Re: Forwarding Packets With Link Local Destination Addresses

神明達哉 <jinmei@wide.ad.jp> Fri, 08 January 2021 14:41 UTC

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Date: Fri, 8 Jan 2021 06:40:53 -0800
Message-ID: <CAJE_bqfpAS0rM4NKuiVu679Dj5f1zYU7iF7ujriiRnM1CYQN-A@mail.gmail.com>
Subject: Re: Forwarding Packets With Link Local Destination Addresses
To: Carsten Bormann <cabo@tzi.org>
Cc: Ron Bonica <rbonica=40juniper.net@dmarc.ietf.org>, Fernando Gont <fgont@si6networks.com>, "6man@ietf.org" <6man@ietf.org>
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At Fri, 8 Jan 2021 10:45:03 +0100,
Carsten Bormann <cabo@tzi.org> wrote:

> > could allow the following:
> >
> > - A node sends a packet with a routing header that would route the
> >  packet to a global address (D1) and then to a link-local (final)
> >  destination (D2).
> > - The packet leaves the source link and is delivered to the interface
> >  corresponding to the global address D1.
> > - The receiving node now sets D2 as the destination address of the
> >  IPv6 header and forwards the packet to the link where the packet is
> >  delivered to D2 (so it does not forward the packet to "other link”).
>
> This is about a hypothetical, but:
> How would it know which of its many links that is?

It would be "the link where the packet is delivered to D2".

> (And how exactly would D2 reply?)

It's tricky (and nearly impossible in practice) as RFC 4007 explains:

   [...]  This will help the receiving node send a
   "response" packet with the final destination of the received packet
   as the source address without breaking its source zone.

--
JINMEI, Tatuya