Joel, Thank for the reply.
Below are the additional resolutions marked as [Linda3] . Please let me know if they are acceptable. Thank you, Linda From: Joel Halpern <j...@joelhalpern.com> Sent: Wednesday, July 30, 2025 7:38 AM To: Linda Dunbar <linda.dun...@futurewei.com>; Joel Halpern <j...@joelhalpern.com>; rtg-...@ietf.org Cc: draft-ietf-rtgwg-multisegment-sdwan....@ietf.org; rtgwg@ietf.org Subject: Re: draft-ietf-rtgwg-multisegment-sdwan-04 early Rtgdir review Trimmed to remove agreements. Context retained for remaining issues. My new notes marked <jmh2></jmh2> Yours, Joel On 7/29/2025 10:25 PM, Linda Dunbar wrote: Joel, Apologies for missing this email through the IETF week. Thank you very much for the additional comments. Please see below under [Linda 2] for the proposed resolutions. Let us know if they are acceptable. Linda From: Joel Halpern <j...@joelhalpern.com><mailto:j...@joelhalpern.com> Sent: Thursday, July 17, 2025 6:50 PM To: Linda Dunbar <linda.dun...@futurewei.com><mailto:linda.dun...@futurewei.com>; rtg-...@ietf.org<mailto:rtg-...@ietf.org> Cc: draft-ietf-rtgwg-multisegment-sdwan....@ietf.org<mailto:draft-ietf-rtgwg-multisegment-sdwan....@ietf.org>; rtgwg@ietf.org<mailto:rtgwg@ietf.org> Subject: Re: draft-ietf-rtgwg-multisegment-sdwan-04 early Rtgdir review Some of your answers address the raised concerns. However, some of them indicate I was insufficiently clear, as they do not address the issue. I will not in line where things are fine,a nd where I think there is still a problem. I will delimit my comments with <jmh></jmh> in case of indenting problems. Yours, Joel On 7/17/2025 9:12 PM, Linda Dunbar wrote: Joel, Thank you very much for reviewing the document and the valuable feedback. Please see below for the detailed resolutions. If they are okay with you, we can upload the revision on Monday. Linda -----Original Message----- From: Joel Halpern via Datatracker <nore...@ietf.org><mailto:nore...@ietf.org> Sent: Thursday, July 17, 2025 10:46 AM To: rtg-...@ietf.org<mailto:rtg-...@ietf.org> Cc: draft-ietf-rtgwg-multisegment-sdwan....@ietf.org<mailto:draft-ietf-rtgwg-multisegment-sdwan....@ietf.org>; rtgwg@ietf.org<mailto:rtgwg@ietf.org> Subject: draft-ietf-rtgwg-multisegment-sdwan-04 early Rtgdir review Document: draft-ietf-rtgwg-multisegment-sdwan Title: Multi-segment SD-WAN via Cloud DCs Reviewer: Joel Halpern Review result: Not Ready Hello I have been selected to do a routing directorate "early" review of this draft. https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fdraft-ietf-rtgwg-multisegment-sdwan%2F&data=05%7C02%7Clinda.dunbar%40futurewei.com%7Cde59685e54d84193978008ddc559be0d%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C638883711415554778%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=0rGQhV01eJsDerr6g1jxCzUIkhF5vlwTPOohcWDo3%2Bg%3D&reserved=0<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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwiki.ietf.org%2Fen%2Fgroup%2Frtg%2FRtgDir&data=05%7C02%7Clinda.dunbar%40futurewei.com%7Cde59685e54d84193978008ddc559be0d%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C638883711415582636%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=rne%2Fx6T0XCvkiaZPqAx%2F6%2BWGFFOY7%2FXs9tPq%2BmBi5G4%3D&reserved=0<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 <jmh2>resolved</jmh2>. And one major concern where a procedural element does nto sem to work. ... 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? [Linda] Some SD-WAN deployments require specific transit segments to be included in the end-to-end path for regulatory, security, or service chaining purposes, rather than for path optimization. The Include-Transit Sub-TLV, an optional field, is used to signal such requirements. It allows explicitly specifying a list of Cloud Availability Regions or Zones that a packet must traverse when forwarded through the Cloud Backbone. <jmh> I apparently did not explain my concern well enough. I understand why one would want to mandate that a (or several (specific SD-WAN are traversed. (I could debate the utility, but operators and customers often want things I wonder about.) That is not the source of my concern. It is unclear who is expected to enforce the mandatory traverse case, and how loops are avoided. Suppose that SD-WAN A is connected to SDS-WAN B, which is connected to SD-WAN C and D. And D is connect to SD-WAN B and E, where the egress exists. A Geneve packet is sent with an include indicating that SD-WAN B must be traversed. The packet happens to go theorugh SD-WAN A to SD-WAN B (meeting the traversal requirement), then to SD-WAN C, and then to the SD-WAN D. However, by the time the packet arrives at SD-WAN D, there is no indication in the packet that it went through SD-WAN B. WHich would seem to require D to send the packet back to SD-WAN B. Which is clearly not what is desired. How does the gateway to SD-WAN D know that it si fine to keep forwarding towards the destination (egress from E) rather than returning the packet to B? I could understand how it worked if there was also a route record. Or if the Include was removed once it was satisfied. But the draft does not call for either of those behaviors. </jmh> [Linda 2] Your illustration regarding potential loops and the lack of explicit enforcement mechanisms is entirely valid. However, as noted in the draft, it is out of scope for the IETF (and this document) to define how the cloud backbone enforces client-specified traversal preferences. The Include-Transit Sub-TLV is intended only to convey the client's desired intent or preferences. How about adding this sentence to the section: "..., this indication reflects preference only and does not imply any guarantee of traversal. Enforcement of the include list is outside the scope of this document and must be realized, if needed, through mutual agreement and provider-specific mechanisms.." <jmh2>Note that in the end I am not the one you have to satisfy. But, from where I sit, a behavioral marking that can't be acted upon without additional protocol behaviors (which ar enot obviously valid to me) is not a marking we can have in an RFC. It does not lead to interopeable implementation. </jmh2> [Linda3] Your points are well taken. That said, there is precedent for this approach in RFCs 8670, 7752, and 8306, where protocol elements convey intent or preference, but their interpretation and enforcement are left to local policy or controller behavior. In the same spirit, the Include-Transit Sub-TLV expresses the originator CPE's intent to prefer certain transit regions, while how the Cloud Backbone enforces that preference is intentionally left out of scope for this document.. Minor Issues: ... 