wdiff draft-ietf-ipsecme-ipsecha-protocol-02.txt draft-ietf-ipsecme-ipsecha-protocol-03.txt

Network Working Group R. Singh, Ed.
Internet-Draft G. Kalyani
Intended status: Standards Track Cisco
Expires: April 28, August 12, 2011 Y. Nir
Check Point
Y. Sheffer
Independent
D. Zhang
Huawei
October 25, 2010
February 8, 2011

Protocol Support for High Availability of IKEv2/IPsec
draft-ietf-ipsecme-ipsecha-protocol-02
draft-ietf-ipsecme-ipsecha-protocol-03

Abstract

The IPsec protocol suite is widely used for the deployment of virtual
private networks (VPNs). business-critical network
traffic. In order to make such VPNs IPsec deployments highly available, more
scalable and failure-resistant, these VPNs they are often implemented as IPsec
High Availability (HA) clusters. However there are many issues in
IPsec HA clustering, and in particular in IKEv2 clustering. An
earlier document, "IPsec Cluster Problem Statement", enumerates the
issues encountered in the IKEv2/IPsec HA cluster environment. This
document attempts to resolve these issues with the least possible
change to the protocol.

This document proposes an extension to the IKEv2 protocol to solve
the main issues of "IPsec Cluster Problem Statement" in the commonly
deployed hot-standby cluster, and provides implementation advice for
other issues. The main issues to be solved are the synchronization
of IKEv2 Message ID counters, and of IPsec Replay Counters.

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 April 28, August 12, 2011.

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 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 5
3. Issues Resolved from IPsec Cluster Problem Statement . . . . . 5 6
4. The IKEv2/IPsec SA Counter Synchronization Problem . . . . . . 5 7
5. SA Counter Synchronization Solution . . . . . . . . . . . . . 8
5.1. Processing Rules for IKE Message ID Synchronization . . . 10
5.2. Processing Rules for IPsec Replay Counter
Synchronization . . . . . . 7 . . . . . . . . . . . . . . . 11
6. IKEv2/IPsec Synchronization Notification Payloads . . . . . . 9 11
6.1. The IKEV2_MESSAGE_ID_SYNC_SUPPORTED Notification . . . . . 11
6.2. The IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED Notification . . . 12
6.3. The IKEV2_MESSAGE_ID_SYNC Notification . . . . . 9
6.2. IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED . . . . . 12
6.4. The IPSEC_REPLAY_COUNTER_SYNC Notification . . . . . . 10
6.3. IKEV2_MESSAGE_ID_SYNC . . 13
7. Implementation Details . . . . . . . . . . . . . . . . . 10
6.4. IPSEC_REPLAY_COUNTER_SYNC . . . 14
8. IKE SA and IPsec SA Message Sequencing . . . . . . . . . . . . 14
8.1. Handling of Pending IKE Messages . 11
7. Implementation Details . . . . . . . . . . . . 15
8.2. Handling of Pending IPsec Messages . . . . . . . . 12
8. Step by Step Details . . . . 15
8.3. IKE SA Inconsistencies . . . . . . . . . . . . . . . . . . 13 15
9. Security Considerations Step by Step Details . . . . . . . . . . . . . . . . . . . 14 . . 15
10. Interaction with other drafts . . . . . . . . . . . . . . . . 14 16
11. Security Considerations . . . . . . . . . . . . . . . . . . . 17
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
12. 17
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
13. 18
14. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 15
13.1. 18
14.1. Draft -03 . . . . . . . . . . . . . . . . . . . . . . . . 18
14.2. Draft -02 . . . . . . . . . . . . . . . . . . . . . . . . 16
13.2. 18
14.3. Draft -01 . . . . . . . . . . . . . . . . . . . . . . . . 16
13.3. 18
14.4. Draft -00 . . . . . . . . . . . . . . . . . . . . . . . . 16
14. 19
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
14.1. 19
15.1. Normative References . . . . . . . . . . . . . . . . . . . 16
14.2. 19
15.2. Informative References . . . . . . . . . . . . . . . . . . 17 19
Appendix A. IKEv2 Message ID Sync Examples . . . . . . . . . . . 17 20
A.1. Normal Failover - Example 1 . . . . . . . . . . . . . . . 17 20
A.2. Normal Failover - Example 2 . . . . . . . . . . . . . . . 18 20
A.3. Simultaneous Failover . . . . . . . . . . . . . . . . . . 18 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 21

1. Introduction

The IPsec protocol suite, including IKEv2, is a major building block
of virtual private networks (VPNs). In order to make such VPNs
highly available, more scalable and failure-resistant, these VPNs are
implemented as IKEv2/IPsec Highly Available (HA) cluster. However
there are many issues with the IKEv2/IPsec HA cluster. The problem
statement draft Section 4 enumerates the issues around the IKEv2/
IPsec HA cluster solution.

