Re: [v6ops] draft-ietf-6man-grand : saving lookups

Mark Smith <> Sun, 09 August 2020 21:43 UTC

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From: Mark Smith <>
Date: Mon, 10 Aug 2020 07:43:16 +1000
Message-ID: <>
To: Philip Homburg <>
Cc: v6ops list <>, "Pascal Thubert (pthubert)" <>, 6man <>
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Subject: Re: [v6ops] draft-ietf-6man-grand : saving lookups
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On Mon, 10 Aug 2020, 01:47 Philip Homburg, <>

> > So what I'm after is the host behavior of "not onlink" for the
> > lookup phase, the router behavior of onlink for the redirect phase,
> > and the L bit set iff the link is P2P or a transit. E.g., in a
> > distributed fabric, all addresses "reside on-link and can be reached
> > directly without going through a router" and yet we want to avoid
> > broadcast lookups.

I'm pretty sure IPv6 can support that already.

RFC5942,  IPv6 Subnet Model: The Relationship between Links and Subnet
Prefixes says hosts are to consider destinations, with exception to
link-local destinations, off-link by default. Off-link by default can be
overridden for individual asdresses via redirects, or for a contiguous
range of addesses, i.e. a prefix, via an RA PIO with L=1 (the A bit value
being irrelevant to this). If you want everything hair pinned through the
router all of the time you disable it sending redirects.

As I mentioned, the exception is link-locals, which RFC5942 says are always
on link. Here is my idea on how to change that - nothing that fancy, create
LL prefix POIs with L=0, that overrides host default of LL prefix being

("Off Link" should really be in quotes in the draft title. "On-Link" is
probably a bit too broad a term, something like "directly link reachable",
meaning to ND for it rather than go via the default router, might have been
a bit more descriptive.)


> Suppose we have a no-multicast bit, that tells a host to send traffic to
> its default router when it doesn't have a neighbor in the NC cache.

> It is not clear to me how the semantics would be different from clearing
> the
> L-bit, but if you think there are considerable differences, why no write
> a draft that describes the use of such a bit.

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