what is subnet and subnetmask

[VideoRusher]

can any one explain simply what is subnet and subnet mask????

[Str_Mape]

I'll do what I can my networking stuff is a little blurry so I may need someone to verify this and hopefully it doesn't add more confusion.

First off, actually making subnets isn't that useful for home networks and is typically for more advanced network designs.

A subnet is a smaller network created from a current network sometimes used to separate different groups in a building.

A subnet mask tells the computer which subnet it belongs to, the one you'll see most often is 255.255.255.0 which allows for 254 devices including the router from .1 to .254 so 253 clients assuming there is only one router with .255 as the broadcast address which is an unusable address, don't worry about it.

Lets use the most common home network address as an example, 192.168.1.0 with a subnet mask of 255.255.255.0

192.168.1.0 is the network identifier and your router is often assigned to the IP 192.168.1.1 the clients will get assigned IP addresses from 192.168.1.2 to 192.168.1.254 with the broadcast IP at 192.168.1.255.
If say you wanted to have two smaller networks separated my a router you could use the subnet 255.255.255.128 which would allow for 126 devices per network and 125 clients.
The first network would run on the 192.168.1.0 identifier with one of the router ports at 192.168.1.1 and clients from 192.168.1.2 to 192.168.1.126 with the broadcast IP address at 192.168.1.127
The second network would run on the 192.168.1.128 identifier with one of the router ports at 192.168.1.129 and clients from 192.168.1.130 to 192.168.1.254 with the broadcast IP address at 192.168.1.255

[Footy]

can any one explain simply what is subnet and subnet mask????

 

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###   It is your computers address. your netmask is like your postcode or town.   ###

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To Understand it though you have to do it in binary

 

Binary columns for 8 bit are as follows

128, 64, 32, 16, 8, 4, 2, 1

 

so

1 = 00000001 (1)

10 = 00001010  (8+2)

128 = 10000000 (128)

163 = 10100011 (128+32+2+1)

 

IP      192.168.0.1         -  11000000 10101000 00000000 00000001

Mask 255.255.255.0  -  11111111 11111111 11111111 00000000

 

Now the first IP in a network is the Network ID, the Last IP in a network is a Broadcast IP these are calculated with a combination of the IP and Mask.

 

 

IP              192.168.0.1           -  11000000 10101000 00000000 00000001

Mask         255.255.255.0    -  11111111 11111111 11111111 00000000

NetID         192.168.0.0         -  11000000 10101000 00000000 00000000

Broadcast 192.168.0.255  -  11000000 10101000 00000000 11111111

 

Where the bits of the netmask are 1 it forces the corresponding bits of the IP to stay the same, where it is 0 it means you can change these bits.

As you can see in the example above the last 8 bits are all 0 for the network ID and all 1 for the broadcast which = 0 and 255. 

 

Any address that doesn't fall between these two addresses is in a different network and your computer will send the connection request to your Default Gateway

 

 

Lets do another more advanced example with a different subnet length.

 

A Subnet = 1 until it = 0 then it is always 0 to the end

 

IP              10.40.82.160        - 00001010 00101000 01010010 10100000 

Mask         255.255.240.0    - 11111111 11111111 11110000 00000000

NetID         10.40.80.0             - 00001010 00101000 01010000 00000000

Broadcast 10.40.95.255    -  00001010 00101000 01011111 11111111

[VideoRusher]

its OK ...... i have to face an exam will held on next week.. I have no clear idea of subnets that's why i am asking..... i want a definition for both... to write a short description of that....