Re: [Detnet] L2/L3 model?

That would be nice to keep L2 and L3 separate, Philippe, and in some
topologies that will be possible.  But, in general, I don’t think so.

Any number of routers can connect to an L2 cloud, and in order to get
spatial diversity for the paths and avoid single points of failure, the
path computation will have to look at the physical topology, including
both bridges and routers.

I think that the the solution needs to work for absolutely any L2/L3
topology, and I think that requires that the application that is laying
out the paths be aware of the complete physical topology.  Interestingly,
in the data center, there can be multiple virtual L2/L3 topologies for
different customers all overlaid on the same physical topology.  To a
first approximation (your implementation may more or less interesting than
mine), the physical topology is all that matters.  The days when you could
easily label a box as a “router”, “bridge”, or “host” are long gone.

— Norm

-----Original Message-----
From: Philippe Klein <philippe@broadcom.com>
Date: Monday, November 17, 2014 at 11:02 AM
To: Erik Nordmark <nordmark@acm.org>
Cc: "detnet@ietf.org" <detnet@ietf.org>
Subject: Re: [Detnet] L2/L3 model?

>Erik,
>In my humble view, the L3 must only indicate the L3 router path over of
>the L2 island with its path attributes  and let the L2 protocol select
>the constrained path.
>Essentially the inner L2 topology could be ignored by the L3.
>
>/Philippe
>Broadcom
>
>Sent from my iPhone
>
>> On Nov 17, 2014, at 20:11, "Erik Nordmark" <nordmark@acm.org> wrote:
>> 
>> 
>> After the BoF I realized there was one thing we didn't talk about which
>>is what combined L2 and L3 topologies that folks have in mind.
>> It is true that from a packet forwarding perspective both L2 and L3
>>have queues and clocks, but the interaction with the control plane and
>>the approach might be different for different forms of combinations.
>> 
>> First of all we have 6TISCH which is an L3-only network.
>> 
>> But in combined L2/L3 networks we could have at least
>> - interconnecting L2 islands using L3
>> - arbitrary topologies with mixtures of L2 and L3 forwarding devices
>> 
>> A suggestion (at the mike during the BoF) was to consider pseudo-wires.
>>That might make sense when interconnecting L2 islands.
>> But with arbitrary topologies one could end with with a path that as a
>>mixture of bridges and routers e.g.
>> 
>>     Sender - B1 - B2 - R1 - B3 - B4 - B5 - R2 - R3 - Listener
>> 
>> Are there use cases that result in such topologies/paths?
>> 
>> Would one need one controller which is aware of both the L2 and L3
>>devices and can pick paths (with resources) that include both?
>> (Typically we separate the layers thus we might have a PCE which sees
>>the L3 topology but not the L2 devices in between the routers.)
>> 
>> I think it would be good to explore the combined L2/L3 use cases and
>>models in more detail.
>> 
>>   Erik
>> 
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