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Last Call Review of draft-ietf-softwire-lw4over6-11

Request Review of draft-ietf-softwire-lw4over6
Requested revision No specific revision (document currently at 13)
Type Last Call Review
Team General Area Review Team (Gen-ART) (genart)
Deadline 2014-10-10
Requested 2014-10-12
Authors Yong Cui , Qiong Sun , Mohamed Boucadair , Tina Tsou (Ting ZOU) , Yiu Lee , Ian Farrer
I-D last updated 2014-10-12
Completed reviews Genart Last Call review of -10 by David L. Black (diff)
Genart Last Call review of -11 by David L. Black (diff)
Secdir Last Call review of -10 by Samuel Weiler (diff)
Opsdir Last Call review of -10 by David L. Black (diff)
Opsdir Telechat review of -11 by David Harrington (diff)
Opsdir Telechat review of -13 by David L. Black
Assignment Reviewer David L. Black
State Completed
Review review-ietf-softwire-lw4over6-11-genart-lc-black-2014-10-12
Reviewed revision 11 (document currently at 13)
Result On the Right Track
Completed 2014-10-12
This is a combined Gen-ART and OPS-DIR review.  Boilerplate for both follows,
and I apologize for it being a day late - United Airlines got me back to
Boston after midnight last night on a plane w/o working WiFi.

I am the assigned Gen-ART reviewer for this draft. For background on
Gen-ART, please see the FAQ at:


Please resolve these comments along with any other Last Call comments
you may receive.

I have reviewed this document as part of the Operational directorate's ongoing
effort to review all IETF documents being processed by the IESG.  These comments
were written primarily for the benefit of the operational area directors.
Document editors and WG chairs should treat these comments just like any other
last call comments.

Document: draft-ietf-softwire-lw4over6-10
Reviewer: David Black
Review Date: October 10, 2014
IETF LC End Date: October 10, 2014
IESG Telechat date: October 16, 2014

Summary: This draft is on the right track, but has open issues
 		described in the review.

This draft describes an extension to Dual-Stack Lite that relocates the NAPT
functionality from the centralized tunnel concentrator to the DS-Lite client
- doing so has significant scalability benefits.  The draft is generally
readable although understanding why some of the processing needs to be done
in the manner specified requires strong familiarity with both DS-Lite and

The draft is generally in good shape - I found three issues that I consider
to be significant, the most important of which are sloppiness in use of
RFC 2119 keywords, particularly in Section 5.1, and omission of what
appears to be a necessary normative reference.

Major issues (2):

[1] There are a number of places where SHOULD is used to refer to requirement
in another RFC, e.g., the following text in section 5.1:

   The DNS considerations described in Section 5.5 and Section 6.4 of
   [RFC6333] SHOULD be followed.

This has the side effect of weakening any MUST requirement in the referenced
RFC(s) to a SHOULD, which was probably not intended, and needs to be explicitly
stated if it was intended.  Here's a possible rephrasing:

   The DNS considerations described in Section 5.5 and Section 6.4 of
   [RFC6333] apply to Lightweight 4over6; lw4o6 implementations MUST
   comply with all requirements stated there.

The additional places where this occurs are:

- Section 5.2.1 (twice):

   For TCP and UDP traffic the NAPT44 implemented in the lwB4 SHOULD
   conform with the behaviour and best current practices documented in
   [RFC4787], [RFC5508], and [RFC5382].  If the lwB4 supports DCCP, then
   the requirements in [RFC5597] SHOULD be implemented.

- Section 8.2:

   The lwB4 SHOULD implement the requirements defined in [RFC5508] for
   ICMP forwarding.

[2] Section 4.  Lightweight 4over6 Architecture

   The consequence of this architecture is that the information
   maintained by the provisioning mechanism and the one maintained by
   the lwAFTR MUST be synchronized (See figure 2).  The details of this
   synchronization depend on the exact provisioning mechanism and will
   be discussed in a companion document.

I believe that this "companion document" needs to be cited as a
normative reference.  The above text's vague allusion to the specification
of how to implement a "MUST" requirement is insufficient.

Minor issues (7):

[3] The lack of discussion of management information is an
omission.  See A.2.2 below in the OPS-Dir review section of this email
and the discussion in Section 3.2 of RFC 5706.  A sentence pointing
at an applicable MIB and/or YANG draft or drafts would suffice.

[4] Section 4.  Lightweight 4over6 Architecture

   The solution specified in this document allows the assignment of
   either a full or a shared IPv4 address requesting CPEs.  [RFC7040]
   provides a mechanism for assigning a full IPv4 address only.

Please explain what entities would share the IPv4 address.  For example,
this is needed as a foundation for the statement in Section 8 that
"ICMPv4 does not work in an address sharing environment without
special handling [RFC6269]."

[5] Section 5.1.  Lightweight B4 Provisioning with DHCPv6

   For DHCPv6 based configuration of these parameters, the lwB4 SHOULD
   implement OPTION_S46_CONT_LW

What are the consequences of not doing that?  The could be addressed
by changing that "SHOULD" to a "MUST", although I suspect that what's
wanted here is a forward reference to the alternatives discussed in
Section 7.

[6] Also in Section 5.1

   If stateful IPv4 configuration or additional IPv4 configuration
   information is required, DHCPv4 [RFC2131] must be used.

