Re: [Lsr] Generic metric: application-specific vs application-independent

[Robert Raszuk <[e-mail]>]

Peter,

Is there a definition of IGP "application" in any of the specs ?

To me application in the context of an IGP is defined by method used to
compute a topology as well as links and their metrics which are used to
consistently select the shortest path in the domain. So even if you happen
to use the exact same algorithm (which may already not be the case) it
seems that it is hard to artificially squeeze two orthogonal topologies
serving completely different purposes under a single flex-algo app
umbrella.

If you go by the notion of let's push everything to FAD then sorry but ASLA
is not making sense anymore as even without it FAD could enumerate what
link attributes and what links (using affinities) can be considered for
topology computation.

Honestly I am not sure where is the resistance to define more bits for flex
algo in SABM is coming from ....

Thx,
R.



On Wed, Aug 18, 2021 at 9:51 AM Peter Psenak <[e-mail]> wrote:

> Shraddha,
>
> On 17/08/2021 20:04, Shraddha Hegde wrote:
> > Peter,
> >
> >> no, I don't want to use affinities to do that. That's the whole point.
> >> ASLA gives you per link per application signaling. No need to use
> affinities.
> >
> > The usecase you are describing to exclude links from an application
> topology is very straight
> > forward and how this is done is defined by applications.
> > TE applications have defined a topology filter data model that uses
> > link-affinities to Include/exclude links from topology
> >
> https://datatracker.ietf.org/doc/html/draft-bestbar-teas-yang-topology-filter-00
> .
> >   In your example if application B is any TE application it would be
> natural to use link-affinities.
> >
> > If application B is LFA, RFC 7916 defines link-coloring and include
> exclude policies to be used (Refer sec 6.2.3).
> > so it cannot use application bits on metric to exclude links.
> >
> > If we assume application A and B are both Flex-algos, ASLA
>
> flex-algo is a single application, so A and B does not make sense.
>
> You can define flex-algo X and flex-algo Y and use different FAD to
> exclude/include links as needed, using single set of affinities that are
> advertised for flex-algo application as such.
>
> I still do not see a problem
>
> thanks,
> Peter
>
>
> > natively doesn't support Per flex-algo attribute advertisement
> > and it is extremely complex to define user-defined bit masks for Each
> > flex-algo and assign the bit masks on the metric on every router.
> > Operator could use link-affinities to Exclude links
> > from flex-algo topology which is much simpler.
> >
> > Rgds
> > Shraddha
> >
> >
> > Juniper Business Use Only
> >
> > -----Original Message-----
> > From: Peter Psenak <[e-mail]>
> > Sent: Saturday, July 31, 2021 1:07 AM
> > To: Shraddha Hegde <[e-mail]>; Robert Raszuk <
> [e-mail]>; Van De Velde, Gunter (Nokia - BE/Antwerp) <
> [e-mail]>
> > Cc: Les Ginsberg (ginsberg) <[e-mail]>; Tony Li <
> [e-mail]>; [e-mail]
> > Subject: Re: [Lsr] Generic metric: application-specific vs
> application-independent
> >
> > [External Email. Be cautious of content]
> >
> >
> > Shraddha,
> >
> > On 30/07/2021 18:45, Shraddha Hegde wrote:
> >> Peter,
> >>
> >>> imagine you have an application A and B and a link X. You advertise
> application independent metric M on that link X >because you want
> application A to use it.
> >>
> >>> Application B is also enabled to use the metric M, but you do not want
> application B to use metric M on the link X >(because you do not want
> application B to include the link X in its topology). How do you do that
> without ASLA? The >answer is you can't.
> >>
> >> This is very straight forward to do without ASLA.
> >>    I would define an admin-group and assign that admin group on link X
> and
> >>    exclude that admin-group from Application B.
> >>    This is much common way how
> >>    operators exclude links from the topology.
> >
> > no, I don't want to use affinities to do that. That's the whole point.
> > ASLA gives you per link per application signaling. No need to use
