1. UCCN 1003 (May 2010)
Data Communications & Networks
(Lecture 04b)
IP Subnets Calculator
2. Making your life easier – IP calculator
• If you find all the IP subnet
rules overwhelming, please
make use of an IP calculator
to help you.
• There are many IP
calculators available free on
the Internet.
– In the following examples, we
will use Bitcricket IP Calculator
3. IP Calculator Demo (1)
• 178.40.143.78/25
– Network address?
– Broadcast address?
– 1st usable IP?
– Last usable IP?
Key in
178.40.143.78
4. IP Calculator Demo (2)
• Choose the subnet mask
1. Click here
2. Choose /25
5. IP Calculator Demo (2)
Network Broadcast
address address
1st usable IP = Last usable IP =
178.40.143.0 + 1 178.40.143.127 - 1
= 178.40.143.1 = 178.40.143.126
7. #Quick Quiz#
• What is the number of usable IP addresses
for 178.40.143.78/25?
• What is the IP range for the 3rd subnet of
178.40.143.78/25 given the subnet bits = 3?
– Subnet number = 1 as the first subnet.
8. Answer #1
• Based on the IP
calculator (and our
hand calculation)
– 32 – 25 = 7 host bits
– # of usable IP = 27 –
2 = 128 – 2 = 126
– 2 represent the
network address and
broadcast address.
• Both are not usable.
9. Answer #2
• Put in IP calculator
CIDR bits = 3
• Choose the 3rd subnet
range
• Network Address
– 178.40.143.48/28
• Usable IP range
– 178.40.143.49 to
– 178.40.143.62
