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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 RFC 7620

Network Working Group                                  M. Boucadair, Ed.
Internet-Draft                                                  D. Binet
Intended status: Informational                                  S. Durel
Expires: October 9, 2015                                      B. Chatras
                                                          France Telecom
                                                                T. Reddy
                                                           Cisco Systems
                                                             B. Williams
                                                            Akamai, Inc.
                                                             B. Sarikaya
                                                                  L. Xue
                                                                  Huawei
                                                             R. Wheeldon
                                                           April 7, 2015


            Scenarios with Host Identification Complications
          draft-boucadair-intarea-host-identifier-scenarios-11

Abstract

   This document describes a set of scenarios in which complications to
   identify which policy to apply for a host are encountered.  This
   problem is abstracted as "host identification".  Describing these
   scenarios allows to identify what is common and then would help
   during the solution design phase.

   The document does not include any solution-specific discussion.

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 http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 9, 2015.






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Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Scenario 1: Carrier-Grade NAT (CGN) . . . . . . . . . . . . .   4
   4.  Scenario 2: Address plus Port (A+P) . . . . . . . . . . . . .   5
   5.  Scenario 3: On-Premise Application Proxy Deployment . . . . .   6
   6.  Scenario 4: Distributed Proxy Deployment  . . . . . . . . . .   7
   7.  Scenario 5: Overlay Network . . . . . . . . . . . . . . . . .   8
   8.  Scenario 6: Policy and Charging Control Architecture (PCC)  .  10
   9.  Scenario 7: Emergency Calls . . . . . . . . . . . . . . . . .  12
   10. Other Deployment Scenarios  . . . . . . . . . . . . . . . . .  13
     10.1.  Open WLAN or Provider WLAN . . . . . . . . . . . . . . .  13
     10.2.  Cellular Networks  . . . . . . . . . . . . . . . . . . .  14
     10.3.  Femtocells . . . . . . . . . . . . . . . . . . . . . . .  15
     10.4.  Traffic Detection Function (TDF) . . . . . . . . . . . .  17
     10.5.  Fixed and Mobile Network Convergence . . . . . . . . . .  18
   11. Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . .  21
   12. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  21
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  22
   14. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
   15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  22
   16. Informative References  . . . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  25

1.  Introduction

   The goal of this document is to enumerate scenarios which encounter
   the issue of uniquely identifying a host among those sharing the same
   IP address.  Within this document, a host can be any device directly
   connected to a network operated by a network provider, a Home
   Gateway, or a roaming device located behind a Home Gateway.




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   An exhaustive list of encountered issues for the Carrier Grade NAT
   (CGN), Address plus Port (A+P), and Application Proxies scenarios are
   documented in [RFC6269].  In addition to those issues, some of the
   scenarios described in this document suffer from additional issues
   such as:

   o  Identify which policy to enforce for a host (e.g., limit access to
      the service based on some counters such as volume-based service
      offering); enforcing the policy will have impact on all hosts
      sharing the same IP address.
   o  Need to correlate between the internal address:port and external
      address:port to generate and therefore to enforce policies.
   o  Query a location server for the location of an emergency caller
      based on the source IP address.

   The goal of this document is to identify scenarios the authors are
   aware of and which share the same complications to identify which
   policy to apply for a host.  This problem is abstracted as host
   identification problem.

   The analysis of the scenarios listed in this document indicates
   several root causes for the host identification issue:

   1.  Presence of address sharing (CGN, A+P, application proxies,
       etc.).
   2.  Use of tunnels between two administrative domains.
   3.  Combination of address sharing and presence of tunnels in the
       path.

   Even if these scenarios share the same root causes, describing the
   scenario allows to identify what is common between the scenarios and
   then would help during the solution design phase.

2.  Scope

   This document can be used as a tool to design solution(s) mitigating
   the encountered issues.  Note, [RFC6967] focuses only on the CGN,
   A+P, and application proxies cases.  The analysis in [RFC6967] may
   not be accurate for some of the scenarios that do not span multiple
   administrative domains (e.g., Section 10.1).

   This document does not target means that would lead to expose a host
   beyond what the original packet, issued from that host, would have
   already exposed.  Such means are not desirable, nor required to solve
   the issues encountered in the scenarios discussed in this document.
   The focus is exclusively on means to restore the information conveyed
   in the original packet issued by a given host.  These means are
   intended to help in identifying which policy to apply for a given



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   flow.  These means may rely on some bits of the source IP address
   and/or port number(s) used by the host to issue packets.

   To prevent side effects and mis-uses of such means on privacy,
   solution specification document(s) should explain, in addition to
   what is already documented in [RFC6967], the following:

   o  To what extent the solution can be used to nullify the effect of
      using address sharing to preserve privacy (see for example
      [EFFOpenWireless]).  Note, this concern can be mitigated if the
      address sharing platform is under the responsibility of the host's
      owner and the host does not leak information that would interfere
      with the host's privacy protection tool.

   o  To what extent the solution can be used to expose privacy
      information beyond what the original packet would have already
      exposed.  Note, the solutions discussed in [RFC6967] do not allow
      to reveal extra information than what is conveyed in the original
      packet.

   This document covers both IPv4 and IPv6.

   This document does not include any solution-specific discussion.  In
   particular, the document does not elaborate whether explicit
   authentication is enabled or not.

   This document does not discuss whether specific information is needed
   to be leaked in packets, whether this is achieved out-of-band, etc.
   Those considerations are out of scope.

