IPv6 Addresses.....

---

Hi Guys,

Have finished the online video's in preparation for my A+ exams and am doing extra study as well as reading my notes and doing lots of tests as want to smash the exams when I sit them; however, am having a hard time trying to get my head around IPv6 when it comes to using the "/" after an address.

I understand that in IPv4 if you use something like 192.168.0.1/16 it means that 192.168 is the network portion and 0.1 is the host (it's the equivalent of a subnet mask of 255.255.0.0) That I'm clear on. I'm also ok with the fact you can use non-standard subnet masks (adjacent 1's in binary) so you could see 255.128.0.0 or /9 after the IP. So I can see a clear split between the network part and the host part. However, from what I'm reading here IPv6 doesn't use a subnet mask but the same convention for stating the network length holds true. A few examples of what I'm looking at are:

2001:db8:3c4d:12::56ab/48 - ok with (see below)
2000::/3 Global unicast address range for use on the Internet?
FC00::/7 Unique local unicast address range?
FE80::/10 Link local unicast range?
FF00::/8 Multicast range?

I understand that :: means add in "0000" between colons until the address is 8 fields in length (128 bits) and you add back in any leading zero's but what I can't get my head around is if each field is 16 bits and theirs four values which make up a field (0-F) then each value is 4 bits. The first address seems to work if I'm doing it right? The address 'rebuilt' is;

2001:0db8:3c4d:0012:0000:0000:1234:56ab/48

So the interface ID/host portion is 000056ab (last three fields - 48bits). However, I don't seem to be able to work out the other examples using my logic.

In second example:

2000:0000:0000:0000:0000:0000:0000:0000/3

What's the 3?? I know /16 would be "0000" (last field or 16bits)

Do you have to convert them to binary and then do the /x bit? Maybe this is a bit advanced and may be covered on CompTIA network plus? If not, can you try and explain it so I'm a little less muddled please ? Thanks guys and hope I've explained this well enough

@Andrew-Gaskell Great questions, and I do feel that these topics go well beyond A+ and even Network+, however that being said, what is important for the exam is to be able to identify the types of addresses there are:

Global Unicast
Unique Local
Link Local
Loopback

The bits that you are mentioning are the bits are the bits that are reserved by ICANN as a part of the standard. The slash notation designation, just like CIDR notation denotes the network prefix identifier ( just like a network ID in IPv4).