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Network Working Group                                         G. Kalyani
Internet-Draft                                                     Cisco
Intended status: Standards Track                           July 29, 2010
Expires: January 30, 2011


                 IKEv2/IPsec SA counter synchronization
               draft-kagarigi-ipsecme-ikev2-windowsync-04

Abstract

   IKEv2 and IPsec protocols are widely used for deploying VPN.  In
   order to make such VPN highly available and failure-prone, these VPNs
   are implemented as IKEv2/IPsec Highly Available (HA) cluster.  But
   there are many issues in IKEv2/IPsec HA cluster.  The draft "IPsec
   Cluster Problem Statement" enumerates all the issues encountered in
   IKEv2/IPsec HA cluster environment.

   This draft proposes an extension to IKEv2 protocol to solve main
   issues of "IPsec Cluster Problem Statement" in Hot Standby cluster
   and gives implementation advice for others.  The main issues to be
   solved are:
   o  IKE Message Id synchronization : This is done by obtaining the
      message Id values from the peer and updating the values at the
      newly active cluster member after the failover.
   o  IPsec SA Counter synchronization : This is done by sending
      incremented the values of replay counters by the newly active
      cluster member to the peer as expected replay counter value.

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 January 30, 2011.

Copyright Notice




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   Copyright (c) 2010 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
   to this document.  Code Components extracted from this document must
   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 . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Issues solved from IPsec Cluster Problem Statement . . . . . .  4
   4.  IKEv2/IPsec SA Counter Synchronization Problem . . . . . . . .  5
   5.  IKEv2/IPsec SA Counter Synchronization Solution  . . . . . . .  6
   6.  SA counter synchronization notify and payload types  . . . . .  8
     6.1.  SYNC_SA_COUNTER_INFO_SUPPORTED . . . . . . . . . . . . . .  8
     6.2.  SYNC_SA_COUNTER_INFO . . . . . . . . . . . . . . . . . . .  8
   7.  Details of implementation  . . . . . . . . . . . . . . . . . . 10
   8.  Step-by-Step details . . . . . . . . . . . . . . . . . . . . . 11
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   10. Interaction with other drafts  . . . . . . . . . . . . . . . . 12
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 13
     13.2. Informative References . . . . . . . . . . . . . . . . . . 14
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14

















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1.  Introduction

   IKEv2 is used for deploying IPsec-based VPNs.  In order to make such
   VPN highly available and failure-prone, these VPNs are inplemented as
   IKEv2/IPsec Highly Available (HA) cluster.  But there are many issues
   in IKEv2/IPsec HA cluster.  The draft "IPsec Cluster Problem
   Statement" enumerates all the issues encountered in IKEv2/IPsec HA
   cluster.

   In case of Hot Standby cluster implementaion of IKEv2/IPsec based
   VPNs, the IKEv2/IPsec session gets established with the peer and the
   active member of cluster.  After that, the active member syncs/
   updates the IKE/IPsec SA state to the standby member of the cluster.
   This primary SA state sync-up is done on SA bring up and/or rekey.
   Doing SA state synchronization/updation between active and peer
   member for each IKE and IPsec message standby cluster is very costly,
   so normally its done periodically.  So, when "failover" event happens
   in the cluster, first "failover' is detected by the standby member
   and then it becomes active member and it takes considerable time.
   During the time of failover and standby member becoming newly active
   member, the peer is unaware of failover and keeps sending IKE request
   and IPsec packets to the cluster which is allowed as per IKEv2 and
   IPsec windowing feature.  Now, newly active member after coming up
   finds the mismtach in IKE message id's and IPsec replay counters.
   Please see Section 4 for more details.

   This draft proposes an extension to IKEv2 protocol to solve main
   issues of IKE message id sync and IPsec SA replay counter sync and
   gives implementation advice for others.  Here is summary of solutions
   provided in this draft:

   IKE Message Id synchronization : This is done by obtaining the
   message Id values from the peer and updating the values at the newly
   active cluster member after the failover.

   IPsec SA Counter synchronization : This is done by sending
   incremented values of replay counters by the newly active cluster
   member to the peer as expected replay counter value.