In the case of a hot-standby cluster implementation of IKEv2/IPsec
based VPNs, the IKEv2/IPsec session is first established between the
peer and the active member of the cluster. Later, the active member
continuously syncs/updates the IKE/IPsec SA state to the standby
member of the cluster. This primary SA state sync-up takes place
upon each SA bring-up and/or rekey. Performing the SA state
synchronization/update for every single IKE and IPsec message is very
costly, so normally it is done periodically. As a result, when the
failover event happens, this is first detected by the standby member
and, possibly after a considerable amount of time, it becomes the
active member. During this failover process the peer is unaware of
the failover event, and keeps sending IKE requests and IPsec packets
to the cluster, as in fact it is allowed to do because of the IKEv2
windowing feature. After the newly-active member starts, it detects
the mismatch in IKE Message ID values and IPsec replay counters and
needs to resolve this situation. Please see Section 4 for more
details of the problem.

This document proposes an extension to the IKEv2 protocol to solve
the main issues of IKE Message ID synchronization and IPsec SA replay
counter synchronization and gives implementation advice for others.
Following is a summary of the solutions provided in this document:

o IKEv2 Message ID synchronization: this is done by syncing up the
expected send and receive Message ID values with the peer, and
updating the values at the newly active cluster member.
o IPsec Replay Counter synchronization: this is done by incrementing
the cluster's outgoing SA replay counter values by a "large"
number, and synchronizing these values with
number; in addition, the newly-active member requests the peer. The peer
send its outgoing SA reply to
increment the replay counter in values it is using for the response. peer's
outgoing traffic.

Although this document describes the IKEv2 Message ID and IPsec
replay counter synchronization in the context of an IPsec HA cluster,
the solution provided is generic and can be used in other scenarios
where IKEv2 Message ID or IPsec SA replay counter synchronization may
be required.

Implementations differ on the need to synchronize the IKEv2 Message
ID and/or IPsec replay counters. Both of these problem problems are handled
separately, using a separate notification for each capability. This
provides the flexibility of implementing either or both of these
solutions.

2. 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 [RFC2119]. [1].

"SA Counter Synchronization Request/Response" are the request viz.
response of the information informational exchange defined in this document to
synchronize the IKEv2/IPsec SA counter information between one member
of the cluster and the peer.

Some of the terms listed below are reused from [RFC6027] [2] with further
clarification in the context of the current document.

o "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" member, whereas the other(s) are
referred to as "standby" members. VRRP [RFC5798] [5] is one method of
building such a cluster. The goal of the Hot Standby Cluster is that
it creates illusion
to create the illusion of a single virtual gateway to the peer(s).
o "Active Member" is the primary member in the Hot-Standby cluster.
It is responsible for forwarding packets on behalf of the virtual
gateway.
o "Standby Member" is the primary backup member. This member takes
control, i.e. becomes the active member, after the failover event.
o "Peer" is an IKEv2/IPsec endpoint that maintains a VPN an IPsec
connection with the Hot-Standby cluster. The Peer identifies the
cluster by the cluster's (single) IP address. If a failover event
occurs, the standby member of the cluster becomes active, and the
peer normally doesn't notice that failover has taken place.
o "Failover Count" is a global failover event counter maintained by
the HA cluster and incremented by 1 upon each failover event in
Although we treat the HA peer as a single entity, it may also be a
cluster. All members of the HA cluster share the failover
count.
o "Multiple failover" is the situation where, in a cluster with
three or more members, multiple failover happens events happen in rapid succession.
succession, e.g. from M1 to M2, and then to M3. It is our goal
that the implementation should be able to handle this situation,
i.e. to handle the new failover event even if it is still
processing the old failover.
o "Simultaneous failover" is the situation where two clusters have a
VPN
an IPsec connection between them, and failover happens at the both
ends at the same time. It is our goal that implementation implementations should
be able to handle simultaneous failover.

The generic term "IKEv2/IPsec SA Counters" is used throughout this
document. This term refers to both IKEv2 Message ID counters
(mandatory, and
IPsec replay counters. According to the IPsec standards, the IKEv2
Message ID counter is mandatory, and used to ensure reliable delivery
as well as to protect against message replay in IKEv2) and IKEv2; the IPsec SA
replay counters
(optional, are optional, and are used to provide the IPsec anti-replay feature). anti-
replay feature.

3. Issues Resolved from IPsec Cluster Problem Statement

The IPsec Cluster Problem Statement [RFC6027] [2] enumerates the problems
raised by IPsec clusters. The following table lists the problem
statement's sections that are resolved by this document.
o 3.2. Lots of Long Lived State
o 3.3. IKE Counters
o 3.4. Outbound SA Counters
o 3.5. Inbound SA Counters
o 3.6. Missing Synchronization 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

The main problem areas are solved using the protocol extension
defined below, and additionally below; additionally, this document provides implementation
advice for other issues, given as follows.
o Section 3.2 This section of the Problem Statement mentions that there is a
large amount of state that needs to be synchronized. However if
state is not synchronized, this is not really an interesting
cluster: failover is equivalent to a reboot of the cluster member,
and so the issue need not be solved with a protocol extensions. extension.
o 3.3, 3.4,3.5, and 3.6 are solved by this document. Please see
Section 4, for more details.
o 3.7 is an implementation problem that needs to be solved while
building IPsec clusters. However, the peers should be required to
accept multiple parallel SAs for 3.7.1.
o 3.8 can be solved by using the IKEv2 Redirect mechanism [RFC5685]. [6].
o 3.9 discusses the avoidance of collisions where the same SPI value
is used by multiple cluster members. This is outside the
document's scope since the problem needs to be solved internally
to the cluster and does not involve the peer.

