Re: [mpls] Comments about draft-xiong-mpls-path-segment-sr-mpls-interworkingand difference between Path Segment and BSID

Dhruv Dhody <dhruv.ietf@gmail.com> Mon, 16 September 2019 09:01 UTC

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From: Dhruv Dhody <dhruv.ietf@gmail.com>
Date: Mon, 16 Sep 2019 14:31:05 +0530
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To: xiong.quan@zte.com.cn
Cc: Loa Andersson <loa@pi.nu>, Tarek Saad <tsaad.net@gmail.com>, mpls@ietf.org, draft-xiong-mpls-path-segment-sr-mpls-interworking@ietf.org
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Subject: Re: [mpls] Comments about draft-xiong-mpls-path-segment-sr-mpls-interworkingand difference between Path Segment and BSID
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Hi Quan,

Thanks for your email..

On Mon, Sep 16, 2019 at 2:12 PM <xiong.quan@zte.com.cn>; wrote:
>
>
> Hi Dhruv,
>
>
> Sorry to reply late! Sorry to misunderstand your comment!
>
> I agree with you.  Path Segment and  Binding SID are different and each serve a specific purpose.
>
> I think the use of the binding SID [RFC8402] is recommended to reduce the size of lable stack in our draft.
>
> But the use of binding SID is not recommended to sticth the inter-domain instead of Path Segment.
>

But Binding SID was meant to be used not just for label stack
reduction, but also for multi-domain scenarios.

See -
https://tools.ietf.org/html/draft-ietf-pce-binding-label-sid-00#section-1
https://tools.ietf.org/html/draft-filsfils-spring-sr-policy-considerations-03#section-6

The key question is - Why are you NOT using binding segment for
stitching? I think you try to explain that below -

>
> The draft proposed two interworking models including Stitching (section-3.1) and Nesting (section-3.2).
>
>
> For the stitching model, there is no end-to-end Path Segment, the end-to-end path across multiple domanins has been partitioned to several
>
> domain segments and each domain segment is identified as an inter-domain Path Segment (i-Path). These i-Paths can be used to correlate the
>
> inter-domain paths whcih can be  stitched to an end-to-end path. In the headend node, the i-Path MUST bind the two unidirectional
>
> paths and correlate the bidirectional path. Moreover, each domain can accomplish the per-segment OAM, PM or protection by using the  i-Path.
>
> If we use Binding SID to stitch the inter-domain, the per-segment or per-domain OAM/PM/protection can not be achieved.
>

May be you need to use *BOTH* path segment and binding segment then!!
But associating the functionality of a binding SID to a path SID is
not correct!

Thanks!
Dhruv

>
> For the nesting model, an end-to-end Path Segment (e-Path) is existed and the end-to-end OAM/PM/protection can be accomplished by using e-Path.
>
> In this model, sub-path Path Segment (s-Path) MAY also be defined and used to indicate the intra-domain path when the per-segment or per-domain
>
> OAM, PM or protection is requried.
>
>
> In both models, the use of the binding SID [RFC8402] is also recommended to reduce the size of lable stack.
>
>
> Best Regards,
>
> Quan
>
>
>
>
> 原始邮件
> 发件人:DhruvDhody <dhruv.ietf@gmail.com>;
> 收件人:熊泉00091065;
> 抄送人:Loa Andersson <loa@pi.nu>;Tarek Saad <tsaad.net@gmail.com>;mpls@ietf.org <mpls@ietf.org>;draft-xiong-mpls-path-segment-sr-mpls-interworking@ietf.org <draft-xiong-mpls-path-segment-sr-mpls-interworking@ietf.org>;;
> 日 期 :2019年09月12日 18:18
> 主 题 :Re: Comments about draft-xiong-mpls-path-segment-sr-mpls-interworkingand difference between Path Segment and BSID
> Hi Quan,
>
> Thanks for your mail and further discussion.
>
> It is not about Path SID v/s Binding SID, both are needed and each serve a specific purpose.
>
> The comment I made during 105 was that you are using Path SID to do the function of Binding SID!
>
> See https://tools.ietf.org/html/draft-xiong-spring-path-segment-sr-inter-domain-00#section-3.1, where you say -
>
>   The border nodes should
>   install the following MPLS data entries for Path segments:
>
>     incoming label: i-Path
>        outgoing label: the SID list of the next domain or link + next i-Path
>
> Here you are not using Path SID for OAM/PM but for the functionality of Binding SID! That seems like a wrong thing to do!
>
> Thanks!
> Dhruv
>
> On Thu, Sep 12, 2019 at 12:35 PM <xiong.quan@zte.com.cn>; wrote:
>>
>> Hi  all,
>>
>>
>> I noticed you proposed comments at the IETF#105 MPLS meeting to the draft "draft-xiong-mpls-path-segment-sr-mpls-interworking". Your comment and review is very appreciated!
>>
>>
>> The Path Segment defined in draft-ietf-spring-mpls-path-segment has been proposed and adopted in Spring WG.
>>
>> The Path Segment is a path identification for Performance measurement and Bidirectional path correlation and End-to-end Path Protection.
>>
>> The draft "draft-xiong-mpls-path-segment-sr-mpls-interworking" mainly focus on the SR and MPLS Interworking with Path Segment to provide
>>
>> end-to-end bidirectional VPN service in inter-domain scenario.
>>
>>
>> I noticed the Binding SID is also used in inter-domain scenario. I think the main difference is as follows:
>>
>> Binding SID indicates a SID List. Selected path by replace the Binding SID to a SID List. Path Segment indicates a path, it can realize OAM,PM,protection. Selected path by path segment correlation.
>>
>> Binding SID can not replace path segment in bidirectional path, OAM, PM and protection etc. If we use Binding SID, the per-segment or per-domain OAM/PM/protection can not be achieved.
>>
>>
>> I just start the discussion and comments and suggestions are very welcome!
>>
>>
>> Best Regards,
>>
>> Quan
>
>