Network T. Pauly
Internet-Draft Apple Inc.
Intended status: Standards Track S. Touati
Expires: July 27, 2017 Ericsson
R. Mantha
Cisco Systems
January 23, 2017
TCP Encapsulation of IKE and IPsec Packets
draft-ietf-ipsecme-tcp-encaps-05
Abstract
This document describes a method to transport IKE and IPsec packets
over a TCP connection for traversing network middleboxes that may
block IKE negotiation over UDP. This method, referred to as TCP
encapsulation, involves sending both IKE packets for tunnel
establishment as well as tunneled packets using ESP over a TCP
connection. This method is intended to be used as a fallback option
when IKE cannot be negotiated over UDP.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 27, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Prior Work and Motivation . . . . . . . . . . . . . . . . 3
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Configuration . . . . . . . . . . . . . . . . . . . . . . . . 4
3. TCP-Encapsulated Header Formats . . . . . . . . . . . . . . . 5
3.1. TCP-Encapsulated IKE Header Format . . . . . . . . . . . 5
3.2. TCP-Encapsulated ESP Header Format . . . . . . . . . . . 6
4. TCP-Encapsulated Stream Prefix . . . . . . . . . . . . . . . 6
5. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Recommended Fallback from UDP . . . . . . . . . . . . . . 7
6. Connection Establishment and Teardown . . . . . . . . . . . . 8
7. Interaction with NAT Detection Payloads . . . . . . . . . . . 9
8. Using MOBIKE with TCP encapsulation . . . . . . . . . . . . . 10
9. Using IKE Message Fragmentation with TCP encapsulation . . . 10
10. Considerations for Keep-alives and DPD . . . . . . . . . . . 11
11. Middlebox Considerations . . . . . . . . . . . . . . . . . . 11
12. Performance Considerations . . . . . . . . . . . . . . . . . 11
12.1. TCP-in-TCP . . . . . . . . . . . . . . . . . . . . . . . 12
12.2. Added Reliability for Unreliable Protocols . . . . . . . 12
12.3. Quality of Service Markings . . . . . . . . . . . . . . 12
12.4. Maximum Segment Size . . . . . . . . . . . . . . . . . . 12
13. Security Considerations . . . . . . . . . . . . . . . . . . . 12
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
16.1. Normative References . . . . . . . . . . . . . . . . . . 13
16.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. Using TCP encapsulation with TLS . . . . . . . . . . 15
Appendix B. Example exchanges of TCP Encapsulation with TLS . . 15
B.1. Establishing an IKE session . . . . . . . . . . . . . . . 15
B.2. Deleting an IKE session . . . . . . . . . . . . . . . . . 17
B.3. Re-establishing an IKE session . . . . . . . . . . . . . 18
B.4. Using MOBIKE between UDP and TCP Encapsulation . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
IKEv2 [RFC7296] is a protocol for establishing IPsec tunnels, using
IKE messages over UDP for control traffic, and using Encapsulating
Security Payload (ESP) messages for tunneled data traffic. Many
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network middleboxes that filter traffic on public hotspots block all
UDP traffic, including IKE and IPsec, but allow TCP connections
through since they appear to be web traffic. Devices on these
networks that need to use IPsec (to access private enterprise
networks, to route voice-over-IP calls to carrier networks, or
because of security policies) are unable to establish IPsec tunnels.
This document defines a method for encapsulating both the IKE control
messages as well as the IPsec data messages within a TCP connection.
Using TCP as a transport for IPsec packets adds a third option to the
list of traditional IPsec transports:
1. Direct. Currently, IKE negotiations begin over UDP port 500.
If no NAT is detected between the initiator and the receiver,
then subsequent IKE packets are sent over UDP port 500 and
IPsec data packets are sent using ESP [RFC4303].
2. UDP Encapsulation [RFC3948]. If a NAT is detected between the
initiator and the receiver, then subsequent IKE packets are
sent over UDP port 4500 with four bytes of zero at the start of
the UDP payload and ESP packets are sent out over UDP port
4500. Some peers default to using UDP encapsulation even when
no NAT are detected on the path as some middleboxes do not
support IP protocols other than TCP and UDP.
3. TCP Encapsulation. If both of the other two methods are not
available or appropriate, both IKE negotiation packets as well
as ESP packets can be sent over a single TCP connection to the
peer.
Direct use of ESP or UDP Encapsulation should be preferred by IKE
implementations due to performance concerns when using TCP
Encapsulation [Section 12]. Most implementations should use TCP
Encapsulation only on networks where negotiation over UDP has been
attempted without receiving responses from the peer, or if a network
is known to not support UDP.
1.1. Prior Work and Motivation
Encapsulating IKE connections within TCP streams is a common approach
to solve the problem of UDP packets being blocked by network
middleboxes. The goal of this document is to promote
interoperability by providing a standard method of framing IKE and
ESP message within streams, and to provide guidelines for how to
configure and use TCP encapsulation.
Some previous alternatives include:
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Cellular Network Access Interworking Wireless LAN (IWLAN) uses IKEv2
to create secure connections to cellular carrier networks for
making voice calls and accessing other network services over
Wi-Fi networks. 3GPP has recommended that IKEv2 and ESP packets
be sent within a TLS connection to be able to establish
connections on restrictive networks.
