Re: [Lsr] FW: New Version Notification for draft-bonica-lsr-ip-flexalgo-00.txt

[Peter Psenak <[e-mail]>]

Hi Jimmy,


On 14/10/2020 10:38, Dongjie (Jimmy) wrote:
> Hi Peter,
> 
>> -----Original Message-----
>> From: Peter Psenak [mailto:[e-mail]]
>> Sent: Tuesday, October 13, 2020 4:53 PM
>> To: Dongjie (Jimmy) <[e-mail]>; Ron Bonica
>> <[e-mail]>; Yingzhen Qu <[e-mail]>; Gyan
>> Mishra <[e-mail]>
>> Cc: [e-mail]; Jeff Tantsura <[e-mail]>
>> Subject: Re: [Lsr] FW: New Version Notification for
>> draft-bonica-lsr-ip-flexalgo-00.txt
>>
>>>>> When one node compute an SR path to a destination, can it compute
>>>>> the path
>>>> to only pass the nodes which bind FA-128 to SR SIDs, and avoid the
>>>> nodes >which bind FA-128 to IP address? If so, how could this node
>>>> know the binding of FA to different data planes on other nodes?
>>>>
>>>> again, it is the participation problem.
>>>>
>>>> Nodes that participate in the SR Flex-algo 128 will advertise the
>>>> participation using the SR-Algorithm Sub-TLV. Only these nodes will
>>>> be used during the SR flex-algo computation for algo 128.
>>>>
>>>> Nodes that participate in IP flex-algo 128 will advertise the
>>>> participation using the IGP Algorithm Sub-TLV. Only these nodes will
>>>> be used during the IP flex-algo computation for algo 128.
>>>
>>> Agree that if participation to Flex-Algo is advertised in a data plane specific
>> manner, then path computation with Flex-Algo constraints could be done only
>> using nodes which bind the Flex-Algo to the same data plane.
>>
>> it's per app, not per data plane, but yes, that is what the base flex-algo spec
>> mandates.
>>
>>> As Robert asked and you confirmed, this implies each data plane needs to be
>> treated as an independent application of Flex-Algo. We have SR-Algorithm
>> sub-TLV and IP Algorithm sub-TLV, while there are actually more data planes to
>> be considered: SR-MPLS, SRv6, IPv4, IPv6, etc., does this mean that Flex-Algo
>> participation needs to be advertised for SR-MPLS, SRv6, IPv4, IPv6, etc.
>> separately?
>>
>> yes, it needs to be advertised per app. We have SR specific algo participation,
>> we need one for IP as proposed in Ron's draft.
> 
> OK. While the meaning of "app" here maybe a little vague, are SR-MPLS and SRv6 considered the same or different apps?

these are considered as single app, and share the same participation 
signaling. Please note that SRv6 support is signaled independently of FA 
participation.

> 
>> Regarding IPv4 vs IPv6, it's up to the authors whether they want to make the
>> participation for IP flex-algo topology specific or topology independent, both
>> could work.
> 
> If the participation is topology specific, do you mean IPv4 and IPv6 could be distinguished by advertising Flex-Algo participation with different Topology IDs (MT-ID)? This way, is the topology ID actually used as the address family distinguisher?

Yes, one can signal participation for each topology and each MT topology 
is associated with one or AF. But let not speculate here and let authors 
decide.

