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Network Working Group                                  V. Narayanan, Ed.
Internet-Draft                                            Qualcomm, Inc.
Intended status: Informational                         December 22, 2006
Expires: June 25, 2007


  IPsec Gateway Failover and Redundancy - Problem Statement and Goals
                     draft-vidya-ipsec-failover-ps-00

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   Copyright (C) The IETF Trust (2006).

Abstract

   Recovering from failure of IPsec gateways or servers maintaining
   large numbers of SAs may take several minutes, if they need to re-
   establish the IPsec SAs by re-running the key management protocol,
   IKEv2.  A similar problem arises in the event of a network outage
   resulting in the failure of several gateways and servers.  The
   latency involved in this approach is significant, leading to a need
   for a faster and yet secure failover solution.  This document
   describes the problem statement and the goals for an IPsec/IKEv2



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   gateway failover/redundancy solution.


Table of Contents

   1.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Applicability and Problem Statement  . . . . . . . . . . . . .  4
   5.  IPsec Failover Redundancy Solution Goals . . . . . . . . . . .  6
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  8
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     9.1.  Normative References . . . . . . . . . . . . . . . . . . .  8
     9.2.  Informative References . . . . . . . . . . . . . . . . . .  9
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .  9
   Intellectual Property and Copyright Statements . . . . . . . . . . 10

































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1.  Contributors

   This document reflects contributions from and active discussions
   among the following individuals (in alphabetical order):

      Lakshminath Dondeti (ldondeti@qualcomm.com)

      Paul Hoffman (paul.hoffman@vpnc.org)

      Tero Kivinen (kivinen@iki.fi)

      Gregory Lebovitz (gregory.ietf@gmail.com)

      Marcus Leech (mleech@nortel.com)

      Cheryl Madson (cmadson@cisco.com)

      Michael Richardson (mcr@sandelman.ottawa.on.ca)

      Sheela Rowles (srowles@cisco.com)

      Yaron Sheffer (yaronf@checkpoint.com)

      Marcus Stenberg (mstenber@cisco.com)

      Brian Weis (bew@cisco.com)


2.  Introduction

   The IKEv2 protocol, while more efficient and involves fewer round
   trips compared to its predecessor is quite computationally intensive,
   especially when entity authentication is by way of public-key based
   certificates.  IKEv2 also needs 2-3 roundtrips when using PSKs or
   public keys for authentication and 4 or more roundtrips when EAP is
   used for client authentication.  Thus, the process of setting up
   IPsec SAs is an expensive process, in terms of the number of messages
   exchanged between the initiator and responder.

   When an IPsec entity has a large number of SAs with various other
   endpoints, establishing all the SAs again upon a failure recovery
   condition takes a long time.  Examples of entities that manage a
   large number of IPsec SAs include IPsec remote access gateways, and
   application servers that use IPsec for protection of signaling
   traffic.  For efficient recovery from gateway or server failure, it
   might make sense to allow those entities to maintain copies of IPsec
   and IKEv2 state (SAD, SPD, and associated state) on other servers
   (for stateful operation) or on the client itself (for stateless



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   operation).  Either the recovered IPsec entity or other entities in
   the server pool may retrieve the stored IPsec and IKEv2 state for
   faster recovery.

   There are a number of proprietary solutions for this problem in the
   industry, however, those solutions do not interoperate.  Applications
   that need IPsec failover capability, such as Mobile IPv6 have
   solutions under development for interoperable Home Agent (HA)
   failover.  Without interoperable (client to server and server to
   server) IPsec failover capability HA failover solutions are
   incomplete.  Thus, there is a need for an interoperable means of
   performing SA uploads and retrieval so that such IPsec redundancy can
   be implemented in an interoperable fashion.


3.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].

   This document uses terminology defined in [2], [3], and [4].  In
   addition, this document uses the following terms:




4.  Applicability and Problem Statement

   There are at least two cases where fast recovery from failure of an
   IPsec entity is applicable.

