Re: [Lsr] LSR WG Adoption Poll for "Flexible Algorithms: Bandwidth, Delay, Metrics and Constraints" - draft-hegde-lsr-flex-algo-bw-con-02

Aijun Wang <wangaijun@tsinghua.org.cn> Fri, 21 May 2021 22:22 UTC

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Cc: lsr <lsr@ietf.org>, draft-hegde-lsr-flex-algo-bw-con@ietf.org, "Acee Lindem (acee)" <acee=40cisco.com@dmarc.ietf.org>
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To: Tony Li <tony.li@tony.li>
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Subject: Re: [Lsr] LSR WG Adoption Poll for "Flexible Algorithms: Bandwidth, Delay, Metrics and Constraints" - draft-hegde-lsr-flex-algo-bw-con-02
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Hi, Tony:

Aijun Wang
China Telecom

> On May 21, 2021, at 23:29, Tony Li <tony.li@tony.li> wrote:
> 
> 
> 
> Hi Aijun,
> 
>> I support the adoption of the “FAD constraint sub-TLV” part(Section 3),  but not support the introduce of  “Bandwidth Metric Advertisement” part (Section 4) and other related parts.
> 
> 
> As I understand it, we don’t get a line item veto, so I don’t know how the chairs will take this.

[WAJ] The reasonable solution is to take out of the controversial part from the adopted document.

> 
> 
>> With the introduce of additional constraint information, the problem described in “Introduction” part(Section 1) can be solved.
> 
> 
> Please say more.  Claims without rationale are not reasoning.
[WAJ]  The introduction part talks mainly how to divert the elephant traffic away from the low bandwidth link. This can be achieved via the introduction of additional constraints information for Flex-ALGO.
> 
>  
>> The usage of bandwidth metric in large network is not feasible. 
> 
[WAJ] The main reason is that bandwidth metric is not cumulative.  
> 
> Ditto.
> 
> 
>> And, would you like to explain more for the following statements(in Section 4.1.1.2)
>> “In the interface group mode, every node MUST identify the set of
>>    parallel links between a pair of nodes based on IGP link
>>    advertisements and MUST consider cumulative bandwidth of the parallel
>>    links while arriving at the metric of each link.”
>> based on example described in Figure 7? 
> 
> 
> The paragraph immediately above explains exactly that. B->C has two parallel 10Gbps links, so it should be considered to be 20Gbps.
> 
>  
>> How the cumulative bandwidth will be used to achieve the result that traffic from B to D will prefer B-C-F-D, not B-E-D? 
> 
> 
> B-C-F-D is 20Gbps. B-E-D is 10Gbps.

[WAJ] OK, let’s add two nodes between node B and C, say they are node M and N. They have also two parallel links to B and C respectively. The two possible path from B to D will be:
Path 1: B-M-N-C-F-D
Path 2: B-E-D
If the “reference bandwidth” is 100G, then metric for each link in B-M-N-C-F-D will be 5, the cumulative metric from B-D for Path 1 “B—N-C-F-D” will be 25, right?
The metric for each link in B-E-D will be 10, the cumulative metric from B-D for Path 2 will be 20, right?
How can you prefer to the high bandwidth path?


> 
> Tony
> 
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