Subject: [mpls] Alissa Cooper's Discuss on draft-ietf-mpls-sfc-05: (with DISCUSS and COMMENT)

From: Datatracker on behalf of Alissa Cooper <[email-masked]>
Date: Wed, 06 Mar 2019 20:06:45 -0800

Alissa Cooper has entered the following ballot position for
draft-ietf-mpls-sfc-05: Discuss

When responding, please keep the subject line intact and reply to all
email addresses included in the To and CC lines. (Feel free to cut this
introductory paragraph, however.)

Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
for more information about IESG DISCUSS and COMMENT positions.

The document, along with other ballot positions, can be found here:
https://datatracker.ietf.org/doc/draft-ietf-mpls-sfc/

----------------------------------------------------------------------
DISCUSS:
----------------------------------------------------------------------

Comparing the requirements in RFC 8300 Section 8.1 under "Single Domain
Boundary" and the text in Section 15 of this document, it seems that the
mechanism specified in this document is not subject to the same normative
requirements as specified for the administrative boundaries of a network where
MPLS is used as the transport encapsulation for NSH. What is the reasoning for
that? I would have expected to see similar normative requirements here as in
RFC 8300 Section 8.1.

----------------------------------------------------------------------
COMMENT:
----------------------------------------------------------------------

= Section 4.5 =

OLD
The application of SR to SFC was considered in early versions of the
   SR architecture [RFC8402] and the MPLS-SR specification
   [I-D.ietf-spring-segment-routing-mpls], but has since been moved out
   of those documents.

NEW
The application of SR to SFC was considered in early versions of the
   SR architecture [RFC8402] and the MPLS-SR specification
   [I-D.ietf-spring-segment-routing-mpls], but was not ultimately adopted.

(I think this is about the ideas, not the organization of documents.)

---

From: "Adrian Farrel" <[email-masked]>
Date: Thu, 7 Mar 2019 11:24:49 -0000

Hey Alissa,

Thanks for reading.

> that? I would have expected to see similar normative requirements here as in

RFC 8300 is concerned with the forwarding plane, so (obviously) includes normative language about packet handling.
But it is worth noting that the term used in 8.1 is "NSH domain".
However, the reference is back to the general SFC architecture in RFC 7665. That's a more appropriate place to look for the constraints on deploying SFC systems.

7665 defines an SFC-Enabled Domain as "A network or region of a network that implements SFC.  An SFC-enabled domain is limited to a single network administrative domain." We should note that an "administrative domain" is (probably?) not the same as a single AS: an administrative domain is often partitioned into multiple ASes.

We do say that "Discussion of the security properties of SFC networks can be found in [RFC7665].  Further security discussion for the NSH and its use is present in [RFC8300]." So we intend to inherit all the security and deployment constraints.

We also have...
   o  The MPLS network is often considered to be a closed network such
      that insertion, modification, or inspection of packets by an
      outside party is not possible.  This is particularly pertinent in
      the SFC context because [RFC7665] notes that "The architecture
      described herein is assumed to be applicable to a single network
      administrative domain."

We could maybe tighten this by clarifying the concept of a closed network. For example,
   o  The MPLS network is often considered to be a closed network such
      that insertion, modification, or inspection of packets by an
      outside party is not possible.  MPLS networks are operated with
      closed boundaries so that MPLS encapsulated packets are not 
      admitted to the network, and MPLS headers are stripped before 
      packets are forwarded from the network.  This is particularly 
      pertinent in the SFC context because [RFC7665] notes that "The
      architecture described herein is assumed to be applicable to a
      single network administrative domain."  Furthermore, [RFC8300]
      states that packets originating outside the SFC-enabled domain
      MUST be dropped if they contain an NSH and packets exiting the 
      SFC-enabled domain MUST be dropped if they contain an NSH.  These
      constraints apply equally to the use of MPLS to encode a logical
      representation of the NSH.

> (I think this is about the ideas, not the organization of documents.)

