AWS Classroom Series – 18/Aug/2021

Networking contd..

• We have three possible subnet masks

255.255.255.0 => 256
255.255.0.0  => 65536
255.0.0.0 => 16777216

• To Create networks we have two addressing mechanisms
  • Classful
  • Classless
• Classful:
  • In this mechanism all the IPv4 addresses are divided into 5 classes
    • A
    • B
    • C
    • D
    • E

	Class A	Class B	Class C
Address Range	0.0.0.0-127.255.255.255	128.0.0.0-192.255.255.255	192.0.0.0 – 223.255.255.255
Defult Subnet Mask	255.0.0.0	255.255.0.0	255.255.255.0
Maximum Number of Hosts	16777214	65534	254
private address range	10.0.0.0 – 10.255.255.255	172.16.0.0 – 172.31.255.255	192.168.0.0 – 192.168.255.255

• Private networks vs Public networks:

  • Public network is accesible from the internet
  • Private network cannot be accesed from internet and is designed for internal communication.

• Classless Inter-Domain Routing (CIDR):

  • Was introduced in 1993 to replace the classful addressing. It uses Variable lenght subnet masks
  • It has CIDR Notation which helps in representing subnet masks and ip ranges

192.168.0.0/24

192.168.0.x
255.255.255.0

192.168.0.0/16
192.168.x.x
255.255.0.0

10.0.0.0/8
10.x.x.x
255.0.0.0

• Advantage of viewing subnet mask as binary

200 devices

(254, 65534, 16777214)


255.255.255.0 (decimal reprsentation)

11111111.11111111.11111111.00000000 (8 zeros) => 2^8 -2 => 256-2 => 254
11111111.11111111.11111110.00000000 (9 zeros) => 2^9-2 => 512-2 => 510
11111111.11111111.11111100.00000000 (10 zeros)
11111111.11111111.11111000.00000000 (11 zeros)

• Lets assume we want to have a network with 2000 devices

2^11 ~= 2000
we need 11 bits for host id
So my subnet mask will be
11111111.11111111.11111000.00000000
255.255.248.0

• We need to create a network with 9000 devices

2^14 = 16384 
i.e 14 bits for host id
11111111.11111111.11000000.00000000
255.255.192.0

• Exercise: We need to create a network with 100 devices

2^7 ~= 126
i.e 7 bits for host id and 32-7 (25) bits for network id

11111111.11111111.11111111.10000000
255.255.255.128

• Possible SM’s in a octect

11111111 => 255
11111110 => 254
11111100 => 252
11111000 => 248
11110000 => 240
11100000 => 224
11000000 => 192
10000000 => 128

• Lets look at the following cidr notation

192.168.0.0/25

SM: 11111111.11111111.11111111.10000000

IP: 11000000.10101000.00000000.00000000
    11000000.10101000.00000000.0 xxxxxx
	11000000.10101000.00000000.0 0000000 => 192.168.0.0
	11000000.10101000.00000000.0 1111111 => 192.168.0.127

192.168.128.0/22

SM: 11111111.11111111.11111100.00000000

IP: 11000000.10101000.10000000.00000000
    11000000.10101000.100000 xx.xxxxxxx
	
	11000000.10101000.100000 00.00000000 => 192.168.128.0
	11000000.10101000.100000 11.11111111 => 192.168.131.255

10.10.0.0/18

SM: 11111111.11111111.11000000.00000000 => 255.255.192.0

IP: 00001010.00001010.00000000.00000000
IP: 00001010.00001010.00xxxxxx.xxxxxxxx
    00001010.00001010.00000000.00000000 => 10.10.0.0
	00001010.00001010.00111111.11111111 =>10.10.63.255

• Exercise:

172.16.0.0/12
192.168.0.0/16
10.0.0.0/8

10.100.192.0/20
10.10.0.0/21