03 February 2014

Setting up an IPv6 only DPM

As part of the general IPv6 testing work, we've just installed a small, single (virtual) node DPM at Oxford that's exclusively available over IPv6. While many client tools will prefer IPv6 to IPv4 given the choice,
some things will prefer IPv4, even if they could work over IPv6, and others might not be able to work over IPv6 at all. Having a dedicated IPv6 only testing target such as this simplifies tests - if something works at all, you know it's definitely doing it over IPv6.

The process was fairly straightforward, with a few minor catches:
  • In the YAIM config, DPM_DB_HOST is set to localhost rather than the FQDN - MySQL is IPv4 only, and if you have it try to use the machines full name, it will try to look up an IPv4 address, and fail when there isn't one.
  • The setting 'BDII_IPV6_SUPPORT=yes' is enabled to make the DPM's node BDII listen on IPv6. This is also required on the site BDII if you want it to do the same, and seems to be completely harmless when set on v4 only nodes. In any case the site BDII will need some degree of IPv6 capability so that it can connect to the DPM server.
  • YAIM requires the 'hostname -f' command to return the machines fully qualified domain name, which it will only do if the name is properly resolvable. Unfortunately, the default behaviour only attempts to look up an IPv4 address record, and so fails. It's possible to fix this cleanly by adding the option 'options inet6' as a line in /etc/resolve.conf, e.g:
    search physics.ox.ac.uk
    nameserver 2001:630:441:905::fa
    options inet6
  • Socket binding. For reasons that are better explained here, /etc/gai.conf needs to be set to something like:
    label ::/0 0
    label 1
    precedence ::/0 40
    precedence 10
    to get some services that don't explicitly bind to IPv6 addresses as well as IPv4 to get both by default.
And then YAIM it as per normal.

In addition to getting the DPM itself running, there are some sundry support services that are needed or helpful for any IPv6 only system (since it won't be able to use services that are only accessible via
IPv4). In the Oxford case, I've installed:
  • A dual stack DNS resolver to proxy DNS requests to the University's DNS servers,
  • A squid proxy to enable access to IPv4-only web services (like the EMI software repositories),
  • A dual stack site BDII. Advertising the DPM server requires the site BDII to be able to connect to it to pick up its information. That means an IPv6 capable site BDII.
The final product is named 't2dpm1-v6.physics.ox.ac.uk', and it (currently) offers support for the ops, dteam and atlas VOs, and should be accessible from any IPv6 capable grid client system.

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