Re: [spring] How to carry metadata/context in an MPLS packet

All,

Is the idea of using data plane to carry complete metadata is "the way" or
"a way" of approaching the problem ? Has this been already discussed ?

I would rather consider to carry metadata in control plane and only attach
a reference_id (and only when it is needed) to the data plane.

Rgs,
R.

On Fri, Jul 18, 2014 at 3:58 AM, Xuxiaohu <xuxiaohu@huawei.com> wrote:

> Hi all,
>
> I'm now considering how to carry metadata/context in an MPLS packet. I
> just noticed that draft-guichard-mpls-metadata-00 (
> http://tools.ietf.org/html/draft-guichard-mpls-metadata-00#page-6)
> proposes a way to carry metadata/context in an MPLS packet (see below):
>
> "3.  Metadata Channel Header Format
>
>    The presence of metadata within an MPLS packet must be indicated in
>    the encapsulation.  This document defines that the G-ACh Generic
>    Associated Channel Label (GAL) [RFC5586] with label value 13 is
>    utilized for this purpose.  The GAL label provides a method to
>    identify that a packet contains an "Associated Channel Header (ACH)"
>    followed by a non-service payload.
>
>    [RFC5586] identifies the G-ACh Generic Associated Channel by setting
>    the first nibble of the ACH that immediately follows the bottom label
>    in the stack if the GAL label is present, to 0001b.  Further
>    [RFC5586] expects that the ACH not be used to carry user data
>    traffic.  This document proposes an extension to allow the first
>    nibble of the ACH to be set to 0000b and, when following the GAL, be
>    interpreted using the semantics defined in
>    [I-D.guichard-metadata-header] to allow metadata to be carried
>    through the G-ACh channel."
>
> However, it seems that the special usage of the GAL as mentioned above
> still conflicts with the following statement quoted from [RFC5586]:
>
> "  The GAL MUST NOT appear in the label stack when transporting normal
>    user-plane packets.  Furthermore, when present, the GAL MUST NOT
>    appear more than once in the label stack."
>
> I wonder whether the special usage of the GAL as proposed in the above
> draft would result in any backward compatibility issue. In addition, I
> wonder whether it's worthwhile to reconsider the possibility of introducing
> a Protocol Type (PT) field immediately after the bottom of the MPLS label
> stack. With such PT field, any kind of future MPLS payload (e.g., metadata
> header or NSH) can be easily identified.
>
> Best regards,
> Xiaohu
>
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