At 7:58 PM -0700 11/12/2000, Irwin Lazar wrote:
>
>
>To further cloud the discussion, I've heard folks argue that MPLS is a layer
>2 1/2 protocol, and I've also heard folks argue that MPLS is a layer 3 1/2
>protocol since it rides on top of IP (though how something could ride "on
>top" of IP yet control the data link layer baffles me).
>
>Would it be fair to say that MPLS is therefore a Layer 2/3 control protocol,
>and is therefore outside the typical OSI layers? Or, is it a Layer 3
>protocol?
Again, I must begin by referring to the full OSI specifications, not
the reference model alone. The Internal Organization of the Network
Layer divides it into three levels:
Subnetwork Independent: IP, CLNP, IPX
Subnetwork Convergence: ARP
Subnetwork Dependent Access: X.25, LLC, etc.
Subnetwork dependent access includes what often get called "layer
2.5" protocols.
To answer your specific question, consider that a MPLS LSP can have
IP endpoints. MPLS is not IP internally, so I would consider it a
subnetwork dependent access protocol.
The LSPs themselves are in the user plane. LDP, RSVP-TE, CR-LDP,
etc., are control/management protocols.
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