One document matched: draft-nir-ike-qcd-00.xml
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<rfc ipr="full3978" docName="draft-nir-ike-qcd-00.txt" category="std">
<front>
<title abbrev="Quick Crash Detection">A Quick Crash Detection Method for IKE</title>
<author initials="Y." surname="Nir" fullname="Yoav Nir">
<organization abbrev="Check Point">Check Point Software Technologies Ltd.</organization>
<address>
<postal>
<street>5 Hasolelim st.</street>
<city>Tel Aviv</city>
<code>67897</code>
<country>Israel</country>
</postal>
<email>ynir@checkpoint.com</email>
</address>
</author>
<date year="2008"/>
<area>Security Area</area>
<keyword>Internet-Draft</keyword>
<abstract>
<t> This document describes an extension to the IKEv2 protocol that allows for faster crash
recovery using a saved token.</t>
<t> When an IPsec tunnel between two IKEv2 implementations is disconnected due to a restart
of one peer, it can take as much as several minutes for the other peer to discover that the
reboot has occurred, thus delaying recovery. In this text we propose an extension to the
protocol, that allows for recovery within a few seconds of the reboot.</t>
</abstract>
</front>
<middle>
<!-- ====================================================================== -->
<section anchor="introduction" title="Introduction">
<t> IKEv2, as described in <xref target="RFC4306"/> has a method for recovering from a reboot
of one peer. As long as traffic flows in both directions, the rebooted peer should
re-establish the tunnels immediately. However, in many cases the rebooted peer is a VPN
gateway that protects only servers, or else the non-rebooted peer has a dynamic IP address.
In such cases, the rebooted peer will not re-establish the tunnels.</t>
<t> <xref target="SCR"/> describes the current procedure, and explains why crash recovery can
take up to several minutes. The method proposed here, is to send a token in the IKE_AUTH
exchange that establishes the tunnel. That token can be maintained on the peer in some kind
of persistent storage such as a disk or a database, and can be used to delete the IKE SA
on the non-rebooted peer after a crash. Deleting the IKE SA results is a quick
re-establishment of the IPsec tunnel.</t>
<section anchor="mustshouldmay" title="Conventions Used in This Document">
<t>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 <xref target="RFC2119"/>.</t>
</section>
</section>
<section anchor="SCR" title="RFC 4306 Crash Recovery">
<t> When one peer reboots, the other peer does not get any notification, so IPsec traffic
can still flow. The rebooted peer will not be able to decrypt it, however, and the only
remedy is to send an unprotected INVALID_SPI notification as described in section 3.10.1
of <xref target="RFC4306"/>. That section also describes the processing of such a
notification: "If this Informational Message is sent outside the context of an IKE_SA,
it should be used by the recipient only as a "hint" that something might be wrong (because
it could easily be forged)."</t>
<t> Since the INVALID_SPI can only be used as a hint, the non-rebooted peer has to determine
whether the IPsec SA, and indeed the parent IKE SA are still valid. The method of doing
this is described in section 2.4 of <xref target="RFC4306"/>. This method, called
"liveness check" involves sending a protected empty INFORMATIONAL message, and awaiting a
response. This procedure is sometimes referred to as "Dead Peer Detection" or DPD.</t>
<t> Section 2.4 does not mandate how many times the INFORMATIONAL message should be
retransmitted, or for how long, but does recommend the following: "It is suggested that
messages be retransmitted at least a dozen times over a period of at least several minutes
before giving up on an SA". Clearly, implementations differ, but all will take a significant
amount of time.</t>
</section>
<section anchor="outline" title="Protocol Outline">
<t> Supporting implementations will send a notification, called a "QCD token", as described
in <xref target="format_notif"/> in the last packets of the IKE_AUTH exchange.