4. The IKEv2/IPsec SA Counter Synchronization Problem

The IKEv2 protocol [RFC5996] [3] states that "An IKE endpoint MUST NOT exceed
the peer's stated window size for transmitted IKE requests".

All IKEv2 messages are required to follow a 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 sender's
window should not move until the oldest message it has sent from one peer to
another is
acknowledged. Loss of even a single message leads to repeated
retransmissions followed by an IKEv2 SA teardown if the
retransmissions are remain unacknowledged.

An IPsec Hot Standby Cluster is required to ensure that in the case
of failover, the standby member becomes active immediately. The
standby member is expected to have the exact value of the Message ID
counter as the active member had before failover. Even assuming the
best effort to update the Message ID values from active to standby
member, the values at the standby member can still be stale due to
the following reasons:
o The standby member is unaware of the last message that was
received and acknowledged by the previously active member, as the
failover event could have happened before the standby member could
be updated.
o The standby member does not have information about on-going
unacknowledged requests received sent by the previously active member. As
a result after the failover event, the newly active member cannot
retransmit those requests.

When a standby member takes over as the active member, it can only
initialize the Message ID values from the previously updated values.
This would make it reject requests from the peer when these values
are stale. Conversely, the standby member may end up reusing a stale
Message ID value which would 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 retransmission of requests, negating the benefits of the
high availability cluster despite the periodic update between the
cluster members.

A similar issue is also observed with IPsec anti-replay counters if
anti-replay protection/ESN protection is implemented, enabled, which is commonly the case.
Regardless of how well the ESP and AH SA counters are synchronized
from the active to the standby member, there is a chance that the
standby member would end up with stale counter values. The standby
member would then use those stale counter values when sending IPsec
packets. The peer would reject/drop such packets since when the
anti-replay protection feature is enabled, duplicate use of counters
is not allowed. Note that IPsec allows the sender to skip some
counter values and continue sending with higher counter values.

We conclude that a mechanism is required to ensure that the standby
member has correct Message ID and IPsec counter values when it
becomes active, so that sessions are not torn down as a result of
mismatched counters.

5. SA Counter Synchronization Solution

This document proposes two separate approaches to resolving the
issues of mismatched IKE Message ID values and IPsec counter values.

o In general, when the standby member becomes case of IKE Message ID values, the newly active cluster
member after and the failover event, peer negotiate a pair of new values so that future
IKE messages will not be dropped.
o For IPsec counter values, the standby newly-active member sends an authenticated IKEv2
request to and the peer, asking it to send its SA counter values.

The standby member then updates its own SA peer
both increment their respective counter values and can
resume normally sending and receiving protocol messages. values, "skipping forward"
by a large number, to ensure that no IPsec counters are ever
reused.

Although conceptually separate, the two synchronization processes
would typically take place simultaneously.

First, the peer MUST and the active member of the cluster negotiate its their
ability to support IKEv2 Message ID synchronization with the active member of the cluster and/or IPsec
Replay Counter synchronization. This is done by sending exchanging one or
both of the IKEV2_MESSAGE_ID_SYNC_SUPPORTED notification in and
IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED notifications during the IKE_AUTH
exchange.

Similarly, to support IPsec Replay Counter synchronization, When negotiating these capabilities, the peer responder MUST negotiate this capability with the active member
NOT assert support of a capability unless such support was asserted
by the cluster initiator. Only a capability whose support was asserted by sending
both parties can be used during the IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED notification in lifetime of the IKE_AUTH exchange. SA.

This per-IKE SA information is shared with the other cluster members.

Peer Active Member
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
HDR, SK {IDi, [CERT], [CERTREQ], [IDr], AUTH,
[N(IKEV2_MESSAGE_ID_SYNC_SUPPORTED),]
[N(IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED),]
SAi2, TSi, TSr} ---------->

<-------- HDR, SK {IDr, [CERT+], [CERTREQ+], AUTH,

[N(IKEV2_MESSAGE_ID_SYNC_SUPPORTED),]
[N(IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED),] SAr2, TSi, TSr}

When the peer and active member both support SA counter
synchronization, the active member MUST inform

After a failover event, the standby member of
the SA counter synchronization capability after the establishment of MAY use the IKE SA. The standby member can then use this Message ID
and/or IPsec Replay Counter synchronization capability when it
becomes the active member after a failover event. member, and provided support for the capabilities
used has been negotiated. Following that, the peer MUST respond to
any synchronization message it receives from the newly-active cluster
member, subject to the rules noted below.