Well, yes and no. There are, in fact, a number of drafts working their way through the system that discuss the use of SR for SFC. Most of these documents are not fully mature, but their proponents remain confident that they will be adopted and become RFCs in the fullness of time. I could list...
- draft-filsfils-spring-srv6-network-programming
- draft-guichard-spring-nsh-sr
- draft-xuclad-spring-sr-service-programming
There are probably others.

So, SFC is clearly in scope for SR and the SPRING charter explicitly says:
  o Source-routed stateless service chaining using SR-MPLS
     and SRv6 dataplanes.

We included the reference to draft-xuclad-spring-sr-service-chaining (now replaced by draft-xuclad-spring-sr-service-programming - we need to make an update!) and believe that and the text cover the point.

Cheers,
Adrian

---

From: Alissa Cooper <[email-masked]>
Date: Thu, 7 Mar 2019 10:05:03 -0500

Hi Adrian,

> On Mar 7, 2019, at 6:24 AM, Adrian Farrel <[email-masked]> wrote:
> 
> Hey Alissa,
> 
> Thanks for reading.

Any time.

> We do say that "Discussion of the security properties of SFC networks can be found in [RFC7665].  Further security discussion for the NSH and its use is present in [RFC8300]." So we intend to inher…

That should be made explicit then, in particular that the normative security requirements from those documents apply to this specification.

>      representation of the NSH.

That works for me.

> There are probably others.

This is not the impression the reader is left with from reading Section 4.5.

> We included the reference to draft-xuclad-spring-sr-service-chaining (now replaced by draft-xuclad-spring-sr-service-programming - we need to make an update!) and believe that and the text cover th…

I wonder about the archival value of the second paragraph altogether, given the multiple streams of work on this. Perhaps it would make more sense to just add a sentence to the end of the first paragraph noting that implementation work was ongoing at the time of this writing, and drop the second paragraph.

Thanks,
Alissa

---

From: "Adrian Farrel" <[email-masked]>
Date: Thu, 7 Mar 2019 15:34:12 -0000

Great. I think we have converged.

Thanks for the Discussion.

Adrian

DISCUSS:

Comparing the requirements in RFC 8300 Section 8.1 under "Single Domain
Boundary" and the text in Section 15 of this document, it seems that the
mechanism specified in this document is not subject to the same normative
requirements as specified for the administrative boundaries of a network
where
MPLS is used as the transport encapsulation for NSH. What is the reasoning
for
that? I would have expected to see similar normative requirements here as in
RFC 8300 Section 8.1.

RFC 8300 is concerned with the forwarding plane, so (obviously) includes
normative language about packet handling.
But it is worth noting that the term used in 8.1 is "NSH domain".
However, the reference is back to the general SFC architecture in RFC 7665.
That's a more appropriate place to look for the constraints on deploying SFC
systems.

7665 defines an SFC-Enabled Domain as "A network or region of a network that
implements SFC.  An SFC-enabled domain is limited to a single network
administrative domain." We should note that an "administrative domain" is
(probably?) not the same as a single AS: an administrative domain is often
partitioned into multiple ASes.

We do say that "Discussion of the security properties of SFC networks can be
found in [RFC7665].  Further security discussion for the NSH and its use is
present in [RFC8300]." So we intend to inherit all the security and
deployment constraints.

That should be made explicit then, in particular that the normative security
requirements from those documents apply to this specification.

[AF] That's easily done.

COMMENT:

= Section 4.5 =

OLD

NEW

Well, yes and no. There are, in fact, a number of drafts working their way
through the system that discuss the use of SR for SFC. Most of these
documents are not fully mature, but their proponents remain confident that
they will be adopted and become RFCs in the fullness of time. I could
list...
- draft-filsfils-spring-srv6-network-programming
- draft-guichard-spring-nsh-sr
- draft-xuclad-spring-sr-service-programming
There are probably others.

We included the reference to draft-xuclad-spring-sr-service-chaining (now
replaced by draft-xuclad-spring-sr-service-programming - we need to make an
update!) and believe that and the text cover the point.

I wonder about the archival value of the second paragraph altogether, given
the multiple streams of work on this. Perhaps it would make more sense to
just add a sentence to the end of the first paragraph noting that
implementation work was ongoing at the time of this writing, and drop the
second paragraph.

[AF] Consider it done.