IKEv2 support for per-resource Child SAs
draft-ietf-ipsecme-multi-sa-performance-02

Network                                                        A. Antony
Internet-Draft                                                   secunet
Intended status: Standards Track                              T. Brunner
Expires: 24 April 2024                                          codelabs
                                                             S. Klassert
                                                                 secunet
                                                              P. Wouters
                                                                   Aiven
                                                         22 October 2023

                IKEv2 support for per-resource Child SAs
               draft-ietf-ipsecme-multi-sa-performance-02

Abstract

   This document defines two Notify Message Type Payloads for the
   Internet Key Exchange Protocol Version 2 (IKEv2) to support the
   negotiation of multiple Child SAs with the same Traffic Selectors
   used on different resources, such as CPUs, to increase bandwidth of
   IPsec traffic between peers.

   The SA_RESOURCE_INFO notification is used to convey information that
   the negotiated Child SA and subsequent new Child SAs with the same
   Traffic Selectors are a logical group of Child SAs where most or all
   of the Child SAs are bound to a specific resource, such as a specific
   CPU.  The TS_MAX_QUEUE notify conveys that the peer is unwilling to
   create more additional Child SAs for this particular negotiated
   Traffic Selector combination.

   Using multiple Child SAs with the same Traffic Selectors has the
   benefit that each resource holding the Child SA has its own Sequence
   Number Counter, ensuring that CPUs don't have to synchronize their
   crypto state or disable their packet replay protection.

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/.

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   Internet-Drafts are draft documents valid for a maximum of six months
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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Performance bottlenecks . . . . . . . . . . . . . . . . . . .   4
   3.  Negotiation of CPU specific Child SAs . . . . . . . . . . . .   4
   4.  Implementation Considerations . . . . . . . . . . . . . . . .   5
   5.  Payload Format  . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  SA_RESOURCE_INFO Notify Status Message Payload  . . . . .   6
     5.2.  TS_MAX_QUEUE Notify Error Message Payload . . . . . . . .   6
   6.  Operational Considerations  . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  Implementation Status . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Linux XFRM  . . . . . . . . . . . . . . . . . . . . . . .   9
     8.2.  Libreswan . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.3.  strongSwan  . . . . . . . . . . . . . . . . . . . . . . .  10
     8.4.  iproute2  . . . . . . . . . . . . . . . . . . . . . . . .  11
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     10.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

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1.  Introduction

   Most IPsec implementations are currently limited to using one queue
   or CPU resource for a Child SA.  The result is that a machine with
   many such resources is limited to only using one of these per Child
   SA.  This severely limits the throughput that can be attained.  An
   unencrypted link of 10Gbps or more is commonly reduced to 2-5Gbps
   when IPsec is used to encrypt the link using AES-GCM.  By using the
   implementation specified in this document, aggregate throughput
   increased from 5Gbps using 1 CPU to 40-60 Gbps using 25-30 CPUs

   While this could be (partially) mitigated by setting up multiple
   narrowed Child SAs, for example using Populate From Packet (PFP) as
   specified in [RFC4301], this IPsec feature is not widely implemented.
   Some route based IPsec implementations might be able to implement
   this with specific rules into separate network interfaces, but these
   methods might not be available for policy based IPsec
   implementations.

   To make better use of multiple network queues and CPUs, it can be
   beneficial to negotiate and install multiple Child SAs with identical
   Traffic Selectors.  IKEv2 [RFC7296] already allows installing
   multiple Child SAs with identical Traffic Selectors, but it offers no
   method to indicate that the additional Child SA is being requested
   for performance increase reasons and is restricted to some resource
   (queue or CPU).  Without this indication, the peer might not accept
   multi Child SAs with identical Traffic Selectors and might delete one
   of the Child SAs it considered an unwanted duplicate.

   When an IKEv2 peer is receiving more additional Child SA's for a
   single set of Traffic Selectors than it is willing to create, it can
   return an error notify of TS_MAX_QUEUE.

