Service Function Chaining (SFC): Subscriber and Host Identification Considerations
draft-sarikaya-sfc-hostid-serviceheader-01

Network Working Group                                        B. Sarikaya
Internet-Draft                                                    Huawei
Intended status: Standards Track                             D. von Hugo
Expires: September 22, 2016              Telekom Innovation Laboratories
                                                            M. Boucadair
                                                                  Orange
                                                          March 21, 2016

  Service Function Chaining (SFC): Subscriber and Host Identification
                             Considerations
             draft-sarikaya-sfc-hostid-serviceheader-01.txt

Abstract

   This document discusses considerations related to passing host- and
   subscriber-related information to upstream Service Functions for the
   sake of policy enforcement and appropriate SFC-inferred forwarding.
   Once the information is consumed by SFC-aware functional elements,
   the information is stripped from packets so that privacy-sensitive
   information is not leaked outside an SFC-enabled domain.

Status of This Memo

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   This Internet-Draft will expire on September 22, 2016.

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   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Terminology . . . . . . . . . . . . . . . . .   3
   3.  Problem Space and Sample Use Cases  . . . . . . . . . . . . .   3
     3.1.  Parental Control Use Case . . . . . . . . . . . . . . . .   4
     3.2.  Traffic Offload Use Case  . . . . . . . . . . . . . . . .   5
     3.3.  Mobile Network Use Cases  . . . . . . . . . . . . . . . .   5
   4.  Host and Subscriber Identification SFC Meta Data  . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   7
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   This document adheres to the architecture defined in [RFC7665].  This
   document assumes the reader is familiar with [RFC7665] and
   [I-D.ietf-sfc-control-plane].

   This document focuses on aspects related to passing host- and
   subscriber-related information to upstream SFs when required for the
   sake of policy enforcement.  Indeed, subscriber-related information
   may be needed for upstream service functions (SFs) when per-
   subscriber policies are to be enforced upstream in the network while
   the information conveyed by the original packets does not allow for
   uniquely identifying a host or a subscriber.

   Host-related information may be required to implement services such
   as Traffic policy control, or Parental Control Function and Traffic
   Offload that are commonly used by operators to enable advanced
   services to the customers used in typical home network architectures
   [I-D.liu-sfc-use-cases].

   Another typical example is the applicability of service chaining in
   the context of mobile networks (typically, in the 3GPP defined (S)Gi
   Interface) [I-D.ietf-sfc-use-case-mobility].  Because of the
   widespread use of private addressing in those networks, if advanced

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   SFs to be invoked are located after a NAT device (that can reside in
   the PGW or in a distinct operator-specific node), the identification
   based on the internal IP address is not anymore possible once the NAT
   has been crossed.  For this reason, means to allow passing the
   internal information may ease the operation of an SFC-enabled domain.
   Furthermore, some SFs that are not enabled on the PGW may require a
   subscriber identifier e.g., International Mobile Subscriber Identity
   (IMSI) to execute their function.  Other use cases that suffer from
   identification problems are discussed in [RFC7620].

   Because both a host and subscriber Identifiers may be required in
   some scenarios, this document requires two objects that allow
   carrying this information which are defined in
   [I-D.quinn-sfc-nsh-tlv].

   NOTE: The TLVs were initially defined in this document but, after a
   discussion with the authors of [I-D.quinn-sfc-nsh-tlv], the formats
   of those TLV were removed to [I-D.quinn-sfc-nsh-tlv].  The present
   document specifies the behavior to support the two TLVs within an
   SFC-enabled domain.

   This document does not make any assumption about the structure of
   these identifiers; each information is treated as an opaque value.
   The meaning and validation of each of these identifiers can be the
   responsibility of the control plane [I-D.ietf-sfc-control-plane].

   Once the host-related and/or subscriber-related information is
   consumed by SFC-aware functional elements, the information is
   stripped from packets so that privacy-sensitive information is not
   leaked outside an SFC-enabled domain.  See Section 7 for more
   discussion on privacy.

   Within this document, only identification issues for the sake of
   services in a local administrative domain are discussed.  Global
   identification issues are out of scope.

