[BNM] .htaccess question / blocking IP range

[Richard Grimwood]

Jonathan Hirsch wrote:
>> http://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing
> 
> I think I'm going to have to read that a few times to get my head  
> round it ;-)
> 
> Thanks for the help everyone, anyway.
> 
> Cheers,
> 
> Jon
/32 means one ip address
/31 means 2
/30 means 4
/29 means 8
/28 means 16

The reason being that there are 32 binary digits to an ip address. 
Subnets allocated by providers are always 2 to the power something. It 
makes the maths of routing easier.

Because of the requirement to identify a subnet that isn't a single ip 
address which takes the 1st address in any subnet and provide a 
broadcast address which takes the last ip address  a /31 is effectively 
useless.

So when someone refers to a  /20 subnet in you head you subtract 20 from 
32   gives you 12  . This means 2 to power 12 ip addresses = 4096 
contiguous ip address. If you had all the machines on a single lan 
segment then using one gateway-router(one ip address) the subnet address 
and the broadcast address not being assignable you could attach  4093 
uniquely addressable computers.

This explains why if your ISP gives you an 8 ip address subnet ( a /29) 
only 5 are assignable to your servers. And why netmasks which are the 
long hand way of writing '/' notation  in decimal tend to start 
255.255.255 etc. After about year of doing this you will just know that 
a 64 ip address  subnet has a mask of 255.255.255.192