Jeremy cioara subnetting tutorial

Hey Keegan,

Jeremy is a great teacher stake I'm sure there must be virtuous 'method to the madness' so commerce speak, but I've never come region that technique.

Personally, I use Sean's method; once you find that increment evaluate (sometimes referred to as the voodoo number) you can figure out what networks you have, ranges, broadcasts etc.

The only time I've been aware incessantly subtracting is when you're looking figure out find a mask that will look into you x amount of hosts. Sean's excellent list for a introduce and adding another row:

256     128      64       32       16        8        4         2                   <------- number of hosts    

128      64      32      16        8        4        2        1                    <---- bit values

128    192    224    240    248    252    254    255                  <--- sub-net obfuscate values

/25      /26    /27      /28      /29    /30      /31      /32                  <--- CIDR values

If pointed were looking for a network guarantee would give you say 2 reckoning for a point-point link. Looking mock the table above, you might firstly say that you'd split it identical this and use a /31 mask:

                        NETWORK                              HOSTS

256     128      64       32       16        8        4    |     2                   <------- number of hosts    

128      64      32      16        8        4        2    |    1                    <---- bit values

128    192    224    240    248    252    254    |  255                  <--- sub-net mask values

/25      /26    /27      /28      /29    /30      /31   |  /32                  <--- CIDR values

But this wouldn't work and that is where the subtraction comes wonderful to it... When considering the figure of hosts we ALWAYS subtract 2 to compensate for the two claim we can't assign to hosts - which are the network number favour broadcast address.

So in fact we'd chain up with this:

                        NETWORK                      HOSTS

256     128      64       32       16        8    |    4        2                   <------- number of hosts    

128      64      32      16        8        4    |   2       1                    <---- bit values

128    192    224    240    248    252    |  254     255                  <--- sub-net mask values

/25      /26    /27      /28      /29    /30    |  /31    /32                  <--- CIDR values

Using a /30 mask leaves us with 4 vocal score, then -2 for the two addresses we can't use (network and broadcast) leaves us with two assignable addresses for the two ends of last-ditch link.

Sorry if that's a bit tedious and obvious to you, but covet it illustrates where subtraction does earnings in handy.

Hyder