Re: [mpls] working group last call on draft-ietf-mpls-spring-entropy-label

<bruno.decraene@orange.com> Fri, 06 May 2016 09:34 UTC

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From: bruno.decraene@orange.com
To: Sri <sriganeshkini@gmail.com>
Thread-Topic: [mpls] working group last call on draft-ietf-mpls-spring-entropy-label
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Date: Fri, 06 May 2016 09:34:41 +0000
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Subject: Re: [mpls] working group last call on draft-ietf-mpls-spring-entropy-label
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Hi Sri,

Thanks for the follow up.
As previously asked, is RLD specific to the use of the entropy label or not? Let’s remember that multipath load balancing existed before EL, and that transit LSR not compliant with EL can still benefit from the presence of the EL label.
If RLD is not specific to EL, I’m not certain that adding the reference to RFC6790 is the best way to clarify.
In all cases, this point should be stated in the document defining RLD. (which may be this one, of maybe the IGP extensions if draft-ietf-mpls-spring-entropy-label gets informational).

> I have not used your suggested sentence "...both the ELI and EL MUST be.." since the ELI is placed above the EL and if the LSR can read the EL, it can obviously have read the ELI.
Agreed. Yet mentioning both labels helps the reader to remember that the limit for the number of “useful” labels is RLD-2. (I mean useful for steering the packet, I’m not implying that EL is not useful). This may be obvious for people coming from the EL space, but less for people coming from the spring space, especially since the text often refers to a/the (i.e. one) EL label. But this points could indeed be stated elsewhere.

Thanks,
-- Bruno

From: Sri [mailto:sriganeshkini@gmail.com]
Sent: Wednesday, May 04, 2016 7:08 PM
To: DECRAENE Bruno IMT/OLN
Cc: LITKOWSKI Stephane OBS/OINIS; draft-ietf-mpls-spring-entropy-label@tools.ietf.org; mpls@ietf.org; mpls-chairs@ietf.org
Subject: Re: [mpls] working group last call on draft-ietf-mpls-spring-entropy-label

Hi Bruno,

Thanks for the clarification. On my first read of your last sentence under NEW it had seemed to me that it is placing a restriction on the ingress. On reading your clarification I understand that it is not your intent. So I accept the comment for the NEW definition but suggest that that we refer to RFC6790 rather than re-stating that EL is used for load-balancing. So how about this for sec 4 para2 (changes highlighted) -


   An LSR may have a limitation on the depth of the label stack that it can read and process

    in order to do multipath load balancing as described in [RFC6790].  This limitation

   expressed in terms of the number of label stack entries that the LSR

   can read is defined as the Readable Label Depth (RLD)

   capability of that LSR.  If an EL does not occur within the RLD of an

   LSR in the label stack of the MPLS packet that it receives, then it

   would lead to poor load balancing at that LSR.  The RLD of an LSR is

   a characteristic of the forwarding plane of that LSR's implementation

   and determining it is outside the scope of this document.

I have not used your suggested sentence "...both the ELI and EL MUST be.." since the ELI is placed above the EL and if the LSR can read the EL, it can obviously have read the ELI.

Thanks
Sri

On Wed, May 4, 2016 at 7:09 AM, <bruno.decraene@orange.com<mailto:bruno.decraene@orange.com>> wrote:
Hi Sri,

> The definition of RLD must not specify conditions on when an EL must be used. RLD is a per LSR characteristic. Any recommendations on placing the EL must be specified outside of the definition.

IMO, the goal of RLD is specifically to say that the EL needs to be within the RLD in order for the EL to be used for load-balancing. Otherwise, can you clarify the goal of signaling this RLD?

(That’s a different point compared to specifying the position of the EL in the stack, which is a freedom of the ingress. (although a secondary goal of this goal seems to be to reduce this freedom))

-- Bruno

From: Sri [mailto:sriganeshkini@gmail.com<mailto:sriganeshkini@gmail.com>]
Sent: Wednesday, May 04, 2016 3:56 PM
To: DECRAENE Bruno IMT/OLN
Cc: LITKOWSKI Stephane OBS/OINIS; draft-ietf-mpls-spring-entropy-label@tools.ietf.org<mailto:draft-ietf-mpls-spring-entropy-label@tools.ietf.org>; mpls@ietf.org<mailto:mpls@ietf.org>; mpls-chairs@ietf.org<mailto:mpls-chairs@ietf.org>
Subject: Re: [mpls] working group last call on draft-ietf-mpls-spring-entropy-label

Hi Bruno,

On Wed, May 4, 2016 at 6:45 AM, <bruno.decraene@orange.com<mailto:bruno.decraene@orange.com>> wrote:
Hi Stéphane,

Thanks for the quote. I had read that sentence, and I think it could be made more precise.
e.g.

OLD: This limitation expressed in terms of the number of label stack entries that the LSR  can read is henceforth referred to as the Readable Label Depth (RLD)  capability of that LSR.

NEW: This limitation expressed in terms of the number of label stack entries that the LSR  can read. This document defines the Readable Label Depth (RLD) as the number of labels that a transit LSR can read for load-balancing purpose.  When EL is used, both ELI and EL MUST be within the RLD, in order for the EL to be used during load-balancing.

The definition of RLD must not specify conditions on when an EL must be used. RLD is a per LSR characteristic. Any recommendations on placing the EL must be specified outside of the definition.


Sri

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