3.  Scenario 1: Carrier-Grade NAT (CGN)

   Several flavors of stateful CGN have been defined.  A non-exhaustive
   list is provided below:

   1.  NAT44 ([RFC6888], [I-D.tsou-stateless-nat44])

   2.  DS-Lite NAT44 [RFC6333]

   3.  NAT64 [RFC6146]

   4.  NPTv6 [RFC6296]

   As discussed in [RFC6967], remote servers are not able to distinguish
   between hosts sharing the same IP address (Figure 1).  As a reminder,
   remote servers rely on the source IP address for various purposes
   such as access control or abuse management.  The loss of the host
   identification will lead to issues discussed in [RFC6269].



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   +-----------+
   |  HOST_1   |----+
   +-----------+    |        +--------------------+      +------------+
                    |        |                    |------|  server 1  |
   +-----------+  +-----+    |                    |      +------------+
   |  HOST_2   |--| CGN |----|      INTERNET      |            ::
   +-----------+  +-----+    |                    |      +------------+
                     |       |                    |------|  server n  |
   +-----------+     |       +--------------------+      +------------+
   |  HOST_3   |-----+
   +-----------+


                   Figure 1: CGN Reference Architecture

   Some of the above referenced CGN scenarios will be satisfied by
   eventual completion of the transition to IPv6 across the Internet
   (e.g., NAT64), but this is not true of all CGN scenarios (e.g.  NPTv6
   [RFC6296]) for which some of the issues discussed in [RFC6269] will
   be encountered (e.g., impact on geolocation).

   Privacy-related considerations discussed in [RFC6967] apply for this
   scenario.

4.  Scenario 2: Address plus Port (A+P)

   A+P [RFC6346][I-D.ietf-softwire-map][I-D.ietf-softwire-lw4over6]
   denotes a flavor of address sharing solutions which does not require
   any additional NAT function be enabled in the service provider's
   network.  A+P assumes subscribers are assigned with the same IPv4
   address together with a port set.  Subscribers assigned with the same
   IPv4 address should be assigned non overlapping port sets.  Devices
   connected to an A+P-enabled network should be able to restrict the
   IPv4 source port to be within a configured range of ports.  To
   forward incoming packets to the appropriate host, a dedicated entity
   called PRR (Port-Range Router, [RFC6346]) is needed (Figure 2).

   Similar to the CGN case, remote servers rely on the source IP address
   for various purposes such as access control or abuse management.  The
   loss of the host identification will lead to the issues discussed in
   [RFC6269].  In particular, it will be impossible to identify hosts
   sharing the same IP address by remote servers.









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   +-----------+
   |  HOST_1   |----+
   +-----------+    |        +--------------------+      +------------+
                    |        |                    |------|  server 1  |
   +-----------+  +-----+    |                    |      +------------+
   |  HOST_2   |--| PRR |----|      INTERNET      |            ::
   +-----------+  +-----+    |                    |      +------------+
                     |       |                    |------|  server n  |
   +-----------+     |       +--------------------+      +------------+
   |  HOST_3   |-----+
   +-----------+


                   Figure 2: A+P Reference Architecture

   Privacy-related considerations discussed in [RFC6967] apply for this
   scenario.

5.  Scenario 3: On-Premise Application Proxy Deployment

   This scenario is similar to the CGN scenario (Section 3).

   Remote servers are not able to distinguish hosts located behind the
   PROXY.  Applying policies on the perceived external IP address as
   received from the PROXY will impact all hosts connected to that
   PROXY.

   Figure 3 illustrates a simple configuration involving a proxy.  Note
   several (per-application) proxies may be deployed.  This scenario is
   a typical deployment approach used within enterprise networks.

   +-----------+
   |  HOST_1   |----+
   +-----------+    |        +--------------------+      +------------+
                    |        |                    |------|  server 1  |
   +-----------+  +-----+    |                    |      +------------+
   |  HOST_2   |--|PROXY|----|      INTERNET      |            ::
   +-----------+  +-----+    |                    |      +------------+
                     |       |                    |------|  server n  |
   +-----------+     |       +--------------------+      +------------+
   |  HOST_3   |-----+
   +-----------+


                  Figure 3: Proxy Reference Architecture

   The administrator of the proxy may have many reasons for wanting to
   proxy traffic - including caching, policy enforcement, malware



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   scanning, reporting on network or user behavior for compliance or
   security monitoring.

   The same administrator may also wish to selectively hide or expose
   the internal host identity to servers.  He/she may wish to hide the
   identity to protect end-user privacy or to reduce the ability of a
   rogue agent to learn the internal structure of the network.  He/she
   may wish to allow upstream servers to identify hosts to enforce
   access policies (for example on documents or online databases), to
   enable account identification (on subscription-based services) or to
   prevent spurious misidentification of high traffic patterns as a DoS
   attack.  Application-specific protocols exist for enabling such
   forwarding on some plain-text protocols (e.g., Forwarded headers on
   HTTP [RFC7239] or time-stamp-line headers in SMTP [RFC5321]).

   Servers not receiving such notifications but wishing to perform host
   or user-specific processing are obliged to use other application-
   specific means of identification (e.g., Cookies [RFC6265]).

   Packets/connections must be received by the proxy regardless of the
   IP address family in use.  The requirements of this scenario are not
   satisfied by eventual completion of the transition to IPv6 across the
   Internet.  Complications will arise for both IPv4 and IPv6.

   Privacy-related considerations discussed in [RFC6967] apply for this
   scenario.

6.  Scenario 4: Distributed Proxy Deployment

   This scenario is similar to the proxy deployment scenario (Section 5)
   with the same use-cases.  However, in this instance part of the
   functionality of the application proxy is located in a remote site.
   This may be desirable to reduce infrastructure and administration
   costs or because the hosts in question are mobile or roaming hosts
   tied to a particular administrative zone of control but not to a
   particular network.

