From: Tim Starling <tstarling@wikimedia.org>
Date: Fri, 8 Jun 2012 02:26:05 +0000 (+1000)
Subject: Increase maximum IPv6 range block size to /19
X-Git-Tag: 1.31.0-rc.0~23351^2
X-Git-Url: http://git.cyclocoop.org/data/%24self?a=commitdiff_plain;h=dd1053bc49b6798e52ed4c352ee5444834c7f8f4;p=lhc%2Fweb%2Fwiklou.git

Increase maximum IPv6 range block size to /19

Increased maximum IPv6 range block size from /32 to /19 and documented
my decision-making process. Many ISPs will be larger than /32 since /32
only allows for 64k sites at most.

Change-Id: Ia25e156fd8234519c4d74f1d41d93f94a313ce14
---

diff --git a/includes/DefaultSettings.php b/includes/DefaultSettings.php
index 0a3d4adead..508add4be8 100644
--- a/includes/DefaultSettings.php
+++ b/includes/DefaultSettings.php
@@ -3459,12 +3459,19 @@ $wgSysopEmailBans = true;
  * Limits on the possible sizes of range blocks.
  *
  * CIDR notation is hard to understand, it's easy to mistakenly assume that a
- * /1 is a small range and a /31 is a large range. Setting this to half the
- * number of bits avoids such errors for IPv4.
+ * /1 is a small range and a /31 is a large range. For IPv4, setting a limit of
+ * half the number of bits avoids such errors, and allows entire ISPs to be
+ * blocked using a small number of range blocks.
+ *
+ * For IPv6, RFC 3177 recommends that a /48 be allocated to every residential
+ * customer, so range blocks larger than /64 (half the number of bits) will
+ * plainly be required. RFC 4692 implies that a very large ISP may be
+ * allocated a /19 if a generous HD-Ratio of 0.8 is used, so we will use that
+ * as our limit. As of 2012, blocking the whole world would require a /4 range.
  */
 $wgBlockCIDRLimit = array(
 	'IPv4' => 16, # Blocks larger than a /16 (64k addresses) will not be allowed
-	'IPv6' => 32, # Blocks larger than a /32 (~7.9x10^28 addresses) will not be allowed
+	'IPv6' => 19,
 );
 
 /**