Subnetting
You have been given the 172.30.0.0/16 network. Your company requires 100 subnets with at least 500 hosts per subnet. What prefix length should you use?
Borrowed bits: 1 2 3 4 5 6 7 Num. of subnets: 2 4 8 16 32 64 128
CIDR Notation
Dotted Decimal CIDR Notation 255.255.255.128 /25 255.255.255.192 /26 255.255.255.224 /27 255.255.255.240 /28 255.255.255.248 /29 255.255.255.252 /30 255.255.255.254 /31 255.255.255.255 /32
PC1 has an IP address of 10.217.182.223/11. Identify the following for PC1's subnet: 1) Network address: 2) Broadcast address: 3) First usable address: 4) Last usable address: 5) Number of host (usable) addresses:
First find the prefix of 11. To find the network address change all the host bits to 0 10.192.0.0 The first usable address adds 1 to the last host address. 10.192.0.1 The Broadcast address change all the host bits to 1 10.223.255.255 Last usable address changes the last host bits of the broadcast address. 10.223.255.254 Number of host addresses: Count the number of host bits. 21 host bits = 221- 2 = 2,097,150 hosts per subnet to find the next set of subnet, use the BC add and add one to find the other network address. continue with the steps to find the /prefix.
What subnet does host 172.21.111.201/20 belong to?
First write out the answers in binary. Then, change all the host bits to 0. Convert the Address back to dotted decimal, and that's the answer.
What is the broadcast address of the network 192.168.91.78/26 belongs to?
First write out the answers in binary. Then, change all the host bits to 1. Convert the Address back to dotted decimal, and that's the answer.
Barrowed Bits = # of subnets
Summary
Subnetting Mask
Summary
You divide the 172.16.0.0/16 network into 4 subnets of equal size. Identify the network and broadcast addresses of the second subnet.
To devide the subnet in to 4 equal part. Have to borrow 2 bits to the power of 2 is 4 That makes a slash 18 prefix length change the last bit to one.
You divide the 172.30.0.0/16 network into subnets of 1000 hosts each. How many subnets are you able to make?
To know how many subnets, we need to know how many bits we can borrow. But to know how many bits we can borrow We need to find how many host bits we need for 1000 hosts. Formula for host bits. 10 host bits = 210- 2 = 1022 hosts 6 borrowed bits = 26 = 64 subnets
