When they write a slash followed by a number after an IP address, what does that mean?
The part after the slash is how many subnet mask bits to use. Since the use of classless routing you use slash instead of saying class A or B whatever. Example:
192.168.1.1/24 is 192.168.1.1 255.255.255.0
255.255.255.0
is using 24
of the 32 bits
to create the subnet.
in binary it looks like this:
11111111.11111111.11111111.00000000
so a /30
would look like:
255.255.255.252 or in binary
11111111.11111111.11111111.11111100
the remaing 00 is for hosts; the 1's are the network.