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rfc:rfc5355

Network Working Group M. Stillman, Ed. Request for Comments: 5355 Nokia Category: Informational R. Gopal

                                                Nokia Siemens Networks
                                                            E. Guttman
                                                      Sun Microsystems
                                                           S. Sengodan
                                                Nokia Siemens Networks
                                                           M. Holdrege
                                                        September 2008
     Threats Introduced by Reliable Server Pooling (RSerPool)
        and Requirements for Security in Response to Threats

Status of This Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Abstract

 Reliable Server Pooling (RSerPool) is an architecture and set of
 protocols for the management and access to server pools supporting
 highly reliable applications and for client access mechanisms to a
 server pool.  This document describes security threats to the
 RSerPool architecture and presents requirements for security to
 thwart these threats.

Stillman, et. al. Informational [Page 1] RFC 5355 RSerPool Threats September 2008

Table of Contents

 1. Introduction ....................................................3
    1.1. Definitions ................................................3
    1.2. Conventions ................................................4
 2. Threats .........................................................4
    2.1. PE Registration/De-Registration Flooding --
         Non-Existent PE ............................................4
    2.2. PE Registration/De-Registration Flooding --
         Unauthorized PE ............................................5
    2.3. PE Registration/De-Registration Spoofing ...................6
    2.4. PE Registration/De-Registration Unauthorized ...............6
    2.5. Malicious ENRP Server Joins the Group of Legitimate
         ENRP Servers ...............................................7
    2.6. Registration/De-Registration with Malicious ENRP Server ....7
    2.7. Malicious ENRP Handlespace Resolution ......................8
    2.8. Malicious Node Performs a Replay Attack ....................9
    2.9. Re-Establishing PU-PE Security during Failover .............9
    2.10. Integrity ................................................10
    2.11. Data Confidentiality .....................................10
    2.12. ENRP Server Discovery ....................................11
    2.13. Flood of Endpoint-Unreachable Messages from the
          PU to the ENRP Server ....................................12
    2.14. Flood of Endpoint Keep-Alive Messages from the
          ENRP Server to a PE ......................................12
    2.15. Security of the ENRP Database ............................13
    2.16. Cookie Mechanism Security ................................13
    2.17. Potential Insider Attacks from Legitimate ENRP Servers ...14
 3. Security Considerations ........................................15
 4. Normative References ...........................................17

Stillman, et. al. Informational [Page 2] RFC 5355 RSerPool Threats September 2008

1. Introduction

 The RSerPool architecture [RFC5351] supports high-availability and
 load balancing by enabling a pool user to identify the most
 appropriate server from the server pool at a given time.  The
 architecture is defined to support a set of basic goals.  These
 include application-independent protocol mechanisms, separation of
 server naming from IP addressing, the use of the end-to-end principle
 to avoid dependencies on intermediate equipment, separation of
 session availability/failover functionality from the application
 itself, the ability to facilitate different server selection
 policies, the ability to facilitate a set of application-independent
 failover capabilities, and a peer-to-peer structure.
 RSerPool provides a session layer for robustness.  The session layer
 function may redirect communication transparently to upper layers.
 This alters the direct one-to-one association between communicating
 endpoints that typically exists between clients and servers.  In
 particular, secure operation of protocols often relies on assumptions
 at different layers regarding the identity of the communicating party
 and the continuity of the communication between endpoints.  Further,
 the operation of RSerPool itself has security implications and risks.
 The session layer operates dynamically, which imposes additional
 concerns for the overall security of the end-to-end application.
 This document explores the security implications of RSerPool, both
 due to its own functions and due to its being interposed between
 applications and transport interfaces.
 This document is related to the RSerPool Aggregate Server Access
 Protocol (ASAP) [RFC5352] and Endpoint Name Resolution Protocol
 (ENRP) [RFC5353] documents, which describe, in their Security
 Consideration sections, the mechanisms for meeting the security
 requirements in this document.  TLS [RFC5246] is the security
 mechanism for RSerPool that was selected to meet all the requirements
 described in this document.  The Security Considerations sections of
 ASAP and ENRP describe how TLS is actually used to provide the
 security that is discussed in this document.

