Subject: Re: [Lsr] Flex Algorithms Drafts

From: Uma Chunduri <[email-masked]>
Date: Tue, 1 May 2018 20:38:51 -0700

Hi Peter,

Thanks for your response. See my questions below -

On Tue, Apr 17, 2018 at 2:31 AM, Peter Psenak <[email-masked]> wrote:

> Hi Uma,
>
> please see inline:
>
>
> On 17/04/18 00:14 , Uma Chunduri wrote:
>
>> Dear All,
>> I am neutral to combining the content of OSPF and IS-IS into a single
>> draft.
>> However, I have 2 questions on this draft.
>> 1.
>>    0                   1                   2                   3
>>      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>>     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>     |      Type     |    Length     |   Algorithm   |  Metric Type  |
>>     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>     |   Alg. Type   |    Priority   |
>>     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>     |                          Sub-TLVs                             |
>>     +                                                               +
>>     |                            ...                                |
>>     |                                                               |
>>     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>> */       Algorithm: Flex-Algorithm number.  Value between 128 and 255/*
>> */      inclusive./*
>> */      Algorithm Type: Single octet identifying the algorithm type used/*
>> */      to compute paths for the Flex-Algoritm.  Values are defined in/*
>> */      "IGP Algorithm Types" registry defined under "Interior Gateway/*
>> */      Protocol (IGP) Parameters" IANA registries./*
>> Why there are two fields "Algorithm" and "Algorithm Type" ?
>>
>
> these are being renamed in the next update to:
>
> Flex-Algorithm - Single octet value between 128 and 255 inclusive
>

1.
"Algorithm "  as defined in the draft -  I see is nothing but a light
weight sub topology (with out MT ADJs)  computed using an "Alg. Type".

As of now -

"Algorithm" type X is using "Alg.Type" Y to compute  routes?

After the change you mentioned, this would become

"Algorithm" type X is using "Alg.Type" Y to compute  routes?

IMO, Overloading of the terms cause lot of  confusion (and
mis-understanding) down the line. This happened already in a different
context for IS-IS; ask me how I will give clear example.

I followed the other thread and agree with some of the points raised by Jie
w.r.t what is being defined and what is being done.

>
> IGP Alg. Type - Single octet. Value between 0 and 127 inclusive, that
> identifies IGP algorithm type used to compute paths for the Flex-Algoritm.
> Values are defined in "IGP Algorithm Types" registry defined under
> "Interior Gateway Protocol (IGP) Parameters" IANA registries

> What are we saving here by overloading the terminology?

---

From: Uma Chunduri <[email-masked]>
Date: Tue, 1 May 2018 21:06:36 -0700

Hi Peter,

The above change would conflict
https://www.iana.org/assignments/igp-parameters/igp-parameters.xhtml (where
it is defined till 255) and

cause changes to

https://tools.ietf.org/html/draft-ietf-ospf-segment-routing-extensions-25
(Which is  in RFC Editor queue)

https://datatracker.ietf.org/doc/draft-ietf-isis-segment-routing-extensions/
(In WG LC)

Are we going in that direction?

I still see "Flex-Algorithm" is light-weight sub-topology with constrains
and still computed using one of the Algorithms as specified in
https://www.iana.org/assignments/igp-parameters/igp-parameters.xhtml.

Kindly avoid confusion around the terminology here, plz -

Thx!

--
Uma C.

---

From: Peter Psenak <[email-masked]>
Date: Wed, 02 May 2018 10:04:42 +0200

Uma,

On 02/05/18 06:06 , Uma Chunduri wrote:
>     identifies IGP algorithm type used to compute paths for the
>     Flex-Algoritm. Values are defined in "IGP Algorithm Types" registry
>     defined under "Interior Gateway Protocol (IGP) Parameters" IANA
>     registries
>
>
> Hi Peter,
>
> https://www.iana.org/assignments/igp-parameters/igp-parameters.xhtml
> (where it is defined till 255) and

how does it conflict? What we are saying is that a field contains value 
from the registry and we limit the values that it can use from such 
registry. I see no conflict.

Peter

>
> cause changes to
>
> https://tools.ietf.org/html/draft-ietf-ospf-segment-routing-extensions-25 (Which
> is  in RFC Editor queue)
>
> I still see "Flex-Algorithm" is light-weight sub-topology with
> constrains and still computed using one of the Algorithms as specified
> in https://www.iana.org/assignments/igp-parameters/igp-parameters.xhtml.
>