After the failover event, when the standby member becomes active, it
has to request the synchronize its SA counters from with the peer. There are now
three possible cases:

1. The newly-active cluster member wishes to only perform IKE Message ID value
synchronization. In this case it initiates the synchronization request with an Informational
exchange
exchange, with Message ID zero containing either the notification
IKEV2_MESSAGE_ID_SYNC or the two notifications IKEV2_MESSAGE_ID_SYNC and IPSEC_REPLAY_COUNTER_SYNC, depending on whether the
synchronization is to be done for IKEv2 Message IDs or for both IKEv2
Message IDs and IPsec replay counters. sole notification
IKEV2_MESSAGE_ID_SYNC.
2. If the active newly-active member has wishes to perform only
negotiated synchronization of IPsec Replay Counters, the request is
sent as replay
counter synchronization, it generates a regular IKEv2
Informational exchange (i.e. with a non-zero using the current Message ID) ID values, and
containing the notification IPSEC_REPLAY_COUNTER_SYNC.

The initiator IPSEC_REPLAY_COUNTER_SYNC notification.
3. If synchronization of both counters is needed, the IKEv2 Message ID synchronization request sends
its expected send and receive Message cluster member
generates a zero-Message ID values message as in case #1, and "failover count"
in a IKEV2_MESSAGE_ID_SYNC notification. The responder compares the
received values with its local values. For both send and receive
values, The higher between the cluster member's and the local value
is selected, and sent in the response message with the notification
IKEV2_MESSAGE_ID_SYNC. The initiator now updates its send and
receive IKEv2 Message IDs to the values received in the response and
can now start a normal IKEv2 message exchange.

The initiator of an IPsec Replay Counter synchronization sends the
incremented outgoing IPsec SA reply counter value and a "failover
count" in a IPSEC_REPLAY_COUNTER_SYNC notification in IKEv2
INFORMATIONAL exchange. The responder updates its incoming IPsec SA
counter values according to the received value. The responder now
sends its own incremented outgoing IPsec SA Replay Counter value in a
synchronization response message, with the same
IPSEC_REPLAY_COUNTER_SYNC notification. The initiator can now update
its incoming IPsec SA counter to values received includes
both notifications in this message.

This figure contains the response IKE message and can start normal IPsec data traffic.

The IKEV2_MESSAGE_ID_SYNC notification payload contain nonce data to
avoid a denial-of-service (DoS) attack due to replay of exchange used for SA counter
synchronization response. The nonce values are selected randomly on
each new notification and MUST be validated by the receiver.
synchronization. The
nonce data sent in the response MUST match the nonce data sent by the
newly-active member in its request. If the nonce data received in
the response does not match the request's nonce data, following subsections describe the cluster
member MUST silently discard this response, and SHOULD revert to
normal IKEv2 behavior details of retransmitting
the request sender and waiting for a
genuine a reply from the peer. Eventually this might result in the
SA being torn down because receiver processing of excessive retransmissions. each message.

Standby [Newly Active] Member Peer
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
HDR, SK {N(IKEV2_MESSAGE_ID_SYNC),
[N(IPSEC_REPLAY_COUNTER_SYNC)]} -------->

<--------- HDR, SK {N(IKEV2_MESSAGE_ID_SYNC),
[N(IPSEC_REPLAY_COUNTER_SYNC)]} {N(IKEV2_MESSAGE_ID_SYNC)}

Alternatively, if only IPsec Replay Counter synchronization is
desired, a normal Information Informational exchange is used, where the Message
ID is non-zero:

Standby [Newly Active] Member Peer
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
HDR, SK{N(IPSEC_REPLAY_COUNTER_SYNC)} -------->

<--------- HDR, SK {N(IPSEC_REPLAY_COUNTER_SYNC)} HDR

5.1. Processing Rules for IKE Message ID Synchronization

The newly-active member sends a request containing two counter value,
one for the member (itself) and another for the peer, as well as a
random nonce. We denote the values M1 and P1. The peer responds
with a message containing two counter values, M2 and P2. The goal of
the rules below is to prevent an attacker from replaying a
synchronization message, thereby invalidating IKE messages that are
currently in process.

o M1 is the next sender's Message ID to be used by the member. M1
MUST be chosen so that it is larger than any value known to have
been used. It is RECOMMENDED to increment the known value at
least by the size of the IKE sender window.
o P1 SHOULD be 1 more than the last Message ID value received from
the peer, but may be any higher value.
o The member SHOULD communicate the sent values to the other cluster
members, so that if a second failover event takes place, the
synchronization message is not replayed. Such a replay would
result in the eventual deletion of the IKE SA (see below).
o The peer MUST reject any received synchronization message if M1 is
lower than or equal to the highest value it has seen from the
cluster. This includes any previous received synchronization
messages.
o M2 MUST be at least the higher of the received M1, and one more
than the highest sender value received from the cluster. This
includes any previous received synchronization messages.
o P2 MUST be the higher of the received P1 value, and one more than
the highest sender value used by the peer.
o The request contains a Nonce field. This field MUST be returned
in the response, unchanged. A response MUST be silently dropped
if the received Nonce does not match the one that was sent.
o Both the request and the response MUST NOT contain any additional
payloads, other than an optional IPSEC_REPLAY_COUNTER_SYNC
notification in the request.
o The request and the response MUST both be sent with a Message ID
value of zero.

