[c-nsp] ipv6 cheat sheet

[Steve Bertrand]

Paul G. Timmins wrote:
> You can subnet ipv6 with your eyeballs, just add or subtract 4 from the
> prefix length for every character you move to the left or right.
> 
> 1234:1234:1234:1234::/64
> 1234:1234:1234:123X::/60
> 1234:1234:1234:12XX::/56
> 1234:1234:1234:1XXX::/52
> 1234:1234:1234::/48

ipv6gen is handy for visualizing different possible addressing scenarios:

% ipv6gen -s 4 -l 2607:f118::/32 48

2607:F118:0000::/48
2607:F118:2000::/48
2607:F118:1000::/48
2607:F118:3000::/48
2607:F118:0800::/48
2607:F118:2800::/48

% ipv6gen -s 4 -l 2607:F118:2800::/48 56

2607:F118:2800:0000::/56
2607:F118:2800:2000::/56
2607:F118:2800:1000::/56
2607:F118:2800:3000::/56
2607:F118:2800:0800::/56

% ipv6gen -s 4 -l 2607:F118:0800::/48 64

2607:F118:0800:0000::/64
2607:F118:0800:2000::/64
2607:F118:0800:1000::/64
2607:F118:0800:3000::/64

etc.

Steve