Hello Neil!
On Fri 09 Jan 1998 at 06:51 you wrote the following to Mike Bilow:
 MB>> 10.0.0.0        -   10.255.255.255  (10/8 prefix)
 MB>> 172.16.0.0      -   172.31.255.255  (172.16/12 prefix)
 MB>> 192.168.0.0     -   192.168.255.255 (192.168/16 prefix)
 NC> OK Mike, I have to admit a gaping hole in my knowledge of IP here.
 NC> What is the difference between a class A, B and C address?
 NC> Also, how exactly does subnetting down work out? I know my employer
 NC> has 10.16 addresses on a 255.255.248.0 subnet mask which gives
 NC> 10.16.72.0=10.16.79 on my site and I know it's something to do with
 NC> bitmasks but I start to lose it a bit here which could prove
 NC> embarrasing if anyone asks.
Basically you convert the subnet mask to a binary number, so you get
11111111 11111111 11111000 00000000
The 1's indicate the bits that don't change within the network segment (etc.) 
- the 0 bits are used to indicate the actual machine number. Many networks 
will use 255.255.255.0 to have 254 addresses in the network.
Your network number is
   10   .   16   .   72   .   0
00001010 00010000 01001000 00000000
                       ------------
The underlined portion can then be changed to indicate a machine number - so 
you basically have 11 bits of addressing - i.e 2^11, 2048 addresses (minus 
the broadcast address, etc)
Of course, you don't need to work all this out when assigning IP numbers, 
just assign a number of the form 10.16.(72-79).(0-255), and give out your 
subnet mask of 255.255.248.0 and network address of 10.16.72.0 (for default 
routing)
 Will                                        
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