Re: [Lsr] Comments on draft-wang-lsr-stub-link-attributes

[Ketan Talaulikar <[e-mail]>]

Hi Aijun,

Please check inline below.

On Thu, Jul 28, 2022 at 1:15 PM Aijun Wang <[e-mail]>
wrote:

> Hi, Ketan:
>
> There are situation that such information is necessary:
> When several ASes are connected via the LAN interface, it is impossible to
> describe the inter-AS relationship with the current descriptors that
> provided by RFC5316 and RFC5392.
>

KT> Note that we have BGP running on these Inter-AS links. Even when there
is an underlying LAN, the BGP sessions are p-t-p and maybe a full or
partial mesh. Therefore, I believe representing such a LAN as a mesh of
p-t-p links that are congruent to the BGP sessions is the right approach. I
am happy to be corrected. In any case, I still fail to see how a prefix
associated with the links helps here.


>
> And another scenario is that when these stub links are used to correct
> servers, there is no remote-AS, remote ASBR ID information. But we can
> distinguish different stub link via their associated prefixes.
>

KT> I disagree - such stub links can be identified by their local interface
ids along with their local IP address. Note that we already have the
corresponding prefix being advertised as prefix reachability. So I don't
see the need to repeat. All of this is already overloading IGPs with info
that is not used by IGPs - at least let us not go overboard and repeat the
same info in multiple places.

Please check the new fresh thread about use-cases.

