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Help understanding subnet addressing

Posted on 2007-12-05
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Last Modified: 2010-04-21
Hello -

Sorry is this is a simple request - but I am not a networking person...

I am provided a Subnet address of 10.xx.xx.0/24

Does this mean I can have a host range of 10.xx.xx.0 - 10.xx.xx.254

Thanks
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Question by:newtontech4
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tonux earned 500 total points
ID: 20413910
Hi,
in this subnet, there must be at least one address for the Router (I.e. default Gateway for hosts)
So you have 2^8 adresses, minus 1 for the router. so it's 255 addresses.
By convention the ".0" address is not use for hosts. and the ".255" is used for broadcasting on this subnet.
So if you have a default GW address on ".254" (which is a common convention to) then you have .1 -> .253 addresses available for hosts.

hope this helps
Tonux
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by:Jeff Perry
Jeff Perry earned 500 total points
ID: 20413920
Yes and No

the /24 means your subnet mask is 255.255.255.0 so your Network is 10.xxx.xxx.0 Your first valid host is 10.xxx.xxx.1 and your last valid host is 10.xxx.xxx.10.xxx.xxx.254 with a broadcast address of 10.xxx.xxx.255
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by:Rob Williams
Rob Williams earned 500 total points
ID: 20414181
Some times a "picture" is worth 1000 words, a very useful on-line tool that will outline all of the above in a very clear list is:
http://tstools.co.uk/ipcalc.php

Should you want a better understanding the following site is great:
http://www.learntosubnet.com
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by:Keith Alabaster
Keith Alabaster earned 500 total points
ID: 20415142
Hey Rob - Merry Chrsitmas (or nearly)

Newton, no - it does not mean that <<Does this mean I can have a host range of 10.xx.xx.0 - 10.xx.xx.254>>

Standard IPv4 ip addresses are 32 bits long and split into 4 'octets', each being 8 bits long. IP addresses are broken down into a network portion and a host portion. The subnet mask or bit mask tells you how many of the 32 bits are part of the network and how many can be used as hosts.

In your example of /24, this tells us that the first 24 bits of the ip address given are for the network and the rest are hosts.
so 10.0.0 is the network (3 x 8-bit octets) and the last octet is the host portion (0 - 255 = 256 addresses). You always take 2 off this number as Rob mentions for the Network ID and the broadcast leaving 254 useable start ing at .1 in this example.

Keith
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by:Rob Williams
ID: 20415415
Hi Keith ! Same to you. It's approaching quickly.
For the record that was not my post <G>.  ==>""You always take 2 off this number as Rob mentions "
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by:Keith Alabaster
ID: 20415434
lol - I'm getting old. I'm sure you would have pointed it out though as it is correct :)
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by:Rob Williams
ID: 20415570
I was thinking it. Does that count :-)
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Author Closing Comment

by:newtontech4
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thanks for your help -
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by:Rob Williams
ID: 20415734
Thanks newtontech4.
Cheers !
--Rob
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