Networking contd

Size of network

• number of devices that can be connected to the network i.e. number of hosts/devices that can be connected in a network

ip: 192.168.100.111
sm: 255.255.255.0

nid: 192.168.100
hid: 111

with in a network
nid = fixed = 3 octets
hid = variable = 1 octet = 8 bits => 2^8 hosts => 256
nid = 192.168.100.0
broadcast = 192.168.100.255
i.e
size of network => 2^ (host id bits) - 2
                => 2^8 -2
                => 254


ip: 10.100.102.32 
sm: 255.255.0.0
nid = 2 octets
hid = 2 octets = 16 bits
size => 2^16 - 2
     => 65536 - 2
     => 65534

• In every network we can use two ip addresses
  • 0: this represents network id
  • 255: this represents broadcast address
• To create networks of different sizes, we have two approaches
  • Classful networking
    
  • Classless interdomain routing (CIDR)
• CIDR Approach

ip: 192.168.100.111
sm: 11111111.11111111.11111111.00000000

nid => number of consecutive 1's = 24 (fixed)
hid => 8 (number of consecutive 0's)

for= 2^ (hid bits) - 2
   = 2^8 -2 = 254

ip: 192.168.100.111
sm: 11111111.11111111.11111110.00000000

size = 2^9 - 2 = 512 - 2 = 510

• I have 2000 devices what should be by subnet mask

2^n-2 ~= 2000

2^n ~ = 2000
n = 11

sm: 11111111.11111111.11111000.00000000
    255.255.248.0

• I have 12000 devices what should be my subnet mask

2^n - 2 ~= 1,20,000
n = 17 (number of zeros)
N = 32 - 17 = 15
sm: 11111111.11111110.00000000.00000000
    255.254.0.0

• I have 27 devices what should be my subnet mask

2^n -2 ~= 27
n = 5
N = 32-5 = 27

sm: 11111111.11111111.11111111.11100000
    255.255.255.224

• I have 2000000 devices what should be my subnet mask

2 ^ n -2 ~= 2000000
n = 21
N = 32 - 21 = 11
sm: 11111111.11100000.00000000.00000000
    255.224.0.0

• public network: This is an ip accessible from internet and private network: These are reserved for private networking
  
• CIDR Notation

x.x.x.x/N

• Expand CIDR
• Sample 1

### sample 1
192.168.0.0/24
N = 24
n = 32 -24 = 8
ip:      192.     168.       0.       0
sm: 11111111.11111111.11111111.00000000
start: 192.168.0.00000000 => 192.168.0.0
end:   192.168.0.11111111 => 192.168.0.255

• sample 2

cidr: 10.0.0.0/11
N = 11 (number of ones)
n = 32 -11 = 21
sm: 11111111.11100000.00000000.00000000

ip:       10.       0.       0.       0
sm: 11111111.11100000.00000000.00000000
range: 10.000xxxxx.xxxxxxxx.xxxxxxxx
start: 10.00000000.00000000.00000000 = 10.0.0.0
end:   10.00011111.11111111.11111111 => 10.31.255.255

• sample 3

cidr: 172.16.0.0/12
N = 12
n = 32 -12 = 20

ip:       172.      16.       0.       0
sm:  11111111.11110000.00000000.00000000
ip:        172.00010000.00000000.00000000
range: 172.0001xxxx.xxxxxxxx.xxxxxxxx
start: 172.00010000.00000000.00000000 => 172.16.0.0
end: 172.00011111.11111111.11111111 => 172.31.255.255

• sample 4

192.168.128.0/22
N = 22
n = 32 - 22 = 10
sm: 11111111.11111111.11111100.00000000
ip:      192.     168.100000xx.xxxxxxxx  
start:   192.168.128.0 
end:     192.168.131.255

• Exercises:

10.132.0.0/23
192.168.0.128/27
172.16.0.0/21