Network                                                        A. Antony
Internet-Draft                                                   secunet
Intended status: Standards Track                              T. Brunner
Expires: 1 April 2022                                           codelabs
                                                             S. Klassert
                                                              P. Wouters
                                                       28 September 2021

                 IKEv2 support for per-queue Child SAs


   This document defines two Notify Message Type Payloads for the
   Internet Key Exchange Protocol Version 2 (IKEv2) indicating support
   for the negotiation of multiple identical Child SAs to optimize

   The CPU_QUEUES notification indicates support for multiple queues or
   CPUs.  The CPU_QUEUE_INFO notification are used to confirm and
   optionally convey information about the specific queue, such as QoS

   Using multiple identical Child SAs has the benefit that each stream
   has its own Sequence Number Counter, ensuring that CPUs don't have to
   synchronize their crypto state or disable their packet replay

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
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   This Internet-Draft will expire on 1 April 2022.

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Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Performance bottlenecks . . . . . . . . . . . . . . . . . . .   3
   3.  Negotiation of CPU specific Child SAs . . . . . . . . . . . .   3
   4.  Implementation Considerations . . . . . . . . . . . . . . . .   5
   5.  Payload Format  . . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  CPU_QUEUES Notify Message Payload . . . . . . . . . . . .   7
     5.2.  CPU_QUEUE_INFO Notify Message Payload . . . . . . . . . .   7
   6.  Operational Considerations  . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  Implementation Status . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Linux XFRM  . . . . . . . . . . . . . . . . . . . . . . .  10
     8.2.  Libreswan . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.3.  strongSwan  . . . . . . . . . . . . . . . . . . . . . . .  11
     8.4.  iproute2  . . . . . . . . . . . . . . . . . . . . . . . .  11
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     10.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   IPsec implementations are currently limited to using one queue or CPU
   per Child SA.  The result is that a machine with many queues/CPUs 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

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   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

   To make better use of multiple network queues and CPUs, it can be
   beneficial to negotiate and install multiple identical Child SAs.
   IKEv2 [RFC7296] already allows installing multiple identical Child
   SAs, it offers no method to negotiate the number of Child SAs or
   indicate the purpose for the multiple Child SAs that are requested.

   When two IKEv2 peers want to negotiate multiple Child SAs, it is
   useful to be able to convey how many Child SAs are required for
   optimized traffic.  This avoids triggering CREATE_CHILD_SA exchanges
   that will only be rejected by the peer.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.  Performance bottlenecks

   Currently, most IPsec implementations are limited by using one CPU or
   network queue per Child SA.  There are a number of practical reasons
   for this, 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-queue or per-CPU basis.

3.  Negotiation of CPU specific Child SAs

   When negotiating CPU specific Child SAs, the first SA negotiated
   either in an IKE_AUTH exchange or CREATE_CHILD_SA is called Fallback
   SA.  This Child SA is similar to a regular Cgild SA in that it is not
   bound to a single CPU.  This Fallback Child SA (or its rekeyed
   successors) MUST remain active for the lifetime of the IPsec session
   to ensure that there is always a Child SA that can be selected to
   send traffic over, in case a per-resource Child SA is not available.
   Additional Child SAs are installed bound to a specific CPU.  These
   Child SAs are responsible for the bulk of the traffic.

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   The CPU_QUEUES notification payload is sent in the IKE_AUTH or
   CREATE_CHILD_SA Exchange indicating the negotiated Child SA is a
   Fallback SA.

   The CPU_QUEUES notification value refers to the number of additional
   resource-specific Child SAs that may be installed for this particular
   TSi/TSr combination excluding the Fallback Child SA.  Both peers send
   the preferred minimum number of additional Child SAs to install.
   Both peers pick the maximum of the two numbers (within reason).  That
   is, if the initiator prefers 16 and the responder prefers 48, then
   the number negotiated is 48.  The responder may at any time reject
   additional Child SAs by returning TS_UNACCEPTABLE.  It should not
   return NO_ADDITIONAL_SAS, as there might be another Child SAs with
   different Traffic Selectors that would still be allowed by the peer.