5.2. Processing Rules for IPsec Replay Counter Synchronization

Upon failover, the newly-active member MUST increment its own Replay
Counter (the counter used for outgoing traffic), so as to prevent the
case of its traffic being dropped by the peer as replay. We note
that IPsec allows the replay counter to skip forward by any amount.
The estimate is based on the outgoing IPsec bandwidth and the
frequency of synchronization between cluster members. In those
implementations where it is difficult to estimate this value, the
counter can be incremented by a very large number, e.g. 2**30. In
the latter case, a rekey SHOULD follow shortly afterwards, to ensure
that the counter never wraps around.

Next, the cluster member estimates the number of incoming messages it
might have missed, using similar logic. The member sends out a
IPSEC_REPLAY_COUNTER_SYNC notification, either stand-alone or
together with a IKEV2_MESSAGE_ID_SYNC notification.

If the IPSEC_REPLAY_COUNTER_SYNC is included in the same message as
IKEV2_MESSAGE_ID_SYNC, the peer MUST process the Message ID
notification first (which might cause the entire message to be
dropped as a replay). Then, it MUST increment the replay counters
for all Child SAs associated with the current IKE SA by the amount
requested by the cluster member.

6. IKEv2/IPsec Synchronization Notification Payloads

This section lists the new notification payloads payload types defined by this
extension.

6.1. The IKEV2_MESSAGE_ID_SYNC_SUPPORTED

IKEV2_MESSAGE_ID_SYNC_SUPPORTED: Notification

This notification payload is included in the IKE_AUTH request/response request/
response to indicate support of the IKEv2 Message ID synchronization
mechanism described in this document.

The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size', and
'Notify Message Type' fields are the same as described in Section 3
of [RFC5996] . [3]. 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. The '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
IKEV2_MESSAGE_ID_SYNC_SUPPORTED, value TBD by IANA. There is no data
associated with this notification.

6.2. The IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED

IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED: Notification

This notification payload is included in the IKE_AUTH request/response request/
response to indicate support for the IPsec SA Replay Counter
synchronization mechanism described in this document.

The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size', and
'Notify Message Type' fields are the same as described in Section 3
of [RFC5996] [3] . 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. The '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
IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED, value TBD by IANA. There is no
data associated with this notification.

6.3. The IKEV2_MESSAGE_ID_SYNC

IKEV2_MESSAGE_ID_SYNC : Notification

This notification payload type (value TBD by IANA) is defined to
synchronize the IKEv2 Message ID values between the newly-active
(formerly standby) cluster member and the peer.

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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Failover Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EXPECTED_SEND_REQ_MESSAGE_ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EXPECTED_RECV_REQ_MESSAGE_ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

It contains the following data.
o Failover Count (4 octets): a running count of failover events
between cluster members, it is initialized to 0 when the cluster
is first set up, and incremented by 1 upon each failover event.
o Nonce Data (4 octets): the random nonce data. The data should be
identical in the synchronization request and response.
o EXPECTED_SEND_REQ_MESSAGE_ID (4 octets): this field is used by the
sender of this notification payload to indicate the Message ID it
will use in the next request that it will send to the other
protocol peer.
o EXPECTED_RECV_REQ_MESSAGE_ID (4 octets): this field is used by the
sender of this notification payload to indicate the Message ID it
is expecting in the next request to be received from the other
protocol peer.

6.4. The IPSEC_REPLAY_COUNTER_SYNC

IPSEC_REPLAY_COUNTER_SYNC: Notification

This notification payload type (value TBD by IANA) is defined to
synchronize the IPsec SA Replay Counters between the newly-active
(formerly standby) cluster member and the peer. Since there may be
numerous IPsec SAs established under a single IKE SA, we do not
directly synchronize the value of each one. Instead, a delta value
is sent and all Replay Counters for child Child SAs of this IKE SA are
incremented by the same value. Note that this solution requires that
all these Child SAs either use or do not use Extended Sequence
Numbers [RFC4301]. [4]. This notification is only sent by the cluster.

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 |E| |C| RESERVED | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Protocol ID(=0)| SPI Size (=0) | Notify Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outgoing Incoming IPsec SA counter delta value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The notification payload contains the following data.
o E (1 bit): The ESN bit. This MUST be 1 if
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The notification payload contains the IPsec SAs were
established with Extended Sequence Numbers. following data.
o Outgoing Incoming IPsec SA delta value (4 or 8 octects): octets): The sender will
increment requests
that the peer should increment all the Child SA Replay Counters
for its outgoing the sender's incoming (the peer's outgoing) traffic by this
value. The size of this field depends on the ESN bit: bit associated
with the Child SAs: if the ESN bit is 1, its the field's size is 8
octets, otherwise it is 4 octets. We note that this constrains
the Child SAs of each IKE SA to either all have the ESN bit on or
off.