ISAKMP over TCP Various non-standard extensions to ISAKMP have been
deployed that send IPsec traffic over TCP or TCP-like packets.
SSL VPNs Many proprietary VPN solutions use a combination of TLS and
IPsec in order to provide reliability.
IKEv2 over TCP IKEv2 over TCP as described in
[I-D.nir-ipsecme-ike-tcp] is used to avoid UDP fragmentation.
The goal of this specification is to provide a standardized method
for using TCP streams to transport IPsec that is compatible with the
current IKE standard, and avoids the overhead of other alternatives
that always rely on TCP or TLS.
1.2. Requirements Language
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 RFC 2119 [RFC2119].
2. Configuration
One of the main reasons to use TCP encapsulation is that UDP traffic
may be entirely blocked on a network. Because of this, support for
TCP encapsulation is not specifically negotiated in the IKE exchange.
Instead, support for TCP encapsulation must be pre-configured on both
the initiator and the responder.
The configuration defined on each peer should include the following
parameters:
o One or more TCP ports on which the responder will listen for
incoming connections. Note that the initiator may initiate TCP
connections to the responder from any local port. The ports on
which the responder listens will likey be based on the ports
commonly allowed on restricted networks.
o Optionally, an extra framing protocol to use on top of TCP to
further encapsulate the stream of IKE and IPsec packets. See
Appendix A for a detailed discussion.
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This document leaves the selection of TCP ports up to
implementations. It is suggested to use TCP port 4500, which is
allocated for IPsec NAT Traversal.
Since TCP encapsulation of IKE and IPsec packets adds overhead and
has potential performance trade-offs compared to direct or UDP-
encapsulated tunnels (as described in Performance Considerations,
Section 12), implementations SHOULD prefer ESP direct or UDP
encapsulated tunnels over TCP encapsulated tunnels when possible.
3. TCP-Encapsulated Header Formats
Like UDP encapsulation, TCP encapsulation uses the first four bytes
of a message to differentiate IKE and ESP messages. TCP
encapsulation also adds a length field to define the boundaries of
messages within a stream. The message length is sent in a 16-bit
field that precedes every message. If the first 32-bits of the
message are zeros (a Non-ESP Marker), then the contents comprise an
IKE message. Otherwise, the contents comprise an ESP message.
Authentication Header (AH) messages are not supported for TCP
encapsulation.
Although a TCP stream may be able to send very long messages,
implementations SHOULD limit message lengths to typical UDP datagram
ESP payload lengths. The maximum message length is used as the
effective MTU for connections that are being encrypted using ESP, so
the maximum message length will influence characteristics of inner
connections, such as the TCP Maximum Segment Size (MSS).
Note that this method of encapsulation will also work for placing IKE
and ESP messages within any protocol that presents a stream
abstraction, beyond TCP.
3.1. TCP-Encapsulated IKE Header Format
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Non-ESP Marker |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ IKE header [RFC7296] ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
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The IKE header is preceded by a 16-bit length field in network byte
order that specifies the length of the IKE message (including the
Non-ESP marker) within the TCP stream. As with IKE over UDP port
4500, a zeroed 32-bit Non-ESP Marker is inserted before the start of
the IKE header in order to differentiate the traffic from ESP traffic
between the same addresses and ports.
o Length (2 octets, unsigned integer) - Length of the IKE packet
including the Length Field and Non-ESP Marker.
3.2. TCP-Encapsulated ESP Header Format
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ESP header [RFC4303] ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2
The ESP header is preceded by a 16-bit length field in network byte
order that specifies the length of the ESP packet within the TCP
stream.
The SPI field in the ESP header MUST NOT be a zero value.
o Length (2 octets, unsigned integer) - Length of the ESP packet
including the Length Field.
4. TCP-Encapsulated Stream Prefix
Each stream of bytes used for IKE and IPsec encapsulation MUST begin
with a fixed sequence of six bytes as a magic value, containing the
characters "IKETCP" as ASCII values. This allows peers to
differentiate this protocol from other protocols that may be run over
the same TCP port. Since TCP encapsulated IPsec is not assigned to a
specific port, responders may be able to receive multiple protocols
on the same port. The bytes of the stream prefix do not overlap with
the valid start of any other known stream protocol. This value is
only sent once, by the Initiator only, at the beginning of any stream
of IKE and ESP messages.
If other framing protocols are used within TCP to further encapsulate
or encrypt the stream of IKE and ESP messages, the Stream Prefix must
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be at the start of the Initiator's IKE and ESP message stream within
the added protocol layer [Appendix A]. Although some framing
protocols do support negotiating inner protocols, the stream prefix
should always be used in order for implementations to be as generic
as possible and not rely on other framing protocols on top of TCP.
0 1 2 3 4 5
+------+------+------+------+------+------+
| 0x49 | 0x4b | 0x45 | 0x54 | 0x43 | 0x50 |
+------+------+------+------+------+------+
Figure 3
5. Applicability
TCP encapsulation is applicable only when it has been configured to
be used with specific IKE peers. If a responder is configured to use
TCP encapsulation, it MUST listen on the configured port(s) in case
any peers will initiate new IKE sessions. Initiators MAