Re: [cobalt-users] OFF TOPIC - CHINESE CYBER ATTACK

["Rodolfo J. Paiz" <rpaiz@xxxxxxxxxxxxxx>]

At 4/20/01 02:06 PM -0400, you wrote:
> Sorry to keep this thread alive, but could you clarify please? I always start
> going dyslectic when dealing with netmasks.
>
> If one wanted to block say for example the range : 202.93.0.0 - 202.93.3.255,
> how would that be inputted? Would it be the same?
>
>
> 202.93.0.0/255.255.0.0

No.

IP numbers and masks work like this:

Decimal:      202   .    93    .     0    .     0
Binary:    11001010 . 01011101 . 00000000 . 00000000

Netmasks work like this:

Decimal:      255   .   255    .    0     .    0
Binary:    11111111 . 11111111 . 00000000 . 00000000

Those binary bits that have 1's in them denote the network; the remaining 
bits name hosts within the network. You'll note that there are exactly 16 
ones (1's) in this netmask, which is why this is equivalent to writing 
202.93.0.0/16.

In this way, 202.93.0.0/255.255.0.0 extends from 202.93.0.0 to 
202.93.255.255 (the bits describing the network are always constant -- 
that's why it's the same network).

To block from 202.93.0.0 to 202.93.3.255, I think you can block:

202.93.0.0/24
202.93.1.0/24
202.93.2.0/24
202.93.3.0/24

or

202.93.0.0/23
202.93.2.0/23

or

202.93.0.0/22

As far as I know, these three are equivalent in terms of describing the IP 
addresses. Note that these are *not* the same networks... hopefully the 
previous explanation should show you why.


--
Rodolfo J. Paiz
rpaiz@xxxxxxxxxxxxxx