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📗 Net Practice

Basic networking exercises.


Explanations:

NOTE: You do not need to know everything below to pass net practice. As long as you understand the basics of subnetting you should be good to go. I would recommend to learn the Subnet Mask Chart

Introduction

This guide explains the basics of IP addressing and subnetting, including how to convert IP addresses to binary, calculate network bits, host bits, and the number of available addresses in a subnet.

What is an IP?

image

An IP (Internet Protocol) address is a unique identifier assigned to each device connected to a computer network that uses the Internet Protocol for communication. It has two main purposes: network interface identification and location addressing. An IP address contains four octets (in IPv4), which can range from 0 to 255 (e.g., 192.168.1.1). This numerical label enables devices to locate and communicate with each other on a network. There is also IPv6, but that is beyond the scope of the project.

What is a subnet mask?

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A subnet mask is a 32-bit number that masks an IP address and divides the IP address into network address and host address. Subnet masks are used to designate which portion of an IP address is allocated to the network and which part is available for host use. This creates subnetworks within a larger network, which basically does the following:
  • Routing efficiency
  • Security
  • Management of IP address allocations.

A subnet mask looks very similar to an IP address (e.g., 255.255.255.0).

When the subnet mask is applied (via a bitwise AND operation) to an IP address, the network portion of the IP address is known. The remaining part, which corresponds to the host on that network, determines the number of hosts that can be assigned in the subnet. A common subnet mask is 255.255.255.0, which allows for 254 host addresses within a single network segment.

Switch

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A switch allows multiple devices to connect with one another in a local network (LAN). It cannot deliver packages outside of its own network.

Router

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The router connects multiple networks. Unlike the switch, the router has an interface for each network it connects to. Make sure the IP's do not overlap when assigning IP's.

Converting IP Addresses to Binary and Decimal

To convert an IP address we will be using the following cheat table:

128 64 32 16 8 4 2 1
2^7 2^6 2^5 2^4 2^3 2^2 2^1 2^0

From Decimal to Binary:

Example of IP address in bits: 11000000.10101000.00000001.00010101.
Place the 8 bits on our table and check the following: When theres a 1, add all the numbers.

So we take the first octet (11000000) and place it on our table:

1 1 0 0 0 0 0 0
128 64 32 16 8 4 2 1

The above gives us, 128 + 64 = 192.
When we do this for the rest of the octets, you get:

192.168.1.21

From binary to decimal:

IP Address: 172.16.34.3
Take the individual octests and ask: Can we subtract the current octet from the table?

  • Yes: Place 1 and use the result from the subtraction and move on.
  • No: Place 0 and move on to the next one.

Taking the first octet, 172 and place it on our table:

172 44 44 12 12 4 0 0
128 64 32 16 8 4 2 1
1 0 1 0 1 1 0 0

From the above we get our first binary octet: 10101100.
Again, we first check, can we subtract 128 from 172 (basically is 172 > 128)? Yes, 172-128 = 44. So then we place a 1 and move on to the next one, but now with the result (44).

If you do this for all of them you get the following:

10101100.00010000.00100010.00000011

What does the binary tell us?

We can calculate the number of network/host bits when converting a subnet mask to binary (see this chart for all the different combinations).

  • 1 = Network bits
  • 0 = Host bits

Example of sub net mask:

  • Decimal: 255.255.255.0
  • Binary: 11111111.11111111.11111111.00000000

The number of 0's in binary = number of hosts. So we can use the following to calculate the number of possible IP's in the the network:

2^(# of 0's) - 2

So given our example above, we can do:

2^8 = 256

This means we can have a total of 256 different IP addresses in the current network.

HOWEVER: 2 IP's are reserved:

  • The first IP = subnet address.
  • The last IP = broadcast address.

So our new total would be 256 - 2 = 254 usable addresses.

Subnet Mask Chart

Subnet Mask CIDR Binary Network Bits Host bits Available addresses/Group size (2^host bits)
255.255.255.255 /32 11111111 11111111 11111111 11111111 32 0 1
255.255.255.254 /31 11111111 11111111 11111111 11111110 31 1 2
255.255.255.252 /30 11111111 11111111 11111111 11111100 30 2 4
255.255.255.248 /29 11111111 11111111 11111111 11111000 29 3 8
255.255.255.240 /28 11111111 11111111 11111111 11110000 28 4 16
255.255.255.224 /27 11111111 11111111 11111111 11100000 27 5 32
255.255.255.192 /26 11111111 11111111 11111111 11000000 26 6 64
255.255.255.128 /25 11111111 11111111 11111111 10000000 25 7 128
255.255.255.0 /24 11111111 11111111 11111111 00000000 24 8 256
255.255.254.0 /23 11111111 11111111 11111110 00000000 23 9 512
255.255.252.0 /22 11111111 11111111 11111100 00000000 22 10 1,024
255.255.248.0 /21 11111111 11111111 11111000 00000000 21 11 2,048
255.255.240.0 /20 11111111 11111111 11110000 00000000 20 12 4,096
255.255.224.0 /19 11111111 11111111 11100000 00000000 19 13 8,192
255.255.192.0 /18 11111111 11111111 11000000 00000000 18 14 16,384
255.255.128.0 /17 11111111 11111111 10000000 00000000 17 15 32,768
255.255.0.0 /16 11111111 11111111 00000000 00000000 16 16 65,536
255.254.0.0 /15 11111111 11111110 00000000 00000000 15 17 131,072
255.252.0.0 /14 11111111 11111100 00000000 00000000 14 18 262,144
255.248.0.0 /13 11111111 11111000 00000000 00000000 13 19 524,288
255.240.0.0 /12 11111111 11110000 00000000 00000000 12 20 1,048,576
255.224.0.0 /11 11111111 11100000 00000000 00000000 11 21 2,097,152
255.192.0.0 /10 11111111 11000000 00000000 00000000 10 22 4,194,304
255.128.0.0 /9 11111111 10000000 00000000 00000000 9 23 8,388,608
255.0.0.0 /8 11111111 00000000 00000000 00000000 8 24 16,777,216