7. Implementation Details

The Message ID value used in the Informational exchange that contains
the IKEV2_MESSAGE_ID_SYNC notification MUST be zero so that it is

This protocol does not
validated upon receipt as required by normal IKEv2 windowing. The
Message ID zero MUST be accepted only in an Informational exchange
that contains a notification of type IKEV2_MESSAGE_ID_SYNC. If change any
Informational exchange has a of the existing IKEv2 rules
regarding Message ID zero, but not this
notification type, such messages MUST be discarded upon decryption
and the INVALID_SYNTAX notification SHOULD be sent. Other payloads
MUST NOT be sent in this Informational exchange. Whenever an
IKEV2_MESSAGE_ID_SYNC or IPSEC_REPLAY_COUNTER_SYNC notification
payload is received with an invalid failover count or invalid nonce
data, the event SHOULD be logged. values.

The standby member can initiate the synchronization of IKEv2 Message
ID's under different circumstances.
o When it receives a problematic IKEv2/IPsec packet, i.e. a packet
outside its expected receive window.
o When it has to send the first IKEv2/IPsec packet after a failover
event.
o When it has just received control from the active member and
wishes to update the values proactively, so that it need not start
this exchange later, when sending or receiving the request.

The standby member can initiate the synchronization of IPsec SA
Replay Counters:
o If there has been traffic using the IPsec SA in the recent past
and the standby member suspects that its Replay Counter may be
stale.

Since there can be a large number of sessions at the standby member,
and sending synchronization exchanges for all of them may result in
overload, the standby member can choose to initiate the exchange in a
"lazy" fashion: only when it has to send or receive the request. In
general, the standby member is free to initiate this exchange at its
discretion.

8. IKE SA and IPsec SA Message Sequencing

The straightforward definitions of message sequence numbers,
retransmissions and replay protection in IPsec and IKEv2 are strained
by the failover scenarios described in this document. This section
describes some policy choices that need to be made by implementations
in this setting.

8.1. Handling of Pending IKE Messages

After sending its "receive" counter, the cluster member which has not announced its capability by using
IKEV2_MESSAGE_ID_SYNC_SUPPORTED MUST NOT send or reject
any incoming IKE messages that are outside its declared window. A
similar rule applies to the peer. Local policies vary, and strict
implementations will reject any incoming IKE message arriving before
Message ID synchronization is complete.

8.2. Handling of Pending IPsec Messages

For IPsec, there is often a trade-off between security and
reliability of the protected protocols. Here again there is some
leeway for local policy. Some implementations might accept incoming
traffic that is outside the
notification IKEV2_MESSAGE_ID_SYNC.

A cluster member which has not announced its capability by using
IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED MUST NOT send or replay window for some time after the
failover event. Strict implementations will only accept traffic
that's inside the
notification IPSEC_REPLAY_COUNTER_SYNC.

If "safe" window.

8.3. IKE SA Inconsistencies

IKEv2 is normally a peer receives reliable protocol. As long as an IKE SA is
valid, both peers share a IKEV2_MESSAGE_ID_SYNC or
IPSEC_REPLAY_COUNTER_SYNC request although it had not announced single, consistent view of the
appropriate capability IKE SA and
all associated Child SAs. Failover situations as described in the IKE_AUTH exchange, then it MUST
silently ignore this message.

As usual
document may involve forced deletion of IKE messages, resulting in IKEv2, if any
inconsistencies, such as Child SAs that exist on only one of the notification payloads defined here
is malformed,
peers. Such SAs would cause an INVALID_SPI to be returned when used
by that peer.

The Working Group discussed at some point a proposed set of rules for
dealing with such situations. However we believe that these
situations should be rare in practice; as a result the receiver must announce this fact using "default"
behavior of tearing down the
INVALID_SYNTAX notification.

8. entire IKE SA is to be preferred over
the complexity of dealing with a multitude of edge cases.

9. Step by Step Details

This section goes through the sequence of steps of a typical failover
event, looking at a case where the IKEv2 Message ID values are
synchronized.
o The active cluster member and the peer device establish the
session. They both announce the capability to synchronize counter
information by sending the IKEV2_MESSAGE_ID_SYNC_SUPPORTED
notification in the IKE_AUTH Exchange.
o The Some time later, the active member dies, and a standby member
takes over. The standby member sends its own idea of the IKE
Message IDs (both incoming and outgoing) to the peer in an
Informational message exchange with Message ID zero.

o The peer first authenticates the message and then validates the
failover count. message. The peer compares the
received values with the values available locally and picks the
higher value. It then updates its Message IDs with the higher
values and also propose the same values in its response.
o The peer should not wait for any pending responses while
responding with the new Message ID values. For example, if the
window size is 5 and the peer's window is 3-7, and if the peer has
sent requests 3, 4, 5, 6, 7 and received responses only for 4, 5,
6, 7 but not for 3, then it should include the value 8 in its
EXPECTED_SEND_REQ_MESSAGE_ID payload and should not wait for a
response to message 3 anymore.
o Similarly, the peer should also not wait for any pending (incoming)
requests. responses while
responding with the new Message ID values. For example example, if the
window size is 5 and the peer's window is 3-7 3-7, and if the peer has received
sent requests 3, 4, 5, 6, 7 but
not 3, then it should send the value 8 in the
EXPECTED_RECV_REQ_MESSAGE_ID payload, and should not expect to
receive message 3 anymore.

