Re: Forwarding Packets With Link Local Destination Addresses

Gyan Mishra <hayabusagsm@gmail.com> Thu, 07 January 2021 23:45 UTC

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From: Gyan Mishra <hayabusagsm@gmail.com>
Date: Thu, 7 Jan 2021 18:45:41 -0500
Message-ID: <CABNhwV2fS6kAA7dusa36y0D4qWwWj1g=Egw+cy0YuQyhh_ZJ1g@mail.gmail.com>
Subject: Re: Forwarding Packets With Link Local Destination Addresses
To: Ron Bonica <rbonica=40juniper.net@dmarc.ietf.org>
Cc: "6man@ietf.org" <6man@ietf.org>
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Ron

In-line

I agree that RFC 4291 although could have been written better.

On Thu, Jan 7, 2021 at 12:54 PM Ron Bonica <rbonica=
40juniper.net@dmarc.ietf.org> wrote:

> Folks,
>
>
>
> According to RFC 4291, “routers must not forward any packets with
> Link-Local source or destination addresses to other links”.
> Gyan>“ Link local source or destination to any other link” it is trying to
> imply “off link”. Link local cannot be used in an off link scenario.
>

 I agree the verbiage includes an SRv6 SRH inclusive that the final SID
> cannot be a link local address.  As the final SID is copied to the
> destination address of the IPv6 header during processing that would be
> construed as explicit forwarding of a packet which is forbidden.  Link
> local due to “local scope” on link non routable scope, so therefore the
> packet cannot be forwarded using destination link local.  Since this is an
> SRV6 SRH steered transitive path and not packets that are transmitted
> locally between two adjacent nodes such as ND or OSPF for example, this is
> clearly forbidden.  I think the  transitive nature even though it’s hop by
> hop steering, makes it off link routed thus link local destination  is not
> in scope for final SID.
>

> I interpret this statement to include packets that contain routing
> headers. For example, it forbids an SRv6 packet whose final segment has a
> locator that begins with FE80.
>
>
>
> Does everyone share this interpretation? If so, do RFC 4291 or RFC 8200
> make this sufficiently clear?
>
>  Agreed.  I think it could be much clearer per my note above.
>
>
>                                                             Ron
>
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