Re: [babel] Dummy source address [was: I-D Action: draft-ietf-babel-v4viav6-01.txt]

Donald Eastlake <d3e3e3@gmail.com> Wed, 14 April 2021 16:10 UTC

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From: Donald Eastlake <d3e3e3@gmail.com>
Date: Wed, 14 Apr 2021 12:10:32 -0400
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To: Juliusz Chroboczek <jch@irif.fr>
Cc: Babel at IETF <babel@ietf.org>
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Subject: Re: [babel] Dummy source address [was: I-D Action: draft-ietf-babel-v4viav6-01.txt]
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Hi Juliusz,

On Wed, Apr 14, 2021 at 8:31 AM Juliusz Chroboczek <jch@irif.fr> wrote:
>
> >> 1. reuse the 4rd dummy address, as David suggested, repurposing it
> >>    to be a generic dummy address?
>
> >> 3. define a cross-protocol dummy address in this draft?
>
> > I don't think (3) exceeds our scope. We need a facility. So we specify
> > it in our draft. And, just in passing, we are liberal and say others
> > can use it. There is no need to make a big point of it being
> > "cross-protocol" and no need to name any other routing protocol(s).
>
> Donald, could you please check RFC 7600, because I'm wondering if that's
> not what they have done already.  Here are the relevant quotations:
>
> Section 4.8:
>
>    R-22: If a CE or BR receives an ICMPv6 error message [RFC4443], it
>          MUST synthesize an ICMPv4 error packet [RFC792].  This packet
>          MUST contain the first 8 octets of the discarded packet's IP
>          payload.  The reserved IPv4 dummy address (192.0.0.8/32; see
>          Section 6) MUST be used as its source address.
>
> IANA Considerations:
>
>    o  Reserved IPv4 address 192.0.0.8/32 to be used as the "IPv4 dummy
>       address" (Section 4.8).
>
> So I'm pretty tempted to say "MAY use 192.0.0.8 if no more suitable IPv4
> address is available", as David originally suggested, and see what the
> IESG says.

I spent a little while looking at RFC 7600. Their use is very close to
ours and they have deliberately chosen a maximally generic name for
192.0.0.8. So I don't have any problem with going with that address in
the draft. This is also a faster way to get to a really stable
address.

The interesting question is whether or not to reference RFC 7600. I
would be tempted not to since, to implement Babel IPv4 via IPv6, there
isn't anything in RFC 7600 you have to know about -- in fact someone
could be confused or at least end up wasting time looking at the 4rd
stuff in RFC 7600. Just use 192.0.0.8/32 are refer to it as "the IPv4
dummy address".

Thanks,
Donald
===============================
 Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
 2386 Panoramic Circle, Apopka, FL 32703 USA
 d3e3e3@gmail.com

> -- Juliusz