Thanks,
Ketan


>
> Aijun Wang
> China Telecom
>
> On Jul 28, 2022, at 15:03, Ketan Talaulikar <[e-mail]> wrote:
>
> 
> Hi Aijun,
>
> Similar to Les, I disagree with you on the use of Prefix TLV as an
> attribute of the "Stub Link". The reason is that this attribute is not
> required for the identification of a link in BGP-LS (or in IGPs for that
> matter) that was the main use case. I also don't see the use of that in
> Inter-AS links. Please justify this.
>
> Thanks,
> Ketan
>
>
> On Thu, Jul 28, 2022 at 12:19 PM Aijun Wang <[e-mail]>
> wrote:
>
>> Hi, Les:
>>
>> Please note the references to RFC5316/RFC5392 in
>> draft-ietf-idr-bgpls-inter-as-topology-ext-11 is for TE scenarios, and
>> what we are discussing are non-TE scenarios.
>> For prefixes sub-TLV, would you like to revisit my responses to Ketan,
>> before make any comments? For your convenience, I can elaborate again to
>> you——-“The prefix sub-TLV is not the link identifier, it is just one kind
>> of link attributes”. Is it clear enough?
>>
>> Based on these facts, I think it is unnecessary to response your other
>> baseless comments.
>>
>> Aijun Wang
>> China Telecom
>>
>> On Jul 28, 2022, at 12:51, Les Ginsberg (ginsberg) <ginsberg=
>> [e-mail]> wrote:
>>
>> 
>>
>> Acee –
>>
>>
>>
>> I have a somewhat different take on this draft.
>>
>>
>>
>> I agree with you that draft-ietf-idr-bgpls-inter-as-topology-ext-11 is
>> relevant – but I disagree that the lsr-stub-link draft is needed at all.
>>
>> In fact one of the main points in the extensive discussion of this draft
>> that occurred several months ago  ( see
>> https://mailarchive.ietf.org/arch/msg/lsr/8pY4d21J1XOb_GfwgrROJUijLQ8/
>>  as a pointer to one email in the thread) was that RFC 5316/RFC 5392 are
>> sufficient to support the use case. This is reinforced by the references to
>> those two RFCs in the bgpls-inter-as-topology draft.
>>
>>
>>
>> The other main point (discussed in #3 below) is that the use of a prefix
>> as a Link Identifier is a flawed concept and has been objected to by many
>> WG members.
>>
>>
>>
>> For these reasons I believe this draft is unnecessary and undesirable.
>>
>>
>>
>> Given the extensive review of the draft by many members of the WG and the
>> failed WG adoption, I believe the WG should move on to other priorities. I
>> understand that the authors of lsr-stub-link have not been convinced and
>> want to continue to advocate for the draft, but at some point the WG needs
>> to say we have done due diligence and the WG consensus is NOT to adopt the
>> draft. The continued discussion of this draft consumes WG resources
>> (including presentation slots) and diverts WG attention from other work.
>>
>>
>>
>>    Les
>>
>>
>>
>>
>>
>> *From:* Lsr <[e-mail]> *On Behalf Of * Acee Lindem (acee)
>> *Sent:* Wednesday, July 27, 2022 11:37 AM
>> *To:* Ketan Talaulikar <[e-mail]>;
>> [e-mail]
>> *Cc:* lsr <[e-mail]>
>> *Subject:* Re: [Lsr] Comments on draft-wang-lsr-stub-link-attributes
>>
>>
>>
>> Hi Ketan,
>>
>> I’m glad you brought this up. The primary (and AFAIK only) reason for
>> this draft is to get the stub-link information to a router in the IGP
>> domain running BGP-LS so that it can be advertised to the controller. For
>> reference, see
>> https://www.ietf.org/archive/id/draft-ietf-idr-bgpls-inter-as-topology-ext-11.txt
>> figure 1. So, the IGP encoding is only to get the stub-link information
>> from B1 and B3 to S2 and from B2 and B4 to T1. Since the IGPs and TE are
>> not consuming the information, the problem could be avoid by simply running
>> BGP-LS on B1-B4. See inline.
>>
>>
>>
>>
>>
>> *From: *Lsr <[e-mail]> on behalf of Ketan Talaulikar <
>> [e-mail]>
>> *Date: *Wednesday, July 27, 2022 at 5:33 AM
>> *To: *"[e-mail]" <
>> [e-mail]>
>> *Cc: *lsr <[e-mail]>
>> *Subject: *[Lsr] Comments on draft-wang-lsr-stub-link-attributes
>>
>>
>>
>> Hello Authors,
>>
>>
>>
>> Please find below my comments/suggestions on this draft. I am sharing
>> them upfront given the packed LSR agenda.
>>
>>
>>
>>    1. Sec 3 the rationale provided for not using the Inter-AS TE
>>    LSAs/TLVs is not sound in my opinion. I would say that the TE encoding may
>>    not be suitable for use in all deployments as their advertisement results
>>    in the addition of those Inter-AS links in a TE topology database and that
>>    may not be desired. So, I would suggest that the draft keeps the option of
>>    use of Inter-AS TE TLVs valid and goes ahead with the Stub Link proposal as
>>    an alternative with broader applicability (also see the next comment).
>>
>>
>>
>> Agree.
>>
>>
>>
>>    1. For the proclaimed wider applicability (e.g., links to
>>    servers/hosts) in the slides, there is no such text in the draft. The draft
>>    seems focused on Inter-AS links. I hope the authors update either the draft
>>    or the slides - to be in sync with their objectives.
>>
>>
>>
>> It is solely for purposes of advertisement in BGP-LS and consumption by
>> the SDN controller as described in
>> https://www.ietf.org/archive/id/draft-ietf-idr-bgpls-inter-as-topology-ext-11.txt
>> .
>>
>>
>>
>>
>>
>>    1. The use of the prefix TLVs in this context is something that is
>>    (in my opinion) broken from day 1 of this draft. Prefixes are for
>>    reachability. For identification of links, we have the local/remote link
>>    identifiers along with the local/remote IP addresses (NOT prefixes!). This
>>    to me is a NO-GO for the progression of this document.
>>
>>
>>
>> I agree, if this draft is to persist, these should be referred to as ASBR
>> addresses as in the IDR draft (the sole raison d’etre for this IGP draft).
>>
>>
>>
>>    1. The placement of the Stub Link TLV should be top-level (similar to
>>    other/existing links). I can share further suggestions offline, provided we
>>    reach an agreement on the above points and we converge on the main
>>    purpose/motivation for this work.
>>
>>
>>
>> I feel that strongly here as this is analogous to the new BGP-LS NLRI
>> type in
>> https://www.ietf.org/archive/id/draft-ietf-idr-bgpls-inter-as-topology-ext-11.txt
>> .
>>
>>
>>
>> Thanks,
>> Acee
>>
>>
>>
>>
>>
>> Thanks,
>>
>> Ketan
>>
>>
>>
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