2.  Conventions and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  Problem Space and Sample Use Cases

   Enforcing Policies based on internal IP address:

   Because of the address sharing, implicit CPE/UE identification that
   relies on the source IP address cannot be implemented within the

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   administrative domain because the same IP address is shared among
   various connected devices (CPE for the fixed case or UE for the
   mobile case).  In the meantime, policies are something provisioned
   based on the internal IP address assigned to those devices.  Means to
   pass the internal IP address beyond an address sharing device for the
   sake of per-host or per-subscriber policy enforcement is needed in
   some SFC deployments.

   Also, stable identifiers such as MAC address, IMSI can be passed.

   Enforcing Policies based on a subscriber identifier:

   In case some deployments may require per-subscriber policies, a means
   is required to pass subscriber ID to those upstream SFs which are
   responsible for or rely on policy enforcement.

   Below we present some use cases where problems related to enforcing
   policies based on subscriber and/or host identities cannot be
   achieved in service function chaining.  It is important to note that
   subscriber and host identification due to address and prefix sharing
   is not specific to the service function chaining.  This problem
   occurs in many other use cases as discussed in [RFC7620].

3.1.  Parental Control Use Case

   Parental control service function searches each packet for certain
   content, e.g. destination addresses corresponding to certain URL like
   www.thisbizarresite.com.  Parental control function should keep this
   information (URL and source IP address) in its cache so that all
   subsequent packets can be filtered for certain users from the Web
   server [WT317].

   Parental control function receives next packet from the recorded URL.
   Enforcing the parental control policies may depend on the internal IP
   address, i.e., the address of the host that is being subject to the
   parental control.  Parental control function must be able to identify
   incoming traffic to be filtered, e.g. specific URL information.  All
   other traffic is not subject to filtering.  Parental control function
   filters all traffic coming from indicated URL only for the specific
   hosts identified by the service logic.

   For the virtual CPE case, the access node will receive privately-
   addressed packets.  Because private addresses are overlapping between
   several subscribers, the internal IP address will need to be copied
   into a dedicated field (Host ID context) so that upstream function
   responsible for Parental Control can process the packets
   appropriately.  Furthermore, the subscriber identifier may also be
   required for authorization purposes.

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3.2.  Traffic Offload Use Case

   Traffic offload service function works on each flow/service
   originated from mobile terminal and decides if it should be offloaded
   to the broadband network or sent back to the mobile network.  In this
   use case policy enforcement is based on the subscriber identifier.
   The broadband network must obtain the subscription profile from the
   mobile network and decide if the traffic coming from this subscriber
   needs to be offloaded or not.  If offloading is needed, this usually
   means that the subscriber identifier needs to be known on the SFC-
   aware forwarders.

3.3.  Mobile Network Use Cases

   Many service functions (SF) can be executed in different combinations
   in a mobile network [I-D.ietf-sfc-use-case-mobility].  Placement of
   NAT function plays an important role if it is used.

   If NAT function is collocated with P-GW as in [TR23.975] or is
   located right after the P-GW then all service functions located
   upstream can only see the translated address as the source address
   from all User Equipments (UEs).  Internal IP address-related part of
   their policy set won't be able to execute their service logic.  As a
   consequence, means to pass the internal IP address (i.e., the
   original one before executing the NAT function) through the service
   chain may be needed.

   Note that the same problem occurs in case IPv6 is being used by UEs
   but UEs need to communicate with an external legacy server which is
   IPv4-only.  This can be made possible with NAT64 as described in
   [RFC6146].  NAT64 uses IPv4 address on its outgoing interface which
   is shared by all UEs.  So in the case of NAT64 host identification
   also becomes an issue in service chaining.

4.  Host and Subscriber Identification SFC Meta Data

   Host Identifier and Subscriber Identifier are defined as optional
   variable length context headers as defined in [I-D.ietf-sfc-nsh].
   These TLVs are defined in [I-D.quinn-sfc-nsh-tlv].  Host Identifier
   context header may convey an internal IP address, VLAN or MAC
   address.

