Subject: [mpls] Non-Standard use of MPLS

From: Bob Anders <[email-masked]>
Date: Fri, 27 May 2005 18:32:37 +0800

Dear MPLS-Experts,

I am aware that MPLS is intended to be used for switching purposes,
but I was wondering if anyone knows about implementations or plans
that make use of MPLS in a non-standard way, like

- MPLS is still used to make forwarding decisions, but the stack
contains also non-forwarding relevant information either in Exp bits
or in separate labels (type of information possibly identified by Exp
bits)
Or
- The MPLS stack is only used as a "vehicle" to encode additional
non-forwarding relevant information. Forwarding decisions are still
based on the underlying protocol (e.g. IPv4).

When talking about non-forwarding relevant data, I am thinking of
information used for encryption, network statistics, billing, etc ...

If there is anything out there (or maybe planed by IETF or whoever)
that makes use of MPLS-like stacks as described above, I would be
happy to hear about it (URLs, papers, ...).

Thanks and have a nice weeked!

  Bob

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From: "Andrew G. Malis" <[email-masked]>
Date: Fri, 27 May 2005 08:02:32 -0400

Bob,

The PWE3 working group has defined a non-IP-forwarding use for the 
innermost label on the stack - it identifies a logical or physical layer 1 
or layer 2 port on a router, plus optionally a layer 2 multiplexing tag or 
label (FR DLCI, Ethernet VLAN tag, ATM VPI/VCI, etc.).

This mechanism is also used by the L2VPN working group for VPLS and other 
layer 2 VPNs over MPLS.

Cheers,
Andy

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From: David Charlap <[email-masked]>
Date: Fri, 27 May 2005 10:10:43 -0400

> or in separate labels (type of information possibly identified by Exp

This is done already for certain features.

EXP bits are used to encode priority levels in E-LSPs.

Non-forwarding labels are used to identify VPNs (PWE3) and to identify 
the payload-type for layer-2 traffic (Martini).

> based on the underlying protocol (e.g. IPv4).

I'm pretty sure that this would violate quite a number of RFCs.  If an 
MPLS router receives labeled traffic, it is supposed to forward that 
traffic according to its label.

If you need to tack additional information onto non-MPLS traffic, there 
are mechanisms for doing so, including options in the IP header and 
various kinds of IP-in-IP encapsulation.

> information used for encryption, network statistics, billing, etc ...

WRT MPLS, this information is probably best propagated by the signaling 
stack.  Adding (possibly new) objects to Path and Resv messages works 
well for propagating information between the connection endpoints.  When 
combined with some form of per-LSP traffic counter, you should get all 
the information you need without having to alter the data-plane traffic 
at all.

Of course, your specific application requirements would dictate the best 
approach.

-- David