Hi Peter, 

I had too long of a context switch on flex algo.... See inline. 

On 9/12/21, 2:15 PM, "Lsr on behalf of Peter Psenak" <[email protected] on 
behalf of [email protected]> wrote:

    Hi Acee,

    On 11/09/2021 16:59, Acee Lindem (acee) wrote:
    > Hi Peter,
    > 
    > On 9/10/21, 1:46 AM, "Lsr on behalf of Peter Psenak" 
<[email protected] on behalf of [email protected]> wrote:
    > 
    >      Linda,
    > 
    >      On 09/09/2021 22:17, Linda Dunbar wrote:
    >      > Peter and Tony,
    >      >
    >      > Thank you very much for the explanation.
    >      >
    >      > Is it necessary to register with IANA on individual Flex-Algo 
value (a value between 128-255)?
    > 
    >      no.
    > 
    > But if the corresponding algorithm is in another standards track 
document, it would need to be registered and part of the standard range.

    sure, the question was if "individual Flex-Algo value" needs to be 
    registered and the answer to that is no. We have reserved the range of 
    algos from 128 to 255 to flex-algos and there is no further IANA 
    registration needed for those.

So, if someone wants to define new constraints (e.g., Linda's 
server/application metrics), they would need to define the semantics and 
encodings similar to what is being done for bandwidth metrics in 
https://datatracker.ietf.org/doc/draft-ietf-lsr-flex-algo-bw-con/ . Then the 
flex algos could be defined using these metrics. Correct? 

Thanks,
Acee




    thanks,
    Peter

    > 
    > Thanks,
    > Acee
    > 
    > 
    >      > Say there are 5 properties associated with the Stub link, one Flex 
algo uses weighted values of 4 properties, another Flex Algo uses Weighted 
values of 5 properties. Can operator use any value they want? As long as the 
value is consistent among all nodes in one IGP domain?
    > 
    >      that is right.
    > 
    >      >
    >      > How is Calc-Type used, especially combined with Flex-Algo?
    > 
    >      we only have a single calculation type for now which is SPF. We 
added it
    >      for future if anyone wants to use a different one.
    > 
    > 
    >      >
    >      > Does the Flex-Algo type already indicate how  Metric are to be 
included in the algorithm? Why need to explicit indicate the "Metric-Type" in 
the FAD Sub-TLV?
    > 
    >      It's the Calc-Type which indicates how metric is used. Metric-Type
    >      indicates which metric is used.
    > 
    >      thanks,
    >      Peter
    > 
    >      >
    >      >
    >      > Linda
    >      >
    >      > -----Original Message-----
    >      > From: Peter Psenak <[email protected]>
    >      > Sent: Thursday, September 9, 2021 1:00 PM
    >      > To: Tony Li <[email protected]>; Linda Dunbar 
<[email protected]>
    >      > Cc: [email protected]; [email protected]
    >      > Subject: Re: [Lsr] draft-ietf-lsr-flex-algo
    >      >
    >      > Hi Linda, Tony,
    >      >
    >      >
    >      > On 09/09/2021 19:37, Tony Li wrote:
    >      >>
    >      >>
    >      >> Hi Linda,
    >      >>
    >      >> Algorithm types 128-255 are intended to be used with the 
constraints
    >      >> that are advertised inside of a FlexAlgo definition.
    >      >>
    >      >> I think what you're proposing is not captured there, so you would 
need
    >      >> to have a defined algorithm from 2-127.
    >      >
    >      > eventually, the usage of the "weighted value of a Stub Link 
property"
    >      > can be added to the FAD and be used with flex-algo.
    >      >
    >      > thanks,
    >      > Peter
    >      >
    >      >
    >      >>
    >      >> Tony
    >      >>
    >      >>
    >      >>> On Sep 9, 2021, at 9:51 AM, Linda Dunbar 
<[email protected]
    >      >>> <mailto:[email protected]>> wrote:
    >      >>>
    >      >>> Peter,
    >      >>>
    >      >>> draft-ietf-lsr-flex-algo-17 currently has registered Algorithm 
Types
    >      >>> 128-255 with IANA.
    >      >>> If we need to add a new Algorithm Type, e.g. using a weighted 
value
    >      >>> of a Stub Link property in calculating the shortest path, do we 
need
    >      >>> to use one of the value within 128-255 or need to ask IANA to 
assign
    >      >>> one of the values within 2-127 (currently shown unassigned on 
IANA page)?
    >      >>>
    >      >>> Linda Dunbar
    >      >>>
    >      >>> -----Original Message-----
    >      >>> From: Lsr <[email protected] <mailto:[email protected]>> On
    >      >>> Behalf Of Peter Psenak
    >      >>> Sent: Thursday, September 9, 2021 7:52 AM
    >      >>> To:[email protected]
    >      >>> <mailto:[email protected]>;[email protected] 
<mailto:[email protected]>
    >      >>> Subject: Re: [Lsr] draft-ietf-lsr-flex-algo
    >      >>>
    >      >>> Hi Bruno,
    >      >>>
    >      >>> On 09/09/2021 14:43, [email protected]
    >      >>> <mailto:[email protected]> wrote:
    >      >>>> Hi authors, all,
    >      >>>>
    >      >>>> I have a question related to the two-way connectivity check
    >      >>>> performed on each link during the FlexAlgo SPF.
    >      >>>
    >      >>> flex-algo is defined as set of:
    >      >>>
    >      >>> (a) calculation-type
    >      >>> (b) metric-type,
    >      >>> (c) a set of constraints
    >      >>>
    >      >>> Two way connectivity check for any link in the MT topology is
    >      >>> orthogonal to flex-algo and is done once only and used for all 
algorithms.
    >      >>>
    >      >>> Flex-algo calculation using (a), (b), and (c) is done on top of 
MT
    >      >>> topology using only links for which the 2WCC has already been 
performed.
    >      >>>
    >      >>>
    >      >>>>
    >      >>>> Is this point documented in the document? I could not find it 
so far.
    >      >>>> If not, what is the (reverse connectivity) check that need to be
    >      >>>> performed on the reverse link?
    >      >>>
    >      >>>
    >      >>> none.
    >      >>>
    >      >>> thanks,
    >      >>> Peter
    >      >>>
    >      >>>
    >      >>>>
    >      >>>> A priori I could see multiple options:
    >      >>>> a) link exist
    >      >>>> b) link exist with a standard IGP metric  (seem the option 
defined
    >      >>>> in the ISO spec §7.2.8.2)
    >      >>>> c) link exist with the FlexAlgo metric used by FlexAlgo
    >      >>>> d) link exist with the FlexAlgo metric used by FlexAlgo and link
    >      >>>> complies to FlexAlgo constraints.
    >      >>>>
    >      >>>> I think we'll agree that this point requires uniformity across 
nodes
    >      >>>> hence standardization.
    >      >>>>
    >      >>>> Personally, I don't have significant preference, but the algo
    >      >>>> defined in §13 "Calculation of Flexible Algorithm Paths" could 
be
    >      >>>> read as defining option "d" (as links not following the 
constraints
    >      >>>> are "pruned from the computation") but I'm not sure that this is
    >      >>>> intended for the two-way connectivity check.
    >      >>>>
    >      >>>> Thanks,
    >      >>>> Regards,
    >      >>>> --Bruno
    >      >>>>
    >      >>>>
    >      >>>>
    >      >>>> 
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