In case multiple successive failover events and sync request getting
lost, the failover count value at peer will not be updated and new
standby member will become active with incremented failover count
value. So, peer can receive valid failover count value which is not
just incremented by 1 in case of multiple failover. Accepting
incremented failover count within a range is allowed and increases
interoperability.

9. Security Considerations

Since Message ID synchronization messages need to be sent with
Message ID zero, they are potentially vulnerable to replay attacks.
Because of the semantics of this protocol, these can only be denial-
of-service (DoS) attacks, and we are aware of two variants.
o Replay of Message ID synchronization request: This is countered by
use of the Failover Count, since synchronization starts after the
failover event and each member of the cluster needs to be aware of
the failover event. The receiver of the synchronization request
should verify the received Failover Count and maintain its own
copy of it. If a peer receives a synchronization request with an
already observed Failover Count, it can safely discard the request
if it has already received valid IKEv2 request/response from other
side peer after sync exchange. The peer will be responses only for 4, 5,
6, 7 but not be aware that
sync response has reached to other side till it receives a valid
IKEv2 request/response from other side. The peer can send the
cached response for sync request till 3, then it has should include the value 8 in its
EXPECTED_SEND_REQ_MESSAGE_ID payload and should not received valid
request/response from other side wait for a
response to message 3 anymore.
o Similarly, the peer or failover count has should also not
increased.
o Replay of wait for pending (incoming)
requests. For example if the Message ID synchronization response: This window size is
countered by sending 5 and the nonce data along with peer's
window is 3-7 and if the synchronization
payload. The same nonce data peer has to be returned in response.
Thus the standby member will accept a reply only for the current
request. After it receives a valid response, received requests 4, 5, 6, 7 but
not 3, then it MUST NOT process should send the same response again value 8 in the
EXPECTED_RECV_REQ_MESSAGE_ID payload, and MUST discard any additional responses. should not expect to
receive message 3 anymore.

10. Interaction with other drafts

The usage scenario of the IKEv2/IPsec SA counter synchronization
proposal is that an IKEv2 SA has been established between the active
member of a hot-standby cluster and a peer, then a failover event
occurred with the standby member becoming active. The proposal
further assumes that the IKEv2 SA state was continuously synchronized
between the active and standby members of the cluster before the
failover event.
o Session resumption [RFC5723] [7] assumes that a peer (client or initiator)
detects the need to re-establish the session. In IKEv2/IPsec SA
counter synchronization, it is the newly-active member (a gateway
or responder) that detects the need to synchronize the SA counter
after the failover event. Also in a hot-standby cluster, the peer
establishes the IKEv2/IPsec session with a single IP address that
represents the whole cluster, so the peer normally does not detect
the event of failover in the cluster unless the standby member
takes too long to become active and the IKEv2 SA times out by use
of the IKEv2 liveness check mechanism. To conclude, session
resumption and SA counter synchronization after failover are
mutually exclusive.
o The IKEv2 Redirect mechanism for load-balancing [RFC5685] [6] can be used
either during the initial stages of SA setup (the IKE_SA_INIT and
IKE_AUTH exchanges) or after session establishment. SA counter
synchronization is only useful after the IKE SA has been
established and a failover event has occurred. So, unlike
Redirect, it is irrelevant during the first two exchanges.
Redirect after the session has been established is mostly useful
for timed or planned shutdown/maintenance. A real failover event
cannot be detected by the active member ahead of time, and so
using Redirect after session establishment is not possible in the
case of failover. So, Redirect and SA counter synchronization
after failover are mutually exclusive.
o IKEv2 Failure Detection [I-D.ietf-ipsecme-failure-detection] [8] solves a similar problem where the
peer can rapidly detect that a cluster member has crashed based on
a token. It is unrelated to the current scenario because the goal
in failover is for the peer
not to notice that peer not to notice that a failure has
occurred.

11. Security Considerations

11. valid response, it MUST NOT process
the same response again and MUST discard any additional responses.

12. IANA Considerations

This document introduces four new IKEv2 Notification Message types as
described in Section 6.The 6. The new Notify Message Types must be
assigned values between 16396 and 40959.
o IKEV2_MESSAGE_ID_SYNC_SUPPORTED.
o IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED.
o IKEV2_MESSAGE_ID_SYNC.
o IPSEC_REPLAY_COUNTER_SYNC.

12.

13. Acknowledgements

We would like to thank Pratima Sethi and Frederic Detienne for their
review comments and valuable suggestions for the initial version of
the document.

We would also like to thank the following people (in alphabetical
order) for their review comments and valuable suggestions: Dan
Harkins, Paul Hoffman, Steve Kent, Tero Kivinen, David McGrew, Pekka
Riikonen, and Yaron Sheffer.

13.
Pekka Riikonen.

14. Change Log

This section lists all the changes in this document.

NOTE TO RFC EDITOR: Please remove this section before publication.

13.1.

14.1. Draft -03

Clarified the rules for Message ID sync, so that replay attacks can
be avoided without a failover counter.

