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Versions: (draft-moustafa-ancp-security-threats) 00 01 02 03 04 05 06 07 08 RFC 5713

ANCP Working Group                                           H. Moustafa
Internet-Draft                                            France Telecom
Intended status: Informational                             H. Tschofenig
Expires: January 10, 2010                         Nokia Siemens Networks
                                                           S. De Cnodder
                                                          Alcatel-Lucent
                                                            July 9, 2009


 Security Threats and Security Requirements for the Access Node Control
                            Protocol (ANCP)
                draft-ietf-ancp-security-threats-08.txt

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on January 10, 2010.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Abstract

   The Access Node Control Protocol (ANCP) aims to communicate QoS-
   related, service-related and subscriber-related configurations and
   operations between a Network Access Server (NAS) and an Access Node
   (e.g., a Digital Subscriber Line Access Multiplexer (DSLAM)).  The
   main goal of this protocol is to allow the NAS to configure, manage
   and control access equipments including the ability for the access
   nodes to report information to the NAS.

   The present document investigates security threats that all ANCP
   nodes could encounter.  This document develops a threat model for
   ANCP security aiming to decide which security functions are required.
   Based on this, security requirements regarding the Access Node
   Control Protocol are defined.


Table of Contents

   1.  Specification Requirements . . . . . . . . . . . . . . . . . .  4

   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4

   3.  System Overview and Threat Model . . . . . . . . . . . . . . .  5

   4.  Objectives of Attackers  . . . . . . . . . . . . . . . . . . .  7

   5.  Potential Attacks  . . . . . . . . . . . . . . . . . . . . . .  8
     5.1.  Denial of Service (DoS)  . . . . . . . . . . . . . . . . .  8
     5.2.  Integrity Violation  . . . . . . . . . . . . . . . . . . .  8
     5.3.  Downgrading  . . . . . . . . . . . . . . . . . . . . . . .  8
     5.4.  Traffic Analysis . . . . . . . . . . . . . . . . . . . . .  9
     5.5.  Management Attacks . . . . . . . . . . . . . . . . . . . .  9

   6.  Attack Forms . . . . . . . . . . . . . . . . . . . . . . . . .  9

   7.  Attacks Against ANCP . . . . . . . . . . . . . . . . . . . . . 11
     7.1.  Dynamic Access Loop Attributes . . . . . . . . . . . . . . 12
     7.2.  Access Loop Configuration  . . . . . . . . . . . . . . . . 13
     7.3.  Remote Connectivity Test . . . . . . . . . . . . . . . . . 14
     7.4.  Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 14

   8.  Security Requirements  . . . . . . . . . . . . . . . . . . . . 16

   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16

   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16




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   11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 16

   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 17
     12.2. Informative References . . . . . . . . . . . . . . . . . . 17

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17












































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1.  Specification Requirements

   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 [RFC2119], with the
   qualification that unless otherwise stated they apply to the design
   of the Access Node Control Protocol (ANCP), not its implementation or
   application.

   The relevant components are described in Section 3.


2.  Introduction

   The Access Node Control Protocol (ANCP) aims to communicate QoS-
   related, service-related and subscriber-related configurations and
   operations between a Network Access Server (NAS) and an Access Node
   (e.g., a Digital Subscriber Line Access Multiplexer (DSLAM)).

   [I-D.ietf-ancp-framework] illustrates the framework, usage scenarios
   and general requirements for ANCP.  This document focuses on
   describing security threats and deriving security requirements for
   the Access Node Control Protocol, considering the ANCP use cases
   defined in [I-D.ietf-ancp-framework] as well as the guidelines for
   IETF protocols' security requirements given in [RFC3365].  Section 5
   and Section 6 respectively describe the potential attacks and the
   different attack forms that are liable to take place within ANCP,
   while Section 7 applies the described potential attacks to ANCP and
   its different use cases.  Security policy negotiation,including
   authentication and authorization to define the per-subscriber policy
   at the policy/AAA server, is out of the scope of this work.  As a
   high-level summary, the following aspects need to be considered:

   Message Protection:

      Signaling message content can be protected against eavesdropping,
      modification, injection and replay while in transit.  This applies
      to both ANCP header and payloads.

