Re: [Lsr] [draft-ietf-lsr-flex-algo-08] Clarification on ASLA usage for flex-algo

Peter Psenak <ppsenak@cisco.com> Mon, 10 August 2020 08:28 UTC

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To: Sarah Chen <sarahchen=40arista.com@dmarc.ietf.org>
Cc: Tony Li <tony.li@tony.li>, "lsr@ietf.org" <lsr@ietf.org>, "draft-ietf-lsr-flex-algo@ietf.org" <draft-ietf-lsr-flex-algo@ietf.org>, "Van De Velde, Gunter (Nokia - BE/Antwerp)" <gunter.van_de_velde@nokia.com>
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From: Peter Psenak <ppsenak@cisco.com>
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Date: Mon, 10 Aug 2020 10:27:43 +0200
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Subject: Re: [Lsr] [draft-ietf-lsr-flex-algo-08] Clarification on ASLA usage for flex-algo
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Hi Sarah,

On 08/08/2020 01:33, Sarah Chen wrote:
> Hi, Peter,
> 
> The flex-algo draft mentions "Min Unidirectional Link Delay as defined 
> in [RFC7810 <https://tools.ietf.org/html/rfc7810>]". When reading 
> RFC7810, I found two Sub-TLVs:
> 
> 4.1. Unidirectional Link Delay Sub-TLV 4.2. Min/Max Unidirectional Link 
> Delay Sub-TLV
> 
> Could you please clarify which one should be used? If "Min/Max 
> Unidirectional Link Delay Sub-TLV" is used, will the max delay carried 
> in the subTLV be ignored?

flex-algo as defined in the draft uses "Min Unidirectional Link Delay", 
which is advertised in the "Min/Max Unidirectional Link Delay Sub-TLV".

The fact that the "Min/Max Unidirectional Link Delay Sub-TLV" carries 
some other data (e.g. Max delay) is orthogonal to the flex-algo usage.

thanks,
Peter



> 
> Thanks,
> Sarah
> 
> On Fri, Aug 7, 2020 at 8:30 AM <tony.li@tony.li 
> <mailto:tony.li@tony.li>> wrote:
> 
> 
>     Peter,
> 
> 
>      >> . The existing description in section 5.1 indicate that legacy
>     encoding (RFC7810 and RFC5305) is used for link attributes. That is
>     not correct based upon section 11. To avoid ambiguity can an
>     explicit reference be added for [I-D.ietf-isis-te-app]?
>      >
>      >
>      > well, section 5.1. is correct. The Min Unidirectional Link Delay
>     and TE Default metric respectively were defined in RFC7810 and
>     RFC5305. The fact that we advertise them in ASLA does not change
>     their origin.
> 
> 
>     Could we please get a clarification in section 5.1 then?  The
>     references there to 7810 and 5305 without any qualification strongly
>     suggest that the encoding from those RFCs should be used.
> 
> 
>      >> Could in section 11 be explicit reference to (e)ag, te-metric
>     and delay link attributes MUST be encoded using ASLA..
>      >
>      > Section 11 already says:
>      >
>      >   Link attribute advertisements that are to be used during Flex-
>      >   Algorithm calculation MUST use the Application Specific Link
>      >   Attribute (ASLA) advertisements defined in
>     [I-D.ietf-isis-te-app] or
>      >   [I-D.ietf-ospf-te-link-attr-reuse].
>      >
>      > I'm not sure what else can we say. Listing the ones we use today
>     wold be dangerous, because we may define additional ones later and
>     we want the ASLA to be mandatory for all of them.
> 
> 
>     You could add a sentence that says:
> 
>              In particular, the Min Unidirectional Link Delay, TE
>     Default Metric, Administrative Group, Extended Administrative Group,
>     Shared Risk Link Group Value TLVs are all to be encoded iin the ASLA
>     advertisements for use with FlexAlgo.
> 
>     Please add any I missed.
> 
>     Regards,
>     Tony
> 
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