> affinities.
> >
> >>
> >>    The alternative being proposed with ASLA is much more fragile.
> >>    An operator would have to set the bits for application A and
> Application B
> >>    for metric M on every link that he wants to include and reset the
> >>    application bit B on links that he wants to exclude for application
> B.
> >
> > sorry, but setting affinities is not any easier, so the above argument
> is not valid.
> >
> >
> > Peter
> >
> >
> >
> >>    Imagine what would happen if he missed setting the bit or resetting
> >>    the bit on some of the links and how difficult it would be to debug.
> >>
> >> Rgds
> >> Shraddha
> >>
> >>
> >> Juniper Business Use Only
> >>
> >> -----Original Message-----
> >> From: Peter Psenak <[e-mail]>
> >> Sent: Friday, July 30, 2021 7:09 PM
> >> To: Shraddha Hegde <[e-mail]>; Robert Raszuk
> >> <[e-mail]>; Van De Velde, Gunter (Nokia - BE/Antwerp)
> >> <[e-mail]>
> >> Cc: Les Ginsberg (ginsberg) <[e-mail]>; Tony Li
> >> <[e-mail]>; [e-mail]
> >> Subject: Re: [Lsr] Generic metric: application-specific vs
> >> application-independent
> >>
> >> [External Email. Be cautious of content]
> >>
> >>
> >> Shraddha,
> >>
> >>
> >> On 30/07/2021 15:22, Shraddha Hegde wrote:
> >>> Robert,
> >>>
> >>>    > Can anyone explain how do I map generic metric to selected
> >>> network applications I am to run in the network ?
> >>>
> >>> Which application uses which metric type is defined by the application.
> >>
> >> imagine you have an application A and B and a link X. You advertise
> application independent metric M on that link X because you want
> application A to use it.
> >>
> >> Application B is also enabled to use the metric M, but you do not want
> application B to use metric M on the link X (because you do not want
> application B to include the link X in its topology). How do you do that
> without ASLA? The answer is you can't.
> >>
> >> thanks,
> >> Peter
> >>
> >>>
> >>> For example in flex-algo FAD defines which metric-type its going to
> use.
> >>>
> >>> In SR-TE, the constraint list specifies which metric-type it is going
> >>> to use.
> >>>
> >>> Rgds
> >>>
> >>> Shraddha
> >>>
> >>> Juniper Business Use Only
> >>>
> >>> *From:* Robert Raszuk <[e-mail]>
> >>> *Sent:* Friday, July 30, 2021 6:20 PM
> >>> *To:* Van De Velde, Gunter (Nokia - BE/Antwerp)
> >>> <[e-mail]>
> >>> *Cc:* Peter Psenak <[e-mail]>; Shraddha Hegde
> >>> <[e-mail]>; Les Ginsberg (ginsberg) <[e-mail]>;
> >>> Tony Li <[e-mail]>; [e-mail]
> >>> *Subject:* Re: [Lsr] Generic metric: application-specific vs
> >>> application-independent
> >>>
> >>> *[External Email. Be cautious of content]*
> >>>
> >>> Hey Gunter,
> >>>
> >>>    > It doesn’t make sense to have Application specific values if a
> >>> particular metric is obtained only dynamically,
> >>>
> >>> It sure does.
> >>>
> >>> Please notice what ASLA RFCs say up front in the abstract. ASLA is
> >>> useful for:
> >>>
> >>> A) application- specific values for a given attribute
> >>>
> >>> AND
> >>>
> >>> B) indication of which applications are using the advertised value
> >>> for a given link.
> >>>
> >>> It does not matter if the value is same or different ... what matters
> >>> is automated and consistent indication which of my applications given
> >>> new metric applies to.
> >>>
> >>> I already mentioned this to Ron here:
> >>> https://urldefense.com/v3/__https://mailarchive.ietf.org/arch/msg/lsr
> >>> /
> >>> OgGLI8yezUDWU-EZePoIj6y6ENk/__;!!NEt6yMaO-gk!VVLJCpIMrWixS17PeaBbfOpe
> >>> b NPO4JUW4jparIn36jHmhv4_-W2_q_Smwo7oIYgk$
> >>> <https://urldefense.com/v3/__https:/mailarchive.ietf.org/arch/msg/lsr
> >>> /
> >>> OgGLI8yezUDWU-EZePoIj6y6ENk/__;!!NEt6yMaO-gk!Tny8sU7cmjqLAbDVnliN7lck
> >>> 7 J4tCBAHr10i3CW2G9oviUWo8b2RTJxCXc0gvWOz$>
> >>>
> >>> Can anyone explain how do I map generic metric to selected network
> >>> applications I am to run in the network ?
> >>>
> >>> Thx,
> >>> Robert.
> >>>
> >>> On Fri, Jul 30, 2021 at 11:05 AM Van De Velde, Gunter (Nokia -
> >>> BE/Antwerp) <[e-mail]
> >>> <mailto:[e-mail]>> wrote:
> >>>
> >>>       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/
> >>>
> >>
> >>
> >
> >
>
>