Re: Limited Domains:

So I think we all agree that backwards compatibility is not possible and
things would break with the restructuring of the flow label.

On Mon, Apr 12, 2021 at 7:55 PM Brian E Carpenter <
brian.e.carpenter@gmail.com> wrote:

> On 13-Apr-21 10:20, Tom Herbert wrote:
> > On Mon, Apr 12, 2021 at 3:10 PM Brian E Carpenter
> > <brian.e.carpenter@gmail.com> wrote:
> >>
> >> On 13-Apr-21 08:52, Fred Baker wrote:
> >>>
> >>>
> >>>> On Apr 12, 2021, at 1:51 PM, Brian E Carpenter <
> brian.e.carpenter@gmail.com> wrote:
> >>>>
> >>>> In other words, a redefined flow label could be used pairwise between
> hosts that have determined that they are both members of a particular
> limited domain.
> >>>
> >>> Which would eliminate the use of the flow label by systems that are
> not part of that domain.
> >>
> >> No, it would create two sets of nodes: nodes using RFC6437 between
> themselves, and nodes using some other interpretation of the flow label
> between themselves. Ships in the night, really just like running IPX and
> CLNP on the same network. We used to do that a lot.
> >
> > Brian,
> >
> > The problem is that there's no code point that  discriminates between
> > the different interpretations of the flow label. So in a limited
> > domain the deployment of the new implementation must be perfect, lest
> > there is at least one router that is inadvertently run with the legacy
> > interpretation, then that router may process the flow label and ECMP
> > per the standard leading to situations where packets of some flow are
> > unexpectedly going over different paths. Since there's nothing in the
> > packet that states what's happening, such problems can be really
> > difficult to debug.
>
> I completely agree. I was thinking about how to code this safely, and
> it's a mess, especially if you want routers to detect it at line speed.
>
>     Brian
>
> >
> > Tom
> >
> >>
> >> I'm not advocating this, just pointing out that it's possible.
> >>
> >>    Brian
> >>
> >>
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