecture Board (IAB). IETF members are drawn from the Internet Society's individual and organization membership. Standards are expressed in the form of Requests for Comments (RFCs).

IP versions 0 to 3 were experimental versions, used between 1977 and 1979.

Version 5 was used by the Internet Stream Protocol, an experimental streaming protocol.

The successor to IPv4 is IPv6.

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Brief history

Its most prominent modification from version 4 is the addressing system.

IPv4 uses 32-bit addresses (c. 4 billion, or 4.3×10⁹, addresses) while IPv6 uses 128-bit addresses (c. 340 undecillion, or 3.4×10³⁸ addresses).

Although adoption of IPv6 has been slow, as of June 2008, all United States government systems have demonstrated basic infrastructure support for IPv6 (if only at the backbone level).

IPv6 was a result of several years of experimentation and dialog during which various protocol models were proposed, such as IPv7 known as TP/IX (The Next Internet) (RFC 1475), IPv8 PIP (RFC 1621) and IPv9 TUBA (TCP and UDP with Bigger Addresses, RFC 1347).

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IP Address

An IP address is a unique global address for a network interface
Connection-less protocol used on packet-switched link layer networks
An IP address:

is a 32 bit long identifier
2³² combinations
Nearly 4.3 billion

encodes a network number (network prefix) and a host number
Not enough and more addresses are needed

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Rule

If a protocol uses N bits to define an address, the address space is 2^N because each bit can have two different values (0 and 1) and N bits can have 2^N values.

The address space of IPv4 is 2³² or 4,294,967,296.

Binary Notation

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Dotted-decimal notation

IP addresses are written in a so-called dotted decimal notation.
Each byte is identified by a decimal number in the range [0..255].

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Problem

Find the error, if any, in the following IP address:

111.56.045.78

Solution:

There are no leading zeros in dotted-decimal notation (045).

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Problem

Find the error, if any, in the following IP address:

75.45.301.14

Solution:

In dotted-decimal notation, each number is less than or equal to 255; 301 is outside this range.

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The Two Parts of an IP Address

An IP address consists of two parts:
Network prefix: The class ID plus network ID portions of the IP address are known as the network prefix

Host number

Network prefix identifies the network and host number identifies the node, or host on the network.

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How do we know how long the network prefix is?

The network prefix is implicitly defined by class-based addressing.

The network prefix is indicated by a netmask.

The Class of the address determines which part belongs to the network address and which part belongs to the node address. All nodes on a given network share the same network prefix but must have a unique host number.

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The old way: Classful IP Addresses

When Internet addresses were standardized (early 1980s), the Internet address space was divided up into classes:
Class A Network:
In a Class A Network binary address start with 0, therefore the decimal number can be anywhere from 0 to 126 (01111110). The number 127 (01111111) is reserved for loopback and is used for internal testing on the local machine. Class A addresses have 8 bit network prefix sometimes referred to as “/8”. The remaining 24 bits indicate the host within the network. An example of a Class A IP address is 102.168.212.226, where "102" identifies the network and "168.212.226" identifies the host on that network.

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Problem

How can we prove that we have 2,147,483,648 addresses in class A?

Solution:

In class A, only 1 bit defines the class. The remaining 31 bits are available for the address.
With 31 bits, we can have 2³¹ or 2,147,483,648 addresses.

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Class B Network

In a Class B Network, binary addresses start with 10, therefore the decimal number can be anywhere from 128 (10000000) to 191 (10111111). The first 16 bits (the first two octets) identify the network and the remaining 16 bits indicate the host within the network. An example of a Class B IP address is 168.212.226.204 where "168.212" identifies the network and "226.204" identifies the host on that network.

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Class C Network

Binary addresses start with 110, therefore the decimal number can be anywhere from 192 (11000000) to 223 (11011111). The first 24 bits (the first three octets) identify the network and the remaining 8 bits indicate the host within the network. An example of a Class C IP address is 200.168.212.226 where "200.168.212" identifies the network and "226" identifies the host on that network.

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Class D Network

Class D addresses are used for multicasting; there is only one block in this class.

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Class E Network

Class E addresses are reserved for special purposes.

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Classful IP Addresses

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Finding the address class

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Problem

Find the class of the address:

11000001 10000011 00011011 11111111

Solution:

The first 2 bits are 1; the third bit is 0. This is a class C address.

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Problem

Find the class of the address: 193.14.56.22

Solution:

The first byte is 193 (between 192 and 223); the class is C.

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Finding the class in decimal notation

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Problem

Find the class of the address: 193.14.56.22

Solution:

The first byte is 193 (between 192 and 223); the class is C.

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Problem

Find the class of the address: 227.12.14.87

Solution:

The first byte is 227 (between 224 and 239); the class is D

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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.

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Problem

Given the network address 17.0.0.0, find the class, the block, and the range of the addresses.

Solution:

The class is A because the first byte is between 0 and 127. The block has a net-id of 17 (00010001). The addresses range from 17.0.0.0 to 17.255.255.255.

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Problem

Given the network address 132.21.0.0, find the class, the block, and the range of the addresses.

Solution:

The class is B because the first byte is between 128 and 191. The block has a net-id of 132.21. The addresses range from 132.21.0.0 to 132.21.255.255.

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Problem

Given the network address 220.34.76.0, find the class, the block, and the range of the addresses.

Solution:

The class is C because the first byte is between 192 and 223. The block has a net-id of 220.34.76. The addresses range from 220.34.76.0 to 220.34.76.255.

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