      IPsec Gateways -- The first case is that of an IPsec remote access
      gateway managing tunnel mode SAs with clients.  The gateway may be
      enforcing access control to an enterprise network; this is the
      typical remote access use case.  The gateway could also be
      enforcing service provider network access control.  In that case,
      clients typically use EAP over IKEv2 to establish an IPsec session
      with a network access gateway.  In either IPsec Gateway use case,
      the IPsec traffic itself flows from the VPN clients or Initiators
      to the VPN gateway; the gateway decapsulates the IPsec packets and
      forwards the cleartext packets based on inner IP headers.  In the
      reverse direction, the VPN gateway uses the security policy
      database (SPD) to lookup the relevant IPsec, encapsulates the
      packets and sends to the appropriate VPN client.






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      IPsec Servers -- The second use is that of an IPsec entity acting
      as a server for an application such as Mobile IP.  In these cases,
      Mobile IP messages are protected using IPsec.  Each Mobile IP Home
      Agent (HA) maintains a large number of transport or tunnel mode
      IPsec sessions with their respective clients.  In this case, IPsec
      protected signaling messages are sent end-to-end, between Mobile
      IP client and HA, respectively.

   In the security gateway mode, while there may be multiple security
   gateways serving a number of remote endpoints, a given remote
   endpoint is typically served by one security gateway.  For instance,
   an IPsec VPN client typically maintains one or more SAs for remote
   access with one VPN gateway.  However, when the serving gateway
   fails, it is desirable for one of the other gateways to seamlessly
   take over and serve the clients affected by the failure.  In some
   deployments, there may be a backup gateway that can take over for the
   primary in case of a failure.  Such gateways may be running a VRRP-
   like protocol to actually share the gateway IP address as known to
   the clients.  In other deployments, a cluster of gateways may load
   balance to serve a number of clients.  In such a case, one or more of
   the gateways in the cluster may take over clients associated with
   another gateway in the cluster in the event of a failure.

   When IPsec is used for protection of signaling between an application
   client and server, server redundancy is often an important
   consideration.  As in the gateway model, it is necessary for another
   server to be able to seamlessly take over clients being served by a
   failed server.

   In addition to server failures, massive network failures of a short
   duration (minutes), followed by network recovery are also a concern.
   The network failure results in all clients being disconnected first
   (e.g. because of dead-peer detection), and then simultaneously
   attempting to reconnect.  This can be classified as a subset of the
   gateway failure case for the purpose of this effort.

   In all these cases outlined above, it is feasible to perform secure
   IPsec and IKEv2 state transfer across endpoints to provide smoother
   failure recovery.  Today, such redundancy operations are performed in
   a vendor specific manner and are not interoperable.  Also, lack of
   client involvement implies a failover mode that is transparent to the
   client.  However, in the above cases, the failover cannot always be
   transparent to the client and hence, an interoperable protocol
   becomes very important.







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5.  IPsec Failover Redundancy Solution Goals

   The following are goals for the IPsec Failover Redundancy solution.
   Note that the motivation for this effort is to develop mechanisms and
   perhaps protocols to facilitate failover capabilities.  It is
   plausible that the design facilitates features such as load
   balancing, but additional signaling or protocol design to facilitate
   load balancing exclusively is outside the scope of this effort.

   o  Distributed Failover Mechanism: Gateways may be located at
      different sites and may not share the same IP address or have the
      same view of the network.  For instance, the various distributed
      gateways may be connected to different backend elements such as
      EAP servers, DHCP servers, etc.  A failover mechanism must be able
      to allow such distributed gateways to take over the clients
      associated with a failed gateway.  The idea here is that there is
      no need for a fully redundant gateway that only starts functioning
      in the event of a failure.  It is more cost-effective to allow
      such failover to distributed gateways that may be functional on
      their own, serving other clients.  The temporary increase in load
      on some gateways in the system may be acceptable to many
      deployments in the event of a failure.  Such a mechanism across
      distributed gateways may also be used for client handoff to other
      gateways due to other reasons, e.g., load balancing.  Gateways
      located on the same link with the same view of the network may be
      viewed as a subset.

   o  Client Involvement: Given that the gateways may be distributed,
      the failover is not intended to be transparent to the client.  The
      goal is to allow the client to initiate the switch to a different
      gateway.

   o  Low Latency failover: One of the major goals is to allow a low
      latency failover, without having to re-establish all the IKEv2 and
      IPsec state all over again.  The bottleneck here is the new IPsec
      gateway trying to handle a flood of IKEv2 exchanges upon a
      failover.  Further, for applications such as Mobile IPv6 that use
      IKEv2/IPsec for securing the signaling, re-establishment of IKEv2
      often adds unacceptable latencies.  Ideally, a mechanism that does
      not need any new messages to exclusively support failover is
      desired.  In general, the goal is to have significantly lower
      latency and to incur a lower computational overhead than a regular
      IKEv2 exchange.  In cases where EAP is used for client
      authentication, the failover should not require EAP
      authentication, to avoid AAA overloading and possible user
      interaction.