Added wording regarding inconsistent IKE state (basically choosing to
ignore the problem) and further rules dealing with pending traffic.

The IPsec replay counter delta value now refers to incoming traffic.
The associated notification is only sent from the cluster to the
peer, and not back.

14.2. Draft -02

Addressed comments by Yaron Sheffer posted on the WG mailing list.

Numerous editorial changes.

13.2.

14.3. Draft -01

Added "Multiple and Simultaneous failover' scenarios as pointed out
by Pekka Riikonen.

Now document provides a mechanism to sync either IKEv2 message or
IPsec replay counter or both to cater different types of
implementations.

HA cluster's "failover count' is used to encounter replay of sync
requests by attacker.

The sync of IPsec SA replay counter optimized to to have just one
global bumped-up outgoing IPsec SA counter of ALL Child SAs under an
IKEv2 SA.

The examples added for IKEv2 Message ID sync to provide more clarity.

Some edits as per comments on mailing list to enhance clarity.

13.3.

14.4. Draft -00

Version 00 is identical to
draft-kagarigi-ipsecme-ikev2-windowsync-04, started as WG document.

Added IPSECME WG HA design team members as authors.

Added comment in Introduction to discuss the window sync process on
WG mailing list to solve some concerns.

14.

15. References

14.1.

15.1. Normative References

[RFC2119]

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

[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol",

[2] Nir, Y., "IPsec Cluster Problem Statement", RFC 4301, December 2005.

[RFC5996] 6027,
October 2010.

[3] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, "Internet Key
Exchange Protocol Version 2 (IKEv2)", RFC 5996, September 2010.

[RFC6027] Nir, Y., "IPsec Cluster Problem Statement",

[4] Kent, S. and K. Seo, "Security Architecture for the Internet
Protocol", RFC 6027,
October 2010.

14.2. 4301, December 2005.

15.2. Informative References

[I-D.ietf-ipsecme-failure-detection]
Nir, Y., Wierbowski, D., Detienne, F., and P. Sethi, "A
Quick Crash Detection Method

[5] Nadas, S., "Virtual Router Redundancy Protocol (VRRP) Version 3
for IKE",
draft-ietf-ipsecme-failure-detection-01 (work in
progress), October IPv4 and IPv6", RFC 5798, March 2010.

[RFC5685]

[6] Devarapalli, V. and K. Weniger, "Redirect Mechanism for the
Internet Key Exchange Protocol Version 2 (IKEv2)", RFC 5685,
November 2009.

[RFC5723]

[7] Sheffer, Y. and H. Tschofenig, "Internet Key Exchange Protocol
Version 2 (IKEv2) Session Resumption", RFC 5723, January 2010.

[RFC5798] Nadas, S., "Virtual Router Redundancy Protocol (VRRP)
Version 3 for IPv4

[8] Nir, Y., Wierbowski, D., Detienne, F., and IPv6", RFC 5798, March 2010. P. Sethi, "A Quick
Crash Detection Method for IKE",
draft-ietf-ipsecme-failure-detection-03 (work in progress),
January 2011.

Appendix A. IKEv2 Message ID Sync Examples

This (non-normative) section presents some examples that illustrate
how the IKEv2 Message ID values are synchronized. We use a tuple
notation, denoting the two counters EXPECTED_SEND_REQ_MESSAGE_ID and
EXPECTED_RECV_REQ_MESSAGE_ID on a member as
(EXPECTED_SEND_REQ_MESSAGE_ID, EXPECTED_RECV_REQ_MESSAGE_ID).

A.1. Normal Failover - Example 1

Standby (Newly Active) Member Peer
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Sync Request (2, 3) -------->

Peer has the values (4, 5) so it sends
<------------- (4, 5) as the Sync Response

A.2. Normal Failover - Example 2

Standby (Newly Active) Member Peer
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Sync Request (2, 5) -------->

Peer has the values (2, 4) so it sends
<-------------(5, 4) as the Sync Response

A.3. Simultaneous Failover

In the case of simultaneous failover, both sides send the
synchronization request, but whichever side has the higher value will
be eventually synchronized.

Standby (Newly Active) Member Peer
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Sync Request (4,4) ----->

<-------------- Sync Request (5,5)

Sync Response (5,5) ---->

<-------- Sync Response (5,5)

Authors' Addresses

Raj Singh (Editor)
Cisco Systems, Inc.
Divyashree Chambers, B Wing, O'Shaugnessy Road
Bangalore, Karnataka 560025
India

Phone: +91 80 4301 3320
Email: rsj@cisco.com

Kalyani Garigipati
Cisco Systems, Inc.
Divyashree Chambers, B Wing, O'Shaugnessy Road
Bangalore, Karnataka 560025
India

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

Yoav Nir
Check Point Software Technologies Ltd.
5 Hasolelim St.
Tel Aviv 67897
Israel

Email: ynir@checkpoint.com
Yaron Sheffer
Independent

Email: yaronf.ietf@gmail.com

Dacheng Zhang
Huawei Technologies Ltd.

Email: zhangdacheng@huawei.com