   In some cases, a distributed proxy is required to identify a host on
   whose behalf it is performing the caching, filtering or other desired
   service - for example to know which policies to enforce.  Typically,
   IP addresses are used as a surrogate.  However, in the presence of
   CGN, this identification becomes difficult.  Alternative solutions
   include the use of cookies, which only work for HTTP traffic, tunnels
   or proprietary extensions to existing protocols.







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   +-----------+             +----------+
   |  HOST_1   |-------------|          |
   +-----------+             |          |   +-------+     +------------+
                             |          |   |       |-----|  server 1  |
   +-----------+             |          |   |       |     +------------+
   |  HOST_2   |----+        | INTERNET |---| Proxy |           ::
   +-----------+  +-----+    |          |   |       |     +------------+
                  |Proxy|----|          |   |       |-----|  server n  |
   +-----------+  +-----+    |          |   +-------+     +------------+
   |  HOST_3   |----+        +----------+
   +-----------+


          Figure 4: Distributed Proxy Reference Architecture (1)

       +-----------+         +---+         +---+  +----------+
       |  Host 1   +---------+ I |         | I +--+ Server 1 |
       +-----------+         | n |  +---+  | n |  +----------+
                             | t |  | P |  | t |
       +-----------+  +---+  | e |  | r |  | e |  +----------+
       |  Host 2   +--+ P |  | r +--+ o +--+ r +--+ Server 2 |
       +-----------+  | r |  | n |  | x |  | n |  +----------+
                      | o |--+ e |  | y |  | e |      ::
       +-----------+  | x |  | t |  +---+  | t |  +----------+
       |  Host 3   +--+ y |  |   |         |   +--+ Server N |
       +-----------+  +---+  +---+         +---+  +----------+


          Figure 5: Distributed Proxy Reference Architecture (2)

   Packets/connections must be received by the proxy regardless of the
   IP address family in use.  The requirements of this scenario are not
   satisfied by eventual completion of the transition to IPv6 across the
   Internet.  Complications will arise for both IPv4 and IPv6.

   If the proxy and the servers are under the responsibility of the same
   administrative entity (Figure 4), no privacy concerns are raised.
   Nevertheless, privacy-related considerations discussed in [RFC6967]
   apply if the proxy and the servers are not managed by the same
   administrative entity (Figure 5).

7.  Scenario 5: Overlay Network

   An overlay network is a network of machines distributed throughout
   multiple autonomous systems within the public Internet that can be
   used to improve the performance of data transport (see Figure 6).  IP
   packets from the sender are delivered first to one of the machines
   that make up the overlay network.  That machine then relays the IP



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   packets to the receiver via one or more machines in the overlay
   network, applying various performance enhancement methods.

                    +------------------------------------+
                    |                                    |
                    |              INTERNET              |
                    |                                    |
     +-----------+  |  +------------+                    |
     |  HOST_1   |-----| OVRLY_IN_1 |-----------+        |
     +-----------+  |  +------------+           |        |
                    |                           |        |
     +-----------+  |  +------------+     +-----------+  |  +--------+
     |  HOST_2   |-----| OVRLY_IN_2 |-----| OVRLY_OUT |-----| SERVER |
     +-----------+  |  +------------+     +-----------+  |  +--------+
                    |                           |        |
     +-----------+  |  +------------+           |        |
     |  HOST_3   |-----| OVRLY_IN_3 |-----------+        |
     +-----------+  |  +------------+                    |
                    |                                    |
                    +------------------------------------+

             Figure 6: Overlay Network Reference Architecture

   Such overlay networks are used to improve the performance of content
   delivery [IEEE1344002].  Overlay networks are also used for peer-to-
   peer data transport [RFC5694], and they have been suggested for use
   in both improved scalability for the Internet routing infrastructure
   [RFC6179] and provisioning of security services (intrusion detection,
   anti-virus software, etc.) over the public Internet [IEEE101109].

   In order for an overlay network to intercept packets and/or
   connections transparently via base Internet connectivity
   infrastructure, the overlay ingress and egress hosts (OVERLAY_IN and
   OVERLAY_OUT) must be reliably in-path in both directions between the
   connection-initiating HOST and the SERVER.  When this is not the
   case, packets may be routed around the overlay and sent directly to
   the receiving host, presumably without invoking some of the advanced
   service functions offered by the overlay.

   For public overlay networks, where the ingress and/or egress hosts
   are on the public Internet, packet interception commonly uses network
   address translation for the source (SNAT) or destination (DNAT)
   addresses in such a way that the public IP addresses of the true
   endpoint hosts involved in the data transport are invisible to each
   other (see Figure 7).  For example, the actual sender and receiver
   may use two completely different pairs of source and destination
   addresses to identify the connection on the sending and receiving




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   networks in cases where both the ingress and egress hosts are on the
   public Internet.

             ip hdr contains:               ip hdr contains:
   SENDER -> src = sender   --> OVERLAY --> src = overlay2  --> RECEIVER
             dst = overlay1                 dst = receiver


              Figure 7: NAT operations in an Overlay Network

   In this scenario, the remote server is not able to distinguish among
   hosts using the overlay for transport.  In addition, the remote
   server is not able to determine the overlay ingress point being used
   by the host, which can be useful for diagnosing host connectivity
   issues.