   Prevention against Impersonation:

      It is important that protection be available against a device
      impersonating an ANCP node (i.e. an unauthorized device generating
      an ANCP message and pretending it was generated by a valid ANCP
      node).






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   Prevention of Denial of Service Attacks:

      ANCP nodes and the network have finite resources (state storage,
      processing power, bandwidth).  Exhaustion attacks against these
      resources and not allowing ANCP nodes to be used to launch attacks
      on other network elements is of great importance.


3.  System Overview and Threat Model

   As described in [I-D.ietf-ancp-framework] and schematically shown in
   Figure 1, the Access Node Control system consists of the following
   components:

   Network Access Server (NAS):

      A NAS provides access to a service (e.g., network access) and
      operates as a client of the AAA protocol.  The AAA client is
      responsible for passing authentication information to designated
      AAA servers and then acting on the response that is returned.

   Authentication, Authorization and Accounting (AAA) server:

      A AAA server is responsible for authenticating users, for
      authorizing access to services, and for returning authorization
      information including configuration parameters back to the AAA
      client to deliver service to the user.  As a consequence, service
      usage accounting might be enabled and information about the user's
      resource usage will be sent to the AAA server.

   Access Node (AN):

      The AN is a network device, usually located at a service provider
      central office or street cabinet, that terminates access loop
      connections from subscribers.  In case the access loop is a
      Digital Subscriber Line (DSL), this is often referred to as a DSL
      Access Multiplexer (DSLAM).

   Customer Premises Equipment (CPE):

      A CPE is a device located inside a subscriber's premise that is
      connected at the LAN side of the HGW.

   Home Gateway (HGW):

      The HGW connects the different Customer Premises Equipments (CPE)
      to the Access Node and the access network.  In case of DSL, the
      HGW is a DSL Network Termination (NT) that could either operate as



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      a layer 2 bridge or as a layer 3 router.  In the latter case, such
      a device is also referred to as a Routing Gateway (RG).

   Aggregation Network:

      The aggregation network provides traffic aggregation from multiple
      ANs towards the NAS.  ATM or Ethernet transport technologies can
      be used.


   For the threat analysis, this document focuses on the ANCP protocol
   communication between the Access Node and the NAS.  However,
   communications with the other components, such as HGW, CPE, AAA
   server play a role in the understanding of the system architecture
   and of what triggers ANCP protocol communications.  Note that the NAS
   and the AN might belong to two different administrative realms.  The
   threat model and the security requirments in this draft consider this
   latter case.


                                                             +--------+
                                                             | AAA    |
                                                             | Server |
                                                             +--------+
                                                                  |
                                                                  |
      +---+   +---+   +------+    +-----------+    +-----+   +--------+
      |CPE|---|HGW|---|      |    |Aggregation|    |     |   |        |
      +---+   +---+   |Access|    | Network   |    |     |   |Internet|
                      | Node |----|           |----| NAS |---|   /    |
      +---+   +---+   | (AN) |    |           |    |     |   |Regional|
      |CPE|---|HGW|---|      |    |           |    |     |   |Network |
      +---+   +---+   +------+    +-----------+    +-----+   +--------+

                         Figure 1: System Overview

   In the absence of an attack, the NAS receives configuration
   information from the AAA server related to a CPE attempting to access
   the network.  A number of parameters, including Quality of Service
   information, need to be conveyed to the Access Node in order to
   become effective.  The Access Node Control Protocol is executed
   between the NAS and the AN to initiate control requests.  The AN
   returns responses to these control requests and provides information
   reports.

   For this to happen, the following individual steps must occur:





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   o  The AN discovers the NAS.
   o  The AN needs to start the protocol communication with the NAS to
      announce its presence.
   o  The AN and the NAS perform a capability exchange.
   o  The NAS sends requests to the AN.
   o  The AN processes these requests, authorizes the actions and
      responds with the appropriate answer.  In order to fulfill the
      commands it might be necessary for the AN to communicate with the
      HGW or other nodes, for example as part of a keep alive mechanism.
   o  The AN provides status reports to the NAS.

