Manual:IPv6 support

MediaWiki has traditionally identified anonymous users (those not logged in) by their IPv4 addresses, which were presumed to be globally unique. For the most part, this approach was valid; the primary exceptions being a few problematic ISP's which displayed all users as being behind a few known proxy servers instead of identifying them by their individual globally-unique IPv4 addresses.

At a time when globally-unique IPv4 address blocks remained freely available to ISP's, one IP address was likely to identify one user (or no more than one small local area network). Unfortunately, the last large blocks of IPv4 addresses (a /8, just over 16 million addresses) were issued on January 31, 2011 to regional Internet registries and will soon be depleted. The availability of new IPv4 space to ISP's has therefore been constrained, providers in the Asia-Pacific region now being allocated blocks of 1024 addresses instead of the formerly-unlimited quantities.

This leaves affected Internet providers with a few limited options. Carrier-grade NAT can be used to cause many users to appear to be coming from the same few IPv4 addresses - a likely short-term approach, but one which will cause problems for MediaWiki sites as blocking these addresses blocks an entire ISP's userbase. IPv6 transition mechanisms are another option, as is full IPv6 deployment. IPv6 can be used to obtain unique addresses for every user or every device from a huge pool of 2128 possible IPv6 addresses.

As more than 95% of websites (as of 2011) support IPv4 only, soon these sites will be seeing the same few IPv4 addresses in Special:Recentchanges repeatedly - but, instead of one address representing one user, one IPv4 will represent multiple users behind one NAT or one gateway. The only way to uniquely identify users from IP addresses will be to offer IPv6 alongside existing IPv4 on all domains. IPv6-aware web browsers, if provided with valid IPv4 and IPv6 paths to reach the same domain, will use IPv6 and continue to appear with globally-unique addresses in Special:Recentchanges on an IPv6-aware site.

As IPv6 users are not affected by IPv4 address blocking (and vice-versa), the risk of blocking a gateway's IPv4 address and all users behind it to stop spam or vandalism from one computer diminishes.

IPv6 in MediaWiki
As of 2011, IPv6 addressing is supported in current versions of MediaWiki (1.17 and above). Earlier versions may have partial support but contain bugs; MediaWiki 1.9 will not handle IPv6 addresses at all.

MediaWiki itself is not tasked with listening for incoming IPv6 connections as this is done by the host Apache webserver or (on high-traffic sites) a web accelerator proxy such as Squid or Varnish.

MediaWiki does, however, record IP addresses for anonymous edits in Special:Recentchanges (and IP's for all edits in CheckUser). It also depends on IP addressing to block users, both in its own internal functionality and in that added by extensions (such as Check Spambots). It is therefore essential that any IPv6 deployment allow MediaWiki to log valid external IPv6 addresses to recent changes (and not the IPv4 address of servers or gateways).

Blocking users also differs between IPv4 and IPv6 in that a typical IPv6 local area network is likely to be assigned not a single IPv6 address but a range of addresses (at least a /64 for a single router) with the lower 64 bits populated by the client PC. Blocking a single address (a /128) therefore may not suffice to block a persistent vandal, leading to more frequent use of range blocks to counter spam and vandalism.

Installation and deployment
This description is aimed at users who control an entire server (be it virtual, dedicated or co-located). For users of shared webhosts, many of the tasks listed here are controlled not by clients but by hosting providers.

It also presumes IPv6 to already be configured on the server at the network and operating system level.

Apache direct-connection
On a high-traffic site (such as Wikipedia) the Apache server does not accept incoming connections from users directly but is located behind a reverse proxy server such as Squid or Varnish.

On a small site in which Apache is accepting direct connections from users, however, Apache will need to be configured to listen to both the external IPv4 and IPv6 ports on your server.

IPv6 addresses in httpd.conf must be surrounded in square brackets, as in the following example:

Listen 192.170.2.1:80
 * 1) Listen for IPv4 connections on one outside address

Listen [2001:db8::a00:20ff:fea7:ccea]:80
 * 1) Listen for IPv6 connections on one address

In Apache 2 or above, the Listen, NameVirtualHost, and VirtualHost directives support IPv6 numeric address strings (e.g., "Listen [2001:db8::1]:8080").

Squid and Varnish reverse proxies
See also Squid or Varnish caching

On high-traffic sites, Apache httpd is normally configured behind a caching reverse proxy server such as Squid so that dynamic content may be served from the cache instead of being regenerated for each viewer.

A simple example (one Squid backed by one Apache webserver) would be:

Squid listens to all external addresses (IPv6 and IPv4), serves the page directly if it is in cache, forwarding any requests it cannot handle on its own (cache misses) to an Apache server (in this example, on the IPv4 loopback address on the same computer). As the connection between Squid and Apache is solely internal, it does not matter whether IPv4 (127.0.0.1) or IPv6 (::1) is used - but there is no purpose in using both except on externally-accessible interfaces.

Squid 3.1 and later support IPv6 addressing but must be configured to list all addresses on which Squid is to listen, ie:

http_port 192.170.2.1:80 vhost defaultsite=example.org
 * 1) Listen for IPv4 connections on an outside address

http_port [2001:db8::2]:80 vhost defaultsite=example.org http_port [2001:db8::123:456]:80 vhost defaultsite=example.org
 * 1) Listen for IPv6 connections on various addresses

MediaWiki's configuration file (LocalSettings.php) does need to list all addresses used by reverse proxy or gateway servers to ensure these do not appear in Special:Recentchanges

Note that the cache 'purge' messages only need to be sent to each Squid once (even if it's listening on multiple addresses) and should not be sent to Apache at all (as it will only be logged as an error). Listing only one of the Squid addresses in $wgSquidServers and the others in $wgSquidServersNoPurge ensures this.

The same requirements (including indication of every address, IPv4 or IPv6, to be monitored) also apply to Varnish. Versions 2.1 or later of Varnish support IPv6; the list of addresses is supplied in the list of options in the format:

-a address[:port][,address[:port][...]

where the address can be a host name (“localhost”), an IPv4 dotted-quad (“127.0.0.1”), or an IPv6 address enclosed in square brackets (“[::1]”).

-a 192.170.2.1:80,[2001:db8::2]:80,[2001:db8::123:456]:80

should therefore be the Varnish equivalent of the Squid example listed above.

Domain name servers
Berkeley Internet Name Domain (BIND) daemon “named” supports IPv6 from version 9 onward, as do other rival DNS programmes.

While BIND is not in any way part of MediaWiki, it (or another Internet name server) will need to be configured to provide the addresses of your IPv6-aware MediaWiki site to your users once your system is ready for deployment.

To tell BIND to listen for IPv6 connections, edit the options section of named.conf to include the listen-on-v6{any;}; directive:

options { directory "/etc"; pid-file "/var/run/named/named.pid"; listen-on-v6{any;}; };

The IPv4 and IPv6 addresses of your publicly available domains will need to be added to the *.hosts files for your nameserver; IPv6 are identified as IN AAAA while IPv4 are A records:

ipv6.example.org  IN      AAAA    2001:db8::2 ipv4.example.org  IN      A       192.170.2.1

IPv6-compatible software
This list indicates status of Internet-facing software typically installed on a deployed MediaWiki server; see the comparison of IPv6 application support for a more general list of all current IPv6-aware applications.

Note that only Internet-facing applications (which accept connections directly from users) need be made IPv6 aware. Services such as mysqld or memcached which perform back-end roles need not be both IPv4 and IPv6 aware as it is not desirable that these be accessible from any except the localhost or local area network for security reasons.