In part "2. The Bits and Bytes of Computer Networking" → "Week 6" → "5. IPv6" → "3. IPv6 and IPv4 Harmony" of the Google IT Support Professional Certificate online course, the topic is IPv4-mapped address space.

One minute into the video, this equivalence between an IPv4 and an IPv6 address is shown: = 0:0:0:0:0:ffff:d1ad:35a7

It says that IPv4 address maps to the IPv6 address 0:0:0:0:0:ffff:d1ad:35a7.

From how I understand IPv4-to-IPv6 mapping, this doesn't add up: represents this binary number:

11000000 10101000 00000001 00000001

Let's convert this to hexadecimal with bc:

bc <<< "obase=16;ibase=2; 11000000101010000000000100000001"

This results in C0A80101, thus the IPv6 address should be ::ffff:c0a8:0101.

According to the converter at vultr.com, ::ffff:d1ad:35a7 should be, not

Also according to vultr.com, translates to ::ffff:c0a8:0101.

Is this an error in the online course, or is something else going on here?

For some context: I don't intend to complete the course to get a certificate. I'm also not aware of any homework that has students convert IP addresses from v4 to v6. I wanted to get confirmation or repudiation of my understanding of IPv4-mapped address space.

  • 4
    Yes, they are wrong. Also, v4 mapped addresses are all but dead in the real world. (you'll never see this on the wire. Internally, applications that can support both v4 and v6 will make v6 api calls with this sort of address to tell the stack to use v4.)
    – Ricky
    Nov 24, 2020 at 15:30
  • 2
    One reason that all "education, certification, or homework" questions are explicitly off-topic here is that there are many errors in course content, and the correct answer is the wrong answer for the course.
    – Ron Maupin
    Nov 24, 2020 at 16:42
  • As an aspiring network professional you should be able to convert decimal in hex and vice versa in your head... ;-)
    – Zac67
    Nov 24, 2020 at 18:33
  • @RonMaupin: I understand. I've added some context to the question to clarify that I'm not looking for the answer to some homework but the truth. Nov 25, 2020 at 12:43

1 Answer 1


Google's course is wrong.

As you correctly discovered, IPv4 address does not map to the IPv6 address 0:0:0:0:0:ffff:d1ad:35a7.

That said, it's possible that you will be marked "wrong" on the coursework's test if you claim otherwise. But know that you are correct, and Google is (once again) wrong.

  • When you say "(once again) wrong", what other errors do you refer to? There's another (more glaring) slip in the same Google course, chapter "History of Computing": The instructor says that Alan Turing helped develop the Enigma machine. Which would make Turing a Nazi^^. Nov 25, 2020 at 12:41
  • @MatthiasBraun That's funny!
    – Ron Trunk
    Nov 25, 2020 at 13:42

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