How do you differentiate public and private IP addresses?

I am spending my summer studying for the CCNA exams and one of the things that has me stumped is private and public IP addresses. Here is a question as an example...

Which two of the following are private IP addresses?

A.) 12.0.0.1
B.) 168.172.19.39
C.) 172.20.14.36
D.) 172.33.194.30
E.) 192.168.24.43

I understand network classes (class A, B and C), and some of the different kinds of addresses (Broadcast, Unicast and Multicast) but I cannot find an explanation for public and private IP addresses.

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Comments

E Double U

C & E are the private addresses.

RFC 1918 private ranges:
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255

http://en.wikipedia.org/wiki/Private_network

jvrlopez

You just have to memorize the ranges.

cyberguypr

Take a peek at RFC 1918 - Address Allocation for Private Internets

https://tools.ietf.org/html/rfc1918

theodoxa

jvrlopez wrote: »

You just have to memorize the ranges.

10.0.0.0/8
172.16.0.0/12
192.168.0.0/16

You just have to memorize these 3 networks and possibly 169.254.0.0/16, which is used for APIPA (Automatic Private IP Addressing).

d4nz1g

224.0.0.0 through 239.255.255.255 for multicast, also.

theodoxa

d4nz1g wrote: »

224.0.0.0 through 239.255.255.255 for multicast, also.

Class D (Multicast) -- 224.0.0.0/4
Class E ("Experimental") -- 240.0.0.0/4

[RANT] The sad thing is that half a billion IPv4 addresses were wasted on Class D (Multicast) and Class E (Experimental). That's 1/8th of the total address space. Very nearsighted of the folks who came up with the address classes. They didn't need anywhere near 256 million Multicast addresses and the experimental range (another 256 million addresses) sits largely unused while some regions exhaust their supply of IPv4 Addresses. [/RANT]

Zefrik

Thanks for the help!