Re: [OSPF] [ospf-sr] regarding Algorithm TLV and other TLVs in RI LSA

Peter Psenak <ppsenak@cisco.com> Fri, 28 April 2017 07:59 UTC

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Date: Fri, 28 Apr 2017 09:56:02 +0200
From: Peter Psenak <ppsenak@cisco.com>
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To: Veerendranatha Reddy Vallem <veerendranatharv@huawei.com>, "draft-ietf-ospf-segment-routing-extensions@ietf.org" <draft-ietf-ospf-segment-routing-extensions@ietf.org>
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Subject: Re: [OSPF] [ospf-sr] regarding Algorithm TLV and other TLVs in RI LSA
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Veerendranatha,

On 28/04/17 09:12 , Veerendranatha Reddy Vallem wrote:
> Dear Authors,
>
> 1.As per section 3.1 SR- Algorithm TLV ,
>
>
>
>         "If the SR-Algorithm sub-TLV appears in multiple Router Information LSAs
>
>            that have different flooding scopes, the SR-Algorithm sub-TLV in the Router Information LSA with
>
>            the lowest flooding scope SHOULD be used."
>
>
>
>        “The RI LSA can be advertised at any of the defined opaque flooding
>
>         scopes (link, area, or Autonomous System (AS)).  For the purpose of
>
>         SR-Algorithm TLV advertisement, area scope flooding is required.”
>
>        As per first  statement, we should use lowest scope (Ex: if the
> algorithm TLV is received in AS ,Area and link, then link SR algorithm
> is preferred)

link scope is not valid per the paragraph above. The first sentence 
talks about RI LSA in general. Second one says what is required for 
SR-Alg. TLV.

>
>         But second statement indicates we use area scope for algorithm
> TLV. These two statements may cause little confusion while implementation.

not really.

First statement resolves the conflict in case the SR-Algorithm sub-TLV 
appears in multiple RI LSAs.

Second statement says that area scope is the minimum needed. AS scope 
works as well BTW.


>
>        As per my understanding,  Area scope will be preferred since Node
> visibility is at area scope.

correct.

>
> 2.Even “SR Local Block Sub-TLV SRMS and Preference Sub-TLV” are top
> level TLVs in RI LSA like SR-Algorithm TLV and “SID/Label Range TLV”,
> may be it is better to replace “Sub TLV” with TLV.

ack.

regards,
Peter

>
> Thanks and Regards,
>
> Veerendranath
>