IP Security Maintenance and Extensions L. Colitti Internet-Draft Google Intended status: Standards Track 25 July 2023 Expires: 26 January 2024 ESP Echo Protocol draft-colitti-ipsecme-esp-ping-00 Abstract This document defines an ESP echo function which can be used to detect whether a given network path supports IPv6 ESP packets. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 26 January 2024. Copyright Notice Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Colitti Expires 26 January 2024 [Page 1] Internet-Draft esp-ping July 2023 Table of Contents 1. Requirements Language . . . . . . . . . . . . . . . . . . . . 2 2. Problem statement . . . . . . . . . . . . . . . . . . . . . . 2 3. Protocol Specification . . . . . . . . . . . . . . . . . . . 3 4. Security Considerations . . . . . . . . . . . . . . . . . . . 3 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 6.1. Normative References . . . . . . . . . . . . . . . . . . 4 6.2. Informative References . . . . . . . . . . . . . . . . . 4 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 4 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 2. Problem statement IPsec sessions between hosts that have global connectivity will by default use unencapsulated IPv6 ESP, i.e., IPv6 packets with a Next Header value of 50. ESP packets may have advantages over ESP-in-UDP encapsulation, such as: * They require fewer keepalive packets to keep sessions open. - On some networks, ESP is be statelessly allowed in both directions, and thus not require any keepalive packets at all. For example, the IPv6 Simple Security recommendations [RFC6092] specify that ESP by default must always be allowed and not be subject to any timeouts. - Even if ESP is not statelessly allowed, experience from real world networks is that timeouts for ESP are higher than for UDP sessions, thus requiring IPsec endpoints to send fewer keepalives. * They provide slightly lower overhead, due to the absence of the UDP header. However, because ESP packets do not share fate with IKE packets, it is possible for the network to allow IKE packets but not ESP packets. This leads to the IPsec session not being able to exchange any packets even though IKE negotiation succeeded. Because ESP is only Colitti Expires 26 January 2024 [Page 2] Internet-Draft esp-ping July 2023 used after IKE negotiation, this failure mode is difficult to predict, difficult to detect, and difficult to recover from. In particular, migrating a session using MOBIKE [RFC4555] to a network that doe snot allow ESP could result in the session blackholing all future packets until the problem is detected and a new migration is performed to enable encapsulation. Operational experience suggests that networks and some home routers that drop ESP packets are common enough to be a problem for general purpose VPN applications desiring to work reliably on the Internet. 3. Protocol Specification An IPv6 node that desires to determine whether the path to a particular destination can support ESP packets can send an ESP Echo Request packet to that destination. ESP Echo Request packets are ESP packets with an SPI value of [ESP-ECHO-REQUEST], a Next Header value of 59 (No Next Header), and no payload. If the destination supports ESP, and wishes to reveal to the sender that it does so, it SHOULD reply with an ESP Echo Reply packet. ESP Echo Reply packets are ESP packets with an SPI value of [ESP-ECHO- REPLY], a Next Header value of 59, and no payload. 4. Security Considerations The security considerations are similar to other unconnected request- reply protocols such as ICMPv6 echo. In particular: * By sending an ESP Echo Request from a spoofed source address, an attacker could cause a server to send an ESP Echo Reply to that address. This does not constitute an amplification attack because the ESP Echo Reply is the same size as the ESP Echo Request. This can be prevented by implementing ingress filtering per BCP 38 [RFC2827]. * An attacker can use ESP Echo Request packets to determine whether a particular destination address is an ESP endpoint. This is not a new attack because any endpoint that supports ESP must also reply to IKE INIT packets. 5. IANA Considerations This memo requests that IANA allocate two new values from the "Security Parameters Index (SPI)" registry. The following entry should be appended: Colitti Expires 26 January 2024 [Page 3] Internet-Draft esp-ping July 2023 +========+==================+=================+ | Number | Description | Reference | +========+==================+=================+ | 7 | ESP Echo Request | [THIS DOCUMENT] | +--------+------------------+-----------------+ | 8 | ESP Echo Reply | [THIS DOCUMENT] | +--------+------------------+-----------------+ Table 1 6. References 6.1. Normative References [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827, May 2000, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)", RFC 4555, DOI 10.17487/RFC4555, June 2006, . [RFC6092] Woodyatt, J., Ed., "Recommended Simple Security Capabilities in Customer Premises Equipment (CPE) for Providing Residential IPv6 Internet Service", RFC 6092, DOI 10.17487/RFC6092, January 2011, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 6.2. Informative References Acknowledgements Thanks to Tero Kivinen, Steffen Klassert, Andrew McGregor, and Paul Wouters for helpful discussion and suggestions. Author's Address Colitti Expires 26 January 2024 [Page 4] Internet-Draft esp-ping July 2023 Lorenzo Colitti Google Shibuya 3-21-3, Japan Email: lorenzo@google.com Colitti Expires 26 January 2024 [Page 5]