   Though this draft describes the IKEv2/IPsec SA counter
   synchronisation in context of hot standby cluster.  This solution can
   be in other scenarios where IKEv2/IPsec SA counters are mis-matched
   and couner sync is needed.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",



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   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   "SA Counter SYNC Request" is the information exchange request defined
   in this draft to synchronize the IKEv2/IPsec SA counter information
   between member of the cluster and the peer.

   "SA Counter SYNC Response" is the information exchange response
   defined in this draft to synchronize the IKEv2/IPsec SA counter
   information between member of the cluster and the peer.

   Below are the terms taken from [IPsec Cluster Problem Statement] with
   added information in context of this draft.

   "Hot Standby Cluster", or "HS Cluster" is a cluster where only one of
   the members is active at any one time.  This member is also referred
   to as the "active", whereas the other(s) are referred to as
   "standbys".  VRRP ([RFC5798]) is one method of building such a
   cluster.  The goal of Hot Standby Cluster is that it creates illusion
   of single virtual gateway to the peer(s).

   "Active Member" is the primary member in the Hot Standby cluster.  It
   is responsible for forwarding packets for the virtual gateway.

   "Standby Member" is the primary backup router.  The member takes
   control i.e. becomes active member after the "failover" event.

   "Peer" is the IKEv2/IPsec endpoint which establishes VPN connection
   with Hot Standby cluster.  The Peer knows Hot Standby Cluster by
   single cluster's IP address.  In case of "failover", the standby
   member of the cluster becomes active, so the peer normally doesn't
   notice that "failover" has occured in the cluster.

   The generic term IKEv1/IPsec SA counters is used throughout.  By
   IKEv2 SA counter stands for IKEv2 message ids and IPsec SA counter
   stands for IPsec SA replay counters which are used to provide
   optional anti-replay feature.


3.  Issues solved from IPsec Cluster Problem Statement

   IPsec Cluster Problem Statement defines the problems encountered in
   IPsec Clusters. .  The problems along with their section names as
   given in the statement are as follows.
   o  3.2.  Lots of Long Lived State
   o  3.3.  IKE Counters





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   o  3.4.  Outbound SA Counters
   o  3.5.  Inbound SA Counters
   o  3.6.  Missing Synch Messages
   o  3.7.  Simultaneous use of IKE and IPsec SAs by Different Members
      *  3.7.1.  Outbound SAs using counter modes
   o  3.8.  Different IP addresses for IKE and IPsec
   o  3.9.  Allocation of SPIs

   This draft solves the main issues using the protocol extention, and
   provides implementation advice for other issues, given as follows.
   o  3.2 This section mentions that there's lots of state that needs to
      be synchronized.  If state is not synchronized, it's not really an
      interesting cluster - failover will be just like a reboot, so the
      issue need not be solved with protocol extensions.
   o  3.3, 3.4,3.5, and 3.6 are solved by this draft.  Please see
      Section 4, for more details.
   o  3.7 is the problem to be solved while building clusters.  However,
      the peers should be mandated to accept multiple parallel SAs for
      3.7.1
   o  3.8 can be solved by using IKEv2 Redirect Mechanism [RFC-5685].
   o  3.9 is the problem about avoiding collision of same SPI's among
      the cluster members.  This is outside the scope of the document
      since this has to be solved within the context of the cluster and
      not with the peer.


4.  IKEv2/IPsec SA Counter Synchronization Problem

   IKEv2 RFC states that "An IKE endpoint MUST NOT exceed the peer's
   stated window size for transmitted IKE requests".

   As per the protocol, all IKEv2 packets follows request-response
   paradigm.  The initiator of an IKEv2 request MUST retransmit the
   request, until it has received a response from the peer.  IKEv2
   introduces a windowing mechanism that allows multiple requests to be
   outstanding at a given point of time, but mandates that the sender
   window does not move until the oldest message sent from one peer to
   another is acknowledged.  Loss of even a single packet leads to
   repeated retransmissions followed by an IKEv2 SA teardown if the
   retransmissions are unacknowledged.

