Help:Range blocks

Range blocks are blocks applied to a group of IP addresses that prevent them from editing, creating new accounts, sending email through the wiki interface, and other wiki functions. If you check the box to prevent logged-in users from editing from these IP addresses, edits from registered accounts will also be disabled while they are connecting from the blocked range.

To block an IP range from Special:Block, enter the first IP address in the range followed by a forward slash and a Classless Inter-Domain Routing (CIDR) suffix. You should avoid performing range blocks unless you understand what you are doing, or you may end up blocking tens of thousands or even millions of people who are not the problem!

This article mainly discusses IPv4; IPv6 blocks work similarly, but have different implications - see mw:Help:Range blocks/IPv6.

Non-technical explanation
IP address are broken up into four chunks of numbers separated by dots, each ranging from 0 to 255. Each of these four chunks is made up of 8 bits, for a total of 32. When specifying a range, the number after the slash means that that many bits counting from the left will remain unchanged, and the remaining possible combinations form the range. More simply, every 8 means another chunk from the left will remain unchanged.

For example, an IP range of  would mean that the first 3 chunks of numbers, or 24 bits that make up   will remain unchanged, but the remaining chunk, or 8 bits, can be any number from 0 to 255, so our range is   through.

For the purposes of blocking,  and   are the most common practical ranges, although the former should generally be used first to avoid blocking unnecessarily many IP addresses.

So if you have an IP address and you want to block the range assigned how do you know which one to use? Let's say you have a problem with. You can lookup who has this IP address at https://search.arin.net/rdap/?query=148.20.57.34. Say this tells us that this IP address is assigned, along with a LOT of others in a  range, to the Department of Defense. We certainly don't want to block a large block of the DoD! The rule of thumb is block as little as possible. Only block a range if there is a cluster of IP addresses giving a problem.

There's a calculator that is very useful for this: http://www.csgnetwork.com/ipinfocalc.html. Go to this site and enter  into the first set of blanks. Now select Network Prefix Length and enter  (this will give a block of 32 addresses) and click Calculate Network Information. This will show us a block of 32 IP addresses that include. (The first—network—and the last—broadcast—addresses will be displayed along with the usable addresses in the range.) You can use this tool to test ranges to be sure they are what you want before entering the information to initiate the block.

Technical explanation
CIDR notation is written as the IP address, a slash, and the CIDR suffix (for example, the IPv4 " " or IPv6 " "). The CIDR suffix is the number of starting digits every IP address in the range have in common when written in binary.

For example: " " is binary " ", so  will match the first 27 digits (" "). The IP addresses –, when converted to binary, all have the same 27 first digits and will be blocked if   is blocked.

As the CIDR suffix increases, the block affects fewer IP addresses (see table of sample ranges). CIDR suffixes are not the same for IPv4 addresses as they are for IPv6 addresses; the same CIDR suffix in IPv4 blocks 296=79,228,162,514,264,337,593,543,950,336 times as many addresses in IPv6.

Calculating the CIDR suffix
You can use the table of sample ranges below to guess the range, use a computer script, or manually calculate the range.

Conversion to binary
The first step in manually calculating a range is to convert the first and last IP address to binary representation. (This assumes you're not using a computer script, which can probably calculate the range for you anyway.) An IP address is composed of four groups of eight ones and zeros. Each group represents a number from 0 to 255. To convert a number to binary, you can use a reference table or know the value of each binary digit:



Proceeding from left to right, fill in  if the number is at least that value, and subtract that value (if it's not, fill in   and don't subtract). For example, to calculate 240: Thus, 240 is  because it can be represented as 128+64+32+16+0+0+0+0.
 * 1) 240 is at least 128, so place   and subtract 128.
 * 2) 112 (240-128) is at least 64, so place   and subtract 64.
 * 3) 48 (112-64) is at least 32, so place   and subtract 32.
 * 4) 16 (48-32) is at least 16, so place   and subtract 16.
 * 5) Since the remaining value is zero, all the remaining places are.

Calculate range

 * 1) Place both IP addresses one atop the other, and count how many starting digits are exactly alike. This is the CIDR suffix.
 * 2) Double-check! Being off by one digit could extend your block by thousands of addresses.

The example below calculates the CIDR range between  and. Note that this is a simple example; some groups of IP addresses do not so neatly fit CIDR suffixes, and need multiple different-sized blocks to block the exact range.


 * IP addresses:


 * Convert to binary:


 * Count identical first numbers:


 * CIDR range:

Table of sample ranges
The table below shows the IPv4 blocks each CIDR suffix affects. Note that MediaWiki only supports blocking CIDR suffixes 16–32 in IPv4 and 64–128 in IPv6 by default (subject to $wgBlockCIDRLimit). See mw:Help:Range blocks/IPv6 for an IPv6 range table.

Default limitation
The default MediaWiki installation limits range blocks to no larger than /16 IPv4 rangeblocks (65,536 addresses). To block larger ranges $wgBlockCIDRLimit needs to be set accordingly in LocalSettings.php.

Range blocking policy
Range blocks should be avoided, except for extreme circumstances, such as severe and prolonged vandalism from a particular range of IP addresses.

In these cases, ensure that you understand the risks associated with blocking IP ranges, how to make them, and that you do not set an infinite duration. When in doubt, contact SOAP.