Subject: Proposal for last open issue re draft-ietf-mpls-diff-ext-04.txt

From: Francois Le Faucheur <[email-masked]>
Date: Thu, 23 Mar 2000 19:10:14 +0100

Hello,

A single issue from the Informal Last Call on
draft-ietf-mpls-diff-ext-03.txt had not been closed as of
draft-ietf-mpls-diff-ext-04.txt. This is the detailed ingress and egress
Diff-Serv behavior when pushing and popping labels.

Here is a high level proposal for resolution of this issue.

The proposal borrows heavily from draft-ietf-diffserv-tunnels-00.txt,
'Differentiated Services and Tunnels' from D Black.

Most of the characteristics of the problem statement addressed by this
draft are common with the issue we need to address in
draft-ietf-mpls-diff-ext-04.txt:
	- intermediate nodes only see and operate on the "outer" Diff-Serv
information
	- IP tunnels/LSPs Tunnels are unidirectionnal
	- the outer Diff-SErv information may get modified somewhere on the span
of the IP Tunnel/LSP Tunnel

There is a few notable differences between an LSP Tunnel and an IP Tunnel
though:
	- Penultimate Hop Popping (PHP) results in the LSP Tunnel Diff-SErv
information not being transmitted to the LSP Tunnel Egress.
	- two level LSP Tunnels from same ingress to same egress are expected to
be common occurence in MPLS-land for MPLS VPN so we need to address this
case. I have only covered below the case of unlabelled packets going into a
two level LSP tunnel because MPLS VPN is the only case I can think of for
this two level LSP tunnels.

Based on this, I would propose that:

	- like with draft-ietf-mpls-diff-ext-04.txt, we recognise that there are
two meaningful conceptual models which are "Uniform" model and "Tunnel" model.

	- like with draft-ietf-mpls-diff-ext-04.txt, we recognise that they are
both useful.

	- unlike with draft-ietf-mpls-diff-ext-04.txt, we can play with PHP to
simplify operations of the egress in case of single level LSP Tunnel

	- for single level LSP Tunnel, to achieve "tunnel" mode:
		* Ingress: Egress PHB is reflected in pushed label. Egress PHB is NOT
reflected in swapped label or encapsulated IP DSCP.
		* Egress: requests PHP and therefore use "outer" Diff-Serv info for
incoming PHB determination (ie outer label for received labelled packet or
DSCP for received unlabelled packet).

	- for single level LSP Tunnel, to achieve "uniform" mode:
		* Ingress: Egress PHB is reflected in pushed label. It does not matter if
Egress PHB is also reflected in swapped label or encapsulated IP DSCP since
this will be rewritten at egress ayway.
		* Egress: requests No-PHP and use "outer" Diff-Serv info for incoming PHB
determination (ie outer label before POP for received labelled packet, or
DSCP for received unlabelled packet). 

	- for two level LSP Tunnel (MPLS VPN), to achieve "tunnel" mode:
		* Ingress: Egress PHB is reflected in both pushed labels. Egress PHB is
NOT reflected in encapsulated IP DSCP.
		* Egress: requests PHP but still can NOT use "outer" label for incoming
PHB determination. Egress must be able to use the DSCP of the packet (as
exposed after the POP) to do PHB determination. In other words, Egress must
be able to (logically) do the PHB determination after the POP.

	- for two level LSP Tunnel (MPLS VPN), to achieve "uniform" mode:
		* Ingress: Egress PHB is reflected in both pushed labels. It does not
matter if it is also reflected in encapsulated IP DSCP since this will be
rewritten at egress ayway.
		* Egress: requests PHP anyway (because with MPLS VPNs both labels are
expected to reflect the same PHB) and use "outer" label/or DSCP for
incoming PHB determination (before doing POP).In other words, Egress must
be able to (logically) do the PHB determination before the POP.

Thanks for comments. 
As soon as we've reached agreement I will proposed detailed text for the
next rev of the draft.

Francois

_________________________________________________________________
Francois Le Faucheur   
Development Engineer, IOS Layer 3 Services 
Cisco Systems 
Office Phone:   	+33 4 92 96 75 64
Home Office Phone:     +33 4 92 94 00 78
Mobile :               +33 6 89 108 159
Vmail:                 +33 1 58 04 62 66
Fax:                   +33 4 92 96 79 08
Email:          	[email-masked]
_________________________________________________________________
Petra B - Les Lucioles - 291, rue Albert Caquot - 06560 Valbonne - France
_________________________________________________________________

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From: Curtis Villamizar <[email-masked]>
Date: Thu, 23 Mar 2000 14:20:31 -0500

In message <[email-masked]>, Francois Le Faucheur write
s:
> 	- like with draft-ietf-mpls-diff-ext-04.txt, we recognise that there
>  are two meaningful conceptual models which are "Uniform" model and "Tunnel"
>  model.

Please explain what "Uniform" model and "Tunnel" model are attempting
to accomplish.  Maybe then the rule set below will be clear.

Also, please state that the egress MAY request PHP, since not
requesting PHP and doing the right thing is also a viable and perhaps
a preferable option.

Curtis