Network Working Group R. Singh, Ed.
Internet-Draft G. Kalyani
Intended status: Standards Track Cisco
Expires: April 28, 2011 Y. Nir
Check Point
D. Zhang
Huawei
October 25, 2010
Protocol Support for High Availability of IKEv2/IPsec
draft-ietf-ipsecme-ipsecha-protocol-02
Abstract
The IPsec protocol suite is widely used for the deployment of virtual
private networks (VPNs). In order to make such VPNs highly
available, more scalable and failure-resistant, these VPNs are
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, 2011.
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Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Issues Resolved from IPsec Cluster Problem Statement . . . . . 5
4. The IKEv2/IPsec SA Counter Synchronization Problem . . . . . . 5
5. Counter Synchronization Solution . . . . . . . . . . . . . . . 7
6. IKEv2/IPsec Synchronization Notification Payloads . . . . . . 9
6.1. IKEV2_MESSAGE_ID_SYNC_SUPPORTED . . . . . . . . . . . . . 9
6.2. IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED . . . . . . . . . . . 10
6.3. IKEV2_MESSAGE_ID_SYNC . . . . . . . . . . . . . . . . . . 10
6.4. IPSEC_REPLAY_COUNTER_SYNC . . . . . . . . . . . . . . . . 11
7. Implementation Details . . . . . . . . . . . . . . . . . . . . 12
8. Step by Step Details . . . . . . . . . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10. Interaction with other drafts . . . . . . . . . . . . . . . . 14
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
13. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 15
13.1. Draft -02 . . . . . . . . . . . . . . . . . . . . . . . . 16
13.2. Draft -01 . . . . . . . . . . . . . . . . . . . . . . . . 16
13.3. Draft -00 . . . . . . . . . . . . . . . . . . . . . . . . 16
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
14.1. Normative References . . . . . . . . . . . . . . . . . . . 16
14.2. Informative References . . . . . . . . . . . . . . . . . . 17
Appendix A. IKEv2 Message ID Sync Examples . . . . . . . . . . . 17
A.1. Normal Failover - Example 1 . . . . . . . . . . . . . . . 17
A.2. Normal Failover - Example 2 . . . . . . . . . . . . . . . 18
A.3. Simultaneous Failover . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
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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
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 the peer. The peer
send its outgoing SA reply counter in the response.
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
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ID and/or IPsec replay counters. Both of these problem 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].
"SA Counter Synchronization Request/Response" are the request viz.
response of the information 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] 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] is one method of
building such a cluster. The goal of Hot Standby Cluster is that
it creates illusion of single virtual gateway to the peer(s).
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 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
the HA 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, failover happens in rapid succession. 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 connection between them, and failover happens at the both ends
at the same time. It is our goal that implementation should be
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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 used to ensure reliable delivery as well as to
protect against message replay in IKEv2) and IPsec SA replay counters
(optional, and used to provide the IPsec anti-replay feature).
3. Issues Resolved from IPsec Cluster Problem Statement
The IPsec Cluster Problem Statement [RFC6027] 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 this document provides implementation
advice for other issues, given as follows.
o 3.2 This section 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 protocol extensions.
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].
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] states that "An IKE endpoint MUST NOT
exceed the peer's stated window size for transmitted IKE requests".
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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
window should not move until the oldest message 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 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 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 is implemented, 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.
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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. Counter Synchronization Solution
In general, when the standby member becomes the active member after
the failover event, the standby member sends an authenticated IKEv2
request to the peer, asking it to send its SA counter values.
The standby member then updates its own SA counter values and can
resume normally sending and receiving protocol messages.
First, the peer MUST negotiate its ability to support IKEv2 Message
ID synchronization with the active member of the cluster by sending
the IKEV2_MESSAGE_ID_SYNC_SUPPORTED notification in the IKE_AUTH
exchange.
Similarly, to support IPsec Replay Counter synchronization, the peer
MUST negotiate this capability with the active member of the cluster
by sending the IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED notification in
the IKE_AUTH exchange.
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 the standby member of
the SA counter synchronization capability after the establishment of
the IKE SA. The standby member can then use this capability when it
becomes the active member after a failover event.
After the failover event, when the standby member becomes active, it
has to request the SA counters from the peer. The newly-active
member initiates the synchronization request with an Informational
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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. If the active member has only
negotiated synchronization of IPsec Replay Counters, the request is
sent as a regular IKEv2 Informational exchange (i.e. with a non-zero
Message ID) containing the notification IPSEC_REPLAY_COUNTER_SYNC.
