Re: [Lsr] Working Group Last Call for draft-ietf-lsr-ip-flexalgo-04 - "IGP Flexible Algorithms (Flex-Algorithm) In IP Networks"

[Peter Psenak <[e-mail]>]

Aijun,

On 03/05/2022 15:52, Aijun Wang wrote:
> Hi, Peter:
> I think the logic is the following:
> FAPM is the sub-TLV of TLV 135,235,236 and 237, then it extends these TLVs for advertising prefixes in algorithm 0 to other Flexible Algorithm.
> Then I see no reason to define the new top-TLV to encoding the similar information.

FAPM is used in SR-MPLS case where algo 0 prefix has multiple flex-algo 
SIDs. So the algo 0 reachability is always advertised in legacy TLV and 
FAPM is used to advertise additional flex-algo metric for inter-area or 
external prefixes.

We can not use it for IP flex-algo.

thanks,
Peter

> 
> Aijun Wang
> China Telecom
> 
>> On May 3, 2022, at 19:16, Peter Psenak <ppsenak=[e-mail]> wrote:
>>
>> Hi Aijun,
>>
>>> On 03/05/2022 11:57, Aijun Wang wrote:
>>> Hi, Peter：
>>> Different data planes use different Flex-Algorithm and associated metric, they can’t be mixed.
>>> Or, would you like to point out why the following scenarios can’t be achieved via the FAPM?
>>> 1) The PE router has three loopback addresses(Lo1-Lo3), each associated with different Flex-ALgorithhms, and also different metrics. They are advertised via the FAPM, no MPLS SIDs are associated with these loopack prefixes advertisements.
>>> 2) The PE router has also another inter-area/inter-domain prefixes(IPextra), with the FAPM and MPLS SID advertised via the prefixes advertisements.
>>> When the PE in other ends want to send the traffic to theses addresses:
>>> 1)  To the formers three destinations(Lo1-Lo3), the FIB that are formed by the associated FAPM will be used, that is, the IP-based forwarding will be selected.
>>> 2) To the Inter-area/inter-domain prefixes the FIB that are formed via the FAPM and the associated SID, the MPLS-based forwarding will be selected.
>>> Why can’t they coexist?
>>
>> FAPM Sub-TLV is a sub-TLV of TLVs 135, 235, 236, and 237. These TLVs advertise the reachability of the prefix in algorithm 0.
>>
>> For an IP algo prefix, which is associated with the flex-algorithm, the reachability in algorithm 0 must not be advertised. So we have to use a different top level TLV.
>>
>>
>> thanks,
>> Peter
>>
>>
>>
>>> Aijun Wang
>>> China Telecom
>>>>> On May 3, 2022, at 16:05, Peter Psenak <ppsenak=[e-mail]> wrote:
>>>>
>>>> Aijun,
>>>>
>>>>> On 03/05/2022 09:59, Aijun Wang wrote:
>>>>> Hi, Peter:
>>>>> The definition of FAPM for IS-IS and OSPF doesn’t prevent from it is used for the intra-area prefixes.
>>>>> If we advertise the different loopback addresses via the FAPM, associate them to different Flex-Algo and related metrics, and does not allocate the MPLS SID, we can achieve the IP-Flex effect then.
>>>>
>>>> as I said, we can not mix metrics for different data-planes.
>>>>
>>>>> So, what’s the additional value of the IP-Flexalgo draft then?
>>>>
>>>> please read the draft. It defines the flex-algo for IP data plane.
>>>>
>>>> thanks,
>>>> Peter
>>>>
>>>>
>>>>
>>>>> Aijun Wang
>>>>> China Telecom
>>>>>>> On May 3, 2022, at 14:46, Peter Psenak <ppsenak=[e-mail]> wrote:
>>>>>>
>>>>>> Aijun,
>>>>>>
>>>>>>> On 03/05/2022 00:47, Aijun Wang wrote:
>>>>>>> Hi, Acee:
>>>>>>> The questions raised at https://mailarchive.ietf.org/arch/msg/lsr/RlHphXCwxMbgGvcBV_m24xiDzS0/ <https://mailarchive.ietf.org/arch/msg/lsr/RlHphXCwxMbgGvcBV_m24xiDzS0/> has not been answered.
>>>>>>
>>>>>> IS-IS Flexible Algorithm Prefix Metric Sub-TLV” and “OSPF Flexible Algorithm Prefix Metric Sub-TLV” are defined for advertisement of algorithm specific metric for inter-area inter-AS prefixes for SR-MPLS data-plane.
>>>>>>
>>>>>> SR MPLS and IP are independent data-planes used for flex-algo. We can not mix their metric.
>>>>>>
>>>>>> thanks,
>>>>>> Peter
>>>>>>
>>>>>>> Aijun Wang
>>>>>>> China Telecom
>>>>>>>>> On May 2, 2022, at 23:00, Acee Lindem (acee) <acee=[e-mail]> wrote:
>>>>>>>>
>>>>>>>> The WG last call has completed. We will submit an updated version of the document for publication with the terminology changes based on the discussion amongst the authors, Ketan, Robert, Gyan, and others.
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Acee
>>>>>>>>
>>>>>>>> *From: *Lsr <[e-mail]> on behalf of "Acee Lindem (acee)" <acee=[e-mail]>
>>>>>>>> *Date: *Thursday, April 7, 2022 at 3:07 PM
>>>>>>>> *To: *"[e-mail]" <[e-mail]>
>>>>>>>> *Cc: *"[e-mail]" <[e-mail]>
>>>>>>>> *Subject: *[Lsr] Working Group Last Call for draft-ietf-lsr-ip-flexalgo-04 - "IGP Flexible Algorithms (Flex-Algorithm) In IP Networks"
>>>>>>>>
>>>>>>>> This begins a WG last call for draft-ietf-lsr-ip-flexalgo-04.  The draft had a lot of support and discussion initially and has been stable for some time. Please review and send your comments, support, or objection to this list before 12 AM UTC on April 22^nd , 2022.
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Acee
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> Lsr mailing list
>>>>>>>> [e-mail]
>>>>>>>> https://www.ietf.org/mailman/listinfo/lsr
>>>>>>
>>>>
>>> _______________________________________________
>>> Lsr mailing list
>>> [e-mail]
>>> https://www.ietf.org/mailman/listinfo/lsr
>>
> 
>