3IMP IP Subnetting

1
3IMP IP Sub-netting

• 3IMP
• Session 4

2
Binary AND
If two conditions are combined by a binary AND,
they must both be true for the compound condition
to be true as well.
3
Determining the network portion of an address

• The router separates the network and host parts
  of an IP address by ANDing the address with its
  Subnet Mask.
• e.g. the destination address 195 . 120 . 24 . 18
  is expressed in binary as
• 11000011 . 01111000 . 00011000 . 00010010
• 11111111 . 11111111 . 11111111 . 11110000
• 11000011 . 01111000 . 00011000 . 00010000

4
Determining the network portion of an address

• IP- 11000011 .01111000 .00011000 . 00010010
• SNM- 11111111 .11111111 .11111111 . 11110000
• Net ID-11000011 . 01111000.00011000 . 00010000
• IP-192.120.24.18
• SNM-255.255.255.240
• Net ID-195 . 120 . 24 . 16

5
Determining the network portion of an address

• Determine the network ID for the following
• IP address 192.100.10.33
• Subnet Mask 255.255.255.0
• HOW??
• Convert the IP address subnet Masks to binary.
• Perform a Binary AND on them.
• Convert the result to Decimal
• THE RESULT?
• 192.100.10.0

6
What About Custom Subnet Masks?

• Determine the network ID for the following
• IP address 192.100.10.33
• Subnet Mask 255.255.255.240
• The Result 192.100.10.32

7
Number of Hosts

• This concept also works for calculating the
  number of hosts on your network but we use all of
  the bit in the address, not just the bits we want
  to pinch for the network subnets
• For example, our problem with the 5000 computers
  what setup would we use to get all 5000 PCs on
  one subnet???
• 2n 2

8
Number of Hosts

• 213 2 8190
• Still just over 3000 spare addresses but better
  than wasting 60,036 addresses!!!)
• Therefore, 13 bits would be used for the host
  portion of the address and 19 would be used for
  the network portion this would give us a CIDR
  (Classless Inter-Domain Routing) notation of /19
• SNM 11111111.111111111.11100000.00000000
• Again, get your lecturer to run through another
  example or three

9
Reserved Addresses

• The following address ranges are PRIVATE
  addresses.
• 10.0.0.0 to 10.255.255.255
• 172.16.0.0 to 172.31.255.255
• 192.168.0.0 to 192.168.255.255