Re: [mpls] working group adaption poll (wgap) for draft-hegde-mpls-spring-epe-oam

[Shraddha Hegde <[e-mail]>]

Hi ketan,

Thanks for the detailed review and comments. Pls see inline for response.


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-----Original Message-----
From: Ketan Talaulikar (ketant) <[e-mail]> 
Sent: Wednesday, May 13, 2020 9:38 AM
To: Loa Andersson <[e-mail]>; [e-mail]
Cc: [e-mail]; [e-mail]
Subject: RE: [mpls] working group adaption poll (wgap) for draft-hegde-mpls-spring-epe-oam

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Hi  Loa,

There is no doubt about the need for LSP ping and traceroute operations to cover BGP EPE SIDs. So the requirement is real and something that the WG should be taking up.

My concerns is that the proposal in the draft is diverging from the control plane protocol semantics for what constitutes the FEC (or context) and how it is to be validated. These are some core aspects that IMHO need to be addressed before adoption while the rest may be taken up during its life as a WG document. I would suggest to wait for the authors response.

Thanks,
Ketan

-----Original Message-----
From: Loa Andersson <[e-mail]>
Sent: 13 May 2020 09:22
To: Ketan Talaulikar (ketant) <[e-mail]>; [e-mail]
Cc: [e-mail]; [e-mail]
Subject: Re: [mpls] working group adaption poll (wgap) for draft-hegde-mpls-spring-epe-oam

Ketan,

Anything of this that need to addressed before wg adoption?


Authors

I leave the wgap opeb a few extra days to llow you to respond to this.


/Loa

On 12/05/2020 23:32, Ketan Talaulikar (ketant) wrote:
> Hello Authors,
>
> I have the following comments on this draft and would be good if you could clarify/respond.
>
> 1)The FEC description should match the "context" that is advertised in 
> the control plane for Peer Adj SID. E.g. the local/remote Interface 
> IDs are not being included from 
> https://urldefense.com/v3/__https://tools.ietf.org/html/draft-ietf-idr
> -bgpls-segment-routing-epe-1__;!!NEt6yMaO-gk!W0-Gp88WKnqRfX4kdfeWV8aIH
> qrXTj0Pzz9Vl-B2ZVn78SFO60XGBDi2Y-5xIny8$
> 9#section-4.2

<Shraddha> The EPE draft mandates interface-ids and allows remote interface-id to be zero.
Remote interface ID being zero does not help in validating the incoming interface which is very
Useful OAM functionality. For this reason, this draft recommends sending interface addresses in the PeerADJ SID
Link descriptors which is optional. 

I have updated the PeerAdj SID section with this information and also updated with the possibility of sending zero
In which case incoming interface validation should be skipped. This is to accommodate cases when the advertising node does not send the interface addresses
>
> 2) For the Peer Node SID, the control plane definition is https://urldefense.com/v3/__https://tools.ietf.org/html/draft-ietf-idr-bgpls-segment-routing-epe-19*section-4.1__;Iw!!NEt6yMaO-gk!W0-Gp88WKnqRfX4kdfeWV8aIHqrXTj0Pzz9Vl-B2ZVn78SFO60XGBDi2Y6sXdlcY$  and the FEC description in this draft is not aligned with the corresponding control plane. The Peer Node SID is meant for the packet to be delivered to a specific BGP peer and it does not matter over which interface it is received. So why have those interface addresses as mandatory in the FEC. The only thing the control plane indicates is the peering session itself.
>
> 3) Same as (2) above, for the Peer Set SID, the interfaces are don't care.
<Shraddha> The reason for need to have interface addresses specified is for incoming interface validation as explained above. For Peer Node SID interfaces are advertised with draft I-D.hegde-idr-bgp-ls-epe-inter-as.I have added this to the reference and updated text as to why it is needed. Also the ingress can send 0 pair of addresses in which case
Incoming interface validation will be skipped and success will be sent based on other validations.
Pls check -07 version and let me know if you are OK with it.
>
> 4) The draft just says that the procedures are borrowed from RFC8287 but I don't think this is so straightforward or trivial. E.g. https://urldefense.com/v3/__https://tools.ietf.org/html/rfc8287*section-7.2__;Iw!!NEt6yMaO-gk!W0-Gp88WKnqRfX4kdfeWV8aIHqrXTj0Pzz9Vl-B2ZVn78SFO60XGBDi2Y3Z0DrZ_$  has the following:
>
>     The network node that is immediately downstream of the node that
>     advertised the Adjacency Segment ID is responsible for generating the
>     FEC Stack Change sub-TLV for POP operation for the Adjacency Segment
>     ID.
>

<shraddha> A new section for EPE FEC validation has been added in -06 version. This section specifies the details when return code 3 
Has to be sent. As per  RFC 8029 sec 3.4.1.3 FEC stack change and IS_EGRESS code are treated identically.
" A Downstream Detailed Mapping TLV containing only one FEC stack
       change sub-TLV with pop operation is equivalent to IS_EGRESS
       (Return Code 3, Section 3.1) for the outermost FEC in the FEC
       stack.  The ingress router performing the LSP traceroute MUST
       treat such a case as an IS_EGRESS for the outermost FEC."

I don't see the need to re-iterate RFC 8029 sections in this draft. If it is still not clear let me know.

> In the case of IGPs, the downstream node does have the label and context for adjacency SID (which is functionally closest to BGP EPE SIDs). In the BGP-EPE SIDs case, this is not always the case. So I believe, it would be better if the entire operation were described.
<Shraddha> EPE SID validation section is added. Pls take a look and let me know if it looks good.
>
> 5) The ping or traceroute done to any of the BGP EPE SID corresponding to an eBGP session may result in the packet being sent to another entity. The security consideration talk about it, but the problem is not addressed by the remote AS dropping the packets. The security issue is that the OAM packet could expose the FECs and information of the local AS to a remote AS. So it is more as an caveat for the operators performing the OAM operation to be mindful of this fact.
>
<Shraddha> Yes. This was raised in RT review and security section has been updated with this info in -06 version.
   
> In general, some more description that set the stage for the introduction of the new extensions and elaborate more on the operations (some considerations above on what is mandatory to evaluate and what is optional).
<Shraddha> Sure. Pls check the -07 version which I'll be posting soon and let me know if you have further comments.
>
> Thanks,
> Ketan
>
> -----Original Message-----
> From: mpls <[e-mail]> On Behalf Of Loa Andersson
> Sent: 30 April 2020 08:26
> To: [e-mail]
> Cc: [e-mail]; [e-mail]
> Subject: [mpls] working group adaption poll (wgap) for 
> draft-hegde-mpls-spring-epe-oam
>
> Working Group,
>
> This is to start a two week poll on adopting draft-hegde-mpls-spring-epe-oam as a MPLS working group document.
>
> Please send your comments (support/not support) to the mpls working group mailing list ([e-mail]). Please give a technical motivation for your support/not support, especially if you think that the document should not be adopted as a working group document.
>
> There is one IPR disclosure against this document.
>
> The authors have stated on the MPLS wg mailing list that they are unaware of any IPRs that relates to this document.
>
> The working group adoption poll ends May 15, 2020.
>
> /Loa
>

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Loa Andersson                        email: [e-mail]
Senior MPLS Expert
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