[Network] Subnet

• subnet : logical subdivision of an IP network.
• subnetting : the process of dividing a network into 2 or more subnetworks
• subnet mask : A subnet mask is used so that a computer knows if a target computer is located in the same network or not.

Subnet	1	2	4	8	16	32	64	128	256
Host	256	128	64	32	16	8	4	2	1
Subnet Mask	/24	/25	/26	/27	/28	/29	/30	/31	/32

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EXAMPLE 1.

• Question

network ID : 192.168.4.0/24

create 3 seperate networks for a coffee shop.

1. for the office
2. for the front desk and storage room
3. for public use

List each network ID, subnet mask, Host ID Range, # of usable host IDs, and Broadcast ID.

 

• Answer

4 subnet is suitable

(why? 4 means 4 subnet. 64 means each subnet will have 64 total host IDs including network ID and Broadcast ID)

/26 is the new subnet mask for these 4 subnets.

 

Network ID	Subnet Mask	Host ID Range	# of Usable Host	Broadcast ID
192.168.4.0	/26	192.168.4.1 - 192.168.4.62	62	192.168.4.63
192.168.4.64	/26	192.168.4.65 - 192.168.4.126	62	192.168.4.127
192.168.4.128	/26	192.168.4.127 - 192.168.4.190	62	192.168.4.191
192.168.4.192	/26	192.168.4.193 - 192.168.4.255	62	192.168.4.255

 

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EXAMPLE 2.

• Question

network ID : 192.168.4.0/24

you are required to get 6 subnets.

List each of new network ID, subnet mask, Host ID range, # of usable hosts, and broadcast ID.

How many subnets are wasted after subnetting?

 

• Answer

subnet : 1 2 4 “8” 16 …

Host : 256 128 64 “32’ 16 …

subnet mask : /24 /25 /26 “/27” …

Network ID	Subnet Mask	Host ID Range	# of Usable Host	Broadcast ID
192.168.4.0	/27	192.168.4.1 - 192.168.4.30	30	192.168.4.31
192.168.4.32	/27	192.168.4.33 - 192.168.4.62	30	192.168.4.63
192.168.4.64	/27	192.168.4.65 - 192.168.4.94	30	192.168.4.95
192.168.4.96	/27	192.168.4.97 - 192.168.4.126	30	192.168.4.127
192.168.4.128	/27	192.168.4.129 - 192.168.4.158	30	192.168.4.159
192.168.4.160	/27	192.168.4.161 - 192.168.4.190	30	192.168.4.191
192.168.4.192	/27	192.168.4.193 - 192.168.4.224	30	192.168.4.225
192.168.4.224	/27	192.168.4.225 - 192.168.4.254	30	192.168.4.255

→ 2 subnets are wasted after subnetting

 

 

Reference