   In some of the above referenced scenarios, IP packets traverse the
   overlay network fundamentally unchanged, with the overlay network
   functioning much like a CGN (Section 3).  In other cases, connection-
   oriented data flows (e.g.  TCP) are terminated by the overlay in
   order to perform object caching and other such transport and
   application layer optimizations, similar to the proxy scenario
   (Section 5).  In both cases, address sharing is a requirement for
   packet/connection interception, which means that the requirements for
   this scenario are not satisfied by the eventual completion of the
   transition to IPv6 across the Internet.

   More details about this scenario are provided in
   [I-D.williams-overlaypath-ip-tcp-rfc].

   This scenario does not introduce privacy concerns since the
   identification of the host is local to a single administrative domain
   (i.e., CDN Overlay Network) or passed to a remote server to help
   forwarding back the response to the appropriate host.  The host
   identification information is not publically available nor it can be
   disclosed to other hosts connected to the Internet.

8.  Scenario 6: Policy and Charging Control Architecture (PCC)

   This issue is related to the Policy and Charging Control (PCC)
   framework defined by 3GPP in [TS23.203] when a NAT is located between
   the PCEF (Policy and Charging Enforcement Function) and the AF
   (Application Function) as shown in Figure 8.

   The main issue is: PCEF, PCRF and AF all receive information bound to
   the same UE ( User Equipment) but without being able to correlate
   between the piece of data visible for each entity.  Concretely,




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   o  PCEF is aware of the IMSI (International Mobile Subscriber
      Identity) and an internal IP address assigned to the UE.

   o  AF receives an external IP address and port as assigned by the NAT
      function.

   o  PCRF is not able to correlate between the external IP address/port
      assigned by the NAT (received from the AF) and the internal IP
      address and IMSI of the UE (received from the PCEF).

               +------+
               | PCRF |-----------------+
               +------+                 |
                  |                     |
   +----+      +------+   +-----+    +-----+
   | UE |------| PCEF |---| NAT |----|  AF |
   +----+      +------+   +-----+    +-----+

                 Figure 8: NAT located between AF and PCEF

   This scenario can be generalized as follows (Figure 9):

   o  Policy Enforcement Point (PEP, [RFC2753])

   o  Policy Decision Point (PDP, [RFC2753])

               +------+
               | PDP  |-----------------+
               +------+                 |
                  |                     |
   +----+      +------+   +-----+    +------+
   | UE |------| PEP  |---| NAT |----|Server|
   +----+      +------+   +-----+    +------+

               Figure 9: NAT located between PEP and Server

   Note that an issue is encountered to enforce per-UE policies when the
   NAT is located before the PEP function (see Figure 10):

                          +------+
                          | PDP  |------+
                          +------+      |
                             |          |
   +----+      +------+   +-----+    +------+
   | UE |------| NAT  |---| PEP |----|Server|
   +----+      +------+   +-----+    +------+

                     Figure 10: NAT located before PEP



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   This scenario does not introduce privacy concerns since the
   identification of the host is local to a single administrative domain
   and is meant to help identifying which policy to select for a UE.

9.  Scenario 7: Emergency Calls

   Voice service providers (VSPs) operating under certain jurisdictions
   are required to route emergency calls from their subscribers and have
   to include information about the caller's location in signaling
   messages they send towards PSAPs (Public Safety Answering Points,
   [RFC6443]), via an Emergency Service Routing Proxy (ESRP, [RFC6443]).
   This information is used both for the determination of the correct
   PSAP and to reveal the caller's location to the selected PSAP.

   In many countries, regulation bodies require that this information be
   provided by the network rather than the user equipment, in which case
   the VSP needs to retrieve this information (by reference or by value)
   from the access network where the caller is attached.

   This requires the VSP call server receiving an emergency call request
   to identify the relevant access network and to query a Location
   Information Server (LIS) in this network using a suitable look-up
   key.  In the simplest case, the source IP address of the IP packet
   carrying the call request is used both for identifying the access
   network (thanks to a reverse DNS query) and as a look-up key to query
   the LIS.  Obviously the user-id as known by the VSP (e.g., telephone
   number, or email-formatted URI) can't be used as it is not known by
   the access network.

   The above mechanism is broken when there is a NAT between the user
   and the VSP and/or if the emergency call is established over a VPN
   tunnel (e.g., an employee remotely connected to a company VoIP server
   through a tunnel wishes to make an emergency call).  In such cases,
   the source IP address received by the VSP call server will identify
   the NAT or the address assigned to the caller equipment by the VSP
   (i.e., the address inside the tunnel).  This is similar to the CGN
   case (Section 3) and overlay network case (Section 7) and applies
   irrespective of the IP versions used on both sides of the NAT and/or
   inside and outside the tunnel.

   Therefore, the VSP needs to receive an additional piece of
   information that can be used to both identify the access network
   where the caller is attached and query the LIS for his/her location.
   This would require the NAT or the Tunnel Endpoint to insert this
   extra information in the call requests delivered to the VSP call
   servers.  For example, this extra information could be a combination
   of the local IP address assigned by the access network to the




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   caller's equipment with some form of identification of this access
   network.

   However, because it shall be possible to setup an emergency call
   regardless of the actual call control protocol used between the user
   and the VSP (e.g., SIP [RFC3261], IAX [RFC5456], tunneled over HTTP,
   or proprietary protocol, possibly encrypted), this extra information
   has to be conveyed outside the call request, in the header of lower
   layers protocols.

   Privacy-related considerations discussed in [RFC6967] apply for this
   scenario.

10.  Other Deployment Scenarios

   This section lists deployment scenarios that are variants of
   scenarios described in previous sections.

10.1.  Open WLAN or Provider WLAN

   In the context of Provider WLAN, a dedicated SSID can be configured
   and advertised by the RG (Residential Gateway) for visiting
   terminals.  These visiting terminals can be mobile terminals, PCs,
   etc.

