Hello

I have been selected to do a routing directorate “early” review of this draft.
https://datatracker.ietf.org/doc/draft-ietf-rtgwg-multisegment-sdwan/

The routing directorate will, on request from the working group chair, perform an “early” review of a draft before it is submitted for publication to the IESG. The early review can be performed at any time during the draft’s lifetime as a working group document. The purpose of the early review depends on the stage that the document has reached.

This draft describes the extensions to Geneve to enable using it to interconnect multiple SD-WAN segments, with particular attention to the case when the carried payload is IPSec protected.

For more information about the Routing Directorate, please see https://wiki.ietf.org/en/group/rtg/RtgDir

Document: draft-ietf-rtgwg-multisegment-sdwan-04
Reviewer: Joel Halpern
Review Date: 17-July-2025
Intended Status: Proposed Standard

Summary:
I have some minor concerns about this document that I think should be resolved before it is submitted to the IESG. I also have one major concern that was flagged by I-D nits. And one major concern where a procedural element does nto sem to work.

Major issues: The example topologies use all sorts of IP v4 addresses.  It should use exclusively example addresses.  And mixing private and public IP addresses in examples is even more confusing.  (Note that this problem might be slightly easier to address if all examples were IPv6 instead of IPv4.)

    Section 4.5 on including specific SD-WAN transitsegments eems an understandable goal.  However, it also seems fraught with failure potential.  In simple topologies, yes, it works.  But suppose that the actual path to the destination is SD-WAN segments A-B-C-D-E.  And suppose the include requirement says "B".  When the GENEVE packet arrives at the C-D boundary, it says that its path must include B.  But the path to the destination from there does not include B.  How is the C-D boundary supposed to know that B has alreay been traversed?

Minor Issues:
    The description of SD-WAN in the second paragraph of the introduction could use some clarification.  The text reads: "Multi-segment SD-WAN refers to SD-WAN deployments where different segments-such as branch offices, cloud regions, and data centers"  But a branch office is a location.  It is not an SD-WAN segment.  Some set of branch offices might be interconnected by an SD-WAN segment, but that is not what this text says.  I think a multi-segment SD-WAN is simply several SD-WAN services from several providers with a means (unclear from whom) to interconnect those SD-WAN services?  The text later refers to a backbone network, which seems to imply a more specific structuring for this interconnection.   If so, a description or reference would seem appropriate.

    Section 3.1 reads more as a marketing section for SD-WAN.  This draft, as I understand it, is for the case where the customer has already chosen to use an SD-WAN, and wants the added benefits of the GENEVE traffic directing encapsulation.  So stick to that.  Don't talk about hypothetical stability benefits of SD-WAN as compared with other inter-connection services.

    Section 4.3 discusses the origin identification sub-TLV.  Having such a sub-TLV seems reasonable.  However, the text in explaining the reason says "These policies may include routing optimization based on the origin,".  I have trouble understanding under what circumstance, given taht the packet is at the processing gateway, knowledge of the origin can enable any more optimal route selection than would otherwise be available.  I can understand that paths may be restricted to certain sources by policy, but that is not an optimization.

    Section 4.4 on the egress gateway identifier again asserts taht allowing the source CPE to specify the egress gateway optimizes path selection.  It seems difficult to construct cases where that will optimize, and easy to construct cases where it will make things worse.  It may again be desirable for policy reasons.  But let's not conflate policy with optimization.

    I presume that the processing SD-WAN gateway logic in section 5 includes checking for the SD-WAN option class being present, as this draft does not otherwise apply?  Shouldn't the text include that check?

   In section 5, in describing the Ingress GW processing, the text is written as if the outer IP destination address will always become the egress gateway.  As I understand it, if the path goes through multiple SD-WAN, the outer IP address at each stage is that of the next gateway?  Could the text be rewritten to make that clear.   Also, doesn't this imply there is a "transit gateway" case as well as ingress and egress?

    I do not know if this is a major concern, a minor concern, or merely a confused reviewer.  There is a description in section 9 of an attack to steal data service (conceptually, an understandable problem.)  However, I am unable to figure out what set of access to what set of places the attacker must have, nor how adding authentication to the CPE / GW exchange would actually help prevent this attack.  In part this is because the attack appears underspecified, and in part this is because the remediation appears underspecified.

    Section 11 on IANA consideration should note that IANA has already assigned the code point.  Otherwise, specifying the value would be improper.