[Lsr] 答复: New Version Notification for draft-xu-lsr-flooding-reduction-in-clos-01.txt

["[e-mail]" <[e-mail]>]

Hi Les,

I have to say that the second draft you mentioned is irrelevant since leaf nodes need to know the topology for performing congestion-aware path selection. In contrast, the goal of that draft is to make the topology invisible for leaf nodes.

As for the first draft, as the draft itself has admitted, “The calculations described here seem complex, which might lead the reader to conclude that the cost of calculation is so much higher than the cost of flooding that this optimization is counter-productive.”  Honestly speaking, it has at least four drawbacks:

1) it’s too complex. For example, the usage of a hash function to select the designated flooding nodes for a given LSP would become a nightmare when debugging LSP flooding issues, IMHO;

2) it’s not useful in the most popular 5-stage CLOS topology for AI networks as described in my draft (please refer to Facebook’s F16 DCN architecture if you are confused about the difference between the two 5-stage CLOS topologies described in these two drafts respectively) since each spine node (located at PoD X and connected to PoD-interconnect plane Y) must flood received LSPs between all leaf nodes in PoD X and all super-nodes in PoD-interconnect plane Y;

3) it’s inefficient to reduce the flooding once the topology becomes asymmetry due to link failure which is common in large networks;

4) it would slow down the IGP convergence which is critical for congestion-aware path selection since it needs to build out the Two-Hop List (THL) and Remote Neighbor's List (RNL) before flooding a received LSP.

Best regards,
Xiaohu



发件人: Les Ginsberg (ginsberg) <[e-mail]>
日期: 星期六, 2023年11月25日 12:55
收件人: Tony Li <[e-mail]>, [e-mail] <[e-mail]>
抄送: [e-mail] <[e-mail]>
主题: RE: [Lsr] New Version Notification for draft-xu-lsr-flooding-reduction-in-clos-01.txt

Xiaohu –

I also point out that there are at least two existing drafts which specifically address IS-IS flooding reduction in CLOS networks and do so in greater detail and with more robustness than what is in your draft:

https://datatracker.ietf.org/doc/draft-ietf-lsr-distoptflood/

https://datatracker.ietf.org/doc/draft-ietf-lsr-isis-spine-leaf-ext/

I do not see a need for yet another draft specifically aimed at CLOS networks.

Note that work on draft-ietf-lsr-isis-spine-leaf-ext was suspended due to lack of interest in deploying an IGP solution in CLOS networks.
You are suggesting in draft-xu-lsr-fare that AI is going to change this. Well, maybe, but if so I think we should return to the solutions already available and prioritize work on them.

   Les


From: Lsr <[e-mail]> On Behalf Of Tony Li
Sent: Thursday, November 23, 2023 8:39 AM
To: [e-mail]
Cc: [e-mail]
Subject: Re: [Lsr] New Version Notification for draft-xu-lsr-flooding-reduction-in-clos-01.txt

Hi,

What you’re proposing is already described in IS-IS Mesh Groups (https://www.rfc-editor.org/rfc/rfc2973.html) and improved upon in Dynamic Flooding (https://datatracker.ietf.org/doc/html/draft-ietf-lsr-dynamic-flooding).

Regards,
Tony



On Nov 23, 2023, at 8:29 AM, [e-mail]<mailto:[e-mail]> wrote:

Hi all,

Any comments or suggestions are welcome.

Best regards,
Xiaohu

发件人: [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>
日期: 星期三, 2023年11月22日 11:37
收件人: Xiaohu Xu <[e-mail]<mailto:[e-mail]>>
主题: New Version Notification for draft-xu-lsr-flooding-reduction-in-clos-01.txt
A new version of Internet-Draft draft-xu-lsr-flooding-reduction-in-clos-01.txt
has been successfully submitted by Xiaohu Xu and posted to the
IETF repository.

Name:     draft-xu-lsr-flooding-reduction-in-clos
Revision: 01
Title:    Flooding Reduction in CLOS Networks
Date:     2023-11-22
Group:    Individual Submission
Pages:    6
URL:      https://www.ietf.org/archive/id/draft-xu-lsr-flooding-reduction-in-clos-01.txt
Status:   https://datatracker.ietf.org/doc/draft-xu-lsr-flooding-reduction-in-clos/
HTMLized: https://datatracker.ietf.org/doc/html/draft-xu-lsr-flooding-reduction-in-clos
Diff:     https://author-tools.ietf.org/iddiff?url2=draft-xu-lsr-flooding-reduction-in-clos-01

Abstract:

   In a CLOS topology, an OSPF (or ISIS) router may receive identical
   copies of an LSA (or LSP) from multiple OSPF (or ISIS) neighbors.
   Moreover, two OSPF (or ISIS) neighbors may exchange the same LSA (or
   LSP) simultaneously.  This results in unnecessary flooding of link-
   state information, which wastes the precious resources of OSPF (or
   ISIS) routers.  Therefore, this document proposes extensions to OSPF
   (or ISIS) to reduce this flooding within CLOS networks.  The
   reduction of OSPF (or ISIS) flooding is highly beneficial for
   improving the scalability of CLOS networks.



The IETF Secretariat

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