   Attackers can be:

   o  off-path, i.e., they cannot see the messages exchange between the
      AN and the NAS;
   o  on-path, i.e., they can see the messages exchange between the AN
      and the NAS.

   Both off-path and on-path attackers can be:

   o  passive, i.e., they do not participate in the network operation
      but rather listen to all transfers to obtain the maximum possible
      information;
   o  active, i.e., they participate to the network operation and can
      inject falsified packets.

   We assume the following threat model:
   o  An off-path adversary located at the CPE or the HGW.
   o  An off-path adversary located on the Internet or a regional
      network that connects one or more NASes and associated Access
      Networks to Network Service Providers (NSPs) and Application
      Service Providers (ASPs).
   o  An on-path adversary located at network elements between the AN
      and the NAS.
   o  An on-path adversary taking control over the NAS.
   o  An on-path adversary taking control over the AN.


4.  Objectives of Attackers

   Attackers may direct their efforts either against an individual
   entity or against a large portion of the access network.  Attacks
   fall into three classes:
   o  attacks to disrupt the communication for individual customers.
   o  attacks to disrupt the communication of a large fraction of
      customers in an access network.  These also include attacks to the
      network itself or a portion of it such as attacks to disrupt the
      network services or attacks to destruct the network functioning.



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   o  attacks to gain profit for the attacker through modifying the QoS
      settings.  Also, through replaying old packets, of another
      privileged client for instance, an attacker can attempt to
      configure a better QoS profile on its own DSL line increasing its
      own benefit.


5.  Potential Attacks

   This section discusses the different types of attacks against ANCP,
   while Section 6 describes the possible means of their occurrence.

   ANCP is mainly susceptible to the following types of attacks:

5.1.  Denial of Service (DoS)

   A number of denial of service (DoS) attacks can cause ANCP nodes to
   malfunction.  When state is established or certain functions are
   performed without requiring prior authorization there is a chance to
   mount denial of service attacks.  An adversary can utilize this fact
   to transmit a large number of signaling messages to allocate state at
   nodes and to cause resources' consumption.  Also, an adversary,
   through DoS, can prevent certain subscribers to access certain
   services.Moreover, DoS can take place at the AN or the NAS
   themselves, where it is possible for the NAS (or the AN) to
   intentionally ignore the requests received from the AN (or the NAS)
   through not replying to them.  This causes the sender of the request
   to retransmit the request, which might allocate additional state at
   the sender side to process the reply.  Allocating more state may
   result in memory depletion.

5.2.  Integrity Violation

   Adversaries gaining illegitimate access on the transferred messages
   can act on these messages causing integrity violation.  Integrity
   violation can cause unexpected network behavior leading to a
   disturbance in the network services as well as the network
   functioning.

5.3.  Downgrading

   Protocols may be useful in a variety of scenarios with different
   security and functional requirements.  Different parts of a network
   (e.g., within a building, across a public carrier's network, or over
   a private microwave link) may need different levels of protection.
   It is often difficult to meet these (sometimes conflicting)
   requirements with a single mechanism or fixed set of parameters, so
   often a selection of mechanisms and parameters is offered.  A



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   protocol is required to agree on certain (security) mechanisms and
   parameters.  An insecure parameter exchange or security negotiation
   protocol can give the oppurtunity to an adversary to mount a
   downgrading attack to force selection of mechanisms weaker than those
   mutually desired.  Thus, without binding the negotiation process to
   the legitimate parties and protecting it, ANCP might only be as
   secure as the weakest mechanism provided (e.g., weak authentication)
   and the benefits of defining configuration parameters and a
   negotiation protocol are lost.

5.4.  Traffic Analysis

   An adversary can be placed at the NAS, or the AN, or any other
   network element capturing all traversing packets.  Adversaries can
   thus have unauthorized information access.  As well, they can gather
   information relevant to the network and then use this information in
   gaining later unauthorized access.  This attack can also help
   adversaries in other malicious purposes, as for example capturing
   messages sent from the AN to the NAS announcing that a DSL line is up
   and containing some information related to the connected client.
   This could be any form of information about the client and could also
   be an indicator whether the DSL subscriber is at home or not at a
   particular moment.