These are the final request and final response that contain the AUTH payloads. The
generation of these tokens is a local matter for implementations, but considerations are
described in <xref target="tokengen"/>. Implementations that send such a token will be
called "token makers".</t>
<t> A supporting implementation receiving such a token SHOULD store it in such a way, that
it will survive a reboot. If the implementation is part of a configuration where there is
a backup gateway as described in <xref target="backupgw"/> (such configurations are often
referred to as high-availability), then the persistent storage module SHOULD be accessible to
all implementations within the configuration. An implementation supporting this part of
the protocol will be called "token taker".</t>
<t> When a token taker receives a protected IKE request message with unknown IKE SPIs, it
MUST scan its saved token store. If a token matching the IKE SPIs is found, it SHOULD be
sent to the requesting peer in an unprotected IKE message as described in
<xref target="format_info"/>.</t>
<t> When a token maker receives the QCD token in an unprotected notification, it MUST verify
that the TOKEN_SECRET_DATA field is associated with the IKE SPIs in the IKE_SPI fields
of the IKE packet. If the verification fails, it SHOULD log the event. If it succeeds,
it MUST delete the IKE SA associated with the IKE_SPI fields, and all dependant child SAs.
This event MAY also be logged. The token maker MUST accept such tokens from any address,
so as to allow different kinds of high-availability configuration of the token taker.</t>
<t> A supporting implementation MAY immediately create new SAs using an Initial exchange,
or it may wait for subsequent traffic to trigger the creation of new SAs.</t>
<t> There is ongoing work on IKEv2 Session Resumption <xref target="resumption"/>. See
<xref target="int_resume"/> for a short discussion about this protocol's interaction with
session resumption.</t>
</section>
<section anchor="format" title="Formats and Exchanges">
<section anchor="format_notif" title="Notification Format">
<t> The notification payload called "QCD token" is formatted as follows:<figure>
<artwork><![CDATA[
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 ! SPI Size ! QCD Token Notify Message Type !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ TOKEN_SECRET_DATA ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure></t>
<t><list style="symbols">
<t>Protocol ID (1 octet) MUST contain 1, as this message is related to an IKE SA.</t>
<t>SPI Size (1 octet) MUST be zero, in conformance with <xref target="RFC4306"/>.</t>
<t>QCD Token Notify Message Type (2 octets) - Must be xxxxx, the value assigned for QCD
token notifications. TBA by IANA.</t>
<t>TOKEN_SECRET_DATA (16-256 octets) contains a generated token as described in
<xref target="tokengen"/>.</t>
</list></t>
</section>
<section anchor="format_auth" title="Authentication Exchange">
<t> For clarity, only the EAP version of an AUTH exchange will be presented here. The
non-EAP version is very similar. The figure below is based on appendix A.3 of
<xref target="RFC4718"/>.<figure>
<artwork><![CDATA[
first request --> IDi,
[N(INITIAL_CONTACT)],
[[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+],
[IDr],
[CP(CFG_REQUEST)],
[N(IPCOMP_SUPPORTED)+],
[N(USE_TRANSPORT_MODE)],
[N(ESP_TFC_PADDING_NOT_SUPPORTED)],
[N(NON_FIRST_FRAGMENTS_ALSO)],
SA, TSi, TSr,
[V+]
first response <-- IDr, [CERT+], AUTH,
EAP,
[V+]
/ --> EAP
repeat 1..N times |
\ <-- EAP
last request --> AUTH
[N(QCD_TOKEN)]
last response <-- AUTH,
[N(QCD_TOKEN)]
[CP(CFG_REPLY)],
[N(IPCOMP_SUPPORTED)],
[N(USE_TRANSPORT_MODE)],
[N(ESP_TFC_PADDING_NOT_SUPPORTED)],
[N(NON_FIRST_FRAGMENTS_ALSO)],
SA, TSi, TSr,
[N(ADDITIONAL_TS_POSSIBLE)],
[V+]
]]></artwork>
</figure></t>
<t> Note that the QCD_TOKEN notification is marked as optional because it is not required
by this specification that every implementation be both token maker and token taker.
