IPSECME Working Group W. Pan Internet-Draft Q. He Intended status: Standards Track Huawei Expires: 4 September 2024 P. Wouters Aiven 3 March 2024 IKEv2 Support for Anti-Replay Status Notification draft-pan-ipsecme-anti-replay-notification-00 Abstract RFC 4302 and RFC 4303 specify that, during Security Association (SA) establishment, IPsec implementation should notify the peer if it will not provide anti-replay protection, to avoid having the peer do unnecessary sequence number monitoring and SA setup. This document defines the ANTI_REPLAY_STATUS Notify Message Status Type Payload in the Internet Key Exchange Protocol Version 2 (IKEv2) to inform the peers of their own anti-replay status when creating the IPsec SAs, to fulfill the above requirement. About This Document This note is to be removed before publishing as an RFC. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-pan-ipsecme-anti-replay- notification/. Discussion of this document takes place on the ipsec Working Group mailing list (mailto:ipsec@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/ipsec/. Subscribe at https://www.ietf.org/mailman/listinfo/ipsec/. 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/. Pan, et al. Expires 4 September 2024 [Page 1] Internet-Draft Anti-Replay Notification in IKEv2 March 2024 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 4 September 2024. Copyright Notice Copyright (c) 2024 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Problem Statement . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 3. Notifying the Anti-replay Status . . . . . . . . . . . . . . 4 4. ANTI_REPLAY_STATUS Notify Payload Format . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction IPsec Authentication Header (AH) [RFC4302] and Encapsulating Security Payload (ESP) [RFC4303] are used to provide security for IP communications. Both AH and ESP support the anti-replay function to prevent an attacker from resending the packets received by the IPsec peer before. Each IPsec packet is sent with a unique sequence number, which the IPsec receiver checks to see whether the sequence number is duplicated. Pan, et al. Expires 4 September 2024 [Page 2] Internet-Draft Anti-Replay Notification in IKEv2 March 2024 RFC 4302 and RFC 4303 specify the details of sequence number generation and verification. When anti-replay is enabled on the receiver, the sender must monitor the sequence number counter and increment the counter with every message sent. The sender must ensure that the counter does not cycle, and trigger the creation and use of a new IPsec SA before the counter is about to cycle. When anti-replay is disabled on the receiver, the sender does not need to monitor or reset the counter. The sender only increments the counter and rolls it over back to zero when it reaches the maximum value. It is specified in both RFC 4302 and RFC 4303 that, during SA establishment, IPsec implementation should notify the peer if it will not provide anti-replay protection, to avoid having the peer do unnecessary sequence number monitoring and SA setup. However, currently, IKEv2 [RFC7296] does not have the notification of anti- replay status when negotiating the creation of an IPsec SA. As a result, IPsec implementations must always assume that the peer has anti-replay enabled. Even though anti-replay is disabled on both ends, they still have to monitor the sequence numbers. This document adds a notification in IKEv2 to inform the peers of their own anti-replay status when creating the IPsec SAs, which can finally avoid unnecessary sequence number monitoring. 1.1. Problem Statement When anti-replay is enabled on the peer, the IPsec implementation needs to monitor the sequence number of outbound packets, and trigger a rekey to generate and use a new Child SA when the sequence number counter is about to cycle. In high-performance scenarios, high-speed traffic causes the 32-bit sequence number to be consumed quickly, resulting in frequent rekeying of Child SAs. For this reason, IPsec defines the Extended Sequence Number (ESN) function, extending the available space for sequence numbers from 32 to 64 bits. Although ESN is good to avoid the sequence number running out in a short period, there is a prerequisite for using ESN - RFC 4302 and RFC 4303 both require ESN to be used in conjunction with the anti-replay function. That is, ESN can only be used if the anti-replay feature is enabled. Pan, et al. Expires 4 September 2024 [Page 3] Internet-Draft Anti-Replay Notification in IKEv2 March 2024 In the high-performance scenario, operators may choose to disable the anti-replay function for the considerations of QoS, performance, and others. For example, the high-level QoS packets arriving first may cause a large number of low-level QoS packets being dropped, when the disordered packets exceed the window size of anti-replay. Disabling anti-replay brings a new problem: IPsec peers cannot successfully negotiate using ESN. The final result is that neither peer of IPsec enables anti-replay, but neither can use ESN, leaving the Child SAs forced to rekey frequently due to the rapid exhaustion of the 32-bit sequence number. The solution to this problem can be approached in two ways. One option is to support the continued use of the ESN when anti-replay is disabled. Because IPsec packets carry only the low-order 32 bits of the sequence number, the ESN has a need for the receiver to manage the anti-replay window in order to determine the correct value for the high-order 32 bits. To use ESN when anti-replay is disabled, the