Re: [mpls] MPLS-RT review of draft-hegde-mpls-spring-epe-oam

[Alexander Vainshtein <[e-mail]>]

Shraddha,
Lots of thanks for a detailed response to my comments and a new version of the draft that addresses most of them.

Please see also some responses inline below. Hopefully they will be useful.


Regards,
Sasha

Office: [phone]
Cell:      [phone]
Email:   [e-mail]

From: Shraddha Hegde <[e-mail]>
Sent: Monday, February 24, 2020 6:56 PM
To: Alexander Vainshtein <[e-mail]>
Cc: [e-mail]; Mach Chen <[e-mail]>; [e-mail]
Subject: RE: MPLS-RT review of draft-hegde-mpls-spring-epe-oam

Hi Sasha,

Thanks for the review. Pls see inline for replies

Rgds
Shraddha

From: Alexander Vainshtein <[e-mail]<mailto:[e-mail]>>
Sent: Tuesday, February 18, 2020 5:34 PM
To: [e-mail]<mailto:[e-mail]>; Mach Chen <[e-mail]<mailto:[e-mail]>>
Cc: [e-mail]<mailto:[e-mail]>
Subject: RE: MPLS-RT review of draft-hegde-mpls-spring-epe-oam


Hello,

I have been selected as one of the  MPLS-RT reviewers of draft-hegde-mpls-spring-epe-oam.



This review presumably is part of the process of adoption of this draft as an MPLS WG document, and should answer the following questions:

  1.  Does this draft address a real problem?
  2.  Is the current version a reasonably good start for solving this problem?
  3.  Are there any issues that must be fixed prior to adoption of the draft as a WG document?



After reading the draft I think that the answers to questions (1) and (2) above are positive.



I have a couple of technical issues with the draft listed below.



  1.  All sub-TLVs defined in the draft include lists of pair of local and remote IPv4 or IPv6 addresses describing links between the advertising node and the eBGP neighbor for which the EPE SID is advertised.
     *   I wonder if link-local IPv6 addresses are acceptable in these lists

              <shraddha> draft-ietf-idr-bgpls-segment-routing-epe does not explicitly specify whether link local addresses are included.

From BGP protocol perspective I do not see any problem with including link local addresses. I have updated this draft to include link-local ipv6 addresses.

[[Sasha]] What the updated draft says is that link-local IPv6 addresses are allowed. But these addresses do not identify the interfaces on which they appear, so I doubt such a clarification is enough.  I think that if link-local IPv6 addresses are used, it should be possible to include some form of identifying the underlying interfaces following RFC 4007. Alternatively, you can say that link-local addresses are left FFS.



     *   I also wonder how unnumbered P2P IPv4 interfaces could be specified in these lists.

             <Shraddha> unnumbered p2p interfaces are out of scope. I have updated the document with this information[[Sasha]] OK with me.



  1.  All sub-TLVs defined in the draft include, as one of their files the field “Local AS” that is always defined as ”4 octet unsigned integer representing the Member ASN inside the Confederation”. I wonder if this definition equally applies to the case when the so-called “Local AS” mechanism defined in RFC 7705<https://clicktime.symantec.com/3KS3q9GHjbBnYp1G2Rk8Z3w6H2?u=https%3A%2F%2Furldefense.com%2Fv3%2F__https%3A%2Ftools.ietf.org%2Fhtml%2Frfc7705__%3B%21%21NEt6yMaO-gk%21VXfhq4-7vne-Eba0WNolAQzJH-fEDF07GOqv-Q6SasdjBzZEdG6DQXAcVwjnSv1I%24> is used vs. a specific eBGP peer. In these scenarios the number of the AS to which the node that advertises an EPE SID differs from the AS number that this node uses in its OPEN message to the specific neighbor.

