[rrg] Happy Eyeballs RFC6555: app changes so dual-stack IPv4/6 is usable

[Robin Whittle <[e-mail]>]

Hi Shane,

Thanks very much for your Happy Eyeballs answer in the "Re: [rrg] ILNP:
existing applications & other critiques" thread to my question about why
people watching the Olympics on a Comcast HFC network would sometimes
have their browser, player or whatever access the videos via IPv6 servers:

  http://en.wikipedia.org/wiki/Happy_Eyeballs
  http://tools.ietf.org/html/rfc6555    April 2012

If the IPv4 connection is behind NAT, including with the NAT box in the
provider network, and if the individual hosts have their own public
unicast IPv6 addresses, then this can reduce the traffic through the
IPv4 NAT box.  The algorithm is designed to generally favor IPv6, with
the long-term intention of reducing the use of IPv4.

   "... the client sends two TCP SYNs at the same time over IPv6 and
    IPv4."

If an ACK is received for both, the client selects whether to use IPv4
or IPv6, and caches this for 10 minutes.

   "The simplest venue for the implementation of Happy Eyeballs is
    within the application itself."

It seems that applications need to be altered, by the addition of a
Happy Eyeballs algorithm, to provide reliable performance when the
dual-stack host is connected to both IPv4 and IPv6.  This is
unfortunate, but not surprising - since these are two separate Internets.

  - Robin