[mpls] Re: Fwd: New Version Notification for draft-li-mpls-mna-entropy-03.txt

[Loa Andersson <[e-mail]>]

+------------------------------------------------------------+
|                                         |
                   +---+                                       |
            +------| D |                                       |
            |      +---+                                       |
            |        |                                         |
          +---+      +---------------------------------------+ |
    +-----| B |                                              | |
    |     +---+      +-------------------------------------+ | |
    |       |        |                                     | | |
    |       |      +---+                                   | | |
    |       +------| E |                                   | | |
    |              +---+                                   | | |
    |                |                                     | | |
    |                +-----------------------------------+ | | |
    |                                                    | | | |
  +---+                                                 +-------+
-| A |                                                 |   Z   |
  +---+ +-------+
    |                                                    | | | |
    | +-----------------------------------+ | | |
    |                |                                     | | |
    |              +---+                                   | | |
    |       +------| F |                                   | | |
    |       |      +---+                                   | | |
    |       |        |                                     | | |
    |     +---+ +-------------------------------------+ | |
    +-----|C |                                              | |
          +---+      +---------------------------------------+ |
            |        |                                         |
            |      +---+                                       |
            +------| G |                                       |
                   +---+                                       |
                     |                                         |
+------------------------------------------------------------+


Not a network model, but a description of load-sharing option. You say that
we need the number of paths that a packet may take through the network. 
In the figure above a packet coming into node from the can be sent 
either "north" or "south". If it sent "north" it will enter node B and 
again go north or south. Once a packet reach node D, E, F, or G, it 
traverses a part of the network that does not do load-sharing. (Yes, I'm 
lazy!) To me the load-sharing decision seem to a local matter, what is 
the impact of the fact that there are 8 routes through the network? What 
seem to have a bigger impact is the number of out going load-sharing 
interface, but again that is local.
/Loa



