Over-utilisation of v6 neighbour slots

[Erik Kline]

I'm not sure what you mean by "impact".

Different OS versions do seem to behave differently.  I think 10.7 is
when the dueling connections implementation was introduced, and it did
drop Safari's IPv6 native preference by basically half.  And if you
think about it, in a perfect network where IPv4 and IPv6 have
identical performance each would likely only be used ~50% of the time.

It looks like you would basically need to penalize IPv4 in order get
your IPv6 ROI, *if* all your customers ever do is surf the web using
Safari on recent Macs to do so.  The total impact of an HE
implementation is obviously in proportion to its use for web traffic.

Let me revise the numbers for this sample network.  I was including
measurements where the client may not have asked for any AAAAs, so let
me restrict my numbers just to measurements where AAAAs were
requested.  That's what I get for not waiting to have my stats-diving
be peer reviewed (different timezone, etc).

"Once more, with feeling!", and I'm sure Lorenzo and correct me later on.

[All MSIE]
    no HE, later versions do a simple reachability check ~once
    96% IPv6 native preference
    7ms average extra latency

[All Chrome]
    HE: 300ms lead for IPv6 then fallback to IPv4
    83% IPv6 native preference
    1.5ms average latency improvement over IPv4

[All Safari + 10.6]
    I think no HE?  (it's been so long...)
    97.5% IPv6 native preference
    0ms average latency delta between IPv4 and IPv6

[All Safari + 10.7,10.8, and 10.9]
    HE: strict connection racing, at one point A record requested
first, I believe
    48% IPv6 native preference
    9ms average latency improvement over IPv4 (by design, working as
intended, etc.)

So the HE implementation does matter.  In this particular sample
network I'm guessing that there may be about an extra 7-8 ms for IPv6
requests to Google (this is end-to-end, so the sources of latency
could be multiple including whether or not the interconnect paths for
IPv4 and IPv6 are the same).

Lastly, I am attaching an old slide from a measurements presentation
we gave at the V6 World Congress in Paris in the very beginning of
this year wherein I attempted to graphically illustrate the effect of
different HE implementations.
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