[9] [svlug] IPV4 Subnetting

Kevin Smathers kevin at ank.com
Fri May 23 14:39:47 PDT 2003

What do you want to know?  Subnetting is just picking how many bits
you want to allocate to machines within a LAN.  At the boundary of 
the LAN, the routers will decide whether to forward packets outside
based on whether the left half of the IP address matches the local
area networking IP address to the number of bits in the net mask.

Change the number of bits in the mask, and you change the number of
bits that are considered by the router to be internal addresses 
rather than external addresses.

The only other thing to know is that there are a two reserved addresses
on each LAN regardless of how many bits are allocated to it.  The .0
address (where all bits to the right of the mask are zeroes) is the
Network address.  The .255 address (where all bits to the right of 
the mask are 1's) is the broadcast address.  No machines can be 
assigned to either of those two addresses.

In general:

   If a network is subnetted with N bits, N>8 if class A, N>16 if
   class B, N>24 if class C; then:

       2^(32-N) - 2    is the number of valid machine addresses on each subnet
       2^(N-classbits) is the number of subnets.

Hope that helps,

On Fri, May 23, 2003 at 03:39:01PM -0400, Penguin Power wrote:
> I am trying to get ccna certified and im trying to understand the concepts
> of subnetting class A,B,C networks to divide the network into segments. I
> am trying to figure out what the easiest method of understanding it. I am stumped, is there
> anybody out there who has a very easy way of doing it? I need a good
> teacher :(
> _______________________________________________
> svlug mailing list
> svlug at lists.svlug.org
> http://lists.svlug.org/lists/listinfo/svlug

Look ma, no threads[1]. 
[1] BitTorrent in C is http://www.sf.net/projects/libbt
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