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

Donald Eastlake <> Wed, 14 April 2021 16:10 UTC

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From: Donald Eastlake <>
Date: Wed, 14 Apr 2021 12:10:32 -0400
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To: Juliusz Chroboczek <>
Cc: Babel at IETF <>
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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 <> 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 (; see
>          Section 6) MUST be used as its source address.
> IANA Considerations:
>    o  Reserved IPv4 address to be used as the "IPv4 dummy
>       address" (Section 4.8).
> So I'm pretty tempted to say "MAY use 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 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

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 are refer to it as "the IPv4
dummy address".

 Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
 2386 Panoramic Circle, Apopka, FL 32703 USA

> -- Juliusz