IP Addressing Tutor

Topics: IP address, Classless Inter-Domain Routing, IPv4 Pages: 69 (4492 words) Published: October 8, 2014

Application Note


IP Addressing
A Simplified Tutorial
July 2002

Avaya Labs


All information in this document is subject to change without notice. Although the information is believed to be accurate, it is provided without guarantee of complete accuracy and without warranty of any kind. It is the user’s responsibility to verify and test all information in this document. Avaya shall not be liable for any adverse outcomes resulting from the application of this document; the user must take full responsibility.


Companion document
• LANs and VLANs: A Simplified Tutorial



The purpose of this tutorial is to give the newcomer to data networking a basic understanding of IP addressing. The following topics are covered.

IP addressing fundamentals
Classful IP addressing
Subnet masks
Variable length subnet masks (VLSM)
Classless inter-domain routing (CIDR)
Routing and routing protocols


IP Addressing Fundamentals


OSI Reference
7 – Application
6 – Presentation
5 – Session
4 – Transport
3 – Network
2 – Data Link
1 – Physical


Terms used in this tutorial

Host – to – Host
Internet (IP)
Network Interface

TCP port, UDP port
IP address
MAC address

• This table is presented for reference purposes.
– The first column shows the 7-layer OSI Reference Model, which is a model used to design protocols that make networking possible.
– The second column shows the TCP/IP protocol stack in reference to the OSI model. TCP/IP is the prevalent protocol stack for data networking. – The third column shows that an IP address is a layer 3 (L3) address, as well as its relationship to the MAC address and TCP/UDP port, which are not covered in this tutorial.


Anatomy of an IP address
• The IP address is a 32-bit address that consists of two components. • One component is the network portion of the address, consisting of the network bits.
– The network bits make up the left portion of the address. – They consist of the first bit up to some boundary, to be discussed later.

• The second component is the host portion of the address, consisting of the host bits.
– The host bits make up the right portion of the address.
– They consist of the remaining bits not included with the network bits.


The mask
• The network portion of the address is separated from the host portion of the address by a mask.
• The mask simply indicates how many bits are used for the network portion, leaving the remaining bits for the host portion.
• A 24-bit mask indicates that the first 24 bits of the address are network bits, and the remaining 8 bits are host bits.
• A 16-bit mask indicates that the first 16 bits of the address are network bits, and the remaining 16 bits are host bits.
• And so forth…
• The difference between a network mask and a subnet mask will be explained as this tutorial progresses.

Quick lesson in binary math
• Binary math is based on powers of 2, as opposed to powers of 10 for decimal math.
– Whereas decimal math has a 1s place, 10s place, 100s place, and so forth… – Binary math has a 1s place, 2s place, 4s place, 8s place, and so forth.

• Given an octet (8 bits), when a bit in the octet is set (1) its value is… –

128 = left-most bit (most significant bit) = 27
64 = next bit = 26
32 = next bit = 25
16 = next bit = 24
8 = next bit = 23
4 = next bit = 22
2 = next bit = 21
1 = right-most bit (least significant bit) = 20

• When a bit in an octet is not set (0) its value is zero. • The decimal value of an octet is the sum of each set bit’s value. – 11000000 = 128 + 64 = 192
– 10101000 = 128 + 32 + 8 = 168
– 11111111 = 128 + 64...
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