   Several deployment scenarios are envisaged:

   1.  Deploy a dedicated node in the service provider's network which
       will be responsible to intercept all the traffic issued from
       visiting terminals (see Figure 11).  This node may be co-located
       with a CGN function if private IPv4 addresses are assigned to
       visiting terminals.  Similar to the CGN case discussed in
       Section 3, remote servers may not be able to distinguish visiting
       hosts sharing the same IP address (see [RFC6269]).

   2.  Unlike the previous deployment scenario, IPv4 addresses are
       managed by the RG without requiring any additional NAT to be
       deployed in the service provider's network for handling traffic
       issued from visiting terminals.  Concretely, a visiting terminal
       is assigned with a private IPv4 address from the IPv4 address
       pool managed by the RG.  Packets issued form a visiting terminal
       are translated using the public IP address assigned to the RG
       (see Figure 12).  This deployment scenario induces the following
       identification concerns:

       *  The provider is not able to distinguish the traffic belonging
          to the visiting terminal from the traffic of the subscriber
          owning the RG.  This is needed to identify which policies are



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          to be enforced such as: accounting, DSCP remarking, black
          list, etc.

       *  Similar to the CGN case Section 3, a misbehaving visiting
          terminal is likely to have some impact on the experienced
          service by the subscriber owning the RG (e.g., some of the
          issues are discussed in [RFC6269]).

   +-------------+
   |Local_HOST_1 |----+
   +-------------+    |
                      |     |
   +-------------+  +-----+ |  +-----------+
   |Local_HOST_2 |--| RG  |-|--|Border Node|
   +-------------+  +-----+ |  +----NAT----+
                       |    |
   +-------------+     |    |  Service Provider
   |Visiting Host|-----+
   +-------------+


           Figure 11: NAT enforced in a Service Provider's Node

   +-------------+
   |Local_HOST_1 |----+
   +-------------+    |
                      |     |
   +-------------+  +-----+ |  +-----------+
   |Local_HOST_2 |--| RG  |-|--|Border Node|
   +-------------+  +-NAT-+ |  +-----------+
                       |    |
   +-------------+     |    |  Service Provider
   |Visiting Host|-----+
   +-------------+


                     Figure 12: NAT located in the RG

   This scenario does not introduce privacy concerns since the
   identification of the host is local to a single administrative domain
   and is meant to help identifying which policy to select for a
   visiting UE.

10.2.  Cellular Networks

   Cellular operators allocate private IPv4 addresses to mobile
   terminals and deploy NAT44 function, generally co-located with
   firewalls, to access to public IP services.  The NAT function is



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   located at the boundaries of the PLMN (Public Land Mobile Network).
   IPv6-only strategy, consisting in allocating IPv6 prefixes only to
   mobile terminals, is considered by various operators.  A NAT64
   function is also considered in order to preserve IPv4 service
   continuity for these customers.

   These NAT44 and NAT64 functions bring some issues very similar to
   those mentioned in Figure 1 and Section 8.  This issue is
   particularly encountered if policies are to be applied on the Gi
   interface.

      Note: 3GPP defines the Gi interface as the reference point between
      the GGSN (Gateway GPRS Support Node) and an external PDN (Packet
      Domain Network).  This interface reference point is called SGi in
      4G networks (i.e., between the PDN Gateway and an external PDN).

   Because private IP addresses are assigned to the mobile terminals,
   there is no correlation between the internal IP address and the
   external address:port assigned by the NAT function, etc.

   Privacy-related considerations discussed in [RFC6967] apply for this
   scenario.

10.3.  Femtocells

   This scenario can be seen as a combination of the scenarios described
   in Section 10.1 and Section 8.

   The reference architecture is shown in Figure 13.

   A FAP (Femto Access Point) is defined as a home base station used to
   graft a local (femto) cell within a users home to a mobile network.



















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   +---------------------------+
   | +----+ +--------+  +----+ |   +-----------+  +-------------------+
   | | UE | | Stand- |<=|====|=|===|===========|==|=>+--+ +--+        |
   | +----+ | alone  |  | RG | |   |           |  |  |  | |  | Mobile |
   |        |  FAP   |  +----+ |   |           |  |  |S | |F | Network|
   |        +--------+  (NAPT) |   | Broadband |  |  |e | |A |        |
   +---------------------------+   |   Fixed   |  |  |G |-|P | +-----+|
                                   |  Network  |  |  |W | |G |-| Core||
   +---------------------------+   |   (BBF)   |  |  |  | |W | | Ntwk||
   | +----+ +------------+     |   |           |  |  |  | |  | +-----+|
   | | UE | | Integrated |<====|===|===========|==|=>+--+ +--+        |
   | +----+ | FAP (NAPT) |     |   +-----------+  +-------------------+
   |        +------------+     |
   +---------------------------+

       <=====>   IPsec tunnel
       CoreNtwk  Core Network
       FAPGW     FAP Gateway
       SeGW      Security Gateway

                Figure 13: Femtocell Reference Architecture

   UE is connected to the FAP at the residential gateway (RG), routed
   back to 3GPP Evolved Packet Core (EPC).  It is assumed that each UE
   is assigned an IPv4 address by the Mobile Network.  Mobile operator's
   FAP leverages the IPsec IKEv2 to interconnect FAP with the SeGW over
   the Broadband Fixed Network (BBF).  Both the FAP and the SeGW are
   managed by the mobile operator which may be a different operator for
   the BBF network.

