Network Working Group R. Singh, Ed.
Internet-Draft G. Kalyani
Intended status: Standards Track Cisco
Expires: August 12, 2011 Y. Nir
Check Point
Y. Sheffer
Independent
D. Zhang
Huawei
February 8, 2011
Protocol Support for High Availability of IKEv2/IPsec
draft-ietf-ipsecme-ipsecha-protocol-03
Abstract
The IPsec protocol suite is widely used for business-critical network
traffic. In order to make IPsec deployments highly available, more
scalable and failure-resistant, 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."
Singh, Ed., et al. Expires August 12, 2011 [Page 1]
Internet-Draft High Availability in IKEv2/IPsec February 2011
This Internet-Draft will expire on August 12, 2011.
Copyright Notice
Copyright (c) 2011 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.
Singh, Ed., et al. Expires August 12, 2011 [Page 2]
Internet-Draft High Availability in IKEv2/IPsec February 2011
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Issues Resolved from IPsec Cluster Problem Statement . . . . . 6
4. The IKEv2/IPsec SA Counter Synchronization Problem . . . . . . 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 . . . . . . . . . . . . . . . . . . . . . 11
6. IKEv2/IPsec Synchronization Notification Payloads . . . . . . 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 . . . . . . . . . . 12
6.4. The IPSEC_REPLAY_COUNTER_SYNC Notification . . . . . . . . 13
7. Implementation Details . . . . . . . . . . . . . . . . . . . . 14
8. IKE SA and IPsec SA Message Sequencing . . . . . . . . . . . . 14
8.1. Handling of Pending IKE Messages . . . . . . . . . . . . . 15
8.2. Handling of Pending IPsec Messages . . . . . . . . . . . . 15
8.3. IKE SA Inconsistencies . . . . . . . . . . . . . . . . . . 15
9. Step by Step Details . . . . . . . . . . . . . . . . . . . . . 15
10. Interaction with other drafts . . . . . . . . . . . . . . . . 16
11. Security Considerations . . . . . . . . . . . . . . . . . . . 17
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
14. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 18
14.1. Draft -03 . . . . . . . . . . . . . . . . . . . . . . . . 18
14.2. Draft -02 . . . . . . . . . . . . . . . . . . . . . . . . 18
14.3. Draft -01 . . . . . . . . . . . . . . . . . . . . . . . . 18
14.4. Draft -00 . . . . . . . . . . . . . . . . . . . . . . . . 19
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
15.1. Normative References . . . . . . . . . . . . . . . . . . . 19
15.2. Informative References . . . . . . . . . . . . . . . . . . 19
Appendix A. IKEv2 Message ID Sync Examples . . . . . . . . . . . 20
A.1. Normal Failover - Example 1 . . . . . . . . . . . . . . . 20
A.2. Normal Failover - Example 2 . . . . . . . . . . . . . . . 20
A.3. Simultaneous Failover . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
Singh, Ed., et al. Expires August 12, 2011 [Page 3]
Internet-Draft High Availability in IKEv2/IPsec February 2011
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; in addition, the newly-active member requests the peer to
increment the replay counter values it is using for the 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.
Singh, Ed., et al. Expires August 12, 2011 [Page 4]
Internet-Draft High Availability in IKEv2/IPsec February 2011
Implementations differ on the need to synchronize the IKEv2 Message
ID and/or IPsec replay counters. Both of these 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 [1].
"SA Counter Synchronization Request/Response" are the request viz.
response of the 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 [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 [5] is one method of
building such a cluster. The goal of the Hot Standby Cluster is
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 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.
Although we treat the peer as a single entity, it may also be a
cluster.
o "Multiple failover" is the situation where, in a cluster with
three or more members, multiple failover events happen in rapid
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
an IPsec connection between them, and failover happens at both
ends at the same time. It is our goal that implementations should
Singh, Ed., et al. Expires August 12, 2011 [Page 5]
Internet-Draft High Availability in IKEv2/IPsec February 2011
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 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; the IPsec SA
replay counters are optional, and are used to provide the IPsec anti-
replay feature.
3. Issues Resolved from IPsec Cluster Problem Statement
The IPsec Cluster Problem Statement [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; additionally, this document provides implementation
advice for other issues, as follows.
o Section 3.2 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 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 [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.