1.1.  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.

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2.  Performance bottlenecks

   There are a number of practical reasons why most Implementations have
   to limit a Child SA to only one specific hardware resource, but a key
   limitation is that sharing the crypto state, counters and sequence
   numbers between multiple CPUs is not feasible without a significant
   performance penalty.  There is a need to negotiate and establish
   multiple Child SAs with identical TSi/TSr on a per-resource basis.

3.  Negotiation of CPU specific Child SAs

   An initial IKEv2 exchange is used to setup an IKE SA and the initial
   Child SA.  If multiple Child SAs with the same Traffic Selectors are
   desired, the initiator will add the SA_RESOURCE_INFO notify payload
   to the Exchange negotiating the Child SA (eg IKE_AUTH or
   CREATE_CHILD_SA).  If this initial Child SA will be tied to a
   specific resource, it MAY indicate this by including an identifier in
   the Notification Data.  A responder that is willing to have multple
   Child SAs for the same Traffic Selectors will respond by also adding
   the SA_RESOURCE_INFO notify payload in which it MAY add a non-zero
   notify data payload.

   Additional resource-specific Child SAs are negotiated as regular
   Child SAs using the CREATE_CHILD_SA exchange and are similarly
   identified by an accompanying SA_RESOURCE_INFO notification.

   Upon installation, each resource-specific Child SA is associated with
   an additional local selector, such as CPU or queue.  These resource-
   specific Child SAs MUST be negotiated with identical Child SA
   properties that were negotiated for the initial Child SA.  This
   includes cryptographic algorithms, Traffic Selectors, Mode (e.g.
   transport mode), compression usage, etc.  However, each Child SA does
   have its own keying material that is individually derived according
   to the regular IKEv2 process.  The SA_RESOURCE_INFO notify payload
   MAY be empty or MAY contain some identifying data that could be
   useful for debugging purposes.

   Additional Child SAs can be started on-demand or can be started all
   at once.  Peers may also delete specific per-resource Child SAs if
   they deem the associated resource to be idle.

   During the CREATE_CHILD_SA rekey for the Child SA, the
   SA_RESOURCE_INFO notification MAY be included, but regardless of
   whether or not it is included, the rekeyed Child SA MUST be bound to
   the same resource(s) as the Child SA that is being rekeyed.

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4.  Implementation Considerations

   There are various considerations that an implementation can use to
   determine the best way to install multiple Child SAs.  Below are
   examples of such strategies.

   A simple distribution could be to install one additional Child SA on
   each CPU.  An implementation MAY ensure that one Child SA can be used
   by all CPUs, so that while negotiating a new per-CPU Child SA, which
   typically takes a 1RTT delay, the CPU with no CPU-specific Child SA
   can still encrypt its packets using the Child SA that is available
   for all CPUs.  Alternatively, if an implementation finds it needs to
   encrypt a packet but the current CPU does not have the resources to
   encrypt this packet, it can relay that packet to a specific CPU that
   does have the capability to encrypt the packet, although this will
   come with a performance penalty.

   Performing per-CPU Child SA negotiations can result in both peers
   initiating additional Child SAs at once.  This is especially likely
   if per-CPU Child SAs are triggered by individual SADB_ACQUIRE
   [RFC2367] messages.  Responders should install the additional Child
   SA on a CPU with the least amount of additional Child SAs for this
   TSi/TSr pair.

   When the number of queue or CPU resources are different between the
   peers, the peer with the least amount of resources MAY decide to not
   install a second outbound Child SA for the same resource as it will
   never use it to send traffic.  However, it MUST install all inbound
   Child SAs as it has committed to receiving traffic on these
   negotiated Child SAs.

   If per-CPU SADB_ACQUIRE messages are implemented (see Section 6), the
   Traffic Selector (TSi) entry containing the information of the
   trigger packet SHOULD be included in the TS set.  This information
   MAY be used by the peer to select the most optimal target CPU to
   install the additional Child SA on.  For example, if the trigger
   packet was for a TCP destination to port 25 (SMTP), it might be able
   to install the Child SA on the CPU that is also running the mail
   server process.  Trigger packet Traffic Selectors are documented in
   [RFC7296] Section 2.9.

