CCNA 200-301: What is the difference between RFC 1918 Private Space and IPv4 Address Classes (based of first octect value)?

[Mj LUITEL]

Hi,

What is the difference between the below two tables classes? Which tables class do i follow when calculating classful addressing/Subnet?

Which of the following are not valid Class B network IDs?
a. 130.0.0.0
b. 191.255.0.0
c. 128.0.0.0
d.150.255.0.0
e.All are valid Class B network IDs.

There could be different answer if i use above two tables?

[Martin L · Accepted solution]

No, there could not be different answer if i use above two tables. Notice 2nd table still follows rules of 1st one. you must memorize both tables but use 1st one when you are calculating classful addressing/Subnet, subnetting.

RFC 1918 is called Private reserved IP ranges for your private use like in your home lab or local LANs at your businesses; those are not public IPs. they will never be found on the Internet nor you can get them thru ISP.  ISP simply blocks those private ranges from going to public domain. 

because of shortages of Public IPs, you will get 1 or small range of Public IPs. But you have 100 PCs that want to go on the Internet.  How to share 1 Public IP with 100 PCs?  you use Private range and do NAT/PAT at the border router.  for example, you will get 1 Public IPs, like 11.0.0.1.  You can set up internal network with 192.168.0.0 /24 range. Now, you can enable NAT/PAT to translate Private into Public IP.

Regards, ML
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[Martin L]

and the answer is e - all are valid Class B network IDs.

[Mj LUITEL]

Thanks