Service Function Chaining (SFC): Subscriber and Host Identification Considerations
draft-sarikaya-sfc-hostid-serviceheader-02

Network Working Group                                       M. Boucadair
Internet-Draft                                                    Orange
Intended status: Standards Track                             D. von Hugo
Expires: December 3, 2016                Telekom Innovation Laboratories
                                                             B. Sarikaya
                                                                  Huawei
                                                            June 1, 2016

  Service Function Chaining (SFC): Subscriber and Host Identification
                             Considerations
             draft-sarikaya-sfc-hostid-serviceheader-02.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 elements of an SFC-
   enabled domain, 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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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  . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   This document focuses on aspects related to passing host- and
   subscriber-related information to upstream Service Functions (SFs)
   when required for the sake of policy enforcement.  Indeed,
   subscriber-related information may be needed for upstream 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.

   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].

   Host-related information may be required to implement services such
   as, but not limited to, traffic policy control, or parental control
   and traffic offload that are commonly used by operators to enable
   added value services to their customers in typical 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

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   widespread use of private addressing in those networks, if advanced
   SFs to be invoked are located after a NAT device (that can reside in
   the Packet Data Network (PDN) Gateway (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.  As
   such, 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
   further are discussed in [RFC7620].

   Because both a host and subscriber identifiers may be required in
   some scenarios, this document defines two objects that allow carrying
   this information.

   This document does not make any assumption about the structure of
   host 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].

   Host-related and/or subscriber-related information is stripped from
   packets exiting an SFC-enabled domain so that privacy-sensitive
   information is not leaked outside the 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].

   The reader should be familiar with the terms defined in [RFC7665].

3.  Problem Space and Sample Use Cases

   Enforcing Policies based on an internal IP address:

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

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   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 SFs 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.

   [I-D.ietf-sfc-use-case-mobility] identifies the following
   information:

   o  Charging ID

   o  Subscriber ID

   o  GGSN or PGW IP address

   o  Serving Gateway Support Node (SGSN) or SGW IP address

   o  International Mobile Equipment Identity (IMEI)

   o  International Mobile Subscriber Identity (IMSI)

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   o  Mobile Subscriber ISDN Number (MSISDN)

   o  UE IP address

4.  Host and Subscriber Identification SFC Meta Data

   Host Identifier and Subscriber Identifier are defined as optional
   variable length context headers.  Their structure is shown in
   Figure 1 and Figure 2, respectively.  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 or an information that is required to enforce a
   per-subscriber policy, the structure of the identifier is deployment-
   specific.  Typically, this header may convey the IMSI, opaque
   subscriber Identifier, etc.

   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

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   (e.g., accept only some lengths, accept some subtypes) 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.

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

   Multiple subscriber Identifier context headers MAY be present in the
   SFC header each conveying a distinct sub-type.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          TLV Class            |C|    Type     |R|R|R|   Len   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                    Host Identifier                            ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 1: Host Identifier Metadata

   The description of the fields is as follows:

   The fields TLV Class, etc. are defined in [I-D.ietf-sfc-nsh]

   Host Identifier: Can be IPv4 or IPv6 address, IPv6 prefix, a subset
   of IP address/prefix, a MAC address, or any deployment-specific
   identifier.  It could also be in Root NAI format containing arbitrary
   number of characters [TS23.003].

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          TLV Class            |C|    Type     |R|R|R|   Len   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   SubT        |                                               |
      +-+-+-+-+-+-+-+-+
      ~                      Subscriber Identifier                    ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 2: Subscriber Identifier Metadata

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   The description of the fields is as follows:

   The fields TLV Class, etc. are defined in [I-D.ietf-sfc-nsh]

   SubT field of 8 bits indicates the sub-type of the information
   conveyed in the "Subscriber Identifier" field.  The following values
   are defined:

   o  0x00: Opaque value

   o  0x01: Charging ID.  The structure of this ID is deployment-
      specific.

   o  0x02: Subscriber ID.  The structure of this ID is deployment-
      specific.

   o  0x03: GGSN or PGW IP address/prefix

   o  0x04: Serving Gateway Support Node (SGSN) or SGW IP address/prefix

   o  0x05: International Mobile Equipment Identity (IMEI)

   o  0x06: International Mobile Subscriber Identity (IMSI)

   o  0x07: Mobile Subscriber ISDN Number (MSISDN)

   o  0x08: UE IP address

   Subscriber Identifier: Conveys an opaque subscriber identifier or an
   identifier that corresponds to the sub-type.

5.  IANA Considerations

   To be completed.

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

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   trusted nodes MUST be able to inject such context headers.  Nodes
   that are involved in a SFC-enabled domain must be trusted.  Means to
   check that only authorized nodes are solicited when a packet is
   crossing an SFC-enabled domain.

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
   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

   Comments from Joel Halpern are appreciated.

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9.  References

9.1.  Normative References

   [I-D.ietf-sfc-control-plane]
              Boucadair, M., "Service Function Chaining (SFC) Control
              Plane Components & Requirements", draft-ietf-sfc-control-
              plane-06 (work in progress), May 2016.

   [I-D.ietf-sfc-nsh]
              Quinn, P. and U. Elzur, "Network Service Header", draft-
              ietf-sfc-nsh-05 (work in progress), May 2016.

   [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>.

   [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>.

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-06 (work in
              progress), April 2016.

   [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.

   [I-D.quinn-sfc-nsh-tlv]
              Quinn, P., Elzur, U., Majee, S., and J. Halpern, "Network
              Service Header TLVs", draft-quinn-sfc-nsh-tlv-01 (work in
              progress), April 2016.

   [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>.

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   [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>.

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

   [TS23.003]
              "3GPP TS23.003, Technical Specification Group Core Network
              and Terminals; Numbering, addressing and identification",
              2015.

   [TS29.212]
              "3GPP TS29.212, Policy and Charging Control (PCC) over Gx/
              Sd reference point", December 2011.

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

Authors' Addresses

   Mohamed Boucadair
   Orange
   Rennes 3500, France

   Email: mohamed.boucadair@orange.com

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

   Email: Dirk.von-Hugo@telekom.de

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   Behcet Sarikaya
   Huawei
   5340 Legacy Dr.
   Plano, TX  75024

   Email: sarikaya@ieee.org

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