   As per RFC 7296, rekeying a Child SA SHOULD use the same (or wider)
   Traffic Selectors to ensure that the new Child SA covers everything
   that the rekeyed Child SA covers.  This includes Traffic Selectors
   negotiated via Configuration Payloads (CP) such as
   INTERNAL_IP4_ADDRESS which may use the original wide TS set or use
   the narrowed TS set.

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5.  Payload Format

   All multi-octet fields representing integers are laid out in big
   endian order (also known as "most significant byte first", or
   "network byte order").

5.1.  SA_RESOURCE_INFO Notify Status Message Payload

                       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  !   SPI Size    !      Notify Message Type      !
   +---------------+---------------+-------------------------------+
   !                                                               !
   ~               Optional resource identifier                       ~
   !                                                               !
   +-------------------------------+-------------------------------+

   *  Protocol ID (1 octet) - MUST be 0.  MUST be ignored if not 0.

   *  SPI Size (1 octet) - MUST be 0.  MUST be ignored if not 0.

   *  Notify Status Message Type (2 octets) - set to [TBD1]

   *  Optional Payload Data.  This value MAY be set to convey the local
      identity of the resource.  The value SHOULD be a unique identifier
      and the peer SHOULD only use it for debugging purposes.

5.2.  TS_MAX_QUEUE Notify Error Message Payload

                       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  !   SPI Size    !      Notify Message Type      !
   +---------------+---------------+-------------------------------+

   *  Protocol ID (1 octet) - MUST be 0.  MUST be ignored if not 0.

   *  SPI Size (1 octet) - MUST be 0.  MUST be ignored if not 0.

   *  Notify Error Message Type (2 octets) - set to [TBD2]

   *  There is no data associated with this Notify type.

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6.  Operational Considerations

   Implementations supporting per-CPU SAs SHOULD extend their local SPD
   selector, and the mechanism of on-demand negotiation that is
   triggered by traffic to include a CPU (or queue) identifier in their
   SADB_ACQUIRE message from the SPD to the IKE daemon.  If the IKEv2
   extension defined in this document is negotiated with the peer, a
   node which does not support receiving per-CPU SADB_ACQUIRE messages
   MAY initiate all its Child SAs immediately upon receiving the (only)
   SADB_ACQUIRE it will receive from the IPsec stack.  Such
   implementations also need to be careful when receiving a Delete
   Notify request for a per-CPU Child SA, as it has no method to detect
   when it should bring up such a per-CPU Child SA again later.  And
   bringing the deleted per-CPU Child SA up again immediately after
   receiving the Delete Notify might cause an infinite loop between the
   peers.  Another issue of not bringing up all its per-CPU Child SAs is
   that if the peer acts similarly, the two peers might end up with only
   the first Child SA without ever activating any per-CPU Child SAs.  It
   is there for RECOMMENDED to implement per-CPU SADB_ACQUIRE messages.

   Peers SHOULD be lenient with the maximum number of Child SAs they
   allow for a given TSi/TSr combination to account for corner cases.
   For example, during Child SA rekeying, there might be a large number
   of additional Child SAs created before the old Child SAs are torn
   down.  Similarly, when using on-demand Child SAs, both ends could
   trigger multiple Child SA requests as the initial packet causing the
   Child SA negotiation might have been transported to the peer via the
   first Child SA where its reply packet might also trigger an on-demand
   Child SA negotiation to start.  As additional Child SAs consume
   little additional overhead, allowing at the very least double its
   intended CPUs is RECOMMENDED.  An implementation MAY limit the number
   of Child SAs only based on its resources - that is only limit these
   based on regular denial of service protection.  Although having too
   many SAs may slow down per-packet SAD lookup.