   [Antony: Valery's feedback was not to use TS_UNACCEPTABLE. instead
   create a new notify or use TEMPORARY_FAILURE.  TEMPORARY_FAILURE
   because the situation may change again if you try again.  I have
   preference to define new NO_CPU_QUEUE_INFO_SA]

   CPU-specific Child SAs are negotiated as regular Child SAs using the
   CREATE_CHILD_SA exchange and are identified by a CPU_QUEUE_INFO
   notification.  Upon installation, each Child SA is associated with an
   additional local selector, such as CPU or queue.  These additional
   Child SAs MUST be negotiated with identical Child SA properties that
   were negotiated for the Fallback SA.  This includes cryptographic
   algorithms, Traffic Selectors, Mode (e.g. transport mode),
   compression usage, etc.  However, the Child SAs do have their own
   individual keying material that is derived according to the regular
   IKEv2 process.  The CPU_QUEUE_INFO can be empty or 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.  The Fallback SA MUST
   NOT be deleted while any per-resource Child SAs are still present.

   During the CREATE_CHILD_SA rekey for the Child SA, the CPU_QUEUE_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.

   As with regular Child SA rekeying, the new Child SA may not be
   different from the rekeyed Child SA with respect to cryptographic
   algorithms and MUST cover the original Traffic Selector ranges.

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   If a CREATE_CHILD_SA exchange request containing both a
   CPU_QUEUE_INFO and a CPU_QUEUES notification is received, the
   responder MUST ignore the CPU_QUEUE_INFO payload.  If a
   CREATE_CHILD_SA exchange reply is received with both CPU_QUEUE_INFO
   and CPU_QUEUES notifications, the initiator MUST ignore the
   notification that it did not send in the request.

   [Steffen: I tend to tread these cases as an error.]

   [Tobias: That's currently how I implemented it (being lenient on what
   I accept).  But we could also treat those cases as errors.  The
   question would just be what we should return (NO_PROPOSAL_CHOSEN and
   keep IKE and other Child SAs or even INALID_SYNTAX and kill the whole
   IKE_SA - and as initiator we either have to terminate the Child or
   the IKE_SA actively if we receive both notifies).]

   The CPU_QUEUES notification, even when it is sent in the IKE_AUTH
   exchange, is not an attribute of the IKE peer.  It is an attribute of
   the Child SA, similar to the USE_TRANSPORT notification.  That is, an
   IKE peer can have multiple Child SAs covering different traffic
   selectors and selectively decide whether or not to enable additional
   per-resource Child SAs for each of these Child SAs covering different
   Traffic Selectors.

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.  The Fallback Child SA ensures that any CPU generating
   traffic to be encrypted has an available (if not optimal) Child SA to
   use.  Any subsequent Child SAs with identical TSi/TSr Traffic
   Selectors are installed in such a way to only be used by a single CPU
   or network queue.

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   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.  It should count outstanding SADB_ACQUIREs as an
   assigned additional Child SA.  It is still possible that when the
   peers only have one slot left to assign, that both peers send a
   CREATE_CHILD_SA request at the same time.  [Paul: Is there anything
   we can do at the protocol level to terminate one of these without
   race conditions?]  [Antony: if CPU_QUEUE_INFO is a MUST, that info
   could be used for better one-to-one mapping, as well as delete the
   extra SAs.  Also, keep in mind the general case IKE window > 1]

   As an optimization, additional Child SAs that see little traffic MAY
   be deleted.  The Fallback Child SA MUST NOT be deleted when idle, as
   it is likely to be idle if enough per-CPU Child SAs are installed.
   However, if one of those per-CPU child SAs is deleted because it was
   idle, and subsequently that CPU starts to generate traffic again,
   that traffic does not have a per-CPU Child SA and will be encrypted
   using the Fallback Child SA.  Meanwhile, the IKE daemon might be
   negotiating to bring up a new per-CPU Child SA.

