Re: [Lsr] 回复: New Version Notification for draft-zhu-lsr-isis-sr-vtn-flexalgo-01.txt

Hi Peter, 

Thanks for your comment. Please see some replies inline:

> -----Original Message-----
> From: Lsr [mailto:lsr-bounces@ietf.org] On Behalf Of Peter Psenak
> Sent: Wednesday, September 16, 2020 4:46 PM
> To: zhuyq8@chinatelecom.cn; lsr@ietf.org
> Subject: Re: [Lsr] 回复: New Version Notification for
> draft-zhu-lsr-isis-sr-vtn-flexalgo-01.txt
> 
> Yongqing,
> 
> I have two basic comments:
> 
> 1. Using L2 Bundle Member Attributes TLV for advertising attributes for VTNs
> seems like a hack.

Yes, the combination of Flex-Algo and L2 bundle can provide the required functionality of VTN.

>
> 2.
> 
>    "In order to correlate the virtual or physical member links with the
>     corresponding VTNs, each member link SHOULD be assigned with a
>     dedicated Admin Group or Extended Admin Group, which is included in
>     the definition of the Flex-Algo of the corresponding VTN.  Note that
>     in this case the Admin Group or Extended Admin Group of the Layer 3
>     link SHOULD be set to the union of all the Admin Groups or Extended
>     Admin Groups of its virtual or physical member links.  This is to
>     ensure that the Layer 3 link is always included in the Flex-Algo
>     specific constraint path computation of the VTNs it participates in."
> 
> Above proposal does not work. Here's the simple example:
> 
> Flex-algo 128, FAD include RED
> Flex-algo 129, FAD exclude RED
> 
> Now you have two VTNs, one for FA 128 (VT1) and one for 129 (VT2).

> So your VT1 member link will have affinity RED and your VT2 will not have any
> affinity set (I presume).

Maybe the text in draft is not clear enough. Take your example, it should be:

Flex-Algo 128, FAD include RED
Flex-Algo 129, FAD include BLUE

On one L3 link (either a physical L2 bundle or not), the member link for VTN-1 will have affinity RED, the member link for VTN-2 will have affinity BLUE, and the L3 link SHOULD be set with affinity RED and BLUE (i.e. the union of its member links).

> Your L3 will have affinity RED set based on your proposal. As a result the L3 link
> will be be excluded for FA 129, but that is not what you want, because your VTN2
> does not have affinity RED set.

Based on the affinity of the L3 link (RED and BLUE), the L3 link will be used for path computation in both FA-128 and FA-129. 

Then in forwarding plane, a received packet with prefix-SID of FA-128 will be steered to use the member link for VTN-1, and a received packet with prefix-SID of FA-129 will be steered to use the member link for VTN-2. This is the expected behavior. 

> 
> The fundamental problem is that FA works on L3 data only. You are trying to make
> it work for L2, but that is not going to work.

The FA based path computation is still based on L3 link attribute, the member link attribute is used to correlate a subset of link resource with a Flex-Algo, which can be used for forwarding packet which carries the FA-specific SIDs.

Best regards,
Jie

> 
> thanks,
> Peter
> 
> 
> On 16/09/2020 08:13, zhuyq8@chinatelecom.cn wrote:
> > Hi WG,
> >
> > We just submitted a new revision of draft-zhu-lsr-isis-sr-vtn-flexalgo. This
> document specifies a mechanism to use Flex-Algo together with small extensions
> to IS-IS L2 bundle to distribute the topology and resource attribute of SR based
> VTN. Your review and comments are appreciated.
> > B.R.
> > Zhu Yongqing
> >
> > -----邮件原件-----
> > 发件人: internet-drafts@ietf.org <internet-drafts@ietf.org>
> > 发送时间: 2020年9月11日 17:11
> > 收件人: Dongjie (Jimmy) <jie.dong@huawei.com>; Yongqing Zhu
> > <zhuyq8@chinatelecom.cn>; Huzhibo <huzhibo@huawei.com>
> > 主题: New Version Notification for
> > draft-zhu-lsr-isis-sr-vtn-flexalgo-01.txt
> >
> >
> > A new version of I-D, draft-zhu-lsr-isis-sr-vtn-flexalgo-01.txt
> > has been successfully submitted by Jie Dong and posted to the IETF repository.
> >
> > Name:           draft-zhu-lsr-isis-sr-vtn-flexalgo
> > Revision:       01
> > Title:          Using Flex-Algo for Segment Routing based VTN
> > Document date:  2020-09-11
> > Group:          Individual Submission
> > Pages:          8
> > URL:
> https://www.ietf.org/id/draft-zhu-lsr-isis-sr-vtn-flexalgo-01.txt
> > Status:
> https://datatracker.ietf.org/doc/draft-zhu-lsr-isis-sr-vtn-flexalgo/
> > Htmlized:
> https://datatracker.ietf.org/doc/html/draft-zhu-lsr-isis-sr-vtn-flexalgo
> > Htmlized:
> https://tools.ietf.org/html/draft-zhu-lsr-isis-sr-vtn-flexalgo-01
> > Diff:
> https://www.ietf.org/rfcdiff?url2=draft-zhu-lsr-isis-sr-vtn-flexalgo-01
> >
> > Abstract:
> >     As defined in I-D.ietf-teas-enhanced-vpn, enhanced VPN (VPN+) aims to
> >     provide enhanced VPN service to support the needs of enhanced
> >     isolation and stringent performance requirements.  VPN+ requires
> >     integration between the overlay VPN and the underlay network.  A
> >     Virtual Transport Network (VTN) is a virtual network which consists
> >     of a subset of network topology and network resources allocated from
> >     the underlay network.  A VTN could be used as the underlay for one or
> >     a group of VPN+ services.
> >
> >     I-D.dong-lsr-sr-enhanced-vpn defines the IGP mechanisms with
> >     necessary extensions to build a set of Segment Routing (SR) based
> >     VTNs.  This document describes a simplified mechanism to build the SR
> >     based VTNs using SR Flex-Algo together with minor extensions to IGP
> >     L2 bundle.
> >
> >
> >
> >
> >
> > Please note that it may take a couple of minutes from the time of submission
> until the htmlized version and diff are available at tools.ietf.org.
> >
> > The IETF Secretariat
> >
> >
> >
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> > Lsr@ietf.org
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> >
> >
> 
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