   Implementations might support dynamically moving a per-CPU Child SAs
   from one CPU to another CPU.  If this method is supported,
   implementations must be careful to move both the inbound and outbound
   SAs.  If the IPsec endpoint is a gateway, it can move the inbound SA
   and outbound SA independently from each other.  It is likely that for
   a gateway, IPsec traffic would be asymmetric.  If the IPsec endpoint
   is the same host responsible for generating the traffic, the inbound
   and outbound SAs SHOULD remain as a pair on the same CPU.  If a host
   previously skipped installing an outbound SA because it would be an
   unused duplicate outbound SA, it will have to create and add the
   previously skipped outbound SA to the SAD with the new CPU ID.  The
   inbound SA may not have CPU ID in the SAD.  Adding the outbound SA to
   the SAD requires access to the key material, whereas for updating the

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   CPU selector on an existing outbound SAs access to key material might
   not be needed.  To support this, the IKE software might have to hold
   on to the key material longer than it normally would, as it might
   actively attempt to destroy key material from memory that the IKE
   daemon no longer needs access to.

   An implementation that does not accept any further resource specific
   Child SAs MUST NOT return the NO_ADDITIONAL_SAS error because this
   can be interpreted by the peer that no other Child SAs with different
   TSi/TSr are allowed either.  Instead, it MUST return TS_MAX_QUEUE.

7.  Security Considerations

   Similar to how an implementation should limit the number of half-open
   SAs to limit the impact of a denial of service attack, an
   implementation SHOULD limit the maximum number of additional Child
   SAs allowed per unique TSi/TSr.

   Using multiple resource specific child SAs makes sense for high
   volume IPsec connections on IPsec gateway machines where the
   administrator has a reasonable trust relationship with the peer's
   administrator and abuse is unlikely and easilly escalated to resolve.

   This trust relationship is usually not present for the Remote Access
   VPN type deployments, and allowing per-CPU Child SA's is NOT
   RECOMMENDED in these scenarios.  Therefor, it is also NOT RECOMMENDED
   to allow per-CPU Child SAs per default.

   The SA_RESOURCE_INFO notify contains an optional data payload that
   can be used by the peer to identify the Child SA belonging to a
   specific resource.  The notify data SHOULD NOT be an identier that
   can be used to gain information about the hardware.  For example,
   using the CPU number itself as identier might give an attacker
   knowledge which packets are handled by which CPU ID and it might
   optimize a brute force attack against the system.

8.  Implementation Status

   [Note to RFC Editor: Please remove this section and the reference to
   [RFC6982] before publication.]

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC7942].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort

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   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to [RFC7942], "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

   Authors are requested to add a note to the RFC Editor at the top of
   this section, advising the Editor to remove the entire section before
   publication, as well as the reference to [RFC7942].

8.1.  Linux XFRM

   Organization:  Linux kernel XFRM

   Name:  XFRM-PCPU-v3
      https://git.kernel.org/pub/scm/linux/kernel/git/klassert/linux-
      stk.git/log/?h=xfrm-pcpu-v3

   Description:  An initial Kernel IPsec implementation of the per-CPU
      method.

   Level of maturity:  Alpha

   Coverage:  Implements a general Child SA and per-CPU Child SAs.  It
      only supports the NETLINK API.  The PFKEYv2 API is not supported.

   Licensing:  GPLv2

   Implementation experience:  The Linux XFRM implementation added two
      additional attributes to support per-CPU SAs.  There is a new
      attribute XFRMA_SA_PCPU, u32, for the SAD entry.  This attribute
      should present on the outgoing SA, per-CPU Child SAs, starting
      from 0.  This attribute MUST NOT be present on the first XFRM SA.
      It is used by the kernel only for the outgoing traffic, (clear to
      encrypted).  The incoming SAs do not need XFRMA_SA_PCPU attribute.
      XFRM stack can not use CPU id on the incoming SA.  The kernel
      internally sets the value to 0xFFFFFF for the incoming SA and the
      initial Child SA that can be used by any CPU.  However, one may
      add XFRMA_SA_PCPU to the incoming per-CPU SA to steer the ESP
      flow, to a specific Q or CPU e.g ethtool ntuple configuration.
      The SPD entry has new flag XFRM_POLICY_CPU_ACQUIRE.  It should be