If only one peer sends the QCD token, then a reboot of the other peer will not be
recoverable by this method. This may be acceptable if traffic typically originates from
the other peer.</t>
<t> In any case, the lack of a QCD_TOKEN notification MUST NOT be taken as an indication
that the peer does not support this standard. Conversely, if a peer does not understand
this notification, it will simply ignore it. Therefore a peer MAY send this notification
freely, even if it does not know whether the other side supports it.</t>
</section>
<section anchor="format_info" title="Informational Exchange">
<t> This informational exchange is non-protected, and is sent as a response to a protected
IKE request, which uses an IKE SA that is unknown. <figure>
<artwork><![CDATA[
request --> N(QCD_TOKEN)
response <--
]]></artwork>
</figure></t>
<t> The QCD_TOKEN is the only notification in the request. Similar to the description
in section 2.21 of <xref target="RFC4306"/>, The IKE SPI and message ID fields in the
packet headers are taken from the protected IKE request.</t>
<t> If the QCD_TOKEN verifies OK, an empty response MUST be sent. If the QCD_TOKEN
cannot be validated, a response SHOULD NOT be sent. <xref target="tokengen"/>
defines token verification.</t>
</section>
</section>
<section anchor="tokengen" title="Token Generation and Verification">
<t> No token generation method is mandated by this document. Two methods are documented in
<xref target="tg1"/> and <xref target="tg2"/>, but they only serve as examples.</t>
<t> The following lists the requirements from a token generation mechanism:<list style="symbols">
<t> Tokens should be at least 16 octets log, and no more than 256 octets long, to
facilitate storage.</t>
<t> It should not be possible for an external attacker to guess the QCD token generated
by an implementation. Cryptographic mechanisms such as PRNG and hash functions are
RECOMMENDED.</t>
<t> The peer that generated the QCD token, should be able to immediately verify it,
provided that the IKE SPIs are given, and that the IKE SA has not expired or been
otherwise deleted.</t>
</list></t>
<section anchor="tg1" title="A Stateful Method of Token Generation">
<t> This describes a stateful method of generating a token:<list style="symbols">
<t> Before sending the QCD token, 32 random octets are generated using a secure random
number generator or a PRNG.</t>
<t> Those 32 bytes are used as the TOKEN_SECRET_DATA field, and stored as part of the
IKE SA.</t>
<t> For verification, the IKE implementation simply retrieves the IKE SA, and compares
the TOKEN_SECRET_DATA field from the notification to the TOKEN_SECRET_DATA field
stored with the SA.</t>
</list></t>
</section>
<section anchor="tg2" title="A Stateless Method of Token Generation">
<t> This describes a stateless method of generating a token.<list style="symbols">
<t> At startup, the IKE implementation generates a 32-octet random buffer using a
cryptographically secure PRNG. This buffer is called the QCD_SECRET.</t>
<t> For each QCD token, the TOKEN_SECRET_DATA field is generated by calculating a
SHA-256 hash over a concatenation of the QCD_SECRET and the IKE SPI as follows:<figure>
<artwork><![CDATA[
TOKEN_SECRET_DATA = HASH(QCD_SECRET | SPI-I | SPI-R)
]]></artwork>
</figure></t>
<t> Verification uses the same calculation, and works even if the IKE SA has been
deleted. Still, if the IKE SA is no longer valid, the notification MUST NOT be
acknowledged, as this could be used in an attempt to guess the QCD_SECRET.</t>
</list></t>
</section>
<section anchor="toklifetime" title="Token Lifetime">
<t> The token is associated with a single IKE SA, and SHOULD be deleted when the SA is
deleted or expires. More formally, the token is associated with the pair (SPI-I, SPI-R).</t>
</section>
</section>
<section anchor="backupgw" title="Backup Gateways">
<t> Making crash recovery quick is important, but since rebooting a gateway takes a non-zero
amount of time, many implementations choose to have a stand-by gateway ready to take over
as soon as the primary gateway fails for any reason. </t>
<t> If such a configuration is available, it is RECOMMENDED that the persistent storage be
shared between the primary and backup gateway. This has the effect of having the crash
recovery available immediately. This recommendation is especially useful if the primary
and backup gateway either share an external IP address or reside on the same LAN. If they
are geographically remote, this may be less practical.</t>
</section>
<section anchor="whynot" title="Alternative Solutions">
<section anchor="saveikesa" title="Why not Save the Entire IKE SA">
<t> IKEv2 does not assume the existence of a persistent storage module. If we are adding
such a module, why not use it to save the entire IKE SA across reboots, nullifying the
need for a crash recovery procedure?</t>
<t> There are several reasons why we believe that this is not a good idea:<list style="numbers">
<t> A token is only 16-256 octets, and is much more compact than all the data
needed to store an IKE SA.</t>
<t> A token is valid for the life of an IKE SA. An IKE SA state is updated whenever a
message is sent, because of the requirement to maintain the sequence of message IDs.
