Saturday, 18 June 2011

IPv6 Day in Cambridge - Success and Non-event!

IPv6 day (8th June) in the University was largely a non-event, and so can be declared a success! This seems to match experiences reported elsewhere.

We are not aware of any significant problems experienced by University users in accessing any services on the day, including external ones known to be participating in IPv6 day such as Google and Facebook. The core of the University network is connected to the global v6 internet, but most distribution networks in departments and colleges only connect using v4 at the moment. Those networks that are connected to the global v6 internet (including the one connecting my desktop workstation) worked fine on the day as expected.

In the run-up to the day we enabled v6 on a number of central services, including the main University web server, the Streaming Media Service (both the web interface and the HTTP download service), the 'new' interface to our search engine, the University Training Booking System, and the central mail service (SMTP, POP, IMAP). On the day we published AAAA records for these services alongside the normal A records from about 08:30 to 19:00 BST.

With the exception of the web server, all these services were enabled more or less as they would be for a v6 production service, though a few features (such as automatic v6 address transition between cluster members, and adapting log analysis to recognise v6 addresses) were not completed in time. The web server used a seperate Apache reverse proxy to provide v6 connectivity to avoid having to disturb its configuration. While doing this, and subsequently, we identified various issues and surprises that I've already mentioned (here, here, and here).

The University web server received 8,981 requests from 280 distinct clients over v6. By comparison it received a total of 1,257,012 requests over both protocols for the entire 24 hour period, meaning that v6 requests probably represented about 1.5% of the total. The breakdown of 8,351 native v6 requests from 230 clients by approximate country of origin appears in the table below.

What was interesting was the relatively high number of clients (50) making requests over transitional 6to4 connections (630). Most of these (36 clients making 476 requests) were from inside the University. Most or all of these clients will have had perfectly good native v4 connectivity to and this confirms (if confirmation were needed) that rather a lot of systems prefer IPv6, even if provided by a transition technology such as 6to4, over IPv4. Interestingly we didn't see any Teredo traffc.

6to4 caused the only significant incident of the day, when a department mail server switched to using IPv6 over a 6to4 route being advertised by a user workstation elsewhere on the department subnet. This mailserver sends all its outgoing mail via the University's central internal mail switch, but that won't accept messages from machines with 6to4 addresses because it doesn't see them as 'inside'. The problem was quickly fixed, but it seems clear that, ironically, problems caused by 6to4 and Toredo 'transitional' connectivity may represent a significant barrier to further IPv6 roll-out.

Native IPv6 requests to on IPv6 Day, by approximate country of origin

[Here 'UCS STAFF' represents clients on the Computing Service staff network, 'UNIVERSIY' represents those elsewhere in the University, 'JANET' those elsewhere on JANET, and 'United Kingdom' those elsewhere in the UK].

  2619 UCS STAFF
  1373 China
  1290 Brazil
   835 JANET
   420 United Kingdom
   293 United States
   171 Greece
   123 France
   110 Czech Republic
    97 Russian Federation
    81 Germany
    66 Japan
    48 Portugal
    47 Netherlands
    36 Finland
    33 Canada
    33 Serbia
    17 Spain
     7 Switzerland
     6 Ireland
     5 Saudi Arabia
     3 Hong Kong
     2 Italy
     2 Korea, Republic of
     2 Norway
     1 Australia
     1 New Zealand
Geolocation provided by Maxmind's free GeoLite IPv6 Country database. "This product includes GeoLite data created by MaxMind, available from"

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