Finding out the Network Address of IP Address
CALCULATING NETWORK ADDRESS OF AN IP ADDRESS:
In CCNA or JNCIA Exams we get questions like:
what is network address of 172.16.12.100/29?
what is network address of 192.168.100.100/26?
If it's a class-full subnet (/8, /16, /24) we can find it out easily but in case of a subnetted IP address we required some more time to identify the Sub network IP address.
Below is a simple 3 steps formula that gives you accurate Sub-network IP address of any given IP:
Step-1: Find out how many hosts we get in that subnet:
(Including Network address and Broadcast address)
Like, in
192.168.1.0/24 we get 255 Hosts.
192.168.1.0/29 we get 8 Hosts.
192.168.1.0/30 we get 4 Hosts.
Below is the chart that explains how many hosts per bit we get:
The above Pic represents the 8 Bits in an octet, And no. of hosts per each bit.
So, Clearly if we have /29 after filling /24 bits we got 5 more bits i.e., strike out the first 5 bits then we have 8 (which is the no. of hosts per subnet).
Example:2 if we have mask /19, it means after filling up /16 (two octets) we have 3 more bits filled for network, Strike off the first 3 bits, then we have 32 ( which is the no. of hosts per subnet).
Step -2: Divide the IP with no. of hosts value.
Let's say the IP 192.168.1.50/29
> so after filling up first 3 octets, 5 more bits filled up for network.
> Strike off the first 5 bits in the last octet. Then we have 8 ( Let's say it "n") hosts per subnet.
> Divide the IP address with the no. of hosts per subnet: 50 Divided by n.
> in the result whatever the decimal values you get just ignore them. 50/8 = 6.25 (ignore .25)
Step-3: Multiply the result with n again:
> 8 * 6 = 48.
> Here you go the Network address is 48. i.e., 192.168.1.48 is the network address.
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