It may not be acceptable to update the persistent storage whenever an IKE message is
sent.</t>
<t> A reboot is usually an unpredictable event, and as such, we cannot know how long it
will last. By the time the machine has rebooted, the peer may have attempted some type
of protected exchange (liveness check, create-child-SA or delete), timed out, and deleted
the SA. It is far better to reboot without SAs and with only a token for quick
recovery.</t>
</list></t>
</section>
<section anchor="newikesa" title="Initiating a new IKE SA">
<t> Instead of sending a QCD token, we could have the rebooted implementation start an
Initial exchange with the peer, including the INITIAL_CONTACT notification. This would
have the same effect, instructing the peer to erase the old IKE SA, as well as establishing
a new IKE SA with fewer rounds.</t>
<t> The disadvantage here, is that in IKEv2 an authentication exchange MUST have
a piggy-backed Child SA set up. Since our use case is such that the rebooted implementation
does not have traffic flowing to the peer, there are no good selectors for such a Child
SA.</t>
<t> Additionally, when authentication is asymmetric, such as when EAP is used, it is not
possible for the rebooted implementation to initiate IKE.</t>
</section>
</section>
<section anchor="int_resume" title="Interaction with IFARE">
<t> IFARE, specified in <xref target="resumption"/> proposes to make setting up a new IKE
SA consume less computing resources. This is particularly useful in the case of a remote
access gateway that has many tunnels. A failure of such a gateway would require all these
many remote access clients to establish an IKE SA either with the rebooted gateway or
with a backup gateway. This tunnel re-establishment should occur within a short period of
time, creating a burden on the remote access gateway. IFARE addresses this problem by
having the clients store an encrypted derivative of the IKE SA for quick re-establishment.</t>
<t> What IFARE does not help, is the problem of detecting that the peer gateway has failed.
A failed gateway may go undetected for an unbounded amount of time, because IPsec does
not have packet acknowledgement. Before establishing a new IKE SA using IFARE, a client
MUST ascertain that the gateway has indeed failed. This could be done using either a
liveness check (as in RFC 4306) or using the QCD tokens described in this document.</t>
<t> A remote access client conforming to both specifications will generate QCD tokens,
and store the IFARE state, if provided by the gateway. A remote access gateway conforming
to both specifications will store the QCD token sent from the client. When the gateway
reboots, the client will discover this in either of two ways:<list style="numbers">
<t> The client does regular liveness checks, or else the time for some other IKE exchange
has come. The IKE times out after several minutes, if the gateway does not finish
rebooting in time. In this case QCD does not help.</t>
<t> Either the primary gateway or a backup gateway (see <xref target="backupgw"/>)
is ready and sends a QCD token to the client. In that case the client will quickly
re-establish the IPsec tunnel, either with the rebooted primary gateway, the backup
gateway as described in this document or another gateway as described in <xref target="resumption"/>
</t></list></t>
<t> The full combined protocol looks like this:<figure>
<artwork><![CDATA[
Initiator Responder
----------- -----------
HDR, SAi1, KEi, Ni -->
<-- HDR, SAr1, KEr, Nr, [CERTREQ]
HDR, SK {IDi, [CERT,]
[CERTREQ,] [IDr,]
AUTH, N(QCD_TOKEN)
SAi2, TSi, TSr,
N(TICKET_REQUEST)} -->
<-- HDR, SK {IDr, [CERT,] AUTH, SAr2, TSi,
TSr, N(TICKET_OPAQUE)
[,N(TICKET_GATEWAY_LIST)]}
---- Reboot -----
HDR, {} -->
<-- HDR, N(QCD_Token)
HDR, Ni, N(TICKET_OPAQUE),
[N+,], SK {IDi, [IDr,]
SAi2, TSi, TSr,
[CP(CFG_REQUEST)]} -->
<-- HDR, SK {IDr, Nr, SAr2, [TSi, TSr],
[CP(CFG_REPLY)]}
]]></artwork>
</figure></t>
</section>
<section anchor="operation" title="Operational Considerations">
<t> To support "token taker" part of this standard, an implementation needs to have access
to a persistent storage module. This could be an internal hard disk, a local or remote
database application, or any other method that persists across reboots. This storage
module and the data links between the storage module and the IKE module must meet the
performance requirements of the IKE module. The storage module MUST support insertion and
deletion rates equal to peek IKE SA setup rates and it SHOULD support query rates that are
fast enough.</t>
<t> See <xref target="security"/> for security considerations for this storage mechanism.</t>
<t> Throughout this document, we have referred to reboot time alternatingly as the time that
the implementation crashes and the time when it is ready to process IPsec packets and IKE
exchanges. Depending on the hardware and software platforms and the cause of the reboot,
rebooting may take anywhere from a few seconds to several minutes. If the implementation
is down for a long time, the benefit of this protocol extension are reduced. For this reason
critical systems should implement backup gateways as described in <xref target="backupgw"/>.
