Manual:$wgBlockCIDRLimit

Access: $wgBlockCIDRLimit
Maximum CIDR range when blocking an IP range.
Introduced in version:	1.16.0 (r58377)
Removed in version:	still in use
Allowed values:	positive integer
Default value:	(See Below)

Other settings: Alphabetical | By Function

Default values

$wgBlockCIDRLimit = array(
       'IPv4' => 16, # Blocks larger than a /16 (65,536 addresses) will not be allowed
       'IPv6' => 64, # 2^64 = ~1.8x10^19 addresses
);

Details

Maximum CIDR range when blocking an IP range.