IPv6 Subnets

[John Blakley]

All,

I understand the / notation for masking, but here's what I don't think I have a full grasp on.

Suppose we have a /64 network of 2001:1000:1000:1000::/64. That leaves 2^64 for the amount of hosts or allows for breaking this block further into smaller networks. Now here's where I don't understand. I've seen examples online about /65, /66, /68, /69.

So for example:

2001:1000:1000:1000:C000::/69

How do the individual bits break up within the block?

I understand if the above was /80, but it doesn't seem like every example that I've seen is consistent with even 16 bit calculations (or even 8 bits for that matter).

Thanks!

[andrew.prince]

I tend not to think about it to much to be honest, reading the RFC's I tend to agree with the general thought that there are so many IPV6 addresses available.  When you are allocated a /48 to then subnet the next 16 bits = 65,000 subnet networks each with 64 bits for host addressing which gives you 18,446,744,073,709,551,616 addresses per subnet - phew!

I think the major headache with subnetting would be host addressing, and I am glad there is stateless autoconfig......saying that I did find a good site a while ago that did shed some light, and can do much of the work fo you.

http://www.gestioip.net/cgi-bin/subnet_calculator.cgi

HTH>