Hi Lars,
Thanks for the comment.
Please see inline.
Cheers,
Med
> -Message d'origine-
> De : Lars Eggert via Datatracker
> Envoyé : lundi 30 mai 2022 13:42
> À : The IESG
> Cc : draft-ietf-alto-cost-m...@ietf.org; alto-cha...@ietf.org;
> alto@ietf.org; kai...@scu.edu.cn; kai...@scu.edu.cn
> Objet : Lars Eggert's No Objection on draft-ietf-alto-cost-mode-
> 03: (with COMMENT)
>
> Lars Eggert has entered the following ballot position for
> draft-ietf-alto-cost-mode-03: No Objection
>
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>
>
> --
>
> COMMENT:
> --
>
>
> # GEN AD review of draft-ietf-alto-cost-mode-03
>
> CC @larseggert
>
> Thanks to Roni Even for the General Area Review Team (Gen-ART)
> review
> (https://mailarchive.ietf.org/arch/msg/gen-
> art/xlaIzXHKY1NzjJRJpuXpzKwP4rc).
>
> ## Comments
>
> ### Section 1, paragraph 4
> ```
> Additional cost modes are required for specific ALTO
> deployment cases
> (e.g., [I-D.ietf-alto-path-vector]). In order to allow for
> such use
> cases, this document relaxes the constraint imposed by the
> base ALTO
> specification on allowed cost modes (Section 3) and creates a
> new
> ALTO registry to track new cost modes (Section 4).
> ```
> I second Rob's DISCUSS, i.e., it's not clear at all that current
> ALTO
> implementations will handle this protocol parameter now taking on
> values other than "numerical" or "ordinal" without explicit
> negotiation.
>
[Med] All what actually this draft does is to declare it legitimate to
manipulate other cost modes for specific cost metrics.
In practice, legacy implementations will only support one cost metric
(routingcost) as per 7285. So far, such a metric can be associated with two
cost types.
If in the future, a document defines a new cost mode that can also be used for
the "routingcost" cost metric or new metrics with additional cost modes, and a
server is upgraded to support that, the procedure in 9.2 of RFC7285 will be
followed by such upgraded servers to announce the new metrics. clients
(including legacy ones) will take these capabilities when building forthcoming
requests.
Note also that legacy servers can also report errors based on unsupported cost
modes as per the following from RFC7285:
A request with the correct fields and types of values for the fields
may specify a wrong value for a field. For example, a Filtered Cost
Map request may specify a wrong value for CostMode in the "cost-type"
field (Section 11.3.2.3). The server indicates such an error with
the error code E_INVALID_FIELD_VALUE. For an E_INVALID_FIELD_VALUE
error, the server may include an optional field named "field" in the
"meta" field of the response, to indicate the field that contains the
wrong value. The server may also include an optional field named
"value" in the "meta" field of the response to indicate the wrong
value that triggered the error.
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