   While the subscriber identifier itself is used to convey an
   identifier already assigned by the service provider to uniquely
   identify a subscriber, the structure of the identifier is deployment-
   specific.  Typically, this header may convey the IMSI, opaque
   subscriber Identifier, etc.

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   The classifier and SFC-aware Service Functions MAY be instructed via
   a control interface to inject or strip a host identifier and/or
   subscriber identifier context headers.  Also, the data to be injected
   in such header SHOULD be configured to nodes authorized to inject
   such headers.  Failures to inject such headers SHOULD be logged
   locally while a notification alarm MAY be sent to a Control Element.
   The level of sending notification alarms SHOULD be configurable by
   the control plane.

   The control plane SHOULD instruct Ingress Border Nodes about the
   behavior to follow when receiving Host ID and/or Subscriber ID
   context headers from external SFC-enabled domain.  If no instruction
   is provided, the default behavior is to strip such context headers
   when received from external SFC-enabled domain.

   The control plane SHOULD instruct Egress Border Nodes about the
   behavior to follow for processing packets conveying Host ID and/or
   Subscriber ID context headers.  If no instruction is provided, the
   default behavior is to strip such context headers before sending the
   packets outside an SFC-enabled domain.

   SFC-aware SFs and Proxies that are not acting as SFC border nodes MAY
   be instructed to strip a host ID and/or subscriber ID from the packet
   or to pass the data to the next SF in the chain after consuming the
   content of the headers.  If no instruction is provided, the default
   behavior is to maintain such context headers so that the information
   can be passed to next SFC-aware hops.

   SFC-aware functions MAY be instructed via the control plane about the
   validation checks to follow on the content of these context headers
   (e.g., accept only some lengths) and the behavior to follow.  For
   example, SFC-aware nodes may be instructed to ignore the context
   header, to remove the context header from the packet, etc.
   Nevertheless, this specification does not require nor preclude such
   additional validation checks.  These validation checks are
   deployment-specific.  If validation checks fail on a context header,
   an SFC-aware node ignores that context header.  The event SHOULD be
   logged locally while a notification alarm MAY be sent to a control
   element if the SFC-aware node is instructed to do so.

   Exactly one Host Identifier context header MUST be present in the SFC
   header.

   Only one Subscriber Identifier context header MUST be present in the
   SFC header.

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5.  IANA Considerations

   This document makes no request to IANA.

6.  Security Considerations

   Data plane SFC-related security considerations are discussed in
   [RFC7665].  Control plane SFC-related security considerations are
   discussed in [I-D.ietf-sfc-control-plane].

   Security considerations that are related to the host identifier are
   discussed in [RFC6967].

   A misbehaving node can inject host/subscriber Identifiers to disturb
   the service offered to some host or subscribers.  Also, a misbehaving
   node can inject host/subscriber identifiers as an attempt to be
   granted access to some services.  To prevent such misbehavior, only
   trusted nodes MUST be able to inject such context headers.  Nodes
   that are involved in a SFC-enabled domain must be trusted.  Means how
   to provide trust between nodes within an SFC-enabled domain are out
   of scope for this document.  More details can be found in SFC
   architecture document [RFC7665] and [I-D.ietf-sfc-control-plane].

7.  Privacy Considerations

   The metadata defined in this document for host and subscriber
   identifiers may reveal private information about the host and/or the
   subscriber.  Some privacy-related considerations for Internet
   Protocols are discussed in [RFC6973].  In the light of these privacy
   considerations, it is important to state that the host and subscriber
   metadata must not be exposed outside the operator's domain
   [I-D.ietf-sfc-control-plane].

   The information conveyed in host and/or subscriber identifiers is
   already known to an administrative entity managing an SFC-enabled
   domain.  Some of that information is already conveyed in the original
   packets from a host (e.g., internal IP address) while other
   information is collected from various sources (e.g., GTP tunnel, line
   identifier, etc.).  Conveying such sensitive information in packets
   may expose subscribers' sensitive data to entities that are not
   allowed to receive such information.  Misconfiguring SFC egress nodes
   is a threat that may have negative impacts on privacy (e.g., some
   operational networks leak the MSISDN outside).  Operators must ensure
   their SFC-enabled domain is appropriately configured so that any
   privacy-related information is not exposed a domain.