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? [Linda] The GENEVE header remains during transit across the Cloud Backbone and is removed by the egress Cloud Gateway before the packet is forwarded to the destination CPE. The packet is forwarded natively on the final SD-WAN segment (egress GW to destination CPE) without GENEVE encapsulation. <jmh>I am still missing something. It may be that I am misunderstanding the interaction between mutli-segment SD-WAN and GENEVE. Suppose that we have GW1 - SDWAN A - GW 2 - SDWAN B - GW-3. When the packet arrives at GW-1 with the multi-segment SD-WAN option, GW1 decides (subject to the constraints of the options in the packet) that the packet should go to GW2 in orderr to get to GW3. As I understand it, GW1 will replace the outer IP destination (which was GW-1 upon arrival) with the IP address of GW2. But the text says that it will replace the destination address with the egress IP address (GW-3, or maybe something beyond that.) </jmh> <jmh2>I do not see a response to this issue</jmh2> [Linda3] Sorry for missing this one. The ingress GW determines the appropriate egress Cloud GW based on its internal logic or policy, or via the Egress GW Sub-TLV included in the Multi-Segment Metadata. The destination address in the outer IP header of the GENEVE packet should be determined by the Cloud Backbone. This address is intended to reach the egress Cloud GW identified by the Egress GW Sub-TLV (if present), or the optimal egress GW selected based on the destination CPE address. Changed the text to the following: 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. [Linda] does it help to add this sentence to the introduction? In this document, "multi-segment SD-WAN" refers specifically to deployments with two SD-WAN edge segments: one from the originating CPE to the ingress Cloud Gateway, and one from the egress Cloud Gateway to the destination CPE. There may be additional SD-WAN segments or forwarding domains between the ingress and egress Cloud Gateways across the Cloud Backbone, but their internal behavior is out of scope for this specification. <jmh>Nope, sorry. That does not tell me what the security threat is that leads to wanting authentication. It also does not tell me how the authentication is actually to be done. (I naive reading is that you are inventing an authentication extension, with insufficient specificity, to some unspecified protocol between the CPE and the first SD-WAN gateway.) </jmh> [Linda2] Section 9 describes the consequence (data theft) but does not clearly articulate the security threat or the authentication model. To clarify: 1. The threat is that a malicious or misconfigured CPE could inject SD-WAN metadata intended for another tenant, attempting to use or redirect traffic through paths it is not authorized for. 2. Authentication is needed to verify the origin and legitimacy of the SD-WAN metadata, ensuring it is associated with an authorized endpoint. <jmh2>At the very least, this needs to be better explained in the draft. I think the issue is larger. Adding security to the CPE-SDWAN connection seems to be largely irrelevant if that CPE is compromised. Additionally, if the SDWAN gateway accepts traffic from arbitrary devices, taht would seem to be an unerlying SDWAN problem, not a multi-segment security issue.</jmh2> [Linda3] do you think the following text for Bullet c) under Section 9.1 can reflect those two key points? (c) Potential stealing of Cloud Backbone bandwidth: A threat actor, such as a malicious or misconfigured C-PE, could inject SD-WAN metadata intended for another tenant, attempting to redirect traffic through Cloud Backbone paths it is not authorized to use. For example, a legitimate Cloud subscriber pays for Cloud Backbone transport between CPE-A and CPE-B. An attacker, who controls two locations (Node-A and Node-B), might construct a packet with CPE-A's address as the source and include CPE-B in the SD-WAN Endpoint Sub-TLV. The packet, when sent to the ingress Cloud GW, would appear to be a legitimate flow between CPE-A and CPE-B. After exiting the egress Cloud GW, the attacker could rewrite the outer addresses to resume communication between Node-A and Node-B, effectively tunneling traffic via the Cloud Backbone without authorization or payment. To prevent such misuse, it is necessary to authenticate and verify the origin and legitimacy of the SD-WAN metadata to ensure it is associated with an authorized and registered CPE endpoint. This validation protects against both spoofing and cross-tenant policy violations. While it is not necessary for Cloud GWs to decrypt or re-encrypt payloads, they must enforce metadata integrity using authentication mechanisms such as those defined in [RFC2403] and [RFC2404]. These mechanisms rely on cryptographic hashing algorithms (e.g., SHA2 224/256/384/512) as part of a Hashed Message Authentication Code (HMAC) to validate packet authenticity. <jmh>Thanks.</jmh>
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