• IPv6, reserved ranges and subnets

Hi,
This question comes after watching Episode 101 of CCENT "Introduction to Routing", but is a general IPv6 question so hopefully it was OK to put it here in the general discussion section.
I ask this not to correct what was said in the episode, but to make sure I understand this properly...
When discussing the IANA IPv6 ranges, specifically the 2000::/3, Don says "This covers anything starting with 20". But, being a /3 range, doesn't that mean this covers anything starting with 2 or 3?
First four bits in binary represent the first hexadecimal digit:
0010 = 2
If the mask is /3, only the first three binary bits are "fixed", therefore the first hexadecimal digit could also be:
0011 = 3
This would also mean that only the first hexadecimal digit is restricted to 2 or 3, the remaining 31 hexadecimal digits (124 bits) could be anything 0 - F, so a network in this range could start 21, 22 ... 3e, 3f, right?
Is this correct, or am I missing something?

• Thank you for pointing that out and you are absolutely correct. When I said that, I didn't mean to imply that 20 was the only thing that it could start with, but that anything with a 20 at the beginning falls within the publicly registered range. If you get a publicly registered address today it will most likely start with 20 since that is the range they are issuing from, but in the future you very well may see all the way through 3f. In hind sight, I can see how that statement was confusing and I should have worded it differently.
Thanks again,
Don Pezet
Host, ITProTV

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