1.1. Definitions

 This document uses the following terms:
 Endpoint Name Resolution Protocol (ENRP):
    Within the operational scope of RSerPool, ENRP[RFC5353] defines
    the procedures and message formats of a distributed fault-tolerant
    registry service for storing, bookkeeping, retrieving, and
    distributing pool operation and membership information.

Stillman, et. al. Informational [Page 3] RFC 5355 RSerPool Threats September 2008

 Aggregate Server Access Protocol (ASAP):
    ASAP [RFC5352] is a session layer protocol that uses ENRP to
    provide a high-availability handlespace.  ASAP is responsible for
    the abstraction of the underlying transport technologies, load
    distribution management, fault management, as well as the
    presentation to the upper layer (i.e., the ASAP User) of a unified
    primitive interface.
 Operational scope:
    The part of the network visible to pool users by a specific
    instance of the Reliable Server Pooling protocols.
 Pool (or server pool):
    A collection of servers providing the same application
    functionality.
 Pool handle:
    A logical pointer to a pool.  Each server pool will be
    identifiable in the operational scope of the system by a unique
    pool handle.
 ENRP handlespace (or handlespace):
    A cohesive structure of pool names and relations that may be
    queried by a client.  A client in this context is an application
    that accesses another remote application running on a server using
    a network.
 Pool element (PE):  A server entity having registered to a pool.
 Pool user (PU):  A server pool user.

1.2. Conventions

 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].

2. Threats

2.1. PE Registration/De-Registration Flooding – Non-Existent PE

2.1.1. Threat

 A malicious node could send a stream of false registrations/de-
 registrations on behalf of non-existent PEs to ENRP servers at a very
 rapid rate and thereby create unnecessary state in an ENRP server.

Stillman, et. al. Informational [Page 4] RFC 5355 RSerPool Threats September 2008

2.1.2. Effect

 The malicious node will corrupt the pool registrar database and/or
 disable the RSerPool discovery and database function.  This
 represents a denial-of-service attack, as the PU would potentially
 get an IP address of a non-existent PE in response to an ENRP query.

2.1.3. Requirement

 An ENRP server that receives a registration/de-registration MUST NOT
 create or update state information until it has authenticated the PE.
 TLS with a pre-shared-key (PSK) is mandatory to implement as the
 authentication mechanism.  For PSK, having a pre-shared-key
 constitutes authorization.  The network administrators of a pool need
 to decide which nodes are authorized to participate in the pool.  The
 justification for PSK is that we assume that one administrative
 domain will control and manage the server pool.  This allows for PSK
 to be implemented and managed by a central security administrator.

2.2. PE Registration/De-Registration Flooding – Unauthorized PE

2.2.1. Threat

 A malicious node or PE could send a stream of registrations/de-
 registrations that are unauthorized to register/de-register to ENRP
 servers at a very rapid rate and thereby create unnecessary state in
 an ENRP server.

2.2.2. Effect

 This attack will corrupt the pool registrar database and/or disable
 the RSerPool discovery and database function.  There is the potential
 for two types of attacks: denial of service and data interception.
 In the denial-of-service attack, the PU gets an IP address of a rogue
 PE in response to an ENRP query, which might not provide the actual
 service.  In addition, a flood of message could prevent legitimate
 PEs from registering.  In the data interception attack, the rogue PE
 does provide the service as a man in the middle (MITM), which allows
 the attacker to collect data.

2.2.3. Requirement

 An ENRP server that receives a registration/de-registration MUST NOT
 create or update state information until the authentication
 information of the registering/de-registering entity is verified.

Stillman, et. al. Informational [Page 5] RFC 5355 RSerPool Threats September 2008

 TLS is used as the authentication mechanism between the ENRP server
 and PE.  TLS with PSK is mandatory to implement as the authentication
 mechanism.  For PSK, having a pre-shared-key constitutes
 authorization.  The network administrators of a pool need to decide
 which nodes are authorized to participate in the pool.

2.3. PE Registration/De-Registration Spoofing

2.3.1. Threat

 A malicious node could send false registrations/de-registrations to
 ENRP servers concerning a legitimate PE, thereby creating false state
 information in the ENRP servers.