   IPsec Hot Standby Cluster is required to ensure that in case of
   failover of active member, the standby member becomes active
   immediately.  The standby member is expected to have the exact values
   of message id fields of active member before failover.  Even with the
   best efforts to update the message Id values from active to standby
   member, the values at standby member can be stale due to following
   reasons:



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   o  Standby member is unaware of the last message that was received
      and acknowledged by the older active member as failover could have
      happened before the standby could be updated.
   o  Standby member does not have information about on-going
      unackowledged requests of active member before the failover event.
      So after failover event when standby member becomes active, it can
      not re-transmit those requests.

   When a standby member takes over as the active member, it would start
   the message id ranges from previously updated values.  This would
   make it reject requests from the peer, since the values would be
   stale.  As a sender, the standby member may end up reusing a stale
   message id which will cause the peer to drop the request.  Eventually
   there is a high probability of the IKEv2 and corresponding IPsec SAs
   getting torn down simply because of a transitory message id mismatch
   and re-transmission of requests.  This is not a desirable feature of
   HA.  Even after updating standby memeber periodically the cluster can
   loose IKE and so all IPsec SA due to message id i.e.  SA counter
   mismatch.

   Similar issue is observed in IPsec counters also if anti-replay
   protection/ESN is implemented.  Even with the best efforts of syncing
   the ESP and AH SA counter numbers from active to stand by member ,
   there is a chance that the stand-by member would have stale counter
   values.  The standby member would then send the stale counter
   numbers.  The peer would reject such packets since in case of anti-
   replay protection feature, duplicate use of counters are not allowed.
   In case of IPsec it is ok to skip some counter values and start with
   the highr counter values.

   Hence a mechanism is required in HA to ensure that the standby member
   has correct values of message Id values and IPsec counters, so that
   sessions are not torn down just because of window ranges.


5.  IKEv2/IPsec SA Counter Synchronization Solution

   After the standby member becomes the active member after failover
   event in the cluster, the standby member would send an authenticated
   IKEv2 request to the peer to send its values of SA counters.

   The standby member would then update its values of SA counters and
   then start sending/receiving the requests.

   The peer MUST negotiate its ability to support SA counter
   synchronization information with active member by sending the
   SYNC_SA_COUNTER_INFO_SUPPORTED notification in IKE_AUTH exchange.




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     Peer                                                Active Member
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    HDR, SK {IDi, [CERT], [CERTREQ], [IDr], AUTH,
     N[SYNC_SA_COUNTER_INFO_SUPPORTED], SAi2, TSi, TSr} ---------->

     <---------- HDR, SK {IDr, [CERT+], [CERTREQ+], AUTH,
                   N[SYNC_SA_COUNTER_INFO_SUPPORTED], SAr2, TSi, TSr}


   When peer and active member both support SA counter synchronization,
   the active member MUST sync/update SA counter synchronization
   capability to the standby member after the establishment of the IKE
   SA.  So that standby member is aware of the capability and can use it
   when it becomes the active member after failover event.

   After failover event, when the standby member becomes the active
   member, it has to request the peer for the SA counters.  Standby
   member would initiate the SYNC Request with an INFORMATIONAL exchange
   containing the notify SYNC_SA_COUNTER_INFO.  The SYNC_SA_COUNTER_INFO
   information can be used for update IKEv2 counters i.e. message ids
   and also IPsec SA replay counters.

   If there are many IPsec SAs and all IPsec SA counters cannot be
   synchronized with a single counter sync exchange, then another
   counter sync exchange SHOULD be send for remaining IPsec SAs, but for
   this exchnage message id would be synced IKE message id after first
   cpunter sync exchnage NOT zero.

   The peer will respond back with the notify SYNC_SA_COUNTER_INFO.  The
   SYNC_SA_COUNTER_INFO request contains NONCE data to avoid DOS attack
   due to replay of SA counter sync response.  The Nonce data send in
   SYNC_SA_COUNTER_INFO response MUST match with nonce data sent by
   newly-active member in SYNC_SA_COUNTER_INFO request.  If nonce data
   received in SYNC_SA_COUNTER_INFO response does not match with nonce
   data sent in SYNC_SA_COUNTER_INFO request, the standby i.e. newly-
   active member MUST discard this SYNC_SA_COUNTER_INFO response, and
   normal IKEv2 behaviour of re-transmitting the request and waiting for
   genuine reply from the peer SHOULD follow, before tearing down the SA
   becuase of re-transmits.


