How to subnet IPv6

2 Networks

Netmasks are multiples of 4 (0, 4, 8, 12, etc) plus 1;
1, 5, 9, 13, 17, 21, 25, 29, 33, 37, 41, 45, 49, 53, 58, 61.

1st network address ends in x::/Mask
2nd network address ends in 8x::/Mask
Where 'x' is empty, '0', '00' or '000'.

Examples
1st network2nd network
 2001:db8::/33 2001:db8:8000::/33
 2001:db8:1000::/37 2001:db8:1800::/37
 2001:db8:1200::/41 2001:db8:1280::/41
 2001:db8:1230::/45 2001:db8:1238::/45

A /45 has the same number of IPv6 addresses as eight /48s.

4 Networks

Netmasks are multiples of 4 plus 2;
2, 6, 10, 14, 18, 22, 26, 30, 34, 38, 42, 46, 50, 54, 58, 62.

1st network address ends in x::/Mask
2nd network address ends in 4x::/Mask
3rd network address ends in 8x::/Mask
4th network address ends in cx::/Mask
Where 'x' is empty, '0', '00' or '000'.

Examples
1st network 2nd network 3rd network 4th network
 2001:db8::/34  2001:db8:4000::/34  2001:db8:8000::/34  2001:db8:c000::/34
 2001:db8:1000::/38  2001:db8:1400::/38  2001:db8:1800::/38  2001:db8:1c00::/38
 2001:db8:1200::/42  2001:db8:1240::/42  2001:db8:1280::/42  2001:db8:12c0::/42
 2001:db8:1230::/46  2001:db8:1234::/46  2001:db8:1238::/46  2001:db8:123c::/46

A /46 has the same number of IPv6 addresses as four /48s.

8 Networks

Netmasks are multiples of 4 plus 3;
3, 7, 11, 15, 19, 23, 27, 31, 35, 39, 43, 47, 51, 55, 59, 63.

1st network address ends in x::/Mask
2nd network address ends in 2x::/Mask
3rd network address ends in 4x::/Mask
4th network address ends in 6x::/Mask
5th network address ends in 8x::/Mask
6th network address ends in ax::/Mask
7th network address ends in cx::/Mask
8th network address ends in ex::/Mask
Where 'x' is empty, '0', '00' or '000'.

Examples
1st network 2nd network 3rd network 4th network
 2001:db8::/35  2001:db8:2000::/35  2001:db8:4000::/35  2001:db8:6000::/35
 2001:db8:1000::/39  2001:db8:1200::/39  2001:db8:1400::/39  2001:db8:1600::/39
 2001:db8:1200::/43  2001:db8:1220::/43  2001:db8:1240::/43  2001:db8:1260::/43
 2001:db8:1230::/47  2001:db8:1232::/47  2001:db8:1234::/47  2001:db8:1236::/47
5th network 6th network 7th network 8th network
 2001:db8:8000::/35  2001:db8:a000::/35  2001:db8:c000::/35  2001:db8:e000::/35
 2001:db8:1800::/39  2001:db8:1a00::/39  2001:db8:1c00::/39  2001:db8:1e00::/39
 2001:db8:1280::/43  2001:db8:12a0::/43  2001:db8:12c0::/43  2001:db8:12e0::/43
 2001:db8:1238::/47  2001:db8:123a::/47  2001:db8:123c::/47  2001:db8:123e::/47

A /47 has the same number of IPv6 addresses as two /48s.

16 Networks

Netmasks are multiples of 4;
4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48, 52, 56, 60.
Network address ends in x::/Mask, where 'x' is empty, '0', '00' or '000'.

2001:db8::/32
2001:db8:1000:/36
2001:db8:1200:/40
2001:db8:1230::/44

A /44 has the same number of IPv6 addresses as 16 /48s.