Re: [mpls] working group adoption poll on draft-sitaraman-mpls-rsvp-shared-labels

"Tarek Saad (tsaad)" <> Wed, 01 November 2017 22:45 UTC

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From: "Tarek Saad (tsaad)" <>
To: Loa Andersson <>
CC: Vishnu Pavan Beeram <>, Lou Berger <>, "" <>, "<>" <>, "" <>, "" <>
Thread-Topic: [mpls] working group adoption poll on draft-sitaraman-mpls-rsvp-shared-labels
Thread-Index: AQHTRP/85dbX584W+UCxGY2NWgHlMaLnBSgAgAq3T4CABtXlAIAGMjKAgAG6kQA=
Date: Wed, 01 Nov 2017 22:44:53 +0000
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Subject: Re: [mpls] working group adoption poll on draft-sitaraman-mpls-rsvp-shared-labels
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Hi all,

I support this work (as co-author) and I see its utility in deployments where RSVP and segment-routing will/can interwork to provide a distributed traffic-engineering solution.
With respect to label terminology used in the current draft, authors had a short discussion and we agreed to align with terminology used in "draft-ietf-spring-segment-routing" for adjacency and binding segment labels so to minimize confusion. This will be clarified in a subsequent update to the document.

-----Original Message-----
From: Vishnu Pavan Beeram <>
Date: Tuesday, October 31, 2017 at 4:20 PM
To: Lou Berger <>
Cc: Loa Andersson <>, "" <>, "<>" <>, "" <>, "" <>
Subject: Re: [mpls] working group adoption poll on draft-sitaraman-mpls-rsvp-shared-labels
Resent-From: <>
Resent-To: <>, <>, <>, Tarek Saad <>
Resent-Date: Tuesday, October 31, 2017 at 4:20 PM

    Lou, Hi!
    Thanks for the feedback!
    Please see inline.
    On Fri, Oct 27, 2017 at 5:43 PM, Lou Berger <> wrote:
    > Hi Pavan,
    >         Sorry about the delayed response.  See below.
    > On 10/23/2017 09:20 AM, Vishnu Pavan Beeram wrote:
    >> Lou, Hi!
    >> Thanks for reviewing this. Please see inline (prefixed VPB) for responses.
    >> Regards,
    >> -Pavan
    >> On Mon, Oct 16, 2017 at 1:41 PM, Lou Berger <> wrote:
    >>> Hi Loa,
    >>>     I have some technical concerns about this document that IMO need to
    >>> be addressed. I think addressing them before adoption would be best but
    >>> is certainly not the only option:
    >>> - The document is completely silent on the impact of shared labels on TE
    >>> bandwidth/tspec/rspec related processing.  Clearly there is some no
    >>> inconsequential impact and this needs to be covered.
    >> [VPB] We will add some text in the next version explaining the mapping
    >> between a shared label and the corresponding bandwidth-reservations.
    >> Implementations that maintain per-label bandwidth accounting at each
    >> hop must aggregate the reservations made for all the LSPs using the
    >> shared-label.
    >> Note that using a shared pop-label (albeit a special
    >> label) along the path of an MPLS RSVP LSP is nothing new. Signaling
    >> for PHP LSPs (we can signal 1-hop PHP LSPs as well) is done today
    >> without any special changes to the tspec/flowspec processing at the
    >> penultimate hop. The only difference now (with the changes proposes in
    >> the draft) is that a pop-label can be used at any given hop along the
    >> path of the LSP.
    > I think sharing in the middle of the network, and potentially onto other
    > hierarchical labels, is a bid different -- this said I think your first
    > couple of sentences above are right on the mark.
    [Pavan] Ack. We'll add relevant text to the next version as indicated.
    >>> - The definition of ' pop and forward tunnel' is a circular at best  (it
    >>> references  'pop and forward labels' which are not defined at all.)  --
    >>> I think I understand what the draft is trying to do, but how do I really
    >>> know that my interpretation is right without a formal definition.  On an
    >>> aside, I think the use of 'pop label' is a poor choice as we'll have an
    >>> architecture that allows for a node to 'pop labels' (i.e., the operation
    >>> defined in RCF3031) and a new RFC that adds 'pop labels' which are
    >>> labels whose value indicates that the node should pop the label and
    >>> forwarded out the interface indicated in the label. BTW this functions
    >>> seems similar to egress control discussed in rfc4003.
    >> [VPB] Please see if the following tweaks to the terminology section
    >> (remove the “verb” vs “noun” ambiguity) address the above concerns.
    >> We’ll fix all occurrences of these terms in the rest of the document.
    >> **
    >> A pop-label:   An incoming label at an LSR that will be popped by the
    >> LSR with the packet being forwarded over a specific outgoing TE link
    >> to a neighbor.
    > How about just avoiding the well established verb altogether? Perhaps
    > "interface label", "TE link label" or even "shared label"?
    [Pavan] We (the authors) aren't too particular about the terms that
    are currently being used in the document. We will be ok with whatever
    terms the WG agrees upon. Personally, I think the terms pop-label and
    swap-label make the operational intent explicit and help make the
    document a better read. That said, I would be ok with "TE link label".
    >> A swap-label:   An incoming label at a LSR that will be swapped to an
    >> outgoing label with the packet being forwarded over a specific
    >> outgoing TE link to a neighbor.
    > isn't this just a "label"?
    [Pavan] Yes, this is just the traditional swap-label. There are
    several places in the document where we refer to this type of label --
    so it seemed useful to define a "term" for this at the beginning and
    use it in the rest of the document.
    >> RSVP-TE pop-and-forward tunnel:   An MPLS RSVP-TE tunnel that requests
    >> the use of a pop-label on every hop of the LSP.
    > I think we can circle back to this after resolving pop-label.  I do
    > think your title is clear and perhaps there's something that can serve
    > as a short hand of that, maybe "Shared Forwarding TE-Tunnel" or "Segment
    > Routing TE Tunnel"?
    >> Pop-and-forward data plane:   A forwarding plane where every
    >> participating LSR uses pop-labels on every LSP.
    >> **
    > I have the same basic comment here as the previous one.
    >>> - In writing this mail, it occurs to me that the addition of this
    >>> function is really an update to RFC3031 defined function and those
    >>> changes should be explicitly and formally described.
    >> [VPB] I believe what you are saying is that the “forward” aspect in
    >> “pop-and-forward” is not discussed in RFC3031. And hence, the need to
    >> formally update RFC3031. We (the authors) would be ok with whatever
    >> the WG deems fit in this regard.
    > I think the draft needs to document how the defined operations fit into
    > 3031 or how they extend / update 3031.
    > Lou
    >>> Lou
    >>> On 10/14/2017 11:20 AM, Loa Andersson wrote:
    >>>> Working Group,
    >>>> This is to start a two week poll on adopting
    >>>> draft-sitaraman-mpls-rsvp-shared-labels-02 as a MPLS working group document.
    >>>> Please send your comments (support/not support) to the mpls working
    >>>> group mailing list ( Please give a technical
    >>>> motivation for your support/not support, especially if you think that
    >>>> the document should not be adopted as a working group document.
    >>>> There are three IPR disclosures (though one disclosure seems to be an
    >>>> update) against this document.
    >>>> All the authors have stated on the MPLS wg mailing list that they are
    >>>> unaware of any other IPRs that those that has been disclosed
    >>>> The working group adoption poll ends October 29, 2017.
    >>>> /Loa
    >>>> mpls wg co-chair
    >>> _______________________________________________
    >>> mpls mailing list