Classless Inter-Domain Routing (CIDR)

Question 1

Classless Inter-Domain Routing (CIDR).

Answer 1

It’s basically the method that Internet service providers (ISPs) use to allocate an amount of addresses to a company, a home—a customer. They provide addresses in a certain block size.

Question 2

What does the slash notation (/) mean?

Answer 2

The slash notation (/) means how many bits are turned on (1s).

Question 3

What is the largest subnet mask available?

Answer 3

/30. 
Obviously, the maximum could only be /32 because a byte is 8 bits and there are 4 bytes in an IP address: 4 × 8 = 32. But keep in mind that the largest subnet mask available (regardless of the class of address) can only be a /30 because you’ve got to keep at least 2 bits for host bits.

Question 4

What is the default subnet mask of Class A?

Answer 4

Class A default subnet mask, which is 255.0.0.0. This means that the first byte of the subnet mask is all ones (1s), or 11111111. When referring to a slash notation, you need to count all the 1s bits to figure out your mask. The 255.0.0.0 is considered a /8 because it has 8 bits that are 1s—that is, 8 bits that are turned on.