IPv6

Member Posts: 103
Hey Everyone,
Was taking a practice quiz for the CEH and I came across this question:

Which of the following is a valid IPv6 IP address?

12ED:20:63E2:21BA:0: 3:FACE:F25I

12ED:0:63E2:21BA:0: 3:FACE:F25F

12ED::63E2:21BA:: 3:FACE:F25F

12ED:2F33:63E2:CB24:2D73:FACE:F25F

I have searched a little to get a better understanding of how to tell what is considered valid and im having a little trouble. Could someone help point me in the right direction?

Thanks!

• Member Posts: 4,024
Well the first one is out because of the I in the address. ipv6 is hex based, which is base 16, so all numbers will be 0-9 or A - F. I comes after F, so it's invalid

The third one is out because of the double ::. :: basically means everything between the last digit and the following digit is all 0's, it's a shortcut notation, but it can only occur once within any address.

The fourth one is out because it doesn't have enough bits. Each digit is 4 bits, so each block seperated by a colon is 16 bits. An ipv6 address is 128 bits. The last one has 7 blocks of 16 bits, so it's short 16 bits of being a full address.

That leaves the second one. I'm assuming the space between the : and the 3 is an artifact of your copy/paste, and isn't there in the real example. Spaces aren't valid in ipv6 addresses. ip ipv6, you can omit leading 0's, and identify a single block with just a 0 if you're not using the :: compression method, so the 2nd address has the proper number of bits, doesn't violate the compression rule, and doesn't have any invalid digits.

12ED:0:63E2:21BA:0:3:FACE:F25F would be the proper way to represent the address
• Member Posts: 941 ■■■■■■■□□□
Agent47 wrote: »
Could someone help point me in the right direction?
Do you know the format of IPv6 addresses?
If not, have a quick look here:
IPv6 - Wikipedia, the free encyclopedia
Agent47 wrote: »
12ED:20:63E2:21BA:0: 3:FACE:F25I
Invalid. The address is in Hex, so it cannot have "I" (last symbol)
Agent47 wrote: »
12ED:0:63E2:21BA:0: 3:FACE:F25F
Valid. 8 groups of 16-bit Hex, single colons.
Agent47 wrote: »
12ED::63E2:21BA:: 3:FACE:F25F
Invalid. Only a single double-colon may appear (otherwise it's impossible to establish how many zeroes were omitted in each)
Agent47 wrote: »
12ED:2F33:63E2:CB24:2D73:FACE:F25F
Invalid. Has only 7 groups of 16-bit Hex.
“You don’t become great by trying to be great. You become great by wanting to do something, and then doing it so hard that you become great in the process.” (c) xkcd #896

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• Banned Posts: 827
If you register for Hurricane Electric's IPv6 free certification program, it will give you a little hands on experience working with IPv6. Not really a reputable (or verifiable) certification, but its worth doing for a decent learning experience. Hurricane Electric IPv6 Certification
• Member Posts: 103
Thank you guys so much for your help, I really appreciate it. I'm trying to practice so that I have a better understanding of it and this definitely helps! Hutch, I will do some research on the program as well.