Subject: bridging over mpls

From: Juha Heinanen <[email-masked]>
Date: Fri, 19 Nov 1999 10:36:08 +0200 (EET)

i read draft-ietf-mpls-label-encaps-07.txt and was surprised that it
(and i guess also the architecture i-d) seem to preclude bridging of
layer 2 packets over mpls lsps:

   "Multi-Protocol Label Switching (MPLS)" [1,2] requires a set of
   procedures for augmenting NETWORK LAYER packets with "label stacks",
   thereby turning them into "labeled packets".

   The label stack entries appear AFTER the data link layer headers, but
   BEFORE any NETWORK LAYER headers.

   The network layer packet immediately follows the label stack entry
   which has the S bit set.

   When the last label is popped from a packet's label stack (resulting
   in the stack being emptied), further processing of the packet is
   based on the packet's network layer header.
   
   etc.

it this intentional?  i need to be able to bridge ethernet packets over
mpls lsps.

also, draft-ietf-mpls-label-encaps-07.txt seems to preclude multiplexing
several protocols over a single mpls lsps, for example, by prexifing the
packet by an llc/snap header:

   This means that the identity of the network layer protocol
   must be inferable from the value of the label which is popped from
   the bottom of the stack, possibly along with the contents of the
   network layer header itself.

is this too intentional, i.e., that the only allowed mode of carrying
packets over mpls lsps is vc muxing?

i hope that the answer to both of the above questions is NO and that the
text will be fixed accordingly.  also, i feel that ldp establishment
message should be extented to indicate the protocol or the protocol
multiplexing method of the lsp.

-- juha

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From: [email-masked] (Anoop Ghanwani)
Date: Sat, 20 Nov 1999 01:03:38 -0500 (EST)

> it this intentional?  i need to be able to bridge ethernet packets over

In the case of bridging, I would assume that the entire packet that
needs to be bridged (including its Layer 2 header) would constitute the
payload of the MPLS packet.  There would be another Layer 2 header
prepended to the MPLS labeled packet that would get the packet from one
hop to another as it traverses the LSP.  At the end of the LSP,
everything up to and including the label would get stripped off, and
you'd have the original Ethernet packet.  This requires that the egress
LSP know that what is coming off the LSP is bridged Ethernet traffic.

-Anoop

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From: Juha Heinanen <[email-masked]>
Date: Sat, 20 Nov 1999 23:27:23 +0200 (EET)

> LSP know that what is coming off the LSP is bridged Ethernet traffic.

i too would assume what you describe, but the spec doesn't allow it nor
tell how to do it.

-- juha

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From: "Scott W Brim" <[email-masked]>
Date: Sat, 20 Nov 1999 20:28:54 -0500

How about using GRE?

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From: Juha Heinanen <[email-masked]>
Date: Mon, 22 Nov 1999 08:26:54 +0200 (EET)

> How about using GRE?  

you are welcome, but i don't want to the overhead.

-- juha