5.5.  Management Attacks

   Since the ANCP sessions are configured in the AN and not in the NAS
   [I-D.ietf-ancp-framework], most configurations of ANCP is done in the
   AN.  Consequently, the management attacks to ANCP mainly concern the
   AN configuration phase.  In this context, the AN MIB module could
   create disclosure and misconfiguration related attacks.
   [I-D.ietf-ancp-mib-an] defines the vulnerabilities on the management
   objects within the AN MIB module.  These attacks mainly concern the
   unauthorized changes of the management objects leading to a number of
   attacks as session deletion, session using undesired/unsupported
   protocol, disabling certain ANCP capabilities or enabling undesired
   capabilities, ANCP packets being sent out to the wrong interface (and
   thus received by an unintended receiver), harming the synchronization
   between the AN and the NAS, and impacting other traffic in the
   network than ANCP.


6.  Attack Forms

   The attacks mentioned above in Section 5 can be carried out through
   the following means:





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   Message Replay:

      This threat scenario covers the case in which an adversary
      eavesdrops, collects signaling messages, and replays them at a
      later time (or at a different place or in a different way; e.g.,
      cut-and-paste attacks).  Through replaying of signaling messages,
      an adversary might mount a denial of service and a theft of
      service attacks.

   Faked Message Injection:

      An adversary may be able to inject false error or response
      messages causing unexpected protocol behavior and succeeding with
      a DoS attack.  This could be achieved at the signaling protocol
      level, at the level of a specific signaling parameters (e.g., QoS
      information), or at the transport layer.  An adversary might, for
      example, inject a signaling message to request allocation of QoS
      resources.  As a consequence, other user's traffic might be
      impacted.  The discovery protocol, especially, exhibits
      vulnerabilities with regard to this threat scenario.

   Messages Modification:

      This involves integrity violation, where an adversary can modify
      signaling messages in order to cause unexpected network behavior.
      Possible related actions an adversary might consider for its
      attack are reordering and delaying of messages causing a
      protocol's process failure.

   Man-in-the-Middle:

      An adversary might claim to be a NAS or an AN acting as a man-in-
      the-middle to later cause communication and services disruption.
      The consequence can range from DoS to fraud.  An adversary acting
      as a man-in-the-middle could modify the intercepted messages
      causing integrity violation, or could drop or truncate the
      intercepted messages causing DoS and a protocol's process failure.
      In addition, a man-in-the-middle adversary can signal information
      to an illegitimate entity in place of the right destination.  In
      this case the protocol could appear to continue working correctly.
      This may result in an AN contacting a wrong NAS.  For the AN, this
      could mean that the protocol failed for unknown reasons.  A man-
      in-the-middle adversary can also cause downgrading attacks through
      initiating faked configuration parameters and through forcing
      selection of weak security parameters or mechanisms.






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   Eavesdropping:

      This is related to adversaries that are able to eavesdrop on
      transferred messages.  The collection of the transferred packets
      by an adversary may allow traffic analysis or be used later to
      mount replay attacks.  The eavesdropper might learn QoS
      parameters, communication patterns, policy rules for firewall
      traversal, policy information, application identifiers, user
      identities, NAT bindings, authorization objects, network
      configuration and performance information, and more.



7.  Attacks Against ANCP

   ANCP is susceptible to security threats, causing disruption/
   unauthorized access to network services, manipulation of the
   transferred data, and interference with network functions.  Based on
   the threat model given in Section 3 and the potential attacks
   presented in Section 5, this section describes the possible attacks
   against ANCP, considering the four use cases defined in
   [I-D.ietf-ancp-framework].

   Although ANCP protocol is not involved in the communication between
   the NAS and the AAA/policy server, the secure communication between
   the NAS and the AAA/policy server is important for ANCP security.
   Consequently, this draft considers the attacks that are related to
   the ANCP operation associated with the communication between the NAS
   and the AAA/Policy server.  In other words, the threat model and
   security requirements in this draft take into consideration the data
   transfer between the NAS and the AAA server, when this data is used
   within the ANCP operation.