IPsec implementation needs to create and maintain a separate window for ESN as well. The other option is to add a notification of anti-replay status in IKEv2. Section 3.4.3 of both RFC 4302 and RFC 4303 specify that the IPsec receiver should notify the sender during SA establishment that the receiver will not provide anti-replay protection. Adding the anti-replay status notification in IKEv2 can fulfill this requirement. When anti-replay is disabled on both peers, neither peer needs to monitor the sequence number counter, thus avoiding frequent rekey of Child SAs. Although the first option could support using ESN when anti-replay is enabled at one peer and disabled at the other, this would require an update to RFC 4302 and RFC 4303. Therefore, this document considers the second option, given that it is only an extension of IKEv2 to fulfill a requirement already defined in RFC 4302 and RFC 4303. 2. 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. 3. Notifying the Anti-replay Status When creating a Child SA, the ANTI_REPLAY_STATUS notify payload can be used by the initiator and the responder to inform each other of their own anti-replay status (enabled or disabled) regarding this SA. Pan, et al. Expires 4 September 2024 [Page 4] Internet-Draft Anti-Replay Notification in IKEv2 March 2024 The initiator includes the ANTI_REPLAY_STATUS notify payload in the IKE_AUTH exchange request for creating the initial Child SA or the CREATE_CHILD_SA exchange request for creating the subsequent Child SAs. A responder that does not support the anti-replay status notification processes the request as normal, and does not include the new Notify in the response. As per regular IKEv2 processing, a responder that does not recognize this new Notify, MUST ignore the notify. As required in RFC 4302 and RFC 4303, this responder should assume the anti-replay is enabled in the initiator. The absence of the Notify in the response indicates to the initiator that the responder doesn't support the anti-replay status notification. The initiator continues the IKEv2 negotiation as usual, and also assumes the anti-replay is enabled in the responder. A responder that supports the anti-replay status notification can understand whether the initiator provides the anti-replay protection for this Child SA, and includes the ANTI_REPLAY_STATUS notify payload in the response to inform its anti-replay status about this Child SA. The IKE_AUTH message exchange in this case is shown below: Initiator Responder ------------------------------------------------------------------- HDR, SK {IDi, [CERT,] [CERTREQ,] [IDr,] AUTH, SAi2, TSi, TSr, N(ANTI_REPLAY_STATUS)} --> <-- HDR, SK {IDr, [CERT,] AUTH, SAr2, TSi, TSr, N(ANTI_REPLAY_STATUS)} The CREATE_CHILD_SA message exchange in this case is shown below: Initiator Responder ------------------------------------------------------------------- HDR, SK {SA, Ni, [KEi,] TSi, TSr, N(ANTI_REPLAY_STATUS)} --> <-- HDR, SK {SA, Nr, [KEr,] TSi, TSr, N(ANTI_REPLAY_STATUS)} After the Child SA is successfully established and the initiator and responder mutually notify each other of their own anti-replay status, the IPsec implementation can choose not to monitor the sequence number counter if the peer's anti-replay is disabled. Pan, et al. Expires 4 September 2024 [Page 5] Internet-Draft Anti-Replay Notification in IKEv2 March 2024 4. ANTI_REPLAY_STATUS Notify Payload Format The ANTI_REPLAY_STATUS Notify Message type notification is used by the initiator and responder to indicate their own anti-replay status to each other when creating the Child SAs. 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +---------------+-+-------------+-------------------------------+ | Next Payload |C| RESERVED | Payload Length | +---------------+-+-------------+-------------------------------+ |Protocol ID(=0)| SPI Size (=0) | Notify Message Type | +---------------+---------------+-------------------------------+ | Status | +---------------------------------------------------------------+ * Protocol ID (1 octet) - this field MUST contain either (2) to indicate AH or (3) to indicate ESP. * SPI Size (1 octet) - MUST be 0. * Notify Message Type (2 octets) - MUST be set to the value TBD1. * Status (4 octets) - this field MUST be 0 to indicate the anti- replay is enabled or 1 to indicate the anti-replay is disabled. The Critical bit MUST be 0. A non-zero value MUST be ignored. 5. IANA Considerations This document defines a new Notify Message Type in the "IKEv2 Notify Message Types - Status Types" registry. IANA is requested to assign the codepoint in this registry. NOTIFY messages: status types Value ---------------------------------------------------------- ANTI_REPLAY_STATUS TBD1 6. Security Considerations TBD 7. Acknowledgments TBD 8. References Pan, et al. Expires 4 September 2024 [Page 6] Internet-Draft Anti-Replay Notification in IKEv2 March 2024 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. Kivinen, "Internet Key Exchange Protocol Version 2 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 2014, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 8.2. Informative References [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, DOI 10.17487/RFC4302, December 2005, . [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, DOI 10.17487/RFC4303, December 2005, . Authors' Addresses Wei Pan Huawei Technologies Email: william.panwei@huawei.com Qi He Huawei Technologies Email: archibald.heqi@huawei.com Paul Wouters Aiven Email: paul.wouters@aiven.io Pan, et al. Expires 4 September 2024 [Page 7]