thanks,
Peter

> 
> Best regards,
> Jie
> 
>> Here's the text from the base flerx-algo draft:
>>
>> 10.2.  Advertisement of Node Participation for Other Applications
>>
>>      This section describes considerations related to how other
>>      applications can advertise their participation in a specific Flex-
>>      Algorithm.
>>
>>      Application-specific Flex-Algorithm participation advertisements MAY
>>      be topology specific or MAY be topology independent, depending on the
>>      application itself.
>>
>>      Application-specific advertisement for Flex-Algorithm participation
>>      MUST be defined for each application and is outside of the scope of
>>      this document.
>>
>> thanks,
>> Peter
>>
>>
>>>
>>> Best regards,
>>> Jie
>>>
>>>>
>>>> thanks,
>>>> Peter
>>>>
>>>>>
>>>>> Best regards,
>>>>> Jie
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Lsr [mailto:[e-mail]] On Behalf Of Peter Psenak
>>>>>> Sent: Friday, October 9, 2020 11:58 PM
>>>>>> To: Dongjie (Jimmy) <[e-mail]>; Ron Bonica
>>>>>> <rbonica=[e-mail]>; Yingzhen Qu
>>>>>> <[e-mail]>; Gyan Mishra <[e-mail]>
>>>>>> Cc: [e-mail]; Jeff Tantsura <[e-mail]>
>>>>>> Subject: Re: [Lsr] FW: New Version Notification for
>>>>>> draft-bonica-lsr-ip-flexalgo-00.txt
>>>>>>
>>>>>> Hi Jimmy,
>>>>>>
>>>>>>
>>>>>>      On 09/10/2020 04:59, Dongjie (Jimmy) wrote:
>>>>>>> Hi Ron,
>>>>>>>
>>>>>>> Thanks for explaining the difference between IP Flex-Algo and SR
>>>>>>> Flex-algo. As
>>>>>> you said, the major difference is the data plane.
>>>>>>>
>>>>>>> If my understanding is correct, for one Flex-Algo to be used
>>>>>>> correctly, the set
>>>>>> of nodes need to apply consistent constraints in computation, and
>>>>>> bind the FAD to the same data plane.
>>>>>>>
>>>>>>> Is it possible that different nodes may use the same Flex-Algo
>>>>>>> with different
>>>>>> data plane, e.g. some with SR-MPLS, some with SRv6, and some with
>>>>>> pure IP etc., or each Flex-Algo is always associated with only one
>>>>>> data plane? In the former case, should the flex-algo definition
>>>>>> also indicate the data plane(s) to be used with the flex-algo?
>>>>>>
>>>>>> let me respond to this query, as this is not specific to Ron's draft.
>>>>>>
>>>>>> FAD is data plane agnostic and is used by all of them.
>>>>>>
>>>>>> thanks,
>>>>>> Peter
>>>>>>
>>>>>>>
>>>>>>> Best regards,
>>>>>>> Jie
>>>>>>>
>>>>>>>> -----Original Message-----
>>>>>>>> From: Lsr [mailto:[e-mail]] On Behalf Of Ron Bonica
>>>>>>>> Sent: Sunday, October 4, 2020 4:34 AM
>>>>>>>> To: Yingzhen Qu <[e-mail]>; Peter Psenak
>>>>>>>> <[e-mail]>; Gyan Mishra <[e-mail]>
>>>>>>>> Cc: [e-mail]; Jeff Tantsura <[e-mail]>
>>>>>>>> Subject: Re: [Lsr] FW: New Version Notification for
>>>>>>>> draft-bonica-lsr-ip-flexalgo-00.txt
>>>>>>>>
>>>>>>>> Hi Yingzhen,
>>>>>>>>
>>>>>>>> IP Flexible Algorithms are like SR Flexible Algorithms in the
>>>>>>>> following
>>>>>> respects:
>>>>>>>>
>>>>>>>> - Links have IGP metrics, TE metrics, delay metrics and
>>>>>>>> administrative colors
>>>>>>>> - FADs define Flexible Algorithms
>>>>>>>>
>>>>>>>> More specifically, the FAD:
>>>>>>>>
>>>>>>>> - Indicates which metric type the Flexible Algorithm uses
>>>>>>>> - Specifies constraints in terms of link colors that are included
>>>>>>>> or excluded from the Flexible Algorithm.
>>>>>>>>
>>>>>>>> The significant difference between IP Flexible Algorithms and SR
>>>>>>>> Flexible Algorithms is:
>>>>>>>>
>>>>>>>> - SR Flexible Algorithms bind FADs to prefix SIDs or SRv6
>>>>>>>> locators
>>>>>>>> - IP Flexible Algorithms bind FADs to IPv4 or IPv6 addresses.
>>>>>>>>
>>>>>>>> So, IP Flexible Algorithms can be deployed in any IP network,
>>>>>>>> even in the absence of SR.
>>>>>>>>
>>>>>>>>                                             Ron
>>>>>>>>
>>>>>>>>
>>>>>>>> Juniper Business Use Only
>>>>>>>>
>>>>>>>> -----Original Message-----
>>>>>>>> From: Yingzhen Qu <[e-mail]>
>>>>>>>> Sent: Saturday, October 3, 2020 2:08 PM
>>>>>>>> To: Peter Psenak <[e-mail]>; Gyan Mishra
>>>>>>>> <[e-mail]>; Ron Bonica <[e-mail]>
>>>>>>>> Cc: [e-mail]; Jeff Tantsura <[e-mail]>
>>>>>>>> Subject: Re: [Lsr] FW: New Version Notification for
>>>>>>>> draft-bonica-lsr-ip-flexalgo-00.txt
>>>>>>>>
>>>>>>>> [External Email. Be cautious of content]
>>>>>>>>
>>>>>>>>
>>>>>>>> Hi Peter,
>>>>>>>>
>>>>>>>> Using flex-algo, a SRv6 locator can be associated with a single
>>>>>>>> algo, which means an IPv6 or IPv4 address can also be associated