   An investigated scenario is the mobile operator to pass on its mobile
   subscriber's policies to the BBF to support traffic policy control .
   But most of today's broadband fixed networks are relying on the
   private IPv4 addressing plan (+NAPT) to support its attached devices
   including the mobile operator's FAP.  In this scenario, the mobile
   network needs to:

   o  determine the FAP's public IPv4 address to identify the location
      of the FAP to ensure its legitimacy to operate on the license
      spectrum for a given mobile operator prior to the FAP be ready to
      serve its mobile devices.

   o  determine the FAP's public IPv4 address together with the
      translated port number of the UDP header of the encapsulated IPsec
      tunnel for identifying the UE's traffic at the fixed broadband
      network.





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   o  determine the corresponding FAP's public IPv4 address associated
      with the UE's inner-IPv4 address which is assigned by the mobile
      network to identify the mobile UE to allow the PCRF to retrieve
      the special UE's policy (e.g., QoS) to be passed onto the
      Broadband Policy Control Function (BPCF) at the BBF network.

   SeGW would have the complete knowledge of such mapping, but the
   reasons for being unable to use SeGW for this purpose are explained
   in Section 2 of [I-D.so-ipsecme-ikev2-cpext].

   This scenario involves PCRF/BPCF but it is valid in other deployment
   scenarios making use of AAA servers.

   The issue of correlating the internal IP address and the public IP
   address is valid even if there is no NAT in the path.

   This scenario does not introduce privacy concerns since the
   identification of the host is local to a single administrative domain
   and is meant to help identifying which policy to select for a UE.

10.4.  Traffic Detection Function (TDF)

   Operators expect that the traffic subject to the packet inspection is
   routed via the Traffic Detection Function (TDF) function as
   requirement specified in [TS29.212]; otherwise, the traffic may
   bypass the TDF.  This assumption only holds if it is possible to
   identify individual UEs behind NA(P)T invoked in the RG connected to
   the fixed broadband network, shown in Figure 14.  As a result,
   additional mechanisms are needed to enable this requirement.






















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                                                              +--------+
                                                              |        |
                                                      +-------+  PCRF  |
                                                      |       |        |
                                                      |       +--------+
 +--------+      +--------+       +--------+     +----+----+
 |        |      |        |       |        +-----+         |
 |  ------------------------------------------------------------------
 |        |      |        |       |        |     |  TDF    |    /      \
 |  ****************************************************************** |
 +--------+      +--------+       +--------+     +----+----+   |       |
 |        |      |        +-------+        |         |         |Service|
 |        |      |        |       |        |         |          \      /
 |        |      |        |       |        |         |        +--------+
 |        |      |        |       |        |         +--------+  PDN   |
 |  >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> |
 |  UE    |      |   RG   |       | BNG    +------------------+ Gateway|
 +--------+      +--------+       +--------+                  +--------+

 Legends:
 ---------   3GPP UE User Plane Traffic Offloaded subject to packet
             inspection
 *********   3GPP UE User Plane Traffic Offloaded not subject to packet
             inspection
 >>>>>>>>>   3GPP UE User Plane Traffic Home Routed

 BNG (Broadband Network Gateway)


                  Figure 14: UE's Traffic Routed with TDF

   This scenario does not introduce privacy concerns since the
   identification of the host is local to a single administrative domain
   and is meant to help identifying which policy to select for a UE.

10.5.  Fixed and Mobile Network Convergence

   In the Policy for Convergence of Fixed Mobile Convergence (FMC)
   scenario, the fixed broadband network must partner with the mobile
   network to acquire the policies for the terminals or hosts attaching
   to the fixed broadband network, shown in Figure 15 so that host-
   specific QoS and accounting policies can be applied.

   A UE is connected to the RG, routed back to the mobile network.  The
   mobile operator's PCRF needs to maintain the interconnect with the
   Broadband Policy Control Function (BPCF) in the BBF network for PCC
   (Section 8).  The hosts (i.e., UEs) attaching to fixed broadband
   network with a NA(P)T deployed should be identified.  Based on the UE



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   identification, the BPCF can acquire the associated policy rules of
   the identified UE from the PCRF in the mobile network so that it can
   enforce policy rules in the fixed broadband network.  Note, this
   scenario assumes private IPv4 address are assigned in the fixed
   broadband network.  Similar requirements are raised in this scenario
   as Section 10.3.

                +------------------------------+   +-------------+
                |                              |   |             |
                |                   +------+   |   | +------+    |
                |                   | BPCF +---+---+-+ PCRF |    |
                |                   +--+---+   |   | +---+--+    |
     +-------+  |                      |       |   |     |       |
     |HOST_1 |Private IP1           +--+---+   |   | +---+--+    |
     +-------+  | +----+            |      |   |   | |      |    |
                | | RG |            |      |   |   | |      |    |
                | |with+-------------+ BNG  +--------+ PGW  |    |
     +-------+  | | NAT|            |      |   |   | |      |    |
     |HOST_2 |  | +----+            |      |   |   | |      |    |
     +-------+Private IP2           +------+   |   | +------+    |
                |                              |   |             |
                |                              |   |             |
                |                       Fixed  |   | Mobile      |
                |                   Broadband  |   | Network     |
                |                     Network  |   |             |
                |                              |   |             |
                +------------------------------+   +-------------+


   Figure 15: Reference Architecture for Policy for Convergence in Fixed
                    and Mobile Network Convergence (1)

   In IPv6 network, the similar issues exists when the IPv6 prefix is
   shared between multiple UEs attaching to the RG (see Figure 16).  The
   case applies when RG is assigned a single prefix, the home network
   prefix, e.g. using DHCPv6 Prefix Delegation [RFC3633] with the edge
   router, BNG acting as the Delegating Router (DR).  RG uses the home
   network prefix in the address configuration using stateful (DHCPv6)
   or stateless address assignment (SLAAC) techniques.












