When refering to IP addresses, what does /16, /32 etc. mean?
 

Often times you'll some address spaces defined as 100.100.100.100/16 etc... so what does that /16 /32, /64 etc. mean? i.e. what address space does that define?

these numbers mean how many bits of the IP address you want to keep in the IP address range.

example
123.45.0.0/16 means all ip addresses from 123.45.0.0 to 123.45.255.255
123.45.67.0/24 means all ip addresses from 123.45.67.0 to 123.45.67.255
123.45.67.89/32 means just this IP address.

yup

thats how dailercompanies give access to certain server in their htaccess, range 0-16 for instance

i know i didn't ask for this info but i can certainly say thanks! i was wondering the same thing myself!

Good info for sure! Thanks!

Interesting... So if I had an adress defined like this:

123.45.67.128/28

That would mean 16 addresses from 123.45.67.128 to 123.45.67.143??

Bump....

i think so

You might want to take a look here: http://www.ralphb.net/IPSubnet/class_a.html
A /28 is indeed 16 addresses in total; 14 usable with 1 network and 1 broadcast address.

Unless you're using a funky ethernet switch that pretends to be on a /24 subnet so you can use IPs that would have been reserved for network and broadcast :)

thats cool, i didnt know that