Why do we use Subnet mask? What are its uses?

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Shahzad Siddiqui

  • Aug 26th, 2006

Subnetmask is use to isolate the network ID and Host ID. eg- if an IP is: then the default subnet is: because it is a C Class Address C Class Add. have 3 network octate and 1 host octate i.e.

network ID :

host ID      :


  • Aug 29th, 2006

Hi Shahzad Siddiqui,thanx for u r response,u r answer is nice,from,Bashur

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Engg Muhammad Waseem

  • Sep 1st, 2006

The main purpose of subnetmasking is to reduce the broadcast domain or in other words to reduce to heavy network traffic.

The use of subnet mask actually tells you the number of host/terminals that could be used on the same network. It is actually very simple, for eg an IP address with the subnet mask of Just look at the 'ON' bits in this subnet mask (11111111.11111111.11111111.00000000), this clearly indicates that the number of host/terminal that can use the same network are configured and assigned from the last octet. So the number of combination one can drive from the last octect (2x2x2x2x2x2x2x2)= 255 (0-254) which is number of devices that can be used over the network

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Rajgopal Medpur

  • Sep 20th, 2006

What is the relation between IP address,Gateway address,Nemask address


  • Sep 20th, 2006

Is there is any  relation between subnet and gateway

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  • Oct 10th, 2006

My question is to know how we calculate subnetmask for 3 classes But I know to calculate subnetmask for class c but other then.

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  • Nov 23rd, 2006

A subnet allows the flow of network traffic between hosts to be segregated based on a network configuration. By organizing hosts into logical groups, subnetting can improve network security and performance. the most recognizable aspect of subnetting is the subnet mask. Like IP addresses, a subnet mask contains four bytes (32 bits) and is often written using the same "dotted-decimal" notation. For example, a very common subnet mask in its binary representation

    11111111 11111111 11111111 00000000
is typically shown in the equivalent, more readable form


Jai Singh

  • Dec 29th, 2006

Subnet mask is 32 bit long TCP/IP address divided in four equal part.It is used for isolation of network address and host address.

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sooraj k r

  • Jun 24th, 2007

Subnetmak is used to identify the network based on the number of bits and the main purpose of subnetmask is to make independent and equal of the network.

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  • Jul 27th, 2007

Actually Subnet mask is used to Separate Network Bits from Host Bits,

For Eg for class C IP address subnet mask is

so here u can see 255.255.255 mask the Network portion ie., 192.168.0. and leave 8 bits i.e.,[.0] 255 for Host. 

So Here we can connect up to 255-1 = 254  Hosts for the 192.168.0 network.
Similarly for class B IP address subnet mask is

so here u can see 255.255 mask the Network portion i.e., 172.168 and leave 16 bits i.e, [0.0.] 255.255 for Host.
So here we can connect up to 65,532 hosts for the Network.

If u have any doubts can ask me...... thanks


  • Sep 27th, 2008

I don't see the reason why a subnet mask has to be used with default networks like Class A-B-C..., unless you a using subnetting.

the reason i say this becasue with the default networks, the ip address itself will help identifying the network and host id.

for example
The very fist octect would tell that this is Class B network.
Here N/w is 128 
Host is 45.56.67.

in the begining when ip address were defined there was no subnetting defined(am i correct here?). And when no subnetting was thought then why did they plan to use a subnet mask?

Any body has a answer,then please help me understand this.

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  • Sep 23rd, 2011

We use sub netting for divide a huge network in subnetwork or some user use for some security reasons

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  • Mar 4th, 2012

sub netting is used to divide an ip address into many ips.
this is must coz we cant give an ip (without sub-netting) to every station. so sub-netting is important

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  • May 3rd, 2012

As its name suggest it is subnetting a big network in to small pieces to effectively use the network bandwidth for e.g the subnet will be in this case all system which are having starting ip number =126 can communication to any other system on the network.in second case class b network eg- the subnet will be here all system which are having first to number as 172.168 can communicate to any other system with in network in third case class C networking eg- subnet will be here only those system can communicate to each other which are having first three number as same......

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if we are having network of no doubt default subnet mask would be
network ip would be and broadcast IP would be but host IDs must fall under to not

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  • Dec 22nd, 2012

Subnet mask is used to Segment the IP address into HOST and NETWOK.

It used to how many bit is used for Netwok and How many for Host.

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  • Dec 22nd, 2012

Subnet mask is use only to identify the class of ip address.
Example : c class ip is and subnet mask is
In class c, three octal are full i.e. three network part and last one is host part.
Three network part full means we cant change the network part.

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Ravinder Kumar

  • Dec 24th, 2012

how is subnetting use in networking and host and subnet id is .i dont understand the subnetting pls deeply and detail wise information send me.

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  • Jun 19th, 2013

Creating multiple indepedentnetworks from a single a network..

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  • Sep 14th, 2013

Subnet mask is used for differentiate the network between network bit and host bit,
by using the subnet mask we know that the how many bit use for network and how many bit use for host

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Er.Harneet Singh

  • Oct 4th, 2014

sub netting is used to reduce the network traffic.

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  • Nov 5th, 2014

Subnet mask is differentiate network and host partitions of address  if ip address as it is in class b here 255,255 are network id and 0 0 host id

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  • Nov 20th, 2014

thank you..... give briefly

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  • Jan 12th, 2015

IP Addresses are divided into 5 Classes, Class A, B, C, D and E. We can control/use maximum or minimum network and hosts by using subnet mask as per network infrastructure requirements.

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  • Jan 13th, 2015

Subnetting helps reduce network traffic and the size of the routing tables. Its also a way to add security to network traffic by isolating it from the rest of the network.

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  • Apr 8th, 2016

My IP address is and my default subnet mask is, I want to restrict my WIFI access up to 2 users then what will be the subnet mask?

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sukhchain singh

  • Apr 28th, 2016

Subnet Mask keeps the difference between net id and host id. For example my IP is then its default subnet mask will it is showing that first 24 bits are on and they are netid and we cant change it. Last 8 bits are host id and we will change it to assign IPs to our system.

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  • Jun 30th, 2016

How many hosts can we use if we have a router with IP and subnet mask ?

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  • Oct 20th, 2016

Subnet mask divide the IP address into network bit and host bit, it show how many bit for network and how many bit for host.

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