The initiator of the IKEv2 Message ID synchronization request sends
its expected send and receive Message ID values 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 in the response
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 SA counter
synchronization response. The nonce values are selected randomly on
each new notification and MUST be validated by the receiver. 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, the cluster
member MUST silently discard this response, and SHOULD revert to
normal IKEv2 behavior of retransmitting the request and waiting for a
genuine a reply from the peer. Eventually this might result in the
SA being torn down because of excessive retransmissions.
Standby [Newly Active] Member Peer
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
HDR, SK {N(IKEV2_MESSAGE_ID_SYNC),
[N(IPSEC_REPLAY_COUNTER_SYNC)]} -------->
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<--------- HDR, SK {N(IKEV2_MESSAGE_ID_SYNC),
[N(IPSEC_REPLAY_COUNTER_SYNC)]}
Alternatively, if only IPsec Replay Counter synchronization is
desired, a normal Information 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)}
6. IKEv2/IPsec Synchronization Notification Payloads
This section lists the new notification payloads types defined by
this extension.
6.1. IKEV2_MESSAGE_ID_SYNC_SUPPORTED
IKEV2_MESSAGE_ID_SYNC_SUPPORTED: 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 [RFC5996] . 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.
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6.2. IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED
IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED: 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 [RFC5996] . 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. IKEV2_MESSAGE_ID_SYNC
IKEV2_MESSAGE_ID_SYNC : 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 | 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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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. IPSEC_REPLAY_COUNTER_SYNC
IPSEC_REPLAY_COUNTER_SYNC: 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 [RFC4301].
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| RESERVED | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Protocol ID(=0)| SPI Size (=0) | Notify Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outgoing IPsec SA counter |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The notification payload contains the following data.
o E (1 bit): The ESN bit. This MUST be 1 if the IPsec SAs were
established with Extended Sequence Numbers.
o Outgoing IPsec SA delta value (4 or 8 octects): The sender will
increment the all the Child SA Replay Counters for its outgoing
traffic by this value. The size of this field depends on ESN bit:
if the ESN bit is 1, its size is 8 octets, otherwise it is 4
octets.
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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 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 any
Informational exchange has a 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.
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 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.
A cluster member which has not announced its capability by using
IKEV2_MESSAGE_ID_SYNC_SUPPORTED MUST NOT send or accept 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 accept the
notification IPSEC_REPLAY_COUNTER_SYNC.
If a peer receives a IKEV2_MESSAGE_ID_SYNC or
IPSEC_REPLAY_COUNTER_SYNC request although it had not announced the
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appropriate capability in the IKE_AUTH exchange, then it MUST
silently ignore this message.
As usual in IKEv2, if any of the notification payloads defined here
is malformed, the receiver must announce this fact using the
INVALID_SYNTAX notification.
8. Step by Step Details
This section goes through the sequence of steps of a typical failover
event, 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 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. 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.
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.
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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 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 it has not received valid
request/response from other side peer or failover count has not
increased.
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 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.
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] 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
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after failover are mutually exclusive.
o The IKEv2 Redirect mechanism for load-balancing [RFC5685] 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]
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. 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.
o IKEV2_MESSAGE_ID_SYNC_SUPPORTED.
o IPSEC_REPLAY_COUNTER_SYNC_SUPPORTED.
o IKEV2_MESSAGE_ID_SYNC.
o IPSEC_REPLAY_COUNTER_SYNC.
12. 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. Change Log
This section lists all the changes in this document.
NOTE TO RFC EDITOR: Please remove this section before publication.
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13.1. Draft -02
Addressed comments by Yaron Sheffer posted on the WG mailing list.
Numerous editorial changes.
13.2. 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. 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. References
14.1. Normative References
[RFC2119] 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", RFC 4301, December 2005.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
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"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, September 2010.
[RFC6027] Nir, Y., "IPsec Cluster Problem Statement", RFC 6027,
October 2010.
14.2. Informative References
[I-D.ietf-ipsecme-failure-detection]
Nir, Y., Wierbowski, D., Detienne, F., and P. Sethi, "A
Quick Crash Detection Method for IKE",
draft-ietf-ipsecme-failure-detection-01 (work in
progress), October 2010.
[RFC5685] Devarapalli, V. and K. Weniger, "Redirect Mechanism for
the Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5685, November 2009.
[RFC5723] 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 and IPv6", RFC 5798, March 2010.
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
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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
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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
Dacheng Zhang
Huawei Technologies Ltd.
Email: zhangdacheng@huawei.com
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