Networking contd

• Any device connected to a network will get an ip address which is a unique id to access that device
• An Ipaddress can be public or private
• public ip (unique globally)
• private ip (unique within network)
• Our discussion will be on private network so private ip’s primarily
• IP Address = network id + host id
  
• IP Address are of two formats
  • IPv4:
    • ip address is a 32 bit number which is divided into 4 parts (octect) x.x.x.x
    • each octet will have 256 numbers ranging from 0 to 255
    • ipv4 range is 0.0.0.0 to 255.255.255.255
  • IPv6:
    • ip address is 128 bit number
      
• To determine what is network id and what is host id we need subnet masks
• Examples

## 1
ip: 10.0.1.7
sm: 255.255.255.0
nid: 10.0.1
hid: 7


## 2
ip: 10.0.1.7
sm: 255.255.0.0
nid: 10.0
hid: 1.7

• network id is constant for every device in the network and host id is variable, this determines the size of network.
• size of network = 2 ^ (n) – 2
  • n = number of host id bits
• we subtract from 2 because
  • all zeros is network id
  • all ones (255) is broadcast id
• Examples

## 1
ip: 10.0.1.7
sm: 255.255.255.0
nid: 10.0.1
hid: 7
hid size = 1 octect = 8 bits
size = 2^8 - 2 = 256 - 2 = 254


## 2
ip: 10.0.1.7
sm: 255.255.0.0
nid: 10.0
hid: 1.7

hid size = 2 octets = 16 bits
size = 2^16-2 = 65536 - 2 = 65534

## 3
ip: 10.0.1.7
sm: 255.0.0.0
nid: 10
hid: 0.1.7

hid size = 3 octects = 24 bits

size = 2^24 -2 = 16777216 - 2 = 16777214

• I want a network to connect 500 devices

size = 500

2 ^n - 2 ~ = 500
valid values of n = 8, 16, 24
in this case lets go with 16

n = 16 = 2 octects for host id

sm = 255.255.0.0

• CIDR (Classless Interdomain routing was introduced). All clouds use CIDR to define network ranges

CIDR

• look at ip address as bits not octets
• lets go with the example

ip: 10.0.1.7
SM: 255.255.255.0 (older)
SM: 11111111.11111111.11111111.00000000

• hostid : will have sequence of 1’s in SM
• network id: will have sequence of zeros
• I want a network with 500 devices

2 ^ n - 2 = 500

valid values of n are any where between 2 to 31

2^n ~= 500
n = 9
hid bits = 9
nid bits = 32 - 9 = 23

SM: 11111111.11111111.11111110.00000000
     255.255.254.0

• I want a network with 100 devices what is SM

2^n - 2 ~ = 100
2^n ~= 100
n = 7

hid bits = 7
nid bits = 32 - 7 = 25

SM: 11111111.11111111.11111111.10000000
    255.255.255.128

• I want a network of size 2000 devices find the subnet mask

2 ^ n -2 ~= 2000
n = 11
hid bits = 11
nid bits = 32 - 11 = 21

SM: 11111111.11111111.11111000.00000000
    255.255.248.0

• CIDR is represented as x.x.x.x/N
  • N = number of network id bits
• Expand CIDR 10.0.0.0/24:

ip:                     10.0.0.xxxxxxxx
ip:                     10.0.0.00000000 = 10.0.0.0
ip:                     10.0.0.11111111 = 10.0.0.255
SM: 11111111.11111111.11111111.00000000
range: 10.0.0.0 to 10.0.0.255

• Expand CIDR: 10.0.0.0/8

ip:       10.xxxxxxxx.xxxxxxxx.xxxxxxxx
ip:       10.00000000.00000000.00000000 = 10.0.0.0
ip:       10.11111111.11111111.11111111 = 10.255.255.255
SM: 11111111.00000000.00000000.00000000

• Expand CIDR: 172.16.0.0/12

ip       172.0001xxxx.xxxxxxxx.xxxxxxxx
ip:      172.00010000.00000000.00000000 = 172.16.0.0
ip       172.00011111.11111111.11111111 = 172.31.255.255
SM: 11111111.11110000.00000000.00000000

• Expand CIDR: 192.168.128.0/18

ip:           192.168.10xxxxxx.xxxxxxxx
ip:           192.168.10000000.00000000 = 192.168.128.0
ip:           192.168.10111111.11111111 = 192.168.191.255
SM: 11111111.11111111.11000000.00000000

• References
  • 2 power table
  • binary to decimal converter
  • decimal to binary converter
  • CIDR Expander