Singh, Ed., et al. Expires August 12, 2011 [Page 6]
Internet-Draft High Availability in IKEv2/IPsec February 2011
4. The IKEv2/IPsec SA Counter Synchronization Problem
The IKEv2 protocol [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's
window should not move until the oldest message it has sent is
acknowledged. Loss of even a single message leads to repeated
retransmissions followed by an IKEv2 SA teardown if the
retransmissions 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 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 is 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
Singh, Ed., et al. Expires August 12, 2011 [Page 7]
Internet-Draft High Availability in IKEv2/IPsec February 2011
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 the case of IKE Message ID values, the newly active cluster
member and the peer negotiate a pair of new values so that future
IKE messages will not be dropped.
o For IPsec counter values, the newly-active member and the peer
both increment their respective counter 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 and the active member of the cluster negotiate their
ability to support IKEv2 Message ID synchronization and/or IPsec
Replay Counter synchronization. This is done by exchanging one or
both of the IKEV2_MESSAGE_ID_SYNC_SUPPORTED and
IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED notifications during the IKE_AUTH
exchange. When negotiating these capabilities, the responder MUST
NOT assert support of a capability unless such support was asserted
by the initiator. Only a capability whose support was asserted by
both parties can be used during the lifetime of the 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,
Singh, Ed., et al. Expires August 12, 2011 [Page 8]
Internet-Draft High Availability in IKEv2/IPsec February 2011
[N(IKEV2_MESSAGE_ID_SYNC_SUPPORTED),]
[N(IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED),] SAr2, TSi, TSr}
After a failover event, the standby member MAY use the IKE Message ID
and/or IPsec Replay Counter synchronization capability when it
becomes the active 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 synchronize its SA counters with the peer. There are now
three possible cases:
1. The cluster member wishes to only perform IKE Message ID value
synchronization. In this case it initiates an Informational
exchange, with Message ID zero and the sole notification
IKEV2_MESSAGE_ID_SYNC.
2. If the newly-active member wishes to perform only IPsec replay
counter synchronization, it generates a regular IKEv2
Informational exchange using the current Message ID values, and
containing the IPSEC_REPLAY_COUNTER_SYNC notification.
3. If synchronization of both counters is needed, the cluster member
generates a zero-Message ID message as in case #1, and includes
both notifications in this message.
This figure contains the IKE message exchange used for SA counter
synchronization. The following subsections describe the details of
the sender and receiver processing of 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)}
Alternatively, if only IPsec Replay Counter synchronization is
desired, a normal Informational exchange is used, where the Message
ID is non-zero:
Singh, Ed., et al. Expires August 12, 2011 [Page 9]
Internet-Draft High Availability in IKEv2/IPsec February 2011
Standby [Newly Active] Member Peer
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.
Singh, Ed., et al. Expires August 12, 2011 [Page 10]
Internet-Draft High Availability in IKEv2/IPsec February 2011
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 payload types defined by this
extension.
6.1. The IKEV2_MESSAGE_ID_SYNC_SUPPORTED Notification
This notification payload is included in the IKE_AUTH request/
response to indicate support of the IKEv2 Message ID 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size', and
'Notify Message Type' fields are the same as described in Section 3
of [3]. The 'SPI Size' field MUST be set to 0 to indicate that the
Singh, Ed., et al. Expires August 12, 2011 [Page 11]
Internet-Draft High Availability in IKEv2/IPsec February 2011
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 Notification
This notification payload is included in the IKE_AUTH request/
response to indicate support for the IPsec SA Replay 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size', and
'Notify Message Type' fields are the same as described in Section 3
of [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 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.
Singh, Ed., et al. Expires August 12, 2011 [Page 12]
Internet-Draft High Availability in IKEv2/IPsec February 2011
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EXPECTED_SEND_REQ_MESSAGE_ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EXPECTED_RECV_REQ_MESSAGE_ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
It contains the following data.
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 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 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 [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 |C| RESERVED | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Protocol ID(=0)| SPI Size (=0) | Notify Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Incoming IPsec SA delta value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Singh, Ed., et al. Expires August 12, 2011 [Page 13]
Internet-Draft High Availability in IKEv2/IPsec February 2011
The notification payload contains the following data.
o Incoming IPsec SA delta value (4 or 8 octets): The sender requests
that the peer should increment all the Child SA Replay Counters
for the sender's incoming (the peer's outgoing) traffic by this
value. The size of this field depends on the ESN bit associated
with the Child SAs: if the ESN bit is 1, 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
This protocol does not change any of the existing IKEv2 rules
regarding Message ID 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.
