IPv6 question

Hello, I was wondering if someone could explain to me the ipv6 address /# meaning. When an address says:

2000::/3 or

FE80::/10

what does the /number signify. I keep reading the CCNA routing and Switch guide I have and it's not clear what this number signifies. I looked at a couple videos on Youtube and they really don't clear up my confusion.

Thanks.

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Comments

PCTechLinc

Subnetting in IPv6 is a bit different to understand than IPv4, since the first 64 bits are ALWAYS designated for the network portion.

That being said, in your first example above, the prefix 2000::/3 means that the first 3 bits MUST be the same in order for the rest of the prefix to be considered as part of the same IPv6 subnet. If we break apart the hex digit 2, that gives us 0010. The /3 prefix says that it can be 0010 or 0011, which would be hex digit 2 or 3. SO, any prefix starting with the hex digit 2 or 3 would be on the same subnet. It gets a LITTLE more complicated as you "subnet" deeper, but with a little practice, it gets easier to understand.

The second example, FE80::/10, that means the first 10 bits need to stay the same. That means that the first hex digit needs to be F, and break apart the second digit E, and you get 1110. The first two digits have to be 11, so anything after would be a part of the same subnet. That means that you can have 1100 (C), 1101 (D), 1110 (E), or 1111 (F).

I really hope that makes sense.

MAC_Addy

2000/3 is the global unicast address range. - First 3 bits.

FE80::/10 is the link-local. - First 10 bits.

It just shows you what the shortened version of the IPv6 address looks like.

TechGromit

PCTechLinc wrote: »

The second example, FE80::/10

So with /10, 1111 1110 01xx must always be the same? but the other bits can be anything I want? That would make FE9x (0101), FEAx (0110), and FEBx (0111), part of the same IPv6 subnet?

PCTechLinc

Oops, you corrected my mistake. I didn't make the bits go far enough; they are supposed to go into the 3rd character. You are correct in your last sentence.

TechGromit

PCTechLinc wrote: »

Oops, you corrected my mistake. I didn't make the bits go far enough; they are supposed to go into the 3rd character. You are correct in your last sentence.

Thanks, this isn't adequately explained in my book, I have two other books at home, but I just assumed the 1050 page bible I have at work would be more than sufficient to explain everything I need to know about the CCNA.