Easy Question, newbie...

M_Boyd

Hey everyone

I started a class in CCNA a week ago - on one of the first modules quiz using a subnet mask of 255.255.255.240

Now converting into binary 240

128 64 32 16 8 4 2 1

1 1 1 1 0 0 0 0

240-128=112-64=48-32=16-16=0

= 11110000

The amount left is 1+2+4+8 = 15

Now the question asked how many usable class C networks are created with this mask....

The answer is 14 - now why is that ????

Webmaster

4 bits allow for 16 different values (including the zero) minus the two according to traditional subnetting (no cidr, no ip subnet-zero)= 14 usable network addresses.

M_Boyd

Webmaster wrote:

(no cidr, no ip subnet-zero)

Questions

What does CIDR stand for ?

perhaps you could elaborate on why these aren't used.... I have a clue but would like comfirmation....

M_Boyd

its ok found a big tutorial on it and found my answers (and then some)