The MPLS WG Archive

[Luca Martini <luca@level3.net>]

Robbie Harrell wrote:
> 
> Luca, I was reading the Internet draft "Transport of Layer 2 frames over
> MPLS" and had the following questions.  Using the example given with R1 an
> R2, does the ingress L2 protocol and the egress L2 protocol have to be the
> same.  For instance can I bring in a L2 ATM cell over ATM at R1, transport
> over my MPLS tunnel and deliver over an Ethernet egress interface at R2.

Yes, they have to be the same. THere is a statement made about not doing
internetworking in this implementation.

> This doesn't seem possible to me unless the router reads the L3 information
> and makes a routing decision on the L3 information irregardless of the L2
> encapsulation.  I am working on a project to build a next generation NAP and
> this would be an ideal scenario for one to many peering connections with
> multiple ingress encapsulations.  We are trying to eliminate the
> intermediate routers found in the NAP so that peers are from ISP router to
> ISP router (like R1 and R2 in the document).  My major concern is whether or
> not this works for a provider who connects on the ingress with say an ATM
> pipe and wants to peer with other providers who may have Frame-Relay,
> Ethernet, or ATM.  There would be multiple peering sessions over MPLS
> tunnels.   It would have to come into the MPLS cloud under one L2
> encapsulation and leave under another.  I am assuming the router would have
> to be involved to assume protocol translations at the egress edge.  Any
> thoughts, hints or clarifications.
> 

It could be possible to actually do the internetworking function in the
end router device.
In this case the traffic would transit the network in native mode. If it
came in ATM AAL5, 
the PDUs would be transported unchanged to the egress router , where
they would be converted to a different protocol. This could be a vendor
specific feature, and does not have to be done "in the network".
In this case the end router doing the conversion has all the information
it could possibly need to do internetworking successfully.

Luca Martini



> Robbie Harrell
> Senior Consultant
> Callisma
> 866-543-5737 pager
> 8772079316@skytel.com

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Luca Martini Senior Network Architect, Level 3 Communications -
Broomfield, CO
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