Re: [v6ops] IPv6 link-local traffic questions

Erik Kline <ek.ietf@gmail.com> Thu, 12 March 2020 23:49 UTC

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From: Erik Kline <ek.ietf@gmail.com>
Date: Thu, 12 Mar 2020 16:49:39 -0700
Message-ID: <CAMGpriXhxfM0b4YdCcB9__b=9Us3NosQMXNF4F7QQmeyOUE4Jg@mail.gmail.com>
Subject: Re: [v6ops] IPv6 link-local traffic questions
To: Toerless Eckert <tte@cs.fau.de>
Cc: Mark Smith <markzzzsmith@gmail.com>, bier@ietf.org, v6ops list <v6ops@ietf.org>, 6MAN <6man@ietf.org>
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On Thu, Mar 12, 2020 at 2:36 PM Toerless Eckert <tte@cs.fau.de> wrote:

> On Thu, Mar 12, 2020 at 12:18:32PM +1100, Mark Smith wrote:
> > RFC4007  allows packets with link-local destinations to be forwarded
> > by a router, but only back onto the same link:
>
> Oh, my favourite coffin nail RFC.
>
> > "Thus, if a
> >    router receives a packet with a link-local destination address that
> >    is not one of the router's own link-local addresses on the arrival
> >    link, the router is expected to try to forward the packet to the
> >    destination on that link (subject to successful determination of the
> >    destination's link-layer address via the Neighbor Discovery protocol
> >    [9]).  The forwarded packet may be transmitted back through the
> >    arrival interface, or through any other interface attached to the
> >    same link."
> >
> >
> > I think in theory that could also mean forwarded to another router on
> > the link that then forwards back again onto the link etc., so it is
> > valid for a packet with a link-local destination address to have an
> > initial Hop Count value that allows it to be forwarded by multiple
> > routers, all limited to being forwarded within the same link.
>
> So this behavior breaks both TTL=1 and RFC5082 packets.
>
> Nice. This RFC is getting better every time i learn more of it.
>

My personal experience is that 255 is standard for link-local unicast
communications, and 1 is commonly used for link-local multicast.

> This draft might be useful, as it collects together and summarises
> > information about using Link-Local Addresses (and is something I've
> > been meaning to get back to updating, suggestions welcome):
> >
> > How to use IPv6 Link-Local Addresses in Applications
> > https://tools.ietf.org/html/draft-smith-ipv6-link-locals-apps-00
>
> Nice.
>
> Let me split that off.
>
> cheers
>     Toerless
>
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