      Standby [Newly Active] Member                            Peer
      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      HDR, SK {N[SYNC_SA_COUNTER_INFO]+} -------->

                <--------- HDR, SK {N[SYNC_SA_COUNTER_INFO]+}





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6.  SA counter synchronization notify and payload types

   Below are the new notify and payload types that are defined

6.1.  SYNC_SA_COUNTER_INFO_SUPPORTED

   SYNC_SA_COUNTER_INFO_SUPPORTED: This notify is included in the
   IKE_AUTH request by the peer to indicate the support for IKEv2/IPsec
   SA counter synchronization mechanism described in this document.


                             1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Next Payload  |C|  RESERVED   |         Payload Length        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Protocol ID(=0)| SPI Size (=0) |      Notify Message Type      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                      SYNC_SA_COUNTER_INFO_SUPPORTED

   The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size', and
   'Notify Message Type' fields are the same as described in Section 3
   of [IKEv2bis].  The 'SPI Size' field MUST be set to 0 to indicate
   that the SPI is not present in this message.  The 'Protocol ID' MUST
   be set to 0, since the notification is not specific to a particular
   security association.  'Payload Length' field is set to the length in
   octets of the entire payload, including the generic payload header.
   The 'Notify Message Type' field is set to indicate the
   SYNC_SA_COUNTER_INFO_SUPPORTED payload.

6.2.  SYNC_SA_COUNTER_INFO

   SYNC_SA_COUNTER_INFO : This payload type is defined to sync the SA
   counter information among newly-active [standby] member and the peer.
   The SYNC_SA_COUNTER_INFO payload can be used to synchronize IKE SA
   counter and IPsec SA counters as well.  So, multiple payloads of this
   type can be used in the single exchange where one payload is used to
   sync the IKE SA counter information, another payload can be used to
   sync the Child SA [ e.g.  ESP, AH etc] information.










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            1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Next Payload  |M|  RESERVED   |         Payload Length        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Protocol ID    | SPI Size      | # of SPI's    |Counter Size   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~                                                               ~
       |                                                               |
       ~                     Nonce Data                                ~
       |                                                               |
       ~                                                               ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             EXPECTED_SEND_REQ_MESSAGE_ID                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             EXPECTED_RECV_REQ_MESSAGE_ID                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            SPI                                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~            Last Counter                                       ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           SYNC_SA_COUNTER_INFO

   It contains the following data.
   o  Protocol ID (1 octet) - Must be 1 for an IKE SA, 2 for AH, or 3
      for ESP.
   o  SPI Size (1 octet) - Length in octets of the SPI as defined by the
      protocol ID.  It MUST be zero for IKE or four for AH and ESP.
   o  # of SPIs (1 octet) - The number of SPIs contained in this
      payload.  The size of each SPI is defined by the SPI Size field.
      It MUST be zero if protocol is IKE.
   o  Counter Size (1 octet) is the size of IPsec SA counter in octets.
      It is 4 if the Extended Sequence Numbers option is not set for the
      SAs described in this payload, or 8 otherwise.  It MUST be zero if
      protocol is IKE.
   o  Nonce Data (16 octets) - The nonce data MUST be present if
      protocol is IKE.  The nonce data is used to counter the replay of
      SYNC_SA_COUNTER_INFO response by the attacker.
   o  EXPECTED_SEND_REQ_MESSAGE_ID (4 octets) : This MUST be present
      only if protocol ID is IKE.  This field is used by the sender of
      this notify, to indicate the message Id it will use in the next
      request, t that it will send to the peer.  It MUST be present only
      in SA counter synchronization response and MUST be ignored in SA



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      counter synchronization request.
   o  EXPECTED_RECV_REQ_MESSAGE_ID(4 octets) : This field is used by the
      sender of this notify, to indicate the message Id it can accept in
      the next request, received from the peer.This data MUST be present
      only in response and MUST be ignored if present in REQUEST.This
      MUST be present only if protocol ID is IKE.
   o  SPI (4 octets) is the Security Parameter Index of the outbound SA
      for the sender, or the inbound SA for the receiver.
   o  Last Counter (4 or 8 octets) is the counter number of the last
      packet sent.  The receiver MUST drop any IPsec packet with replay
      counter lower than this.
   o  M (More - 1 bit) - This flag MUST be set when there are some IPsec
      are left to be synced, but can not be send due to packet size or
      some other limitation.  When M bit is zero it, it tell it is last
      SA counter sync message.