>>>>>>>> with a single algo. So my understanding is Ron's proposal is
>>>>>>>> making the
>>>>>> configuration of flex-algo easier?
>>>>>>>> Instead of using the exclude or include list you can configure a
>>>>>>>> loopback address to a flex-algo directly?
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Yingzhen
>>>>>>>>
>>>>>>>> On 10/3/20, 2:47 AM, "Peter Psenak" <[e-mail]> wrote:
>>>>>>>>
>>>>>>>>         Hi Yingzhen,
>>>>>>>>
>>>>>>>>         On 02/10/2020 22:15, Yingzhen Qu wrote:
>>>>>>>>         > Hi Peter,
>>>>>>>>         >
>>>>>>>>         > My understanding of flex-algo is that for traffic
>>>>>>>> destined to a prefix on a particular algo, it can only be routed
>>>>>>>> on routers belong to that algo, which also means only routers in
>>>>>>>> that algo calculates how to reach that prefix and install it into
>>>>>>>> the routing table. It seems to me that using flex-algo (section
>>>>>>>> 12 of the
>>>>>>>> draft) it's possible to have a loopback address associated with
>>>>>>>> only one algo, please correct me if I'm missing or misunderstood
>>>> something.
>>>>>>>>
>>>>>>>>         you are right. That is exactly what is being done for flex-algo
>> with
>>>>>>>>         SRv6 - locator is associated with a single algo only. The
>>>>>>>> proposal
>>>> uses
>>>>>>>>         the same concept.
>>>>>>>>
>>>>>>>>         thanks,
>>>>>>>>         Peter
>>>>>>>>
>>>>>>>>         >
>>>>>>>>         > Thanks,
>>>>>>>>         > Yingzhen
>>>>>>>>         >
>>>>>>>>         > On 10/2/20, 9:43 AM, "Lsr on behalf of Peter Psenak"
>>>>>>>> <[e-mail] on behalf of
>>>>>>>> ppsenak=[e-mail]>
>>>>>>>> wrote:
>>>>>>>>         >
>>>>>>>>         >      Gyan,
>>>>>>>>         >
>>>>>>>>         >      On 02/10/2020 18:30, Gyan Mishra wrote:
>>>>>>>>         >      > All,
>>>>>>>>         >      >
>>>>>>>>         >      > With SRv6 and IP based flex algo a generic question
>> as it
>>>>>> applies
>>>>>>>> to
>>>>>>>>         >      > both. Is it possible to have within a single IGP
>> domain
>>>>>> different
>>>>>>>> sets
>>>>>>>>         >      > of nodes or segments of the network running
>> different
>>>>>>>> algorithms.
>>>>>>>>         >
>>>>>>>>         >      absolutely.
>>>>>>>>         >
>>>>>>>>         >      > From
>>>>>>>>         >      > both drafts it sounds like all nodes have to agree on
>>>> same
>>>>>>>> algorithm
>>>>>>>>         >      > similar to concept of metric and reference
>> bandwidth
>>>> all
>>>>>> have to
>>>>>>>> have
>>>>>>>>         >      > the same style metric and play to the same sheet of
>>>> music.
>>>>>>>>         >
>>>>>>>>         >      all participating nodes need to agree on the definition
>> of
>>>> the
>>>>>>>> flex-algo
>>>>>>>>         >      and advertise the participation. That's it.
>>>>>>>>         >
>>>>>>>>         >      > If there was
>>>>>>>>         >      > a way to use multiple algorithms simultaneously
>> based
>>>> on
>>>>>> SFC
>>>>>>>> or services
>>>>>>>>         >      > and instantiation of specific algorithm based on
>> service
>>>> to
>>>>>> be
>>>>>>>>         >      > rendered.  Doing so without causing a routing loop
>> or
>>>> sub
>>>>>>>> optimal
>>>>>>>>         >      > routing.
>>>>>>>>         >
>>>>>>>>         >      you can certainly use multiple algorithms
>> simultaneously
>>>> and
>>>>>> use
>>>>>>>> algo
>>>>>>>>         >      specific paths to forward specific traffic over it. How
>> that
>>>> is
>>>>>> done
>>>>>>>>         >      from the forwarding perspective depends in which
>>>>>> forwarding
>>>>>>>> plane you
>>>>>>>>         >      use. Flex-algo control plane is independent of the
>>>> forwarding
>>>>>>>> plane.
>>>>>>>>         >
>>>>>>>>         >
>>>>>>>>         >      >I thought with flex algo that there exists a feature
>> that
>>>> on
>>>>>>>>         >      > each hop there is a way to specify which algo to use
>>>> hop by
>>>>>> hop
>>>>>>>> similar
>>>>>>>>         >      > to a hop by hop policy based routing.
>>>>>>>>         >
>>>>>>>>         >      no, there is no hop-by-hop classification, that is
>>>> problematic
>>>>>> and
>>>>>>>> does
>>>>>>>>         >      not scale for high speeds. Classification is done at the
>>>>>> ingress only.
>>>>>>>>         >
>>>>>>>>         >      thanks,
>>>>>>>>         >      Peter
>>>>>>>>         >
>>>>>>>>         >      >
>>>>>>>>         >
>>>>>>>>         >
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> 
>