   Besides the attacks against the four ANCP use cases described in the
   following subsections, ANCP is susceptible to a number of attacks
   that can take place during the protocol establishment phase.  These
   attacks are mainly on-path attacks, taking the form of DoS or man-in-
   the-middle attacks, which could be as follows:
   o  Attacks during the session initiation from the AN to the NAS: DoS
      attacks could take place affecting the session establishment
      process.  Also, Man-in-the-middle attacks could take place,
      causing message truncation or message modification and leading to
      session establishment failure.
   o  Attacks during the peering establishment: DoS attacks could take
      place during states synchronization between the AN and the NAS.
      Also, man-in-the-middle attack could take place through messages
      modification during identity discovery that may lead to loss of
      contact between the AN and the NAS.



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   o  Attacks during capabilities negotiation: Messages replay could
      take place leading to DoS.  Also, man-in-the-middle attack could
      take place leading to message modification, message truncation, or
      downgrading through advertising lesser capabilities.

7.1.  Dynamic Access Loop Attributes

   This use case concerns the communication of access loop attributes
   for dynamic access line topology discovery.  Since the access loop
   rate may change overtime, advertisement is beneficial to the NAS to
   gain knowledge about the topology of the access network for QoS
   scheduling.  Besides data rates and access loop links identification,
   other information may also be transferred from the AN to the NAS
   (examples in case of DSL access loop are: DSL Type, Maximum
   achievable data rate, and maximum data rate configured for the access
   loop).  This use case is thus vulnerable to a number of on-path and
   off-path attacks that can be either active or passive.

   On-path attacks can take place between the AN and the NAS, on the AN
   or on the NAS during the access loop attributes transfer.  These
   attacks may be:
   o  Active, acting on the transferred attributes and injecting
      falsified packets.  The main attacks here are:
      *  Man-in-the-middle attack can cause access loop attributes
         transfer between the AN and a forged NAS or a forged AN and the
         NAS which can directly cause faked attributes and message
         modification or truncation.
      *  Signaling replay, by an attacker between the AN and the NAS, on
         the AN or on the NAS itself, causing DoS.
      *  An adversary acting as man-in-the-middle can cause downgrading
         through changing the access loop actual data rate, which
         impacts the downstream shaping from the NAS.
   o  Passive, only learning these attributes.  The main attacks here
      are caused by:
      *  Eavesdropping through learning access loop attributes and
         learning information about the clients' connection state and
         thus impacting their privacy protection.
      *  Traffic analysis allowing unauthorized information access, that
         could allow later unauthorized access to the NAS.

   Off-path attacks can take place on the Internet affecting the access
   loop attributes sharing between the NAS and the policy server.  These
   attacks may be:
   o  Active attacks, which are mainly concerning:
      *  DoS through flooding the communication links to the policy
         server causing service disruption.





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      *  Man-in-the-middle, causing access loop configuration retrieval
         by an illegitimate NAS.
   o  Passive attacks, gaining information on the access loop
      attributes.  The main attacks in this case are:
      *  Eavesdropping through learning access loop attributes and
         learning information about the clients'connection state and
         thus impacting their privacy protection.
      *  Traffic analysis allowing unauthorized information access, that
         could allow later unauthorized access to the NAS.

7.2.  Access Loop Configuration

   This use case concerns the dynamic local loop line configuration
   through allowing the NAS to change the access loop parameters (e.g.
   rate) in a dynamic fashion.  This allows for centralized subcriber-
   related service data.  This dynamic configuration can be achieved for
   instance through profiles that are pre-configured on ANs.  This use
   case is vulnerable to a number of on-path and off-path attacks.