Den 03/09/2024 kl. 04:02, skrev Stewart Bryant:
> @Loa:
>
> As part of determining the number of entropy bits we need, we need to consider the number of paths that a packet may take through the network.
>
> What normally happens is that the entropy is reduced to a much smaller number of bits at each path split point to pick - from n possible next hops for the packet.
>
> So prior question: for any given communicating pair, how many end to end paths do we need to design for?
>
> Best regards
>
> Stewart
>
>> On 2 Sep 2024, at 9:56 AM, Loa Andersson <[e-mail]> wrote:
>>
>> Adrian,
>>
>> inlline.
>>
>>> Den 02/09/2024 kl. 16:20, skrev Adrian Farrel:
>>> How do you measure?
>>> Size : 2^20 bits available in EL and LSE-C
>>> Place in stack : No restriction on either
>>> Repetition in stack : No restriction on either
>>>
>>> A
>> OK, I was struggling  before, this does not make it better :(.
>>
>> If all our methods are "equal", why do we struggle to develop
>> new methods?
>>
>> One question I really can't keep from asking. Hope someone can
>> lay it to rest.
>>
>> In hashing the stack a stack with 6 non-SPL labels gives me entropy
>> based on 6 x 2^20 bits, to give me entropy based on the same number of bit with EL/ELI I need 12 LSEs, right?
>>
>> AS for an MNA based method you can use 20 bits in the LSE Format C and
>> another 30 in an LSE Format D, right
>>
>> /Loa
>>> -----Original Message-----
>>> From: Loa Andersson <[e-mail]>
>>> Sent: 02 September 2024 09:11
>>> To: Stewart Bryant <[e-mail]>; Tony Li <[e-mail]>
>>> Cc: mpls <[e-mail]>
>>> Subject: [mpls] Re: Fwd: New Version Notification for draft-li-mpls-mna-entropy-03.txt
>>>
>>> Stewart and Tony,
>>>
>>> This might be classified as naive questions :).
>>>
>>>> Den 02/09/2024 kl. 15:15, skrev Stewart Bryant:
>>>> Hi Tony
>>>>
>>>> I am struggling to see whether this has a sufficient advantage over
>>>> the existing EL/ELI mechanism to justify us recommending it existence.
>>>>
>>>> It is obvious that this can be done, and it saves an LSE, but is that
>>>> sufficient justification for the complexity introduced by having two
>>>> mechanisms that of necessity need to co-exist?
>>>>
>>>> We also need to understand what happens in a legacy routers that are
>>>> looking for EL/ELI and older routers that just hash the stack. I think
>>>> they just provide less (no?) entropy.
>>> Is there a scientific way of calculating "how much" entropy the
>>> different  generate?
>>>
>>> Is more entropy always better?
>>>
>>> What are the factors that determine how much entropy you need?
>>>
>>> /Loa
>>>
>>>
>>>> I imagine this ends with routers needing to parse for both types of
>>>> entropy which is not a great position to be in.
>>>>
>>>> Best regards
>>>>
>>>> Stewart
>>>>
>>>>> On 30 Aug 2024, at 5:26 PM, Tony Li <[e-mail]> wrote:
>>>>>
>>>>>  [WG chair hat: off]
>>>>>
>>>>> Hi,
>>>>>
>>>>> This update addresses comments from Adrian Farrel as part of the WG
>>>>> adoption process.
>>>>>
>>>>> Comments and corrections are most welcome.
>>>>>
>>>>> Thanks,
>>>>> Tony
>>>>>
>>>>>
>>>>>> Begin forwarded message:
>>>>>>
>>>>>> *From: *"internet-drafts at ietf.org" <[e-mail]>
>>>>>> *Subject: **New Version Notification for
>>>>>> draft-li-mpls-mna-entropy-03.txt*
>>>>>> *Date: *August 30, 2024 at 9:24:05 AM PDT
>>>>>> *To: *"John Drake" <[e-mail]>, "Tony Li" <[e-mail]>
>>>>>> *Reply-To: *[e-mail]
>>>>>>
>>>>>> A new version of Internet-Draft draft-li-mpls-mna-entropy-03.txt has
>>>>>> been
>>>>>> successfully submitted by Tony Li and posted to the
>>>>>> IETF repository.
>>>>>>
>>>>>> Name:     draft-li-mpls-mna-entropy
>>>>>> Revision: 03
>>>>>> Title:    MPLS Network Action for Entropy
>>>>>> Date:     2024-08-28
>>>>>> Group:    Individual Submission
>>>>>> Pages:    5
>>>>>> URL:
>>>>>>       https://www.ietf.org/archive/id/draft-li-mpls-mna-entropy-03.txt
>>>>>> Status:   https://datatracker.ietf.org/doc/draft-li-mpls-mna-entropy/
>>>>>> HTMLized:
>>>>>> https://datatracker.ietf.org/doc/html/draft-li-mpls-mna-entropy
>>>>>> Diff:
>>>>>>      https://author-tools.ietf.org/iddiff?url2=draft-li-mpls-mna-entropy-03
>>>>>>
>>>>>> Abstract:
>>>>>>
>>>>>>    Load balancing is a powerful tool for engineering traffic across a
>>>>>>    network and has been successfully used in MPLS as described in RFC
>>>>>>    6790, "The Use of Entropy Labels in MPLS Forwarding".  With the
>>>>>>    emergence of MPLS Network Actions (MNA), there is signficant benefit
>>>>>>    in being able to invoke the same load balancing capabilities within
>>>>>>    the more general MNA infrastructure.
>>>>>>
>>>>>>    This document describes a network action for entropy to be used in
>>>>>>    conjunction with "MPLS Network Action (MNA) Sub-Stack Solution".
>>>>>>
>>>>>>
>>>>>>
>>>>>> The IETF Secretariat
>>>>>>
>>>>>>
>>>>> _______________________________________________
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>> --
>> Loa Andersson
>> Senior MPLS Expert
>> Bronze Dragon Consulting
>> [e-mail]
>> [e-mail]
>>

-- 
Loa Andersson
Senior MPLS Expert
Bronze Dragon Consulting
[e-mail]
[e-mail]