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   o  Application Usage of IPsec: When IPsec is used to protect other
      protocols, the extent of failover interoperability that can be
      expected by such protocols greatly hinge on the interoperability
      of IPsec failover mechanisms.  For e.g., Mobile IP Home Agent
      reliability [5] mechanisms are intended to be standardized for
      interoperability.  However, it is incomplete without IPsec
      failover.  So, it is important to allow applications that use
      IPsec to take advantage of the IPsec failover mechanism.  It is
      not expected that the IPsec failover solution will address this,
      but a guidance needs to be provided to allow application
      specifications to specify the appropriate interface/interaction
      needed (e.g., if synchronization between application state and
      IPsec state is needed).

   o  Interoperability: Client-gateway and gateway-gateway
      interoperability is required.  This follows from the discussion on
      the other goals stated above.

   o  Stateless Gateway Operation: The IPsec failover mechanism should
      specify a mode of operation that will allow the backup gateways to
      remain stateless until a failover occurs or during a temporary
      service interruption.  This will allow for better scalability of
      the solution, since a given gateway only needs to store state for
      clients that are being served by it.

   o  Support for IPsec transport and tunnel modes: As noted in the
      applicability section of this document, the IPsec infrastructure
      endpoint may either be an IPsec VPN gateway employing tunnel mode
      SAs with the client or an application server that uses IPsec
      transport or tunnel mode to protect signaling exchanges with the
      client.  Hence, a solution developed for failover must support
      failover of both transport and tunnel mode SAs.


6.  Security Considerations

   This document provides the problem description and goals for an IPsec
   failover solution.  The solution must ensure secure operation and
   there are several important points to consider for that.  We
   highlight a few of the important ones below :

   o  First, any SA storage and retrieval mechanisms specified between
      the backend entities must be protected with a secure channel that
      has the following properties: confidentiality, integrity
      protection, and replay protection.

   o  Solutions for a client-server model, where the client always
      initiates the secure communication may allow the client to find



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      the new server address through external means.  Subsequently, the
      client must be able to verify the server's authorization by
      verifying the proof of possession of the IKEv2 key material at the
      new server.  A client should be able to initiate a new IKEv2 SA
      with one or more auxiliary servers without interrupting a
      connection to the currently used primary server.  The client must
      consider the new server as a provisional server until it has
      verified a new server is the appropriate replacement for the
      primary server.

   o  Any solution must adequately describe the consequences to replay
      protection as a result of IPsec failover.  For replay protection,
      it may be best for the replacement server to assume that the IPsec
      SA state is outdated and reestablish the IPsec SA using an IKEv2
      CREATE_CHILD_SA exchange.  (Perhaps this can be relaxed after a
      more in-depth analysis).

   o  IPsec failover facilitates the replacement of an IPsec GW serving
      a client with another GW.  The design must take into account the
      possibility of an adversary creating a ping-ponging scenario where
      a client may be forced to move between two or more GWs
      persistently.


7.  IANA Considerations

   No IANA action is required for this document.


8.  Acknowledgments

   We thank Russ Housley, Jun Wang, Marcello Lioy, and Raymond Hsu for
   technical discussions and/or help with standardization aspects
   related to this work.


9.  References

9.1.  Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Kent, S. and K. Seo, "Security Architecture for the Internet
        Protocol", RFC 4301, December 2005.

   [3]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306,
        December 2005.



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   [4]  Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)",
        RFC 4555, June 2006.

9.2.  Informative References

   [5]  Wakikawa, R., "Home Agent Reliability Protocol",
        draft-ietf-mip6-hareliability-00 (work in progress), June 2006.


Author's Address

   Vidya Narayanan (editor)
   Qualcomm, Inc.
   5775 Morehouse Dr
   San Diego, CA
   USA

   Phone: +1 858-845-2483
   Email: vidyan@qualcomm.com
































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