Re: [Detnet] L2/L3 model?

["Norman Finn (nfinn)" <[e-mail]>]

Catching up on my email.

I agree most definitely that we want to explore arbitrary combinations of
L2/L3, with paths including any combination of routers and bridges.

Without going too deep into MPLS/Pseudo-wire topics, let me point out that
what the bridges need is a pair {VLAN, multicast destination MAC address}
that uniquely identifies the flow to which the Ethernet frame belongs (at
least among the packets seen by that bridge).  The bridges don’t care
whether MPLS is present in the frame or not.  So, if the routers can apply
a {VLAN, MAC address} to the packet that will be handled by a bridge, then
the routers can switch on the MPLS labels and the bridges on the Ethernet
stuff.

Note that MPLS labels can go end-to-end, or as close to the ends as you
want them to go, as is normal for MPLS; you don’t need to get rid of MPLS
when going through the bridges.

How close this gets to the Talker and Listener is another matter, and we
can talk about that in another message.

— Norm

-----Original Message-----
From: Erik Nordmark <[e-mail]>
Date: Monday, November 17, 2014 at 10:11 AM
To: "[e-mail]" <[e-mail]>
Subject: [Detnet] L2/L3 model?

>
>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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