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                +------------------------------+   +-------------+
                |                              |   |             |
                |                              |   | +------+    |
                |                      +-------------+ PCRF |    |
                |                      |       |   | +---+--+    |
     +-------+  |                      |       |   |     |       |
     |HOST_1 |--+                   +--+---+   |   | +---+--+    |
     +-------+  | +----+            |      |   |   | |      |    |
                | | RG |            |      |   |   | |      |    |
                | |    +------------+ BNG  +---------+ PGW  |    |
     +-------+  | |    |            |      |   |   | |      |    |
     |HOST_2 |--+ +----+            |      |   |   | |      |    |
     +-------+  |                   +------+   |   | +------+    |
                |                              |   |             |
                |                              |   |             |
                |                       Fixed  |   | Mobile      |
                |                   Broadband  |   | Network     |
                |                     Network  |   |             |
                |                              |   |             |
                +------------------------------+   +-------------+

   Figure 16: Reference Architecture for Policy for Convergence in Fixed
                    and Mobile Network Convergence (2)

   BNG acting as PCEF initiates an IP Connectivity Access Network (IP-
   CAN) session with the policy server, a.k.a.  Policy and Charging
   Rules Function (PCRF), to receive the Quality of Service (QoS)
   parameters and Charging rules.  BNG provides to the PCRF the IPv6
   Prefix assigned to the host, in this case the home network prefix and
   an ID which in this case has to be equal to the RG specific home
   network line ID.

   HOST_1 in Figure 16 creates an 128-bit IPv6 address using this prefix
   and adding its interface id.  Having completed the address
   configuration, the host can start communication with a remote host
   over Internet.  However, no specific IP-CAN session can be assigned
   to HOST_1, and consequently the QoS and accounting performed will be
   based on RG subscription.

   Another host, e.g.  HOST_2, attaches to RG and also establishes an
   IPv6 address using the home network prefix.  Edge router, the BNG, is
   not involved with this and all other such address assignments.

   This leads to the case where no specific IP-CAN session/sub-session
   can be assigned to the hosts, HOST_1, HOST_2, etc., and consequently
   the QoS and accounting performed can only be based on RG subscription
   and not host specific.  Therefore IPv6 prefix sharing in Policy for




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   Convergence scenario leads to similar issues as the address sharing
   as explained in the previous scenarios in this document.

11.  Synthesis

   The following table shows whether each scenario is valid for IPv4/
   IPv6 and if it is within one single administrative domain or spans
   multiple domains.  The table also identifies the root cause of the
   identification issues.

   The IPv6 column indicates for each scenario whether IPv6 is supported
   at the client's side and/or server's side.

+-------------------+----+-------------+------+-----------------+
|                   |    |    IPv6     |Single|    Root Cause   |
|    Scenario       |    |------+------|Domain+-------+---------+
|                   |IPv4|Client|Server|      |Address|Tunneling|
|                   |    |      |      |      |sharing|         |
+-------------------+----+------+------+------+-------+---------+
|        CGN        |Yes |Yes(1)|  No  |  No  |  Yes  |   No    |
|        A+P        |Yes |  No  |  No  |  No  |  Yes  |   No    |
| Application Proxy |Yes | Yes  | Yes  |  No  |  Yes  |   No    |
| Distributed Proxy |Yes | Yes  | Yes  |Yes/No|  Yes  |   No    |
|  Overlay Networks |Yes |Yes(2)|Yes(2)|  No  |  Yes  |   No    |
|        PCC        |Yes |Yes(1)|  No  | Yes  |  Yes  |   No    |
|  Emergency Calls  |Yes | Yes  | Yes  |  No  |  Yes  |   No    |
|   Provider WLAN   |Yes |  No  |  No  | Yes  |  Yes  |   No    |
| Cellular Networks |Yes |Yes(1)|  No  | Yes  |  Yes  |   No    |
|     Femtocells    |Yes |  No  |  No  |  No  |  Yes  |  Yes    |
|        TDF        |Yes | Yes  |  No  | Yes  |  Yes  |   No    |
|        FMC        |Yes |Yes(1)|  No  |  No  |  Yes  |   No    |
+-------------------+----+------+------+------+-------+---------+

 Notes:
      (1) e.g., NAT64
      (2) This scenario is a combination of CGN and Application Proxies.

                              Table 1: Synthesis

12.  Privacy Considerations

   Privacy-related considerations that apply to means to reveal a host
   identifier are discussed in [RFC6967].  This document does not
   introduce additional privacy issues than those discussed in
   [RFC6967].

   None of the scenarios inventoried in this document aims at revealing
   a Customer Identifier, account Identifier, profile Identifier, etc.



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   Particularly, none of these scenarios is endorsing the functionality
   provided by the following proprietary headers (but not limited to)
   that are known to be used to leak subscription-related information:
   HTTP_MSISDN, HTTP_X_MSISDN, HTTP_X_UP_CALLING_LINE_ID,
   HTTP_X_NOKIA_MSISDN, HTTP_X_HTS_CLID, HTTP_X_MSP_CLID,
   HTTP_X_NX_CLID, HTTP__RAPMIN, HTTP_X_WAP_MSISDN, HTTP_COOKIE,
   HTTP_X_UP_LSID, HTTP_X_H3G_MSISDN, HTTP_X_JINNY_CID,
   HTTP_X_NETWORK_INFO, etc.

