Re: [secdir] secdir review of draft-ietf-alto-protocol

"Dan Harkins" <dharkins@lounge.org> Tue, 18 February 2014 21:39 UTC

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Date: Tue, 18 Feb 2014 13:39:49 -0800 (PST)
From: "Dan Harkins" <dharkins@lounge.org>
To: "Y. Richard Yang" <yry@cs.yale.edu>
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Cc: secdir@ietf.org, Richard Alimi <ralimi@google.com>, "draft-ietf-alto-protocol.all@tools.ietf.org" <draft-ietf-alto-protocol.all@tools.ietf.org>, The IESG <iesg@ietf.org>
Subject: Re: [secdir] secdir review of draft-ietf-alto-protocol
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  Hi Richard (Y),

On Mon, February 17, 2014 2:17 pm, Y. Richard Yang wrote:
> Dan, Richard A.
>
> On Mon, Feb 17, 2014 at 4:10 PM, Richard Alimi <ralimi@google.com>; wrote:
>>
>>
>> On Mon, Feb 17, 2014 at 6:26 AM, Dan Harkins <dharkins@lounge.org>;
>> wrote:
>>
>>>
>>>   Hi Richard,
>>>
>>> On Sun, February 9, 2014 10:58 pm, Richard Alimi wrote:
>>> > Thank you very much for the review!
>>> >
>>> > Responses inline...
>>> >
>>> >
>>> > On Sat, Feb 1, 2014 at 10:54 AM, Dan Harkins <dharkins@lounge.org>;
>>> wrote:
>>> >
>>> >>
>>> [snip]
>>> >>   - 6.1.2, while a particular Cost Map may contain only one of the
>>> >>      two cost modes, servers MUST implement support for both,
>>> >>      right? It's not clear from the text.
>>> >>
>>> >
>>> > Servers only need to implement at least one, but not necessarily
>>> both.
>>> >  Section 6.1.2 states the following:
>>> >
>>> >
>>> >    An ALTO Server MUST support at least one of 'numerical' and
>>> 'ordinal'
>>> >    modes.
>>> >
>>> >
>>> > Can you suggest which text was misleading so that we can address it?
>>>
>>>   It's not clear to me how this interoperates unless it's possible to
>>> infer
>>> one from the other and if that's the case then why are there two things
>>> to choose to support?
>>>
>>
>> The key is that the client needs to handle both types, not the server.
>>  During working group discussions, it was not clear that a server would
>> always wish to provide both and may opt to expose one or the other.
>>
>> For example, one cited reason for a server not exposing numerical costs
>> was concerns over revealing too many details of internal network
>> topology.
>>
>> It is possible to derive ordinal costs from numerical costs.  Thus, we
>> could require servers to provide ordinal costs and optionally provide
>> numerical costs.  We opted to put this logic in the client-side, though,
>> in
>> the interest of keeping the server simpler.
>>
>> Richard/Reinaldo: do you believe this is still a reasonable tradeoff and
>> am I missing any other rationale for this?  I'm typically on the side of
>> keeping servers simpler, but we could reconsider if necessary.
>>
>
> I remember extensive discussions on the two modes. Given the dependency
> between the numerical and the ordinal modes (one can derive the ordinal
> from numerical but not the other way around), we can say that the ordinal
> mode is always provided, either implicitly (only numerical) or explicitly
> (when both are provided). This will allow interop.

  That is a good suggestion.

> At the same time, the discussion was that we do not enforce the explicit
> approach to keep the Server simple, as Richard A. mentioned. Also, the
> less
> redundancy at the source (maintaining both numerical and ordinal), the
> less
> likely we encounter inconsistency.

  That makes sense, one side would have to do both. If you want to keep
the server simple I guess that's the way to do it.

  thanks,

  Dan.

> Richard
>