Re: Additional Documentation Prefixes (was Re: AD Evaluation : draft-ietf-6man-ra-pref64-06)

Michael Richardson <> Mon, 04 November 2019 00:21 UTC

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From: Michael Richardson <>
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Subject: Re: Additional Documentation Prefixes (was Re: AD Evaluation : draft-ietf-6man-ra-pref64-06)
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Date: Sun, 03 Nov 2019 19:21:10 -0500
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Brian E Carpenter <> wrote:
    >> I guess L=1 is why you call it ULA-L. I have known it as ULA-Random.
    >> We are both talking about RFC4193 though.  So such a document would need to
    >> update RFC4193.

    > I think this is a bad and pointless idea. Pointless because it is 100% OK
    > to use any RFC4193 prefix as an example, since by definition it will never
    > be used on the Internet, and the chance of collision on a given ULA site
    > is 1 in 2**40 (and who cares anyway?). Bad because it means that millions
    > of existing boxes that can generate ULA prefixes would be non-conformant
    > and, seriously, is any vendor going to update date their firmware for this?

So, each time a document uses a ULA-Random in an example that calls for ULAs,
someone will ask why they didn't use 2001:db8::/32.

The other plus is places that ask for a ULA to be typed in can recognize the
Documentation prefix, and suggest that maybe that's not what they wanted to do.

{I don't expect any ULA generator to get updated, as you said, 1/2**40.
But, on the other hand, how many ULA generators are out there?}

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