13.  Security Considerations

   This document does not define an architecture nor a protocol; as such
   it does not raise any security concern.  Host identifier related
   security considerations are discussed in [RFC6967].

14.  IANA Considerations

   This document does not require any action from IANA.

15.  Acknowledgments

   Many thanks to F.  Klamm, D.  Wing, D. von Hugo, G.  Li, D.  Liu, and
   Y.  Lee for their review.

   J.  Touch, S.  Farrel, and S.  Moonesamy provided useful comments in
   the intarea mailing list.

   Figure 8 and part of the text in Section 10.3 are inspired from
   [I-D.so-ipsecme-ikev2-cpext].

16.  Informative References

   [EFFOpenWireless]
              EFF, , "Open Wireless, https://www.eff.org/issues/open-
              wireless", 2014.

   [I-D.ietf-softwire-lw4over6]
              Cui, Y., Qiong, Q., Boucadair, M., Tsou, T., Lee, Y., and
              I. Farrer, "Lightweight 4over6: An Extension to the DS-
              Lite Architecture", draft-ietf-softwire-lw4over6-13 (work
              in progress), November 2014.

   [I-D.ietf-softwire-map]
              Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S.,
              Murakami, T., and T. Taylor, "Mapping of Address and Port
              with Encapsulation (MAP)", draft-ietf-softwire-map-13
              (work in progress), March 2015.




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   [I-D.so-ipsecme-ikev2-cpext]
              So, T., "IKEv2 Configuration Payload Extension for Private
              IPv4 Support for Fixed Mobile Convergence", draft-so-
              ipsecme-ikev2-cpext-02 (work in progress), June 2012.

   [I-D.tsou-stateless-nat44]
              Tsou, T., Liu, W., Perreault, S., Penno, R., and M. Chen,
              "Stateless IPv4 Network Address Translation", draft-tsou-
              stateless-nat44-02 (work in progress), October 2012.

   [I-D.williams-overlaypath-ip-tcp-rfc]
              Williams, B., "Overlay Path Option for IP and TCP", draft-
              williams-overlaypath-ip-tcp-rfc-04 (work in progress),
              June 2013.

   [IEEE101109]
              Salah, K., Calero, J., Zeadally, S., Almulla, S., and M.
              ZAaabi, "Using Cloud Computing to Implement a Security
              Overlay Network, IEEE Security & Privacy, 21 June 2012.
              IEEE Computer Society Digital Library.", June 2012.

   [IEEE1344002]
              Byers, J., Considine, J., Mitzenmacher, M., and S. Rost,
              "Informed content delivery across adaptive overlay
              networks: IEEE/ACM Transactions on Networking, Vol 12,
              Issue 5, ppg 767-780", October 2004.

   [RFC2753]  Yavatkar, R., Pendarakis, D., and R. Guerin, "A Framework
              for Policy-based Admission Control", RFC 2753, January
              2000.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              December 2003.

   [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              October 2008.

   [RFC5456]  Spencer, M., Capouch, B., Guy, E., Miller, F., and K.
              Shumard, "IAX: Inter-Asterisk eXchange Version 2", RFC
              5456, February 2010.





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   [RFC5694]  Camarillo, G. and IAB, "Peer-to-Peer (P2P) Architecture:
              Definition, Taxonomies, Examples, and Applicability", RFC
              5694, November 2009.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.

   [RFC6179]  Templin, F., "The Internet Routing Overlay Network
              (IRON)", RFC 6179, March 2011.

   [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
              April 2011.

   [RFC6269]  Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
              Roberts, "Issues with IP Address Sharing", RFC 6269, June
              2011.

   [RFC6296]  Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
              Translation", RFC 6296, June 2011.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.

   [RFC6346]  Bush, R., "The Address plus Port (A+P) Approach to the
              IPv4 Address Shortage", RFC 6346, August 2011.

   [RFC6443]  Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,
              "Framework for Emergency Calling Using Internet
              Multimedia", RFC 6443, December 2011.

   [RFC6888]  Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
              and H. Ashida, "Common Requirements for Carrier-Grade NATs
              (CGNs)", BCP 127, RFC 6888, April 2013.

   [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, June 2013.

   [RFC7239]  Petersson, A. and M. Nilsson, "Forwarded HTTP Extension",
              RFC 7239, June 2014.

   [TS23.203]
              3GPP TS23.203, "Policy and charging control architecture
              (Release 11)", September 2012.




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   [TS29.212]
              3GPP TS29.212, "Policy and Charging Control (PCC) over Gx/
              Sd reference point (Release 11)", December 2013.

Authors' Addresses

   Mohamed Boucadair (editor)
   France Telecom
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


   David Binet
   France Telecom
   Rennes
   France

   Email: david.binet@orange.com


   Sophie Durel
   France Telecom
   Rennes
   France

   Email: sophie.durel@orange.com


   Bruno Chatras
   France Telecom
   Paris
   France

   Email: bruno.chatras@orange.com


   Tirumaleswar Reddy
   Cisco Systems
   Cessna Business Park, Varthur Hobli
   Sarjapur Marathalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Email: tireddy@cisco.com





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   Brandon Williams
   Akamai, Inc.
   Cambridge  MA
   USA

   Email: brandon.williams@akamai.com


   Behcet Sarikaya
   Huawei
   5340 Legacy Dr. Building 3,
   Plano, TX  75024
   USA

   Email: sarikaya@ieee.org


   Li Xue
   Huawei
   Beijing
   China

   Email: xueli@huawei.com


   Richard Stewart Wheeldon
   UK

   Email: richard@rswheeldon.com






















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