Gunter,
I think we agree that some link attributes are application specific while
others are application independent. However, it is not so easy to figure out
which link attributes should be assigned to each category.
In your message below, you suggest that any attribute whose value is learned
from configuration is application specific. But wouldn't the following
attributes break that model, if we ever needed to advertise them:
- Circuit mileage
- monetary cost
We might have to decide whether link attributes are application specific or
application independent on a case-by-case basis.
Ron
Juniper Business Use Only
-----Original Message-----
From: Lsr <[email protected]> On Behalf Of Van De Velde, Gunter (Nokia -
BE/Antwerp)
Sent: Friday, July 30, 2021 5:06 AM
To: Peter Psenak <[email protected]>; Shraddha Hegde
<[email protected]>; Les Ginsberg (ginsberg)
<[email protected]>; Tony Li <[email protected]>
Cc: [email protected]
Subject: Re: [Lsr] Generic metric: application-specific vs
application-independent
[External Email. Be cautious of content]
A little late in the discussion... (PTO events do happen)
a quick opinion on the below discussion on whether Generic metric sub-tlv
should be encoded on a ASLA or not.
For me, it depends on how the metric for the corresponding metric-type is
obtained and if it can be configured (static).
It doesn’t make sense to have Application specific values if a particular
metric is obtained only dynamically, for eg, dynamically measured delay is
going to be same for all applications.
On the contrary, te-metric can be configured, and we can in principle configure
different values for different applications.
My opinion is that if any of the metric-types in the Generic metric sub-tlv can
be configured, it should be inside the ASLA.
G/
-----Original Message-----
From: Lsr <[email protected]> On Behalf Of Peter Psenak
Sent: Friday, July 30, 2021 9:42 AM
To: Shraddha Hegde <[email protected]>; Les Ginsberg
(ginsberg) <[email protected]>; Tony Li <[email protected]>
Cc: [email protected]
Subject: Re: [Lsr] Generic metric: application-specific vs
application-independent
Shraddha,
On 30/07/2021 06:53, Shraddha Hegde wrote:
> Operators have built their networks with link attributes
>
> being configured and used by any application. For example
>
> igp-metric is used by ISIS, then came LDP that used same igp-metric,
>
> RSVP could also use igp-metric. Then came ISIS-SR and SR-TE
>
> and even flex-algo. All these applications could use the same igp-metric.
>
> The networks have evolved like this for 20-30 years.
>
> If an operator wants to design his network for this kind of
>
> network evolution with generic metric going forward, ASLA does not
>
> currently provide an effective solution.
please be more specific as to what exactly "ASLA does not currently provide an
effective solution" for.
> ASLA currently has limitations
>
> that make it more complex than necessary for operators who want to
>
> evolve their networks this way.
above seems more like your opinion than the fact. I have not seen any evidence
that would prove the above statement.
>
> I am working on a draft to propose improvements to ASLA to
>
> make this kind of evolution less complex. I'll post a draft
>
> soon that will describe limitations of ASLA in its current form
>
> along with proposed improvements.
hard to comment on something that does not exist.
>
> I would still like to hear about use cases that require
>
> generic metric to be applications-specific and cannot be solved with
>
> application-independent generic metric.
it has been explained on the list multiple times.
thanks,
Peter
>
> Rgds
>
> Shraddha
>
> Juniper Business Use Only
>
> *From:* Les Ginsberg (ginsberg) <[email protected]>
> *Sent:* Thursday, July 29, 2021 2:00 AM
> *To:* Tony Li <[email protected]>
> *Cc:* [email protected]; Shraddha Hegde <[email protected]>
> *Subject:* RE: [Lsr] Generic metric: application-specific vs
> application-independent
>
> *[External Email. Be cautious of content]*
>
> Tony –
>
> You ask very important questions – but – as Acee has answered in a
> subsequent email – all of these questions were openly debated in the
> WG during the work on what became RFC8919/8920. This debate was
> contentious, took years, and the WG eventually reached consensus on
> what became the two RFCs.
>
> If every time a new attribute is defined we reopen the original
> debate, then we will never move forward and we will have great
> difficulty in deploying interoperable implementations.
>
> I can respect that you might have preferred a different conclusion on
> the part of the WG – but I hope you will also acknowledge that this is
> now a resolved issue and we need to move forward following the
> existing RFCs.
>
> Parenthetically, I do believe that answers to your questions can be
> found in the RFCs. The answers may not satisfy you – but we did
> attempt to include the context which drove the ASLA solution.
>
> Thanx.
>
> Les
>
> *From:* Lsr <[email protected] <mailto:[email protected]>> *On
> Behalf Of *Tony Li
> *Sent:* Wednesday, July 28, 2021 1:06 PM
> *To:* Les Ginsberg (ginsberg) <[email protected]
> <mailto:[email protected]>>
> *Cc:* [email protected] <mailto:[email protected]>; Shraddha Hegde
> <[email protected]
> <mailto:[email protected]>>
> *Subject:* Re: [Lsr] Generic metric: application-specific vs
> application-independent
>
> Les,
>
> ASLA exists to support the advertisement of attributes which can be
> used in application specific ways.
>
> Why do we need separate and different copies of attributes for
> different applications?
>
> The SRLG tries to capture the risk relationships between multiple links.
> Those relationships don’t change depending on the application.
>
> Link attributes don’t require the variability that ASLA provides, and
> the overhead is high. How does this cost/benefit ratio make sense?
>
> In any particular deployment case, a given attribute advertisement
> might be used by one app, multiple apps, or all apps.
>
> ASLA allows to unambiguously support all of these cases with a
> single advertisement encoding format.
>
> The correct question to be resolving here is indeed the question
> which has been discussed in an earlier thread: Is Generic Metric a
> link attribute which can have application specific use cases? I
> think the question to that is unquestionably “yes”.
>
> That should be enough (IMO of course) to close the discussion.
>
> Well, one nice thing is that there is an entire space of metrics
> available. If application A wants to use metric 16 and application B
> wants to use metric 122, that’s already doable.
>
> Why do we need a separate space per application????
>
> Tony
>
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