7.  Details of implementation

   The message Id used in this exchange MUST be zero so that it is not
   vaildated upon receipt.  Message Id zero MUST be permitted only for
   informational exchange that would have NOTIFY of type
   SYNC_SA_COUNTER_INFO.  If any packet uses the message Id Zero,
   without having this Notify along with the Nonce payload, then such
   packets MUST be discarded upon decryption.  No other payloads are
   allowed in this Informational exchange.

   The standby member can initiate the synchronization of IKEv2 Message
   Id's
   o  When it receives the bad IKEv2/IPsec packet.  The 'bad" IKEv2/
      IPsec packet means a packet outside receive window.
   o  When it has to send an IKEv2/IPsec packet after failover event.
   o  It has just got the control from active member and would require
      to update the values before-hand, so that it need not start this
      exchange at the time of sending/receiving the request.

   The standby member can initiate the synchronization of IPsec SA
   Counters
   o  If there is traffic using the IPsec SA in the recent past and
      there could be stale replay counter at standby member

   Since there can be many sessions at Standby member, and sending
   exchanges from all of the sessions can cause throttling, the standby
   member can choose to initiate the exchange when it has to send or
   receive the request.  Thus the trigger to initiate this exchange
   depends on the requirement/discretion of the standby member.

   The member which has not announced its capability



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   SYNC_SA_COUNTER_INFO_SUPPORTED MUST NOT send/receive the notify
   SYNC_SA_COUNTER_INFO.

   If a peer gets SYNC_SA_COUNTER_INFO request even though it did not
   announce its capability in IKE_AUTH exchange, then it MUST ignore
   this message.


8.  Step-by-Step details

   The step by step details of the synchronisation of IKE message Id is
   as follows.
   o  Active member and peer device establish the session .  They
      announce the capability to sync the counter info by sending
      SYNC_SA_COUNTER_INFO_SUPPORTED notify in AUTH Exchange.
   o  Active member dies and Stand-by member takes over. .  Stand-by
      Member sends its own idea of the IKE Message ID (its side) to
      peer.
   o  The peer will send its EXPECTED_SEND_REQ_MESSAGE_ID and
      EXPECTED_RECV_REQ_MESSAGE_ID.  Since the message Id values
      received are higher than values at the stand-by member , itwould
      update its local values of message Id's with the received values.
   o  The peer should not wait for pending response while responding
      with this message Id values.  For example if window size is 5 and
      peer window is 3-7 and if peer has sent requests 3, 4,5,6,7 and
      but got response only for 4,5,6,7 but not 3 then it should send
      the EXPECTED_SEND_REQ_MESSAGE_ID as 8 and should not wait for
      response of 3 anymore.
   o  The peer should not wait for pending request also.  For example if
      window size is 5 and peer window is 3-7 and if peer has received
      requests 4,5,6,7 but not 3 then it should send the
      EXPECTED_RECV_REQ_MESSAGE_ID as 8 and should not wait for 3
      anymore.

   The step by step details of the synchronisation of IPsec SA Counter
   synchronization is as follows.
   o  Active member and peer device establish the session .  They
      announce the capability to sync the counter info by sending
      SYNC_SA_COUNTER_INFO_SUPPORTED notify in AUTH Exchange.
   o  Active member dies and Stand-by member takes over.  Stand-by
      Member increments its values of Outbound SA Counters for each
      IPsec SA and sends them to the peer.
   o  The peer will update its Inbound SA Counter corresponding to each
      IPsec SA and send its Outbound SA Counter value for each IPsec SA
      on it.
   o  If replay counters were bumped by large amount, we MAY slowly do
      child sa rekey to reset counter when member is less loaded after
      failover event.