   Some use cases that rely upon the solution defined in this document
   may disclose some additional privacy-related information (e.g., a

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   host identifier of a terminal within a customer premises for the
   parental control case).  It is assumed that this information is
   provided upon approval from a subscriber.  For example, a customer
   may provide the information as part of its service management
   interface or as part of explicit subscription form.  As a common
   recommendation for deployment relying on SFC header, a CPE MUST NOT
   leak non-authorized information to the service provider by means of
   an SFC header.  Note, the use cases discussed in this document assume
   the service header is used exclusively within the service
   administrative domain.  CPEs are not required to be SFC-aware.

8.  Acknowledgements

   TBD.

9.  References

9.1.  Normative References

   [I-D.ietf-sfc-control-plane]
              Li, H., Wu, Q., Huang, O., Boucadair, M., Jacquenet, C.,
              Haeffner, W., Lee, S., Parker, R., Dunbar, L., Malis, A.,
              Halpern, J., Reddy, T., and P. Patil, "Service Function
              Chaining (SFC) Control Plane Components & Requirements",
              draft-ietf-sfc-control-plane-03 (work in progress),
              January 2016.

   [I-D.ietf-sfc-nsh]
              Quinn, P. and U. Elzur, "Network Service Header", draft-
              ietf-sfc-nsh-02 (work in progress), January 2016.

   [I-D.quinn-sfc-nsh-tlv]
              Quinn, P., Elzur, U., Majee, S., and J. Halpern, "Network
              Service Header TLVs", draft-quinn-sfc-nsh-tlv-00 (work in
              progress), October 2015.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

9.2.  Informative References

   [I-D.ietf-sfc-use-case-mobility]
              Haeffner, W., Napper, J., Stiemerling, M., Lopez, D., and
              J. Uttaro, "Service Function Chaining Use Cases in Mobile
              Networks", draft-ietf-sfc-use-case-mobility-05 (work in
              progress), October 2015.

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   [I-D.liu-sfc-use-cases]
              Will, W., Li, H., Huang, O., Boucadair, M., Leymann, N.,
              Qiao, F., Qiong, Q., Pham, C., Huang, C., Zhu, J., and P.
              He, "Service Function Chaining (SFC) General Use Cases",
              draft-liu-sfc-use-cases-08 (work in progress), September
              2014.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
              April 2011, <http://www.rfc-editor.org/info/rfc6146>.

   [RFC6967]  Boucadair, M., Touch, J., Levis, P., and R. Penno,
              "Analysis of Potential Solutions for Revealing a Host
              Identifier (HOST_ID) in Shared Address Deployments",
              RFC 6967, DOI 10.17487/RFC6967, June 2013,
              <http://www.rfc-editor.org/info/rfc6967>.

   [RFC6973]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
              Morris, J., Hansen, M., and R. Smith, "Privacy
              Considerations for Internet Protocols", RFC 6973,
              DOI 10.17487/RFC6973, July 2013,
              <http://www.rfc-editor.org/info/rfc6973>.

   [RFC7620]  Boucadair, M., Ed., Chatras, B., Reddy, T., Williams, B.,
              and B. Sarikaya, "Scenarios with Host Identification
              Complications", RFC 7620, DOI 10.17487/RFC7620, August
              2015, <http://www.rfc-editor.org/info/rfc7620>.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,
              <http://www.rfc-editor.org/info/rfc7665>.

   [TR23.975]
              "3GPP TR23.975, IPv6 Migration Guidelines", June 2011.

   [WT317]    BBF, , "Network Enhanced Residential Gateway", August
              2015.

Authors' Addresses

   Behcet Sarikaya
   Huawei
   5340 Legacy Dr.
   Plano, TX  75024

   Email: sarikaya@ieee.org

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   Dirk von Hugo
   Telekom Innovation Laboratories
   Deutsche-Telekom-Allee 7
   D-64295 Darmstadt
   Germany

   Email: Dirk.von-Hugo@telekom.de

   Mohamed Boucadair
   Orange
   Rennes 3500, France

   Email: mohamed.boucadair@orange.com

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