Re: [v6ops] PI heresy [draft-ietf-v6ops-ula-usage-recommendations - work or abandon?]

Mark Andrews <marka@isc.org> Fri, 13 November 2015 21:10 UTC

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To: Philip Homburg <pch-v6ops-3@u-1.phicoh.com>
From: Mark Andrews <marka@isc.org>
References: <20151106.063106.74659839.sthaug@nethelp.no> <CAO42Z2x3O8A1XKqN3PTcvM=xpF8W_WNSL1rVhHQ4ZY5HbVG=OQ@mail.gmail.com> <20151106.081425.74651560.sthaug@nethelp.no> <6ED54502-C5D1-4D09-877C-FE283E3EF142@delong.com> <5644EE46.7000805@gmail.com> <CAKr6gn1KokTGJ0cg70OR=q8Uv-1mr7TmjcYJwLVgsK_3i6tcpw@mail.gmail.com> <56453026.3090607@gmail.com> <CAKD1Yr1nb1svwHDE3Z7a1xF00CRw-kOrN6+Xgd6fVjqrN=gb+g@mail.gmail.com> <20151113080508.GB89490@Space.Net> <CAKD1Yr2paTyq7L8-dU9vhtxhDd17LvKPoQt4YY2DDxB-_5ZRbA@mail.gmail.com> <20151113112141.GN89490@Space.Net> <m1ZxDn5-0000EpC@stereo.hq.phicoh.net> <564633AB.9000509@gmail.com> <m1ZxJsW-0000GnC@stereo.hq.phicoh.net>
In-reply-to: Your message of "Fri, 13 Nov 2015 20:19:19 +0100." <m1ZxJsW-0000GnC@stereo.hq.phicoh.net>
Date: Sat, 14 Nov 2015 08:10:15 +1100
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Subject: Re: [v6ops] PI heresy [draft-ietf-v6ops-ula-usage-recommendations - work or abandon?]
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In message <m1ZxJsW-0000GnC@stereo.hq.phicoh.net>, Philip Homburg writes:
> >> I don't think a host should try to figure out which paths work and which
> >> don't.
> >> 
> >> Maybe somebody can come up with a simple algorithm that generalises
> >> happy-eyeballs and that is compatible with today's host operating systems.
> >> But I doubt it. 
> >
> >We tried. It's called shim6. Firewalls break it.
> 
> I'd call shim6 a protocol and not an algorithm. Happy eyeballs is quite 
> compatible with firewalls, NAT, etc. No problem there. I'm sure happy
> eyeballs-like approaches can be tried for the multiple-prefix case.
> 
> The problem I ran into is that by the time my happy eyeballs implementation
> did everything I wanted it do, it was way to complex. Adding support for
> many source prefixes would just be too much.
> 
> Now, maybe somebody can come up with an approach that doesn't have that
> problem. Don't know.
> 
> Mean while, I have something that works with every operating system today.
> It may not be perfect. So I'm not terribly motivated to add more host
> complexity to solve those edge cases.

The simplest way will probably be to extend getaddrinfo to return
pairs of address and just work down the list until you get a working
connection starting new ones relatively quickly after waiting 50
ms or so between first few to reduce the number of embryonic connects
that you kill when you get success.  It adds one more system call
to the default loop when starting a tcp connection.

	socket, fcntl, fcntl, bind, connect, select/poll

		vs

	socket, fcntl, fcntl, connect, select/poll

For subsequent connections to the same node from the same application
for the same session you just re-use the discovered pair of addresses.

Mark

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Mark Andrews, ISC
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