   On-path attacks can take place, where the attacker is between the AN
   and the NAS, is on the AN, or is on the NAS.  These can be as
   follows:
   o  Active attacks, taking the following forms:
      *  DoS attacks of the AN can take place by an attacker, through
         replaying of the Configure Request messages.
      *  An attacker on the AN can prevent the AN from reacting on the
         NAS request for the access loop configuration, leading to the
         NAS continually sending the configure request message and hence
         allocating additional states.
      *  Damaging clients' profiles at ANs can take place by hackers
         that gained control on the network through discovery of users
         information from a previous Traffic Analysis.
      *  An adversary can replay old packets, modify messages, or inject
         faked messages.  Such adversary can also be a man-in-the-
         middle.  These attack forms can be related to a privileged
         client profile (having more services), so that to configure
         this profile on the adversary's own DSL line which is less
         privileged.  In order that the attacker does not expose its
         identity, he may also use these attack forms related to the
         privileged client profile to configure a number of illegitimate
         DSL lines.  The adversary can also force other configuration
         parameters than the selected ones leading to for instance
         downgrading the service for a privileged client.
   o  Passive attacks, where the attacker listens to the ANCP messages.
      This can take place as follows:
      *  Learning configuration attributes is possible during the update
         of the access loop configuration.  An adversary might profit to
         see the configuration that someone else gets (e.g. one ISP



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         might be interested to know what the customers of another ISP
         gets and therefore might break into the AN to see this).

   Off-path attacks can take place as follows:
   o  Off-path passive adversary on the Internet can exert eavesdropping
      during the access loop configuration retrieval by the NAS from the
      policy server.
   o  Off-path active adversary on the Internet can threaten the
      centralized subscribers-related service data in the policy server,
      through for instance making subscribers records inaccessible.

7.3.  Remote Connectivity Test

   In this use case, the NAS can carryout Remote Connectivity Test using
   ANCP to initiate an access loop test between the AN and the HGW.
   Thus, multiple access loop technologies can be supported.  This use
   case is vulnerable to a number of active attacks.  Most of the
   attacks in this use case concern the network operation.

   On-path active attacks can take place in the following forms:
   o  Man-in-the-middle attack during the NAS triggering to the AN to
      carryout the test, where an adversary can inject falsified signals
      or can truncate the triggering.
   o  Message modification can take place during the Subscriber Response
      message transfer from the AN to the NAS announcing the test
      results, causing failure of the test operation.
   o  An adversary on the AN can prevent the AN from sending the
      Subscriber Response message to the NAS announcing the test
      results, and hence the NAS will continue triggering the AN to
      carryout the test, which results in more state being allocated at
      the NAS.  This may result in unavailability of the NAS to the ANs.

   Off-path active attacks can take place as follows:
   o  An adversary can cause DoS during the access loop test, in case of
      ATM based access loop, when the AN generates loopback cells.  This
      can take place through signal replaying.
   o  Message truncating can take place by an adversary during the
      access loop test, which can lead to service disruption due to test
      failures assumption.

7.4.  Multicast

   In this use case, ANCP could be used in exchanging information
   between the AN and the NAS allowing the AN to perform replication
   inline with the policy and configuration of the subscriber.  Also,
   this allows the NAS to follow subscribers' multicast (source, group)
   membership and control replication performed by the AN.  Four
   multicast uses cases are expected to take place, making use of ANCP



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   protocol, these are typically: multicast conditional access,
   multicast admission control, multicast accounting, and multicast
   termination.  This section gives a high-level description of the
   possible attacks that can take place in this case.  Attacks that can
   occur are mostly active attacks.

   On-path active attacks can be as follows:
   o  DoS attacks, causing certain subscribers inability to access
      particular multicast streams, or only access the multicast stream
      at a reduced bandwidth impacting the quality of the possible video
      stream.  This can take place through messages replay by an
      attacker between the AN and the NAS, on the AN or on the NAS.
      Such DoS attacks can also be done by tempering, for instance, with
      White/Black list configuration or by placing attacks to the
      bandwidth admission control mechanism.
   o  An adversary on the NAS can prevent the NAS from reacting on the
      AN requests for white/black/grey lists or for admission control
      for the access line.  The AN in this case would not receive a
      reply and would continue sending its requests resulting in more
      states being allocated at the AN.  A similar case happens for
      admission control when the NAS can also send requests to the AN.
      When the NAS does not receive a response, it could also retransmit
      requests resulting in more state being allocated at the NAS side
      to process responses.  This may result in unavailability of the
      NAS to the ANs.
   o  Man-in-the-middle causing messages' exchange between the AN and a
      forged NAS or a forged AN and the NAS.  This can lead to the
      following:
      *  Messages' modification, which can cause services' downgrading
         for legitimate subscriber, as for instance, an illegitimate
         change of a subscriber's policy.
      *  Messages truncation between the AN and the NAS, which can
         result in service's non continuity.
      *  Messages replay between the AN and the NAS, on the AN or on the
         NAS leading to a DoS or services' fraud.
      *  Messages' modifications to temper with accounting information,
         for example in order to avoid service charges or conversely in
         order to artificially increase service charges on other users.