Note that the lower-case should in the previous sentence is intentional, as we do not specify
this in the sense of RFC 2119.</t>
<t> Implementing the "token taker" side of QCD makes sense for IKE implementation where protected
connections originate from the peer, such as inter-domain VPNs and remote access gateways.
Implementing the "token maker" side of QCD makes sense for IKE implementations where protected
connections originate, such as inter-domain VPNs and remote access clients.</t>
<t> To clarify the requirements: <list style="symbols">
<t> A remote-access client MUST be a token maker and MAY be a token taker.</t>
<t> A remote-access gateway MAY be a token maker and MUST be a token taker.</t>
<t> An inter-domain VPN gateway MUST be both token maker and token taker.</t></list></t>
<t> In order to limit the effects of DoS attacks, an implementation SHOULD limit the rate
of queries into the token storage so as not to overload it. If excessive amounts of IKE
requests protected with unknown IKE SPIs arrive, the IKE module SHOULD revert to the
behavior described in section 2.21 of <xref target="RFC4306"/> and either send an
INVALID_IKE_SPI notification, or ignore it entirely.</t>
</section>
<section anchor="security" title="Security Considerations">
<t> Tokens MUST be hard to guess. This is critical, because if an attacker can guess the
token associated with the IKE SA, she can tear down the IKE SA and associated tunnels at
will. When the token is delivered in the IKE_AUTH exchange, it is encrypted. When it is
sent back in an informational exchange it is not encrypted, but that is the last use
of that token.</t>
<t> An aggregation of some tokens generated by one peer together with the related IKE SPIs
MUST NOT give an attacker the ability to guess other tokens. Specifically, if one peer
does not properly secure the QCD tokens and an attacker gains access to them, this
attacker MUST NOT be able to guess other tokens generated by the same peer. This is the
reason that the QCD_SECRET in <xref target="tg2"/> needs to be long.</t>
<t> The persistent storage MUST be protected from access by other parties. Anyone gaining
access to the contents of the storage will be able to delete all the IKE SAs described
in it.</t>
<t> The tokens associated with expired and deleted IKE SAs MUST be deleted from the storage,
so that a future compromise of the storage does not reveal enough tokens to facilitate
an attack against the QCD tokens.</t>
<t> The QCD token is sent by the rebooted peer in an unprotected message. A message like
that is subject to modification, deletion and replay by an attacker. However, these
attacks will not compromise the security of either side. Modification is meaningless
because a modified token is simply an invalid token. Deletion will only cause the
protocol not to work, resulting in a delay in tunnel re-establishment as described in
<xref target="SCR"/>. Replay is also meaningless, because the IKE SA has been deleted
after the first transmission.</t>
</section>
<section anchor="iana" title="IANA Considerations">
<t> IANA is requested to assign a notify message type from the error types range
(43-8191) of the "IKEv2 Notify Message Types" registry with name
"QUICK_CRASH_DETECTION".</t>
</section>
<section anchor="ack" title="Acknowledgements">
<t> We would like to thank Hannes Tschofenig and Yaron Sheffer for their comments about
IFARE.</t>
</section>
<section anchor="history" title="Change Log">
<t> This section lists all changes in this document</t>
<t> NOTE TO RFC EDITOR : Please remove this section in the final RFC</t>