Singh, Ed., et al. Expires August 12, 2011 [Page 14]
Internet-Draft High Availability in IKEv2/IPsec February 2011
8.1. Handling of Pending IKE Messages
After sending its "receive" counter, the cluster member MUST 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 replay window for some time after the
failover event. Strict implementations will only accept traffic
that's inside the "safe" window.
8.3. IKE SA Inconsistencies
IKEv2 is normally a reliable protocol. As long as an IKE SA is
valid, both peers share a single, consistent view of the IKE SA and
all associated Child SAs. Failover situations as described in this
document may involve forced deletion of IKE messages, resulting in
inconsistencies, such as Child SAs that exist on only one of the
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 "default"
behavior of tearing down the 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 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.
Singh, Ed., et al. Expires August 12, 2011 [Page 15]
Internet-Draft High Availability in IKEv2/IPsec February 2011
o The peer first authenticates the 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 pending (incoming)
requests. For example if the window size is 5 and the peer's
window is 3-7 and if the peer has received requests 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.
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 [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 [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
Singh, Ed., et al. Expires August 12, 2011 [Page 16]
Internet-Draft High Availability in IKEv2/IPsec February 2011
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 [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 a failure has
occurred.
11. 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
the requirement that the Send counter sent by the cluster member
should always be monotonically increasing, a rule that the peer
enforces by silently dropping messages that contradict it.
o Replay of the Message ID synchronization response: This is
countered by sending the nonce data along with the synchronization
payload. The same nonce data has to be returned in the response.
Thus the standby member will accept a reply only for the current
request. After it receives a 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 new Notify Message Types must be
assigned values between 16396 and 40959.
+-------------------------------------+-------------+
| Name | Value |
+-------------------------------------+-------------+
| IKEV2_MESSAGE_ID_SYNC_SUPPORTED | TBD by IANA |
| IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED | TBD by IANA |
| IKEV2_MESSAGE_ID_SYNC | TBD by IANA |
| IPSEC_REPLAY_COUNTER_SYNC | TBD by IANA |
+-------------------------------------+-------------+
Singh, Ed., et al. Expires August 12, 2011 [Page 17]
Internet-Draft High Availability in IKEv2/IPsec February 2011
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, and
Pekka Riikonen.
14. Change Log
This section lists all the changes in this document.
NOTE TO RFC EDITOR: Please remove this section before publication.
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.
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.
Singh, Ed., et al. Expires August 12, 2011 [Page 18]
Internet-Draft High Availability in IKEv2/IPsec February 2011
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.
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.
15. References
15.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Nir, Y., "IPsec Cluster Problem Statement", RFC 6027,
October 2010.
[3] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, "Internet Key
Exchange Protocol Version 2 (IKEv2)", RFC 5996, September 2010.
[4] Kent, S. and K. Seo, "Security Architecture for the Internet
Protocol", RFC 4301, December 2005.
15.2. Informative References
[5] Nadas, S., "Virtual Router Redundancy Protocol (VRRP) Version 3
for IPv4 and IPv6", RFC 5798, March 2010.
[6] Devarapalli, V. and K. Weniger, "Redirect Mechanism for the
Internet Key Exchange Protocol Version 2 (IKEv2)", RFC 5685,
November 2009.
[7] Sheffer, Y. and H. Tschofenig, "Internet Key Exchange Protocol
Version 2 (IKEv2) Session Resumption", RFC 5723, January 2010.
[8] Nir, Y., Wierbowski, D., Detienne, F., and P. Sethi, "A Quick
Singh, Ed., et al. Expires August 12, 2011 [Page 19]
Internet-Draft High Availability in IKEv2/IPsec February 2011
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.
Singh, Ed., et al. Expires August 12, 2011 [Page 20]
Internet-Draft High Availability in IKEv2/IPsec February 2011
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
Singh, Ed., et al. Expires August 12, 2011 [Page 21]
Internet-Draft High Availability in IKEv2/IPsec February 2011
Yaron Sheffer
Independent
Email: yaronf.ietf@gmail.com
Dacheng Zhang
Huawei Technologies Ltd.
Email: zhangdacheng@huawei.com
Singh, Ed., et al. Expires August 12, 2011 [Page 22]