Re: Forwarding Packets With Link Local Destination Addresses

神明達哉 <jinmei@wide.ad.jp> Fri, 08 January 2021 05:52 UTC

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Date: Thu, 7 Jan 2021 21:52:13 -0800
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Subject: Re: Forwarding Packets With Link Local Destination Addresses
To: Alexandre Petrescu <alexandre.petrescu@gmail.com>
Cc: IPv6 IPv6 List <ipv6@ietf.org>
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At Thu, 7 Jan 2021 20:05:47 +0100,
Alexandre Petrescu <alexandre.petrescu@gmail.com> wrote:

> > Thanks! I think that the following text from RFC 4007 covers the
> > issue:
> >
> > "   A node that receives a packet addressed to itself and containing
> > a Routing Header with more than zero Segments Left (Section 4.4 of
> > [3]) first checks the scope of the next address in the Routing
> > Header.  If the scope of the next address is smaller than the scope
> > of the original destination address, the node MUST discard the
> > packet. "
>
> Are scopes bigger one than another?
>
> In multicast that may be true, but in unicast it's hard to say a scope
> might be smaller or bigger than another scope.
>
> In unicast, there might be only two scopes: LL and global.  It might be
> that there is no inclusion from one into another, or it might be that a
> size comparison might not be possible.

RFC 4007 explicitly defines the size relationship between scopes:

   There is a size relationship among scopes:

   o  For unicast scopes, link-local is a smaller scope than global.

   o  For multicast scopes, scopes with lesser values in the "scop"
      subfield of the multicast address (Section 2.7 of [1]) are smaller
      than scopes with greater values, with interface-local being the
      smallest and global being the largest.

The above cited text should be interpreted with this definition.

--
JINMEI, Tatuya