I've recently been studying the fundamentals on IPv6, but there are some things that I don't quite understand about how the addressing is structured.
I know that link local addresses start with FE80, unique local addresses start with FC00 and global unicast addresses start with 2001 for example. Also from what I've seen, most addresses use the /64, sometimes accompanied by EUI-64.
What I don't understand is the slash notation ranges with some of the address types. For example:
Global Unicast
2000::/3
Link Local
FE80::/10
Unique Local
FC00::/7
With the above three address types for example, could someone please explain to me what the slash notations indicate? I can't seem to find a proper explanation for this anywhere.
For the Global Unicast address for example, I've mostly seen 2001:0000 etc etc addresses. Does the notation mean the most I can go up to is 2003 as it's a /3?The same with the Link Local and Unique Local. The slash notations just don't make sense to me, and the books just don't seem to bring any logic to the table. I'm more than likely way off with my assumptions here, so some clarity would be good.
I'd really like to understand this, rather than just assigning 2001:0000 etc etc Global Unicast addresses, without truly understanding why I'm doing it.
Thanks in advance.
Best Answer
The slash notation is another way of writing the subnet mask. It works the same for IPv4 and IPv6.
The number /3 indicates the number of consecutive 1's in the mask. Since the mask is the same size as the address, that means that for IPv6, the subnet mask is three 1's followed by 125 0's (3+125=128 bits).
For an IPv4 address it means three 1's followed by 29 0's (3+29=32 bits). It can also be written as 192.0.0.0.