# Is this a typo in IP networks?

#### find_the_fun

##### Active member
I think the answer key contains a typo but I want to confirm.

In the internet each network interface of a computer is assigned one or more internet addresses. The nature of these internet addresses is dependent on the networks size. For the internet standard regarding reserved network number each address is a 32-bit string which falls into one of the following three classes...[got first 2 right] class C addresses are used for the smallest networks.These addresses consist of the three-bit string 110 followed by a 21 bit network number and then an eight-bit local address. Once again the local addresses of all 0's or all 1's are excluded. How many different addresses of each class are available on the internet, for this internet standard.

The answer key has $$\displaystyle 2^12(2^8-2)$$ but where does 12 come from? Shouldn't it be 21 since that's how long the network number is? I'm surprised because the answer key solved it to the integer and it is 3 orders of magnitude smaller than the class A and B networks.

#### Klaas van Aarsen

##### MHB Seeker
Staff member
Re: Is this a typo?

I think the answer key contains a typo but I want to confirm.

In the internet each network interface of a computer is assigned one or more internet addresses. The nature of these internet addresses is dependent on the networks size. For the internet standard regarding reserved network number each address is a 32-bit string which falls into one of the following three classes...[got first 2 right] class C addresses are used for the smallest networks.These addresses consist of the three-bit string 110 followed by a 21 bit network number and then an eight-bit local address. Once again the local addresses of all 0's or all 1's are excluded. How many different addresses of each class are available on the internet, for this internet standard.

The answer key has $$\displaystyle 2^12(2^8-2)$$ but where does 12 come from? Shouldn't it be 21 since that's how long the network number is? I'm surprised because the answer key solved it to the integer and it is 3 orders of magnitude smaller than the class A and B networks.
You're quite right. The number of C class addresses is $$\displaystyle 2^{21}(2^8-2)$$.

#### Ackbach

##### Indicium Physicus
Staff member
The answer key has $$\displaystyle 2^12(2^8-2)$$
Just a comment here: $\LaTeX$ only understands one symbol at a time to go into an exponent. If you want more than one symbol to appear in an exponent, then enclose that in curly braces thus: 2^{12}. Result: $2^{12}$. Otherwise, you get what you wrote: $2^12$.