[c-nsp] MPLS over VLAN

[Rob Shakir]

On 27 Apr 2010, at 06:50, Samit wrote:

> But my understanding is it should not...because the c-tag and s-tag or
> whatsoever like b-vid.....it..would be considered as a  payload when it
> enters the MPLS network.Appreciate if someone comment or confirm this..

Seems to me like the confusion here is around the fact that you've forgotten where MPLS sits in the stack :-)

Bear in mind that the frame that comes out of your PE looks something like the following:

+------------------------------+
|  Ethernet Header with 802.1q |
+------------------------------+
|  MPLS Label(s) + Headers     |
+------------------------------+
|  Customer's Ethernet Header  |
+------------------------------+
|  Customer's Packet Payload   |
+------------------------------+

Your infrastructure just looks at the top Ethernet header, if it's an L2 device. If it's an MPLS (L2.5) device, then it looks at the MPLS label, at which time it'll have a VFI ID or a VC ID, and this will be forwarded according to that (assuming it's an edge LSR - if it's a midpoint, it'll just swap the labels as usual). Nothing in your infrastructure (assuming that you're looking at VPLS with the customer connected to the PE, rather than H-VPLS or so with some metro L2 at the edge), will look at the customer's frame.

If there is a metro, then as you say, you'll likely have QinQ or similar, so you'll look at your outer 802.1q on the popped packet. As Gert says, any L2 switches a frame, it'll do so on MAC, and has no awareness of what's in the packet, or what relevance it has to any service.

Kind regards,
Rob

-- 
Rob Shakir                      <rjs at eng.gxn.net>
Network Development Engineer    GX Networks/Vialtus Solutions
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