MultiCloud Classroom notes 02/Jan/2025

Private Networking

• Private networks have predefined ip ranges
  • 192.168.0.0 to 192.168.255.255
  • 10.0.0.0 to 10.255.255.255
  • 172.16.0.0 to 172.31.255.255
• When we get an ip address it carries network id and host id
• To find the network id and host id we use subnet mask
  
• The above case

     1   2  3  4
ip: 192.168.0.167
sm: 255.255.255.0
-------------------

nid: 255 is in octets 1,2,3
     192.168.0 (nid)
    this is constant for all devices in network

hid: 0 is in octet 4
       167 (hid)
    this represents the variable part

size = 2^8 - 2
     = 256 - 2
     = 254

network id = 192.168.0.0
broadcast ip = 192.168.0.255

• We can use the above to calculate the size of network

size = 2 ^ n - 2
n = number of bits reserved for host id

• Two ips cannot be allocated
  • all 0’s represent network id
  • all 1’s represent broadcast ip
• Lets try for the following ip info

ip: 192.168.10.17
sm: 255.255.0.0

nid: 192.168
hid: 10.17

size: 2^n - 2 = 2^16 - 2
      = 65536 - 2  = 65534

• I want to create a private network for 1000 devices, possible values of n are 8,16,24

size = 2 ^ n - 2
1000 ~= 2 ^ n 
n = 16

• CIDR (Classless interdomain routing) can help in creating networks closer to required sizes

CIDR

• • I want to create a private network for 1000 devices, possible values of n are 2 to 31

size = 2 ^ n - 2
1000 ~= 2 ^ n 

n (host id) = 10
N (network id) = 32 - 10 = 22

SM = 11111111.11111111.11111100.00000000
   = 255.255.252.0

• Total SM possibilities in an octet

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

• I want a network of 50 devices

2^n ~= 50
n = 6
N = 32 - 6 = 26

SM: 11111111.11111111.11111111.11000000
     255.255.255.192

• Choosing an ip can happen over 3 possibilities
  • 192.168.0.0 to 192.168.255.255
  • 10.0.0.0 to 10.255.255.255
  • 172.16.0.0 to 172.31.255.255
• For a network with 1000 devices the host bits are 10

size = 2 ^ n - 2
1000 ~= 2 ^ n 

n (host id) = 10
N (network id) = 32 - 10 = 22

SM = 11111111.11111111.11111100.00000000
   = 255.255.252.0

ip =           192.168.000000xx.xxxxxxxx
sip =          192.168.00000000.00000000 = 192.168.0.0
eip =          192.168.00000011.11111111 = 192.168.3.255
SM = 11111111.11111111.11111100.00000000

• For a network with 50 devices

2^n ~= 50
n = 6
N = 32 - 6 = 26


ip:                     10.0.0.00xxxxxx
sip:                    10.0.0.00000000 = 10.0.0.0
eip:                    10.0.0.00111111 = 10.0.0.63
SM: 11111111.11111111.11111111.11000000
     255.255.255.192

• Try the same for a private network with 500 devices

2^n ~= 500
n = 9
N = 32 - 9 = 23

ip:           192.168.0000000x.xxxxxxxx
sip:          192.168.00000000.00000000 = 192.168.0.0
eip:          192.168.00000001.11111111 = 192.168.1.255
SM: 11111111.11111111.11111110.00000000 = 255.255.254.0

• I want a private network with 100000 devices

2^n ~= 100000
n = 17
N = 32 - 17 = 15


ip:        10.0000000x.xxxxxxxx.xxxxxxxx
sip:       10.00000000.00000000.00000000 = 10.0.0.0
eip:       10.00000001.11111111.11111111 = 10.1.255.255
SM : 11111111.11111110.00000000.00000000 = 255.254.0.0

• CIDR has a notation which is expressed as Start-IP/N
• Example 1

10.0.0.0/8
N (fixed bits)  = 8
n (variable) = 32 - 8 = 24

ip: 10.0.0.0/8
ip:       10.xxxxxxxx.xxxxxxxx.xxxxxxxx
sip:                                   = 10.0.0.0
eip:      10.11111111.11111111.11111111 = 10.255.255.255
SM: 11111111.00000000.00000000.00000000

• Example 2: 192.168.0.0/18

sip = 192.168.0.0

N = 18
n = 32 -18 = 14

ip:           192.168.00xxxxxx.xxxxxxx
sip:                                   = 192.168.0.0
eip:          192.168.00111111.1111111 = 192.168.63.255
SM: 11111111.11111111.11000000.00000000

• Example 3: 10.10.10.0/23

sip = 10.10.10.0
N = 23
n = 32 - 23 = 9

ip:             10.10.0000101x.xxxxxxxx
                                        = 10.10.10.0
eip:            10.10.00001011.11111111 = 10.10.11.255
SM: 11111111.11111111.11111110.00000000

• All private ip ranges can be expressed in cidr ranges
  • 192.168.0.0/16 = 192.168.0.0 to 192.168.255.255
  • 10.0.0.0/8 = 10.0.0.0 to 10.255.255.255
  • 172.16.0.0/12 = 172.16.0.0 to 172.31.255.255

I want to create a private network of size 100 devices

• Calculate n (variable bits)

2^n - 2 ~= 100
2^n ~= 100
n = 7
N = 32 - 7 = 25

172.16.0.0/25
ip:                   172.16.0.0xxxxxxx
sip:                                    = 172.16.0.0
eip:                  172.16.0.01111111 = 172.16.0.127
SM: 11111111.11111111.11111111.10000000

I want to create a network of size 2000 devices

2^n  = 2000
n = 11
N = 32 - 11 = 21

ip: 10.100.0.0/21
sip: 10.100.0.0
ip:            10.100.00000xxx.xxxxxxxx
eip:           10.100.00000111.11111111 = 10.100.7.255
SM: 11111111.11111111.11111000.00000000

• Exercises: Create private networks of following sizes
  • 25
  • 70000
• Default gateway represents the ipaddress of router