   An off-path active attack is as follows:
   o  DoS could take place through message replay of join/leave requests
      by the HGW or CPE, frequently triggering the ANCP protocol
      activity between the AN and the NAS.  DoS could also result from
      generating heaps of IGMP join/leaves by the HGW or CPE, leading to
      very high rate of ANCP query/response.






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8.  Security Requirements

   This section presents a number of requirements motivated by the
   different types of attacks defined in the previous section.  These
   requirements are as follows:
   o  The protocol solution MUST offer authentication of the AN to the
      NAS.
   o  The protocol solution MUST offer authentication of the NAS to the
      AN.
   o  The protocol solution MUST allow authorization to take place at
      the NAS and the AN.
   o  The protocol solution MUST offer replay protection.
   o  The protocol solution MUST provide data origin authentication.
   o  The protocol solution MUST be robust against denial of service
      (DoS) attacks.  In this context, the protocol solution MUST
      consider a specific mechansim for the DoS that the user might
      create by sending many IGMP messages.
   o  The protocol solution SHOULD offer confidentiality protection.
   o  The protocol solution SHOULD ensure that operations in default
      configuration guarantees low level of AN/NAS protocol
      interactions.
   o  The protocol solution SHOULD ensure the access control of the
      management objects and possibly encrypt the values of these
      objects when sending them over the networks.
   o  The protocol solution SHOULD ensure the security of the management
      channels.


9.  Security Considerations

   This document focuses on security threats deriving a threat model for
   ANCP and presenting the security requirements to be considered for
   the design of ANCP protocol.


10.  IANA Considerations

   This document does not require actions by IANA.


11.  Acknowledgments

   Many thanks go to Francois Le Faucher for reviewing this draft and
   for all his useful comments.  The authors would also like to thank
   Philippe Niger, Curtis Sherbo and Michael Busser for reviewing this
   draft.  Other thanks go to Bharat Joshi, Mark Townsley, Wojciech Dec,
   and Kim Hylgaard who have had valuable comments during the
   development of this work.



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12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", March 1997.

   [RFC3365]  Schiller, J., "Strong Security Requirements for Internet
              Engineering  Task Force Standard Protocols", August 2002.

12.2.  Informative References

   [I-D.ietf-ancp-framework]
              Ooghe, S., Voigt, N., Platnic, M., Haag, T., and S.
              Wadhwa, "Framework and Requirements for an Access Node
              Control Mechanism in Broadband  Multi-Service Networks",
              draft-ietf-ancp-framework-10 (work in progress), May 2009.

   [I-D.ietf-ancp-mib-an]
              Cnodder, S. and M. Morgenstern, "Access Node Control
              Protocol (ANCP) MIB module for Access Nodes",
              draft-ietf-ancp-mib-an-03 (work in progress), June 2008.


Authors' Addresses

   Hassnaa Moustafa
   France Telecom
   38-40 rue du General Leclerc
   Issy Les Moulineaux,   92794 Cedex 9
   France

   Email: hassnaa.moustafa@orange-ftgroup.com


   Hannes Tschofenig
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  02600
   Finland

   Phone: +358 (50) 4871445
   Email: Hannes.Tschofenig@gmx.net
   URI:   http://www.tschofenig.priv.at







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   Stefaan De Cnodder
   Alcatel-Lucent
   Copernicuslaan 50
   B-2018 Antwerp,
   Belgium

   Phone: +32 3 240 85 15
   Email: stefaan.de_cnodder@alcatel-lucent.com











































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