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# subnetwark

Posted on 2004-11-20
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what is the different be taween  255.255.255.0  and 255.255.255.252 and 255.255.0.0
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Question by:teera

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Saqib Khan earned 200 total points
ID: 12636543
255.255.255.0  = 254 Computers
255.255.255.252  = 3 Computers
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ID: 12636555
How do you known 254 computer or 3 computer
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Lee W, MVP earned 400 total points
ID: 12636857
It's based on the bits.  255.255.255.0 is equal to 11111111.11111111.11111111.00000000 (in binary).  It defines the network.

For a clearer, more detailed explanation, you might want to have a look at these links:
http://www.troutman.org/tech/linux_guides/subnet.html

http://www.blogontheweb.com/ccda/archive/2004/02/17/3736.aspx

http://www.windowsitlibrary.com/Content/121/01/2.html
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rafael_acc earned 800 total points
ID: 12638178
here we go ...

consider you want 10 subnetworks.
2^2 = 4 (4 - 2 = 2 => 2 usable subnetworks; you will always have two reserved network addrs: the broadcast addr and the network addr)
2^3 = 8 (8 - 2 = 6 => 6 usable subnetworks)
2^4 = 16 (16 - 2 = 14 => 14 subnetworks - this is what u want)

Therefore you will have to use 4 bits for the netowrk addr
what this means is that your network mask will be something like:

1. 255.[1111 0000].0.0 = 255.240.0.0 (if you are subnetting a class A addr) / here u will have 20 bits for hosts (2^20 - 2 hosts / per subnet)
2. 255.255.[1111 0000].0 = 255.255.240.0 (if you are subnetting a class B addr) / here u have 12 bits for hosts
3. 25.255.255.[1111 0000]  = 255.255.255.240 (in case you are subnetting a class C addr) / here u have 4 bits for hosts

This is it! Basically!!!

On some configurations you might be able to use what is called the "subnet zero" subnetwork which for a cisco router is configured using the "ip subnet zero" command. ... but this is another "area" ...

;)
Cheers.
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