TCP/IP Fundamentals

All possible Subnets and Hosts in a Class C Address

# of Bits Borrowed from the IP Address

Total Number of Subnets * 2^n

Total Available Number of Subnets **2^n-2

Total Number of Host Addresses ***2^n

Total Number of Available Hosts ****2^n-2

TCP/IP Subnetting

TCP

Transmission Control Protocol

TCP is a connection oriented transport protocol that sends data as unstructured streamed of bytes. By using sequence numbers and acknowledgment messages, TCP can provide a sending node with delivery information about packets transmitted to a destination node. When data has been lost in transit from source to destination, TCP can retransmit the data either until a time-out condition is reached or until successful delivery has been achieved. TCP can also recognize duplicate messages and will discard them appropriately.

If the sending computer is transmitting too fast for the receiving computer, TCP can employ flow control mechanisms to slow data transfer. TCP can also communicate delivery information to the upper layer protocols and applications that it supports.

IP Internet Protocol

IP is the primary Layer 3 Protocol in the Internet suite. In addition to inter-network routing, IP provides error reporting, fragmentation, and reassemble of information units called data grams for transmission over networks with different maximum data unit sizes. IP represents the heart of the Internet protocol suite. Every host computer must have a unique IP number for Internet delivery, just like every phone must have a unique phone number to receive a call.

IP addresses are globally unique, 32 bit numbers assigned by the Network Information Center. Globally unique addresses permit IP networks anywhere in the world to communicate with each other. An IP address is divided into three parts. The first part designates the network address, the second part designates the subnet address, and the third part designates the host address.

Each IP number is associated with a Class that is designated by the first part of the number.

Routing in IP Environments

An "internet" is a group of interconnected networks within a company, while the Internet, is the collection of networks that permits communication between organizations around the world.

Router's within the Internet are organized hierarchically. Some router's are used to move information through one particular group of networks under the same administrative authority and control. Router's used for information exchange within autonomous systems are called interior router's, and they use a variety of interior gateway protocols (IGPs) to accomplish this end. Router's that move information between autonomous systems are called exterior router's; they use the Exterior Gateway Protocol (EGP) or Border Gateway Protocol (BGP).

Routing protocols used with IP are dynamic in nature. Dynamic routing requires the software in the routing devices to calculate routes. Dynamic routing algorithms adapt to changes in the network and automatically select the best routes. In contrast with dynamic routing, static routing calls for routes to be established by the network administrator. Static routes do not change until the network administrator changes them.

Four Classes of IP addresses
Class A	Networks begin with 0 and end with 126. All addresses within this range are considered Class. (Network.Host.Host.Host) It uses the remaining seven bits to designate a specific Class A network.
Class B	Networks begin with 128 (10) and ends with 191, Class B uses 14 bits to designate individual network ID's. Class B Address are very hard to obtain today, as most have already been given out.
Class C	Networks begin with 192 (110) and ends with 223, Class C uses 21 bits to designate individual network ID's. This allows for 2 million possible Class C networks. Unfortunately, each of these networks can only have a few hosts. With only 8 of the 32 address bits left for host IDs, each Class C network can only have 256 possible hosts.
Class D & E	Networks begin with 224 and end with 254, Class D is Reserved multicasting and Class E is Reserved for Experimental Purposes.

How to sub-net an IP Address:

IP Addressing Basics:

	32 Bits in an IP address
	4 Octets in an IP address
	4 Bytes make up an IP address
	8 Bits per each octet

Class	Start	End	# of Networks	# of Hosts	Max # of Bits Borrowed
A	0	126	126	16,777,214	24
B	128	191	16,384	65,534	14
C	192	223	2,097,152	254	6
D E	224, 240	239, 254	N/A	N/A	N/A

Binary Conversion Place Values
Place Value	7	6	5	4	3	2	1	0
2^ by Place Value	2^⁷	2^⁶	2^⁵	2^⁴	2^³	2^²	2^¹	2^⁰
Decimal Value	128	64	32	16	8	4	2	1

*Total number of Subnets is calculated by raising 2 to the power of the number of bits borrowed (n)

**Total number of Available Subnets is calculated the same as above except you subtract 2 for the unusable addresses of all ones and all zeros

***Total number of Host Address is calculated by raising 2 the power of the number of bits remaining in the IP Address after you have borrowed some to make sub nets

****Total Available number of Hosts Addresses is calculated the same as above except you subtract 2 for the unusable hosts

Sub Net Masking

A Subnet mask is a binary number designed to separate the Network ID from the Host ID on an IP address.

Why Subnet?

Organizing departments, use of different physical media (like Ethernet, FDDI, and WAN's), and conserve on address space, security, and reducing network traffic.

127 IP Address is RESERVED FOR LOOP BACK PURPOSES

CLASS D IS RESERVED FOR MULTICASTING

CLASS E IS RESERVED FOR EXPERIMENTAL PURPOSES

Rules for Sub-netting

Subnet mask must be equal to or greater than default subnet

You must always start at the MSB (Most Significant Bit)

Cannot use all ones or zeros for node addresses

You cannot use a Private IP address to access the Internet

Sub netting reduces the number of possible nodes on a network

Without sub netting, a Class C Address supports 254 nodes

Example

I will borrow 3 bits from the last octet of a Class C Address, leaving 5 bits, of which 3 bits are used for host address and 2 bits for the Network ID.

