Re: [Lsr] [mpls] Comments on draft-ietf-mpls-spring-entropy-label

"Ketan Talaulikar (ketant)" <> Fri, 06 July 2018 02:23 UTC

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From: "Ketan Talaulikar (ketant)" <>
To: "徐小虎(义先)" <>, Jeff Tantsura <>, "stephane.litkowski" <>, "" <>
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Thread-Topic: [mpls] Comments on draft-ietf-mpls-spring-entropy-label
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Date: Fri, 06 Jul 2018 02:23:16 +0000
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Subject: Re: [Lsr] [mpls] Comments on draft-ietf-mpls-spring-entropy-label
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Hi Xiaohu,

The IGP drafts define MSD as a framework that enable advertisements for various type of SID limits – starting with the Base MSD Type – 1. You are referring to this generic construct of MSD in the text you quote below. It is, however, the Base MSD (type 1) which is aligned with the definition in PCEP-SR.

IMHO the PCEP-SR draft definition should be updated to refer to this base MSD type.


From: mpls <> On Behalf Of ???(??)
Sent: 06 July 2018 06:55
To: Jeff Tantsura <>; stephane.litkowski <>;
Subject: Re: [mpls] Comments on draft-ietf-mpls-spring-entropy-label

Hi Jeff,

Thanks for your clarification. IMHO, no matter the MSD information is provided by whatever protocol, the semantics of the MSD itself should be unified in the IETF community. Otherwise, it would introduce unnecessary confusion to implementors and operators.

It said in the OSPF-MSD draft:

   MSD: Maximum SID Depth - the number of SIDs a node or one of its

   links can support"

What does the "support" exactly mean? It seems at least to me a little bit ambiguous compared to the MSD concept as defined in the PCEP-SR draft.

Best regards,


From:Jeff Tantsura <<>>
Send Time:2018年7月6日(星期五) 07:48
To:stephane.litkowski <<>>; 徐小虎(义先) <<>>;<> <<>> <<>>;<> <<>>
Subject:Re: [mpls] Comments on draft-ietf-mpls-spring-entropy-label


Please see inline (MSD section).
Hope this clarifies, thanks!


[jeff] both IGP drafts have identical description of the BMI-MSD:
“Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS labels a node is capable of imposing, including all service/transport/special labels.”
PCEP draft supports only a subset of overall MSD functionality and in general it is expected that this info would come from IGPs(BGP-LS).
However the functoriality provided by PCEP is inline with the  BMI-MSD definition in the IGP drafts, at the node granularity only though.

3. Section 5 introduces the MSD concept. I wonder whether this concept is aligned with the MSD concept as defined in the PCEP-SR draft or the MSD concept as defined in the IGP-MSD draft. In PCEP-SR draft, it said "

The "Maximum SID Depth" (1

   octet) field (MSD) specifies the maximum number of SIDs (MPLS label

   stack depth in the context of this document) that a PCC is capable of

   imposing on a packet.

In the IGP-MSD draft, it said "

MSD of type 1 (IANA Registry), called Base MSD is used to signal the

   total number of SIDs a node is capable of imposing, to be used by a

   path computation element/controller.  "

If I understand it correctly, the MSD in this draft==the MSD in PCEP-SR draft==the Base MSD (i.e., the MSD of type 1), No?

[SLI] Today, the two IGP drafts does not seem to agree on the definition

ISIS says:” Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS
   labels a node is capable of imposing, including all
   service/transport/special labels.”

OSPF says:” MSD of type 1 (IANA Registry) is used to signal the number of SIDs a
   node is capable of imposing, to be used by a path computation
   element/controller and is only relevant to the part of the stack
   created as the result of the computation.”

MSD is just MSD is defines a maximum number of labels to be pushed. This is the definition we use and it is compliant with the one used in PCEP-SR:

“The "Maximum SID Depth" (1
   octet) field (MSD) specifies the maximum number of SIDs (MPLS label
   stack depth in context of this document) that a PCC is capable of
   imposing on a packet.”

As we also say: “This includes any kind of labels (service, entropy, transport...).”, we are compliant with the BMI-MSD defined in IS-IS.

Best regards,


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