<section anchor="history01" title="Changes from draft-nir-qcr-00">
<t><list style="symbols">
<t> Changed name to reflect that this relates to IKE. Also changed from quick crash
recovery to quick crash detection to avoid confusion with IFARE.</t>
<t> Added more operational considerations. </t>
<t> Added interaction with IFARE.</t>
<t> Added discussion of backup gateways.</t>
</list></t>
</section>
</section>
</middle>
<!-- ====================================================================== -->
<back>
<references title="Normative References">
<reference anchor='RFC2119'>
<front>
<title abbrev='RFC Key Words'>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='S.' surname='Bradner' fullname='Scott Bradner'>
<organization>Harvard University</organization>
<address>
<postal>
<street>1350 Mass. Ave.</street>
<street>Cambridge</street>
<street>MA 02138</street>
</postal>
<phone>- +1 617 495 3864</phone>
<email>sob@harvard.edu</email>
</address>
</author>
<date year='1997' month='March' />
<area>General</area>
<keyword>keyword</keyword>
</front>
<seriesInfo name='BCP' value='14' />
<seriesInfo name='RFC' value='2119' />
<format type='TXT' octets='4723' target='ftp://ftp.isi.edu/in-notes/rfc2119.txt' />
<format type='HTML' octets='16553' target='http://xml.resource.org/public/rfc/html/rfc2119.html' />
<format type='XML' octets='5703' target='http://xml.resource.org/public/rfc/xml/rfc2119.xml' />
</reference>
<reference anchor='RFC4306'>
<front>
<title>Internet Key Exchange (IKEv2) Protocol</title>
<author initials='C.' surname='Kaufman' fullname='C. Kaufman'>
<organization /></author>
<date year='2005' month='December' />
</front>
<seriesInfo name='RFC' value='4306' />
<format type='TXT' target='http://www.ietf.org/rfc/rfc4306.txt' />
<format type='HTML' target='http://xml.resource.org/public/rfc/html/rfc4306.html' />
<format type='XML' target='http://xml.resource.org/public/rfc/xml/rfc4306.xml' />
</reference>
<reference anchor='RFC4718'>
<front>
<title>IKEv2 Clarifications and Implementation Guidelines</title>
<author initials='P.' surname='Eronen' fullname='P. Eronen'>
<organization>Nokia</organization></author>
<author initials='P.' surname='Hoffman' fullname='P. Hoffman'>
<organization>VPN Consortium</organization></author>
<date year='2006' month='October' />
</front>
<seriesInfo name='RFC' value='4718' />
<format type='TXT' target='http://www.ietf.org/rfc/rfc4718.txt' />
<format type='HTML' target='http://xml.resource.org/public/rfc/html/rfc4718.html' />
<format type='XML' target='http://xml.resource.org/public/rfc/xml/rfc4718.xml' />
</reference>
</references>
<references title="Informative References">
<reference anchor='resumption'>
<front>
<title>IPsec Gateway Failover Protocol</title>
<author initials='Y.' surname='Sheffer' fullname='Y. Sheffer'>
<organization>Check Point</organization></author>
<author initials='H.' surname='Tschofenig' fullname='H. Tschofenig'>
<organization>Nokia Siemens Networks</organization></author>
<author initials='L.' surname='Dondeti' fullname='L. Dondeti'>
<organization>QUALCOMM, Inc.</organization></author>
<author initials='V.' surname='Narayanan' fullname='L. Narayanan'>
<organization>QUALCOMM, Inc.</organization></author>
<date year='2008' month='March' />
</front>
<seriesInfo name='Internet-Draft' value='draft-sheffer-ipsec-failover-03' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-sheffer-ipsec-failover-03.txt' />
</reference>
</references>
<!-- ====================================================================== -->
</back>
</rfc>
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