The number of possible sub net works is

2^3 = 8 Total Subnets

8 – 2 = 6 Total Available Subnets.

Subnet numbers that are all one's and zero's can not be used, they are reserved for broadcasting and specifying the network address.

How To Make Subnet Numbers from an IP Address

First

Convert the IP Address to a Binary Number so you can borrow the bits from the last octet. The links below can be used in this conversion process.

DECIMAL TO BINARY CHART

BINARY TO DECIMAL CHART

When Borrowing 3 bits from the subnet host portion of the last octet, always borrow from the Most Significant Bit (MSB) which is the far left side of the last octet or host field (00000000)

Second

Place the Binary Representation of N in the first three bits of the last octet after the dot and before the remaining binary numbers.

Last Octet in Binary format:

NNN00000 where NNN represents the bits you borrowed to make the new sub nets and the 00000 remain the same

Third

Create Sub Networks using the number of bits you borrowed, by writing a numeric list of the number of subnets you plan to create and write the binary number for the numeric subnet number only using the binary bits you borrowed.

Quick Example: If I borrow 2 bits from a class C address, then I can make my subnet list using 0-3 which represents the number of new subnets I will have.

Subnet

     0

     1

     2

     3

Now I have to convert these four numbers in to binary format only using 2 bits

Subnet            Binary Format

     0                        00

     1                        01

     2                        10

     3                        11

Now add back the remaining 6 bits of the binary number you borrowed from to create the new binary number.

Subnet       Binary Format   New Binary Number

     0                    00                00000000

     1                    01                01000000

     2                    10                10000000

     3                    11                11000000

Now convert the New Binary Number to a decimal

New Binary Number     New Decimal Number

       00000000                               0

       01000000                              64

       10000000                             128

       11000000                             192

The Host Addresses are the numbers that fall between two subnet numbers, 64-128 and 128-192

Class C Address

Creating New Sub Network ID's

IP Address: 193.1.1.0
Binary: 1000001.00000001.00000001.00000000

Subnet #	Create a Binary IP Address	Covert to Decimal
0	11000001.00000001.00000001.00000000	193.1.1.0
1	11000001.00000001.00000001.00100000	193.1.1.32
2	11000001.00000001.00000001.01000000	193.1.1.64
3	11000001.00000001.00000001.01100000	193.1.1.96
4	11000001.00000001.00000001.10000000	193.1.1.128
5	11000001.00000001.00000001.10100000	193.1.1.160
6	11000001.00000001.00000001.11000000	193.1.1.192
7	11000001.00000001.00000001.11100000	193.1.1.224

More Rules:

You cannot use the all ones or the all zeros sub net numbers

All ones are used for specifying all hosts on network or broadcasting

All zeros are used for specifying the local network

Subtract 2 from the total number of subnets to find total usable subnets

HOST ADDRESSING:

Borrowing 3 bits from the host portion of the IP address, leaves 5 bits to create hosts. The number of bits not borrowed (or unmasked bits) when raising 2 to a power:

Example: 23 - 2 = 30

There are 30 Host addresses available per subnet work

Each subnet can have Hosts assigned to any address between the Subnet Address and the Broadcast Address

There are 32 Values between each subnet in a Class C Address

Range	Valid #'s	Network Address	Range	Valid #'s	Network Address
0-31	Not Valid		129-158	129-158	128
32-63	33-63	32	160-190	161-190	160
64-94	65-94	64	192-223	193-222	192
96-127	97-126	96	224-255	Not Valid

HOW TO FIND THE NETWORK NUMBER USING ANDING:

Applying a subnet mask to an IP Address allows you to identify the network and the host parts of the address

This is accomplished by performing a bit wise logical AND operation between the IP address and the subnet mask.

The Logical AND operation compares 2 bits, (one from IP address and one from subnet mask), if they are both “1”, then the answer will be “1”, other wise the result is zero.

Example:         0 0 0
                      1 0 1
                      0 0 1

Address	Dotted Decimal Notation	Binary Representation
IP Address	192.168.16.42	11000000.10101000.00010000.00101010
Subnet Mask	255.255.255.0	11111111.11111111.11111111.00000000
Network ID	192.168.16.0	11000000.10101000.00010000.00000000

By ANDing together the senders IP address and the subnet mask, and then ANDing together the destination IP address with the senders subnet mask, and comparing the two results, you can tell if the destination is local (in same network) or remote (sent to a default gateway)

How to determine which host ID belongs to which IP Address:

Step Value found in the number between subnets
The first valid address begins at the value of the last masked bit and the step value is the value of the first valid address.
- If the address were, 200.107.31.0 and we borrowed two bits from the last octet, then the first subnet would be 200.107.31.64, and 64 would be the step value, (or the value of the last masked bit)

The last valid IP address is the value of the subnet mask –1
- Where the subnet mask is 200.107.31.192
- The value of the subnet mask –1 would be 200.107.31.191
Step Value is 64
- Ranges for Subnet 1 200.107.31.64 – 200.107.31.127
(64 host Ids)
- Ranges for Subnet 2 200.107.31.128 – 200.107.31.191
(64 host Ids)

Private Addresses:

Class A:     10.0.0.0

Class B:     172.16.0.1   -   172.31.255.254

Class C:     192.168.0.1 -   192.168.255.254