Re: [v6ops] ULA precedence [Thoughts about wider operational input]

Ed Horley <ed@hexabuild.io> Wed, 04 May 2022 18:02 UTC

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From: Ed Horley <ed@hexabuild.io>
Date: Wed, 04 May 2022 11:02:10 -0700
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To: Fred Baker <fredbaker.ietf@gmail.com>
Cc: Erik Auerswald <auerswald@fg-networking.de>, v6ops list <v6ops@ietf.org>, 6man list <ipv6@ietf.org>
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Subject: Re: [v6ops] ULA precedence [Thoughts about wider operational input]
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On Wed, May 4, 2022 at 10:54 AM Fred Baker <fredbaker.ietf@gmail.com> wrote:

>
>
> > On Apr 28, 2022, at 12:50 AM, Erik Auerswald <auerswald@fg-networking.de>
> wrote:
> >
> > I'd say that _remote_ ULAs are less reliable than GUAs. Selecting ULA
> > source to reach GUA destination risks that the return traffic would be
> > sent to a _remote_ ULA (if the initial packet even reaches the
> > destination; it could be filtered because of using a "wrong" source
> > address).
> >
> > The RFC 6724 default errs on the side of caution by assuming that ULA
> > are non-local, unless either auto-detected or configured as local.
>
> From a specification perspective, it seems to me that the two cases should
> be separated. If I have a local ULA address and a peer I want to
> communicate with has an address in the same prefix, then I probably should
> prefer to use that address pair unless I have a reason not to. In any other
> case, I should use my own GUA and send the message to my peer's GUA - I
> have no guarantee of connectivity otherwise.
>
> Just for clarification - when you say "same prefix" for ULA - are you
assuming in the same /48? Or do you mean within all of ULA (fc00::/7 or the
useable fd00::/8)?

In fact, I'm not sure how I would know that my peer has an address that is
> not in my ULA prefix. It shouldn't be in DNS, as I recall (RFC 4193 section
> 4.4). That might mean a split DNS implementation...


The majority of customers we are working with are doing split DNS in some
capacity. However, we are running into designs where they are planning on
doing ULA everywhere and NPTv6 or NAT66 to a GUA at the Internet edge. Plus
they are dual-stacked (which is why Nick's ULA draft is important for us.
We can point customers to something that explains the problem space.)

>
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-- 
Ed Horley
ed@hexabuild.io | (925) 876-6604
Advancing Cloud, IoT, and Security with IPv6
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