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uk.comp.home-networking (UK home networking) (uk.comp.home-networking) Discussion of all aspects of computer networking in the home, regardless of the platforms, software, topologies and protocols used. Examples of topics include recommendations for hardware or suppliers (e.g. NICs and cabling), protocols, servers, and specific network software. Advertising is not allowed.

Technical question of networks



 
 
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  #1  
Old August 30th 06, 07:54 PM posted to uk.comp.home-networking
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Default Technical question of networks

- well for me anyway.

Given I understand basic 8 octlet network addressing and subnets; can
someone clarify the notation w.x.y.z/a for me. I've determined 'a' as a
subnet number (does /16 gives me the whole range w.x.y.??) but what is the
basis; is it always 0 OR a or is it in segments? I wonder if this notation
is older than describing subnets themselves or a modern equivalent. Taa.

  #2  
Old August 30th 06, 08:22 PM posted to uk.comp.home-networking
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Default Technical question of networks

"William4" wrote in message
...
- well for me anyway.

Given I understand basic 8 octlet network addressing and subnets; can
someone clarify the notation w.x.y.z/a for me. I've determined 'a' as a
subnet number (does /16 gives me the whole range w.x.y.??) but what is the
basis; is it always 0 OR a or is it in segments?


Written in binary, a subnet mask is n ones followed by 32-n zeros.
Therefore, a subnet mask can be specified by simply stating n, the number of
ones. That is what the notation is: a concise way to describe a
(sub)network. For instance, 192.168.0.0/255.255.255.0 means the same as
192.168.0.0/24.

Alex


  #3  
Old August 30th 06, 09:47 PM posted to uk.comp.home-networking
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Default Technical question of networks

Alex Fraser wrote:
"William4" wrote in message
...
- well for me anyway.

Given I understand basic 8 octlet network addressing and subnets; can
someone clarify the notation w.x.y.z/a for me. I've determined 'a'
as a subnet number (does /16 gives me the whole range w.x.y.??) but
what is the basis; is it always 0 OR a or is it in segments?


Written in binary, a subnet mask is n ones followed by 32-n zeros.
Therefore, a subnet mask can be specified by simply stating n, the
number of ones. That is what the notation is: a concise way to
describe a (sub)network. For instance, 192.168.0.0/255.255.255.0
means the same as 192.168.0.0/24.

Yes.
The common subnet masks are
24 bit - class c - 255 available addresses
16 bit - class b - 65 thousand odd addresses
8 bit - class a - 16 million odd addresses per network

--
Alex

Piece by piece the penguins have taken my sanity
www.drzoidberg.co.uk www.ebayfaq.co.uk


  #4  
Old August 30th 06, 09:58 PM posted to uk.comp.home-networking
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Default Technical question of networks


"Alex Fraser" wrote in message
...
"William4" wrote in message
...
- well for me anyway.

Given I understand basic 8 octlet network addressing and subnets; can
someone clarify the notation w.x.y.z/a for me. I've determined 'a' as a
subnet number (does /16 gives me the whole range w.x.y.??) but what is
the
basis; is it always 0 OR a or is it in segments?


Written in binary, a subnet mask is n ones followed by 32-n zeros.
Therefore, a subnet mask can be specified by simply stating n, the number
of ones. That is what the notation is: a concise way to describe a
(sub)network. For instance, 192.168.0.0/255.255.255.0 means the same as
192.168.0.0/24.

Alex

Thanks, I think I was working this backwards (from the lsb). So anything/0
is the whole caboodle and anything/31 is just two address then? - will they
always be .0 & .1 or can you have w.x.y.120/31 for .121 & .121 ?

  #5  
Old August 31st 06, 05:38 AM posted to uk.comp.home-networking
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Default Technical question of networks

"William4" wrote in message
...
"Alex Fraser" wrote in message
...

[snip]
That is what the notation is: a concise way to describe a (sub)network.
For instance, 192.168.0.0/255.255.255.0 means the same as 192.168.0.0/24.


Thanks, I think I was working this backwards (from the lsb). So
anything/0 is the whole caboodle and anything/31 is just two address then?
- will they always be .0 & .1 or can you have w.x.y.120/31 for .121
& .121 ?


A /30 is the smallest useful subnet you can have, but yes, you could have
w.x.y.120/30 for w.x.y.120-123. However, the address ANDed with the
complement of the subnet mask must be zero. So, for example, w.x.y.121/30 is
not valid (use a monospaced font):

mask = /30 (255.255.255.252) = 11111111 11111111 11111111 11111100
~mask = 00000000 00000000 00000000 00000011
address = w.x.y.121 = wwwwwwww xxxxxxxx yyyyyyyy 01111001
address & ~mask = 00000000 00000000 00000000 00000001

This is equivalent to saying that for /30, the last octet of the address
must be a multiple of four. For /29, it must be a multiple of eight, and so
on. For /24 down to /17, similar applies to the third octet and the last
octet must be zero, eg for /22, the third octet must be a multiple of four.
You can probably guess the rest .

Alex


 




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