   When the number of queues or CPUs are different between the peers,
   the peer with the least amount of queues or CPUs 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 still 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.  CPU_QUEUES Notify 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      !
   !  Minimum number of IPsec SAs                                  !

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

   *  Minimum number of per-CPU IPsec SAs (4 octets).  MUST be greater
      than 0.  If 0 is received, it MUST be interpreted as 1.

   Note: The Fallback Child SA that is not bound to a single CPU is not
   counted as part of these numbers.

5.2.  CPU_QUEUE_INFO Notify 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 queue 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.

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   *  Notify Message Type (2 octets) - set to [TBD3]

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

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 Fallback SA without ever activating any per-CPU Child SAs.  It is
   there for RECOMMENDED to implement per-CPU SADB_ACQUIRE messages.  [
   Antony: It would be nice to add manual/scripts for starting of
   connection and bringing up per-CPU SAs.  It could be very simple, a
   external program decides to start a per-CPU SA. ]

   The minimum number of Child SAs negotiated should not be treated as
   the maximum number of allowed Child SAs.  Peers SHOULD be lenient
   with this number 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 Fallback SA where its reply
   packet might also trigger an on-demand Child SA negotiation to start.
   A peer may want to allow up to double the negotiated minimum number
   of Child SAs, and rely on idleness of Child SAs to tear down any
   unused Child SAs gradually to to reach an optimal number of Child
   SAs.  Adding 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

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   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
   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 memorya that it
   no longer needs access to.

7.  Security Considerations

   [TO DO]

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
   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

   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].

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8.1.  Linux XFRM

   Organization:  Linux kernel XFRM

   Name:  XFRM-PCPU-v1

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

   Level of maturity:  Alpha

   Coverage:  Implements Fallback 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 Fallback XFRM
      SA.  It is used by the kernel only for the outgoing traffic,
      (clear to encrypted).  The incoming SAs, both the Fallback and the
      per-CPU SA, 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 Fallback SA.
      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 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 Fallback 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

8.2.  Libreswan

   Organization:  The Libreswan Project

   Name:  pcpu-3

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

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   Level of maturity:  Alpha

   Coverage:  implements Fallback Child SA and per-CPU additional Child

   Licensing:  GPLv2

   Implementation experience:  TBD

   Contact:  Libreswan Development:

8.3.  strongSwan

   Organization:  The StrongSwan Project

   Name:  StrongSwan

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

   Level of maturity:  Alpha

   Coverage:  implements Fallback Child SA and per-CPU additional Child

   Licensing:  GPLv2

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

   Contact:  Tobias Brunner

8.4.  iproute2

   Organization:  The iproute2 Project

   Name:  iproute2

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

   Level of maturity:  Alpha

   Licensing:  GPLv2

   Implementation experience:  TBD

   Contact:  Antony Antony

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9.  IANA Considerations

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

         Value   Notify Type Messages - Status Types    Reference
         -----   ------------------------------    ---------------
         [TBD1]   CPU_QUEUES                        [this document]
         [TBD3]   CPU_QUEUE_INFO                    [this document]

                                  Figure 1

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,

   [RFC2367]  McDonald, D., Metz, C., and B. Phan, "PF_KEY Key
              Management API, Version 2", RFC 2367,
              DOI 10.17487/RFC2367, July 1998,

   [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, <>.

10.2.  Informative References

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <>.

   [RFC6982]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", RFC 6982,
              DOI 10.17487/RFC6982, July 2013,

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   [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,

Authors' Addresses

   Antony Antony
   secunet Security Networks AG


   Tobias Brunner
   codelabs GmbH


   Steffen Klassert
   secunet Security Networks AG


   Paul Wouters


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