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9.  Security Considerations

   There can be two types of DOS attacks.
   o  Replay of Message SYNC Request.  This can be countered by rate
      limiting the number of such requests a peer can receive.  The rate
      limiting can be done either by number or the time delay between
      which Message SYNC request can be received or both.These options
      are configurable.
   o  Replay of Message SYNC Response.  This can be countered by sending
      the NONCE data along with the SYNC_SA_COUNTER_INFO notify.  The
      same NONCE data has to be returned in response.  Thus the standby
      member can accept the reply only for the current request.  After
      it receives the response, it MUST not accept the same response
      again and MUST drop the response.


10.  Interaction with other drafts

   The primary assumption of IKEv2/IPsec SA Counter Synchronization
   prososal is IKEv2 SA has been established between active member of
   Hot Standby Cluster and peer, after that the failover event occurred
   and now standby member has "become" active.  It also assumes the
   IKEv2 SA state was synced between active and standby member of the
   Hot Standby Cluster before the failover event.
   o  Session Resumption.  Session resumption assumes that peer i.e.
      client or initiator detects the need to re-establish the session.
      In IKEv2/IPsec SA counter cynchronization, standby member which
      becomes active i.e. gateway or responder detects the need to
      synchronize the SA counter after the failover event.  Also in Hot
      Standby Cluster, peer establishes the IKEv2/IPsec session with
      single cluster's IP address, so peer normally does not detect the
      event of failover in the cluster until standby member took very
      long to become active and IKEv2 SA times out via liveness check.
      So, session resumption and SA counter synchronization after
      failover are mutually exclusive.
   o  This document describes the operation of tightly coupled clusters,
      which are the common way of building IPsec clusters.  In these
      clusters, all members appear to the peer as one gateway,
      specifically they share a single IP address.  High availability
      can also be provided by loosely coupled clusters (for lack of a
      better term), which are a group of gateways that do not share an
      IP address and do not synchronize state.  In this architecture,
      the client can use Session Resumption to fail-over from one
      cluster member to another.  Specifically this requires:
      *  Support of session resumption on peers and gateways.
      *  A common session resumption ticket format on all gateways (not
         currently standardized).




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      *  Configuration on the peers of the group of gateways that
         constitute the cluster.
   o  Redirect.  Redirect mechanism for load-balancing can be used
      during init (IKE_SA_INIT) and auth (IKE_AUTH) and after session
      establishment.  While SA counter sync is used after IKE SA has
      been established and failover event has occurred.  So it is
      mutually exclusive with redirect during init and auth.  The
      redirect after session established is used for timed or planned
      shutdown/maintenance.  The failover event can not be detected on
      active member beforehand and so using redirect after session
      establishment is not possible in case of failover.  So, Redirect
      and SA counter synchronization after failover are mutually
      exclusive.
   o  Crash detection.  Either SA counter information sync or crash
      detection approach can be taken by standby member on failover
      event.


11.  IANA Considerations

   This document introduces two new IKEv2 Notification Message types as
   described in Section 6.The new Notify Message Types must be assigned
   values between 16396 and 40959.
   o  SYNC_SA_COUNTER_INFO_SUPPORTED
   o  SYNC_SA_COUNTER_INFO


12.  Acknowledgements

   This draft is the combined effort of IPSECME WG assigned HA Design
   team which consists of the following members (in alphabetical order)
   Dacheng Zhang, Min Huang, Raj Singh, Yaron Sheffer and Yoav Nir. I
   would like to thank Pratima Sethi and Frederic Detienne for their
   valuable reviews and suggestions.


13.  References

13.1.  Normative References

   [IKEv2bis]
              Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
              "Internet Key Exchange Protocol: IKEv2",
              draft-ietf-IPsecme-ikev2bis (work in progress), May 2010.

   [IPsec Cluster Problem Statement]
              Nir, Y., "IPsec Cluster Problem Statement", July 2010.




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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

13.2.  Informative References

   [RFC5685]  Devarapalli, V. and K. Weniger, "Redirect Mechanism for
              IKEv2", RFC 5685, November 2009.

   [RFC5723]  Sheffer, Y. and H. Tschofenig, "IKEv2 Session Resumption",
              RFC 5723, January 2010.


Author's Address

   Kalyani Garigipati
   Cisco Systems, Inc.
   SEZ Unit, Cessna Business Park
   Bangalore, Karnataka  560025
   India

   Phone: +91 80 4426 4831
   Email: kagarigi@cisco.com





























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