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

Fred Baker <fredbaker.ietf@gmail.com> Wed, 04 May 2022 17:54 UTC

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From: Fred Baker <fredbaker.ietf@gmail.com>
In-Reply-To: <20220428075001.GA86458@fg-networking.de>
Date: Wed, 04 May 2022 10:53:58 -0700
Cc: Mark Smith <markzzzsmith@gmail.com>, 6man list <ipv6@ietf.org>, v6ops list <v6ops@ietf.org>
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References: <CAM5+tA8WvjvWirxqE6kQ9LQAG0NcpWyCLGVooB=G7gZ9ETb2zQ@mail.gmail.com> <20220424172743.GA218999@fg-networking.de> <CAKD1Yr1v0Tkh+pWD-ts=PL3gZf7Qj6OHW6Cuvj8iGcSSMibjew@mail.gmail.com> <20220425100310.GF67548@fg-networking.de> <CAPt1N1=XedJ7tY9pKDS3LvDMak6iPsK9fA=oF7Z0KkmGcA6-_A@mail.gmail.com> <CAO42Z2ydhe3hVOqSaN814hYh3oF3yG_du+gRkg6yD5haCqDnLQ@mail.gmail.com> <CAPt1N1=YdnZ_N+47v4A_EM70TobSt1sw5tcmBfQJEP5Y1zCwMg@mail.gmail.com> <CAO42Z2xyx2MpCCYQoXA9izRM7Xk42+Z-1OnL2PuzgsGfw1SFiw@mail.gmail.com> <20220428075001.GA86458@fg-networking.de>
To: Erik Auerswald <auerswald@fg-networking.de>
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Subject: Re: [v6ops] ULA precedence [Thoughts about wider operational input]
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> 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.

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...

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