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      set only on the "out" policy.  The flag should be disabled when
      the policy is a trap policy, without SPD entries.  After a
      successful negotiation of CPU_QUEUES, while adding the first Child
      SA, the SPD entry can be updated with the XFRM_POLICY_CPU_ACQUIRE
      flag.  When XFRM_POLICY_CPU_ACQUIRE is set, the XFRM_MSG_ACQUIRE
      generated will include the XFRMA_SA_PCPU attribute.

   Contact:  Steffen Klassert steffen.klassert@secunet.com

8.2.  Libreswan

   Organization:  The Libreswan Project

   Name:  pcpu-3 https://libreswan.org/wiki/XFRM_pCPU

   Description:  An initial IKE implementation of the per-CPU method.

   Level of maturity:  Alpha

   Coverage:  implements combining a regular (all-CPUs) Child SA and
      per-CPU additional Child SAs

   Licensing:  GPLv2

   Implementation experience:  TBD

   Contact:  Libreswan Development: swan-dev@libreswan.org

8.3.  strongSwan

   Organization:  The StrongSwan Project

   Name:  StrongSwan https://github.com/strongswan/strongswan/tree/per-
      cpu-sas-poc/

   Description:  An initial IKE implementation of the per-CPU method.

   Level of maturity:  Alpha

   Coverage:  implements combining a regular (all-CPUs) Child SA and
      per-CPU additional Child SAs

   Licensing:  GPLv2

   Implementation experience:  StrongSwan use private space values for
      notifications CPU_QUEUES (40970) and QUEUE_INFO (40971).

   Contact:  Tobias Brunner tobias@strongswan.org

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8.4.  iproute2

   Organization:  The iproute2 Project

   Name:  iproute2 https://github.com/antonyantony/iproute2/tree/pcpu-v1

   Description:  Implemented the per-CPU attributes for the "ip xfrm"
      command.

   Level of maturity:  Alpha

   Licensing:  GPLv2

   Implementation experience:  TBD

   Contact:  Antony Antony antony.antony@secunet.com

9.  IANA Considerations

   This document defines two new IKEv2 Notify Message Type payloads for
   the IANA "IKEv2 Notify Message Types - Status Types" registry.

         Value   Notify Type Messages - Status Types    Reference
         -----   ------------------------------    ---------------
         [TBD1]   SA_RESOURCE_INFO                    [this document]

                                  Figure 1

   This document defines one new IKEv2 Notify Message Type payloads for
   the IANA "IKEv2 Notify Message Types - Error Types" registry.

         Value   Notify Type Messages - Status Types    Reference
         -----   ------------------------------    ---------------
         [TBD2]   TS_MAX_QUEUE                        [this document]

                                  Figure 2

10.  References

10.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

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   [RFC2367]  McDonald, D., Metz, C., and B. Phan, "PF_KEY Key
              Management API, Version 2", RFC 2367,
              DOI 10.17487/RFC2367, July 1998,
              <https://www.rfc-editor.org/info/rfc2367>.

   [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, <https://www.rfc-editor.org/info/rfc7296>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

10.2.  Informative References

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <https://www.rfc-editor.org/info/rfc4301>.

   [RFC6982]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", RFC 6982,
              DOI 10.17487/RFC6982, July 2013,
              <https://www.rfc-editor.org/info/rfc6982>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

Authors' Addresses

   Antony Antony
   secunet Security Networks AG
   Email: antony.antony@secunet.com

   Tobias Brunner
   codelabs GmbH
   Email: tobias@codelabs.ch

   Steffen Klassert
   secunet Security Networks AG
   Email: steffen.klassert@secunet.com

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   Paul Wouters
   Aiven
   Email: paul.wouters@aiven.io

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