           <Shraddha> This is a good point draft draft-ietf-idr-bgpls-segment-routing-epe does not talk about RFC 7705 and does not include MUST statements to indicate what should be sent if migration with RFC 7705 is in force. Although I personally think that it should be possible to support OAM when RFC 7705 is in force by including the AS numbers from “local AS”, it should be specified clearly in draft

draft-ietf-idr-bgpls-segment-routing-epe and this document should just inherit from draft-ietf-idr-bgpls-segment-routing-epe. It may be too late to update draft-ietf-idr-bgpls-segment-routing-epe as its already in RFC editor queue. For now I have updated OAM draft and mentioned that if RFC 7705 is in force and if global AS number is sent, remote node may fail the validation [[Sasha]] OK with me.

Looking for feedback if there is a better way to handle this.





  1.  The document states in Section 1 that “Other procedures for mpls ping and traceroute as defined in [RFC8287<https://clicktime.symantec.com/365NBZRjaAtFck4LPHPDaZb6H2?u=https%3A%2F%2Furldefense.com%2Fv3%2F__https%3A%2Ftools.ietf.org%2Fhtml%2Frfc8287__%3B%21%21NEt6yMaO-gk%21VXfhq4-7vne-Eba0WNolAQzJH-fEDF07GOqv-Q6SasdjBzZEdG6DQXAcVx_5oIeQ%24>] are applicable for EPE-SIDs as well”.
     *   Such a blank statement requires some clarification IMHO

<shraddha> referred section 7 of RFC 8287

     *   Specifically, RFC 8287 states in Section that the Traceroute initiator, upon receiving an MPLS Echo Reply message that includes the FEC Stack Change TLV with one or more of the original segments being popped “MAY remove a corresponding FEC(s) from the Target FEC          Stack TLV in the next (TTL+1) traceroute request”. I wonder if, in the case of EPE SIDs, MAY requirement should not be upgraded to SHOULD or even MUST for security reasons

<shraddha> This is up for discussion.If the FEC stack is not removed, it exposes the details of the previous AS and hence the security risk.

This usecase is applicable when the involved ASes belong to same operator so keeping MAY  might be ok. I am looking for input from WG.

[[Sasha]] Waiting for the WG input is, of course, OK with me. However:

-           We seem to agree that this may be a security risk, but I have not found anything in the Security Considerations section about this risk

-          FWIW, I prefer to be prepared and not to wait for DISCUSS be raised by the Security ADs:-). Adding some text that describes this risk and the way to mitigate it could help to avoid this IMHO.



Neither of the issues mentioned above looks to be as blocking WG adoption of the draft. They can safely be resolved after adoption.



Hopefully this review will be useful.



Regards,

Sasha



Office: [phone]

Cell:      [phone]

Email:   [e-mail]<mailto:[e-mail]>



-----Original Message-----
From: Loa Andersson <[e-mail]<mailto:[e-mail]>>
Sent: Friday, February 14, 2020 6:53 AM
To: Bocci, Matthew (Nokia - GB) <[e-mail]<mailto:[e-mail]>>; Alexander Vainshtein <[e-mail]<mailto:[e-mail]>>; Sam Aldrin <[e-mail]<mailto:[e-mail]>>; Italo Busi <[e-mail]<mailto:[e-mail]>>
Cc: [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: MPLS-RT review of draft-hegde-mpls-spring-epe-oam



Mathew, Sam, Sasha and Italo,



You have be selected as MPLS-RT reviewers for draft-hegde-mpls-spring-epe-oam.



Note to authors: You have been CC'd on this email so that you can know that this review is going on. However, please do not review your own document.



Reviews should comment on whether the document is coherent, is it useful (ie, is it likely to be actually useful in operational networks), and is the document technically sound?  We are interested in knowing whether the document is ready to be considered for WG adoption (ie, it doesn't have to be perfect at this point, but should be a good start).



Reviews should be sent to the document authors, WG co-chairs and WG secretary, and CC'd to the MPLS WG email list. If necessary, comments may be sent privately to only the WG chairs.



If you have technical comments you should try to be explicit about what

*really* need to be resolved before adopting it as a working group document, and what can wait until the document is a working group document and the working group has the revision control.



Are you able to review this draft by Feb 28, 2020? Please respond in a timely fashion.





Thanks, Loa

(as MPLS WG chair)

--

--





Loa Andersson                        email: [e-mail]<mailto:[e-mail]>

Senior MPLS Expert

Bronze Dragon Consulting             phone: [phone]

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