Help:Range blocks/IPv6

See Help:Range blocks for the main page on rangeblocking, and for IPv4. IPv6 rangeblocks are subject to $wgBlockCIDRLimit, which by default allows rangeblocks of up to /64 in size (before MediaWiki 1.20wmf5, which changes the default to /19).

Technical explanation
IPv6 addresses are each 128 bits long. Because each digit in an IPv6 address can have 16 different values (from 0 to 15), each digit represents the overall value of 4 bits (one nibble), with 32 digits total. As with IPv4, CIDR notation describes ranges in terms of a common prefix of bits. For example 2001:db8::/32 means that the range described has the first 32 bits set to the binary digits 00100000000000010000110110101000. Also like IPv4, MediaWiki implements IPv6 rangeblocks using CIDR notation.

Collateral damage
The best guideline for assessing collateral damage for an IPv6 rangeblock is to check the WHOIS and actual amount of activity from the range. A single /64 subnet can represent anything from a single user to hundreds or even thousands of users; simply counting addresses may not be accurate enough, unlike in IPv4.

How to calculate an IPv6 CIDR range

 * 1) Find the common prefix - that is, the string of digits shared by all of your addresses.
 * 2) Expand the common prefix completely (including redundant zeros), and multiply the total number of digits by 4 - that's the size of your common prefix.
 * 3) Use the table below, and add the specified number to your prefix size (this is your CIDR suffix, the number of bits common to all addresses in the range). Append the specified digit to the common prefix you found above. Complete the group of four digits with zeros if necessary.
 * 4) The CIDR is then [common prefix (with additional digit as specified by table below, followed by zeros as necessary to keep the group of four digits complete)]/[common prefix length (plus 1,2, or 3 as specified by the table below)].

Prefix modification table
Example: If your prefix is 2001:db8:abcd:: (completely expanded to 2001:0db8:abcd::), and you have addresses like 2001:db8:abcd:9:abe:: and 2001:db8:abcd:a::, you'd use the entry saying that the digits after your prefix match 8-b, append 8 to the prefix, and add 2 to your common prefix's size. This would generate 2001:db8:abcd:8000::/50.

Range table
The color-coding is approximate, and there will be overlaps. Key