"must" -> "MUST"

   In the event that the lwB4's encapsulation source address is changed
   for any reason (such as the DHCPv6 lease expiring), the lwB4's
   dynamic provisioning process must be re-initiated.

"must" -> "MUST"

[7] Also in Section 5.1

   Unless an lwB4 is being allocated a full IPv4 address, it is
   RECOMMENDED that PSIDs containing the well-known ports (0-1023) are
   not allocated to lwB4s.

Please explain why.  Also, "well-known ports" is not the right term;
I believe those are the "system ports", e.g., see:

[8] Still in Section 5.1

   In the event that the lwB4 receives an ICMPv6 error message (type 1,
   code 5) originating from the lwAFTR, the lwB4 SHOULD interpret this
   to mean that no matching entry in the lwAFTR's binding table has been
   found.  The lwB4 MAY then re-initiate the dynamic port-restricted
   provisioning process.  The lwB4's re-initiation policy SHOULD be

What happens if the lwB4 ignores the first "SHOULD"?

[9] Section 8.1.  ICMPv4 Processing by the lwAFTR

This describes two approaches to ICMPv4 processing.  Are there any others?
If so, please add some text about them, otherwise, I suggest this change:

   Additionally, the lwAFTR MAY implement:

   o  Discarding of all inbound ICMP messages.
   Otherwise the lwAFTR MUST discard all inbound ICMPv4 messages.

Nits/editorial comments:

-- Section 1.  Introduction

   Basic Bridging BroadBand element: A B4 element is a function
                                     implemented on a dual-stack capable
                                     node, either a directly connected
                                     device or a CPE, that creates a
                                     tunnel to an AFTR.

I suggest changing "a tunnel to an AFTR" to "an IPv4-in-IPv6 tunnel
to an AFTR" for consistency with the AFTR definition.

-- Section 5.2.  Lightweight B4 Data Plane Behavior

   Internally connected hosts source IPv4 packets with an [RFC1918]

Internal to what?  Please explain.

-- Section 6.2.  lwAFTR Data Plane Behavior

   The lwAFTR MUST support hairpinning of traffic between two lwB4s, by
   performing de-capsulation and re-encapsulation of packets.  The
   hairpinning policy MUST be configurable.

Please explain "hairpinning" - it should suffice to add "from one lwB4
that need to be sent to another lwB4 associated with the same AFTR"
after "de-capsulation and re-encapsulation of packets".

-- Section 7.  Additional IPv4 address and Port Set Provisioning Mechanisms

   In a Lightweight 4over6 domain, the binding information MUST be
   aligned between the lwB4s, the lwAFTRs and the provisioning server.

"aligned between" -> "synchronized across" for consistency with use
of forms of "synchronize" elsewhere in this draft.

idnits found a few things to complain about:

- The use of "the well-known range" in Section 5.1.  This is ok,
	as it's describing DS-Lite use of that range that is documented
	elsewhere.  If lw4o6 is using that range, an explanation ought to be
	added to Section 5.1.

- Three references have been updated:

  == Outdated reference: A later version (-09) exists of

  == Outdated reference: draft-ietf-dhc-dhcpv4-over-dhcpv6 has been published
     as RFC 7341

  == Outdated reference: A later version (-06) exists of

--- Selected RFC 5706 Appendix A Q&A for OPS-Dir review ---

A.1.1.  Has deployment been discussed?

	Yes, this protocol is intended to improve scalability over the existing
	DS-Lite mechanism.

A.1.2.  Has installation and initial setup been discussed?

	No, there are vague references to a provisioning mechanism and
	synchronization functionality that need to be set up.  See
	major open issue [2] above which calls out a missing normative
	reference that should address these topics.

A.1.3.  Has the migration path been discussed?

	No, but I suspect that this concern is inapplicable, as I think
	a carrier would not migrate from DS-Lite to lw4o6, but would
	deploy lw4o6 instead of DS-Lite.

A.1.4.  Have the Requirements on other protocols and functional
       components been discussed?

	Yes, but major open issue [1] is effectively in this area.

A.1.6.  Have suggestions for verifying correct operation been discussed?

	No, and they probably should be, as this protocol requires state
	synchronization among the lwB4, lwAFTR and the provisioning system,
	and is likely to exhibit problematic behavior if the relevant state
	information gets out of sync.

A.1.9.  Is configuration discussed?

	Yes, the draft does a good job of discussing what needs to be
	configured to set up the protocol (aside from state synchronization)
	and calling out protocol behavior aspects that should be configurable.

A.2 Management

	This is really not discussed, and in particular the lack of discussion
	of management information is notable because this protocol has a
	different operational structure than DS-Lite.  So, specifically:

 A.2.2.  Is management information discussed?

	No, this is minor open issue [3].  A sentence pointing to applicable
	MIB and/or YANG draft(s) would suffice to address this.

A.2.4.  Is configuration management discussed?

	Yes - the discussion is ok, even though specific configuration mechanisms
	are not discussed.

A.3.  Documentation

	The protocol does have significant operational impacts on the Internet.

	The shepherd's writeup indicates that multiple implementations exist
	among which interoperability has been tested.

David L. Black, Distinguished Engineer
EMC Corporation, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953             FAX: +1 (508) 293-7786 at        Mobile: +1 (978) 394-7754