2.3.2. Effect

 This would generate misinformation in the ENRP server concerning a PE
 and would be propagated to other ENRP servers, thereby corrupting the
 ENRP database.  Distributed Denial of Service (DDoS) could result: if
 a PE that is a target for a DDoS attack for some popular high-volume
 service, then the attacker can register a PE to which a lot of PUs
 will try to connect.  This allows man-in-the-middle or masquerade
 attacks on the service provided by the legitimate PEs.  If an
 attacker registers its server address as a PE and handles the
 requests, he can eavesdrop on service data.

2.3.3. Requirement

 An ENRP server that receives a registration/de-registration MUST NOT
 create or update state information until it has authenticated the PE.
 TLS is used as the authentication mechanism between the ENRP server
 and the PE.  TLS with PSK is mandatory to implement as the
 authentication mechanism.  For PSK, having a pre-shared-key
 constitutes authorization.  The network administrators of a pool need
 to decide which nodes are authorized to participate in the pool.  A
 PE can register only for itself and cannot register on behalf of
 other PEs.

2.4. PE Registration/De-Registration Unauthorized

2.4.1. Threat

 A PE that is not authorized to join a pool could send registrations/
 de-registrations to ENRP servers, thereby creating false state
 information in the ENRP servers.

Stillman, et. al. Informational [Page 6] RFC 5355 RSerPool Threats September 2008

2.4.2. Effect

 This attack would generate misinformation in the ENRP server
 concerning a PE and would be propagated to other ENRP servers thereby
 corrupting the ENRP database.  This allows man-in-the-middle or
 masquerade attacks on the service provided by the legitimate PEs.  If
 an attacker registers its server address as a PE and handles the
 requests, he can eavesdrop on service data.

2.4.3. Requirement

 An ENRP server that receives a registration/de-registration MUST NOT
 create or update state information until it has authorized the
 requesting entity.  TLS is used as the authentication mechanism.  TLS
 with PSK is mandatory to implement as the authentication mechanism.
 For PSK, having a pre-shared-key constitutes authorization.  The
 network administrators of a pool need to decide which nodes are
 authorized to participate in the pool.

2.5. Malicious ENRP Server Joins the Group of Legitimate ENRP Servers

2.5.1. Threat

 A malicious ENRP server joins the group of legitimate ENRP servers
 with the intent of propagating inaccurate updates to corrupt the ENRP
 database.  The attacker sets up an ENRP server and attempts to
 communicate with other ENRP servers.

2.5.2. Effect

 The result would be Inconsistent ENRP database state.

2.5.3. Requirement

 ENRP servers MUST perform mutual authentication.  This would prevent
 the attacker from joining its ENRP server to the pool.  TLS is used
 as the mutual authentication mechanism.  TLS with PSK is mandatory to
 implement as the authentication mechanism.  For PSK, having a
 pre-shared-key constitutes authorization.  The network administrators
 of a pool need to decide which nodes are authorized to participate in
 the pool.

2.6. Registration/De-Registration with Malicious ENRP Server

2.6.1. Threat

 A PE unknowingly registers/de-registers with a malicious ENRP server.

Stillman, et. al. Informational [Page 7] RFC 5355 RSerPool Threats September 2008

2.6.2. Effect

 The registration might not be properly processed or it might be
 ignored.  A rogue ENRP server has the ability to return any address
 to a user requesting service; this ability could result in denial of
 service or connection to a rogue PE that is the attacker's choice for
 service.

2.6.3. Requirement

 The PE MUST authenticate the ENRP server.  TLS is the mechanism used
 for the authentication.  TLS with PSK is mandatory to implement as
 the authentication mechanism.  For PSK, having a pre-shared-key
 constitutes authorization.  The network administrators of a pool need
 to decide which nodes are authorized to participate in the pool.
 This requirement prevents malicious outsiders and insiders from
 adding their own ENRP server to the pool.

2.7. Malicious ENRP Handlespace Resolution

2.7.1. Threat

 The ASAP protocol receives a handlespace resolution response from an
 ENRP server, but the ENRP server is malicious and returns random IP
 addresses or an inaccurate list in response to the pool handle.

2.7.2. Effect

 The PU application communicates with the wrong PE or is unable to
 locate the PE since the response is incorrect in saying that a PE
 with that handle did not exist.  A rogue ENRP server has the ability
 to return any address to ASAP requesting an address list that could
 result in denial of service or connection to a rogue PE of the
 attacker's choice for service.  From the PE, the attacker could
 eavesdrop or tamper with the application.

2.7.3. Requirement

 ASAP SHOULD authenticate the ENRP server.  TLS with certificates is
 the mandatory-to-implement mechanism used for authentication.  The
 administrator uses a centralized Certificate Authority (CA) to
 generate and sign certificates.  The certificate is stored on the
 ENRP server.  A CA trusted root certification authority certificate
 is sent to the client out of band, and the certificate signature on
 the ENRP server certificate is checked for validity during the TLS
 handshake.  This authentication prevents malicious outsiders and
 insiders from adding an ENRP server to the pool that may be accessed
 by ASAP.

Stillman, et. al. Informational [Page 8] RFC 5355 RSerPool Threats September 2008

2.8. Malicious Node Performs a Replay Attack

2.8.1. Threat

 A malicious node could replay the entire message previously sent by a
 legitimate entity.  This could create false/unnecessary state in the
 ENRP servers when the replay is for registration/de-registration or
 update.

2.8.2. Effect

 The result is that false/extra state is maintained by ENRP servers.
 This would most likely be used as a denial-of-service attack if the
 replay is used to de-register all PEs.

2.8.3. Requirement

 The protocol MUST prevent replay attacks.  The replay attack
 prevention mechanism in TLS meets this requirement.

2.9. Re-Establishing PU-PE Security during Failover

2.9.1. Threat

 The PU fails over from PE A to PE B.  In the case that the PU had a
 trusted relationship with PE A, the PU will likely not have the same
 relationship established with PE B.

2.9.2. Effect

 If there was a trust relationship involving security context between
 PU and PE A, the equivalent trust relationship will not exist between
 PU and PE B.  This will violate security policy.  For example, if the
 security context with A involves encryption and the security context
 with B does not, then an attacker could take advantage of the change
 in security.

2.9.3. Requirement

 The application SHOULD be notified when failover occurs so the
 application can take appropriate action to establish a trusted
 relationship with PE B.  ENRP has a mechanism to perform this
 function.

Stillman, et. al. Informational [Page 9] RFC 5355 RSerPool Threats September 2008

2.10. Integrity

2.10.1. Threat

 The following are all instances of the same class of threats, and all
 have similar effects.
 a.  ENRP response to pool handle resolution is corrupted during
     transmission.
 b.  ENRP peer messages are corrupted during transmission.
 c.  PE sends an update for values, and that information is corrupted
     during transmission.

2.10.2. Effect

 The result is that ASAP receives corrupt information for pool handle
 resolution, which the PU believes to be accurate.  This corrupt
 information could be an IP address that does not resolve to a PE so
 the PU would not be able to contact the server.

2.10.3. Requirement

 An integrity mechanism MUST be present.  Corruption of data that is
 passed to the PU means that the PU can't rely on it.  The consequence
 of corrupted information is that the IP addresses passed to the PU
 might be wrong, in which case, it will not be able to reach the PE.
 The interfaces that MUST implement integrity are PE to ENRP server
 and ENRP to ENRP server.  The integrity mechanism in TLS is used for
 this.

2.11. Data Confidentiality

2.11.1. Threat

 An eavesdropper capable of snooping on fields within messages in
 transit may be able to gather information, such as
 topology/location/IP addresses, etc., which may not be desirable to
 divulge.

2.11.2. Effect

 Information that an administrator does not wish to divulge is
 divulged.  The attacker gains valuable information that can be used
 for financial gain or attacks on hosts.

Stillman, et. al. Informational [Page 10] RFC 5355 RSerPool Threats September 2008

2.11.3. Requirement

 A provision for data confidentiality service SHOULD be available.
 TLS provides data confidentiality in support of this mechanism.

2.12. ENRP Server Discovery

2.12.1. Threats

 a.  Thwarting successful discovery: When a PE wishes to register with
     an ENRP server, it needs to discover an ENRP server.  An attacker
     could thwart the successful discovery of ENRP server(s), thereby
     inducing the PE to believe that no ENRP server is available.  For
     instance, the attacker could reduce the returned set of ENRP
     servers to null or a small set of inactive ENRP servers.  The
     attacker performs a MITM attack to do this.
 b.  A similar thwarting scenario also applies when an ENRP server or
     ASAP on behalf of a PU needs to discover ENRP servers.
 c.  Spoofing successful discovery: An attacker could spoof the
     discovery by claiming to be a legitimate ENRP server.  When a PE
     wishes to register, it finds the spoofed ENRP server.  An
     attacker can only make such a claim if no security mechanisms are
     used.
 d.  A similar spoofing scenario also applies when an ENRP server or
     ASAP on behalf of a PU needs to discover ENRP servers.

2.12.2. Effects (Letters Correlate with Threats above)

 a.  A PE that could have been in an application server pool does not
     become part of a pool.  The PE does not complete discovery
     operation.  This is a DoS attack.
 b.  An ENRP server that could have been in an ENRP server pool does
     not become part of a pool.  A PU is unable to utilize services of
     ENRP servers.
 c.  This malicious ENRP would either misrepresent, ignore, or
     otherwise hide or distort information about the PE to subvert
     RSerPool operation.
 d.  Same as above.

Stillman, et. al. Informational [Page 11] RFC 5355 RSerPool Threats September 2008

2.12.3. Requirement

 A provision for authentication MUST be present and a provision for
 data confidentiality service SHOULD be present.  TLS has a mechanism
 for confidentiality.

2.13. Flood of Endpoint-Unreachable Messages from the PU to the ENRP

     Server

2.13.1. Threat

 Endpoint-unreachable messages are sent by ASAP to the ENRP server
 when it is unable to contact a PE.  There is the potential that a PU
 could flood the ENRP server intentionally or unintentionally with
 these messages.  The non-malicious case would require an incorrect
 implementation.  The malicious case would be caused by writing code
 to flood the ENRP server with endpoint unreachable messages.

2.13.2. Effect

 The result is a DoS attack on the ENRP server.  The ENRP server would
 not be able to service other PUs effectively and would not be able to
 take registrations from PEs in a timely manner.  Further, it would
 not be able to communicate with other ENRP servers in the pool to
 update the database in a timely fashion.

2.13.3. Requirement

 The number of endpoint unreachable messages sent to the ENRP server
 from the PU SHOULD be limited.  This mechanism is described in the
 ASAP [RFC5352] protocol document.

2.14. Flood of Endpoint Keep-Alive Messages from the ENRP Server to a

     PE

2.14.1. Threat

 Endpoint Keep-Alive messages would be sent from the ENRP server to
 the PEs during the process of changing the Home ENRP server for this
 PE.

2.14.2. Effect

 If the ENRP server maliciously sent a flood of endpoint Keep-Alive
 messages to the PE, the PE would not be able to service clients.  The
 result is a DoS attack on the PE.

Stillman, et. al. Informational [Page 12] RFC 5355 RSerPool Threats September 2008

2.14.3. Requirement

 ENRP MUST limit the frequency of Keep-Alive messages to a given PE to
 prevent overwhelming the PE.  This mechanism is described in the ENRP
 [RFC5353] protocol document.

2.15. Security of the ENRP Database

2.15.1. Threat

 Another consideration involves the security characteristics of the
 ENRP database.  Suppose that some of the PEs register with an ENRP
 server using security and some do not.  In this case, when a client
 requests handlespace resolution information from ENRP, it would have
 to be informed which entries are "secure" and which are not.

2.15.2. Effect

 This would not only complicate the protocol, but actually bring into
 question the security and integrity of such a database.  What can be
 asserted about the security of such a database is a very thorny
 question.

2.15.3. Requirement

 The requirement is that either the entire ENRP server database MUST
 be secure; that is, it has registrations exclusively from PEs that
 have used security mechanisms, or the entire database MUST be
 insecure; that is, registrations are from PEs that have used no
 security mechanisms.  ENRP servers that support security MUST reject
 any PE server registration that does not use the security mechanisms.
 Likewise, ENRP servers that support security MUST NOT accept updates
 from other ENRP servers that do not use security mechanisms.  TLS is
 used as the security mechanism so any information not sent using TLS
 to a secure ENRP server MUST be rejected.

2.16. Cookie Mechanism Security

 The application layer is out of scope for RSerPool.  However, some
 questions have been raised about the security of the cookie
 mechanism, which will be addressed.
 Cookies are passed via the ASAP control channel.  If TCP is selected
 as the transport, then the data and control channel MUST be
 multiplexed.  Therefore, the cases:
 a.  control channel is secured; data channel is not

Stillman, et. al. Informational [Page 13] RFC 5355 RSerPool Threats September 2008

 b.  data channel is secured; control channel is not
 are not possible, as the multiplexing onto one TCP port results in
 security for both data and control channels or neither.
 The multiplexing requirement results in the following cases:
 1.  the multiplexed control channel-data channel is secure; *or*
 2.  the multiplexed control channel-data channel is not secured.
 This applies to cookies in the sense that, if you choose to secure
 your control-data channel, then the cookies are secured.
 A second issue is that the PE could choose to sign and/or encrypt the
 cookie.  In this case, it must share keys and other information with
 other PEs.  This application-level state sharing is out of scope of
 RSerPool.

2.17. Potential Insider Attacks from Legitimate ENRP Servers

 The previous text does not address all byzantine attacks that could
 arise from legitimate ENRP servers.  True protection against
 misbehavior by authentic (but rogue) servers is beyond the capability
 of TLS security mechanisms.  Authentication using TLS does not
 protect against byzantine attacks, as authenticated ENRP servers
 might have been maliciously hacked.  Protections against insider
 attacks are generally specific to the attack, so more experimentation
 is needed.  For example, the following discusses two insider attacks
 and potential mitigations.
 One issue is that legitimate users may choose not to follow the
 proposed policies regarding the choice of servers (namely, members in
 the pool).  If the "choose a member at random" policy is employed,
 then a pool user can always set its "random choices" so that it picks
 a particular pool member.  This bypasses the "load sharing" idea
 behind the policy.  Another issue is that a pool member (or server)
 may report a wrong policy to a user.
 To mitigate the first attack, the protocol may require the pool user
 to "prove" to the pool member that the pool member was chosen
 "randomly", say by demonstrating that the random choice was the
 result of applying some hash function to a public nonce.  Different
 methods may be appropriate for other member scheduling policies.

Stillman, et. al. Informational [Page 14] RFC 5355 RSerPool Threats September 2008

 To mitigate the second attack, the protocol might require the PE to
 sign the policy sent to the ENRP server.  During pool handle
 resolution, the signed policy needs to be sent from an ENRP server to
 an ASAP endpoint in a way that will allow the user to later hold the
 server accountable to the policy.

3. Security Considerations

 This informational document characterizes potential security threats
 targeting the RSerPool architecture.  The security mechanisms
 required to mitigate these threats are summarized for each
 architectural component.  It will be noted which mechanisms are
 required and which are optional.
 From the threats described in this document, the security services
 required for the RSerPool protocol suite are given in the following
 table.

Stillman, et. al. Informational [Page 15] RFC 5355 RSerPool Threats September 2008

 +--------------+----------------------------------------------------+
 |    Threat    |           Security mechanism in response           |
 +--------------+----------------------------------------------------+
 |  Section 2.1 |          ENRP server authenticates the PE.         |
 |  Section 2.2 |          ENRP server authenticates the PE.         |
 |  Section 2.3 |          ENRP server authenticates the PE.         |
 |  Section 2.4 |          ENRP server authenticates the PE.         |
 |  Section 2.5 |         ENRP servers mutually authenticate.        |
 |  Section 2.6 |          PE authenticates the ENRP server.         |
 |  Section 2.7 |    The PU authenticates the ENRP server.  If the   |
 |              |   authentication fails, it looks for another ENRP  |
 |              |                       server.                      |
 |  Section 2.8 | Security protocol that has protection from replay  |
 |              |                      attacks.                      |
 |  Section 2.9 |    Either notify the application when failover     |
 |              |   occurs so the application can take appropriate   |
 |              | action to establish a trusted relationship with PE |
 |              |        B *or* re-establish the security context    |
 |              |                   transparently.                   |
 | Section 2.10 |     Security protocol that supports integrity      |
 |              |                     protection.                    |
 | Section 2.12 |        Security protocol that supports data        |
 |              |                  confidentiality.                  |
 | Section 2.11 |    The PU authenticates the ENRP server.  If the   |
 |              |   authentication fails, it looks for another ENRP  |
 |              |                       server.                      |
 | Section 2.13 |      ASAP must control the number of endpoint      |
 |              |   unreachable messages transmitted from the PU to  |
 |              |                  the ENRP server.                  |
 | Section 2.14 |       ENRP server must control the number of       |
 |              |       Endpoint_KeepAlive messages to the PE.       |
 +--------------+----------------------------------------------------+
 The first four threats, combined with the sixth threat, result in a
 requirement for mutual authentication of the ENRP server and the PE.
 To summarize, the first twelve threats require security mechanisms
 that support authentication, integrity, data confidentiality, and
 protection from replay attacks.  For RSerPool, we need to
 authenticate the following:
 o  PU -----> ENRP Server (PU authenticates the ENRP server)
 o  PE <----> ENRP Server (mutual authentication)
 o  ENRP server <-----> ENRP Server (mutual authentication)

Stillman, et. al. Informational [Page 16] RFC 5355 RSerPool Threats September 2008

 Summary by component:
 RSerPool client --  mandatory-to-implement authentication of the ENRP
    server is required for accurate pool handle resolution.  This is
    to protect against threats from rogue ENRP servers.  In addition,
    confidentiality, integrity, and preventing replay attack are also
    mandatory to implement to protect from eavesdropping and data
    corruption or false data transmission.  Confidentiality is
    mandatory to implement and is used when privacy is required.
 PE to ENRP communications --  mandatory-to-implement mutual
    authentication, integrity, and protection from replay attack is
    required for PE to ENRP communications.  This is to protect the
    integrity of the ENRP handlespace database.  Confidentiality is
    mandatory to implement and is used when privacy is required.
 ENRP to ENRP communications --  mandatory-to-implement mutual
    authentication, integrity, and protection from replay attack is
    required for ENRP to ENRP communications.  This is to protect the
    integrity of the ENRP handlespace database.  Confidentiality is
    mandatory to implement and is used when privacy is required.

4. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.2", RFC 5246, August 2008.
 [RFC5352]   Stewart, R., Xie, Q., Stillman, M., and M. Tuexen,
            "Aggregate Server Access Protocol (ASAP)", RFC 5352,
            September 2008.
 [RFC5353]  Xie, Q., Stewart, R., Stillman, M., Tuexen, M., and A.
            Silverton, "Endpoint Handlespace Redundancy Protocol
            (ENRP)", RFC 5353, September 2008.
 [RFC5351]  Lei, P., Ong, L., Tuexen, M., and T. Dreibholz, "An
            Overview of Reliable Server Pooling Protocols", RFC 5351,
            September 2008.

Stillman, et. al. Informational [Page 17] RFC 5355 RSerPool Threats September 2008

Authors' Addresses

 Maureen Stillman, Ed.
 Nokia
 1167 Peachtree Court
 Naperville, IL  60540
 USA
 EMail: maureen.stillman@nokia.com
 Ram Gopal
 Nokia Siemens Networks
 12278 Scripps Summit Drive
 San Diego, CA  92131
 USA
 EMail: ram.gopal@nsn.com
 Erik Guttman
 Sun Microsystems
 Eichhoelzelstrasse 7
 74915 Waibstadt
 DE
 EMail: Erik.Guttman@sun.com
 Senthil Sengodan
 Nokia Siemens Networks
 6000 Connection Drive
 Irving, TX  75039
 USA
 EMail: Senthil.sengodan@nsn.com
 Matt Holdrege
 EMail: Holdrege@gmail.com

Stillman, et. al. Informational [Page 18] RFC 5355 RSerPool Threats September 2008

Full Copyright Statement

 Copyright (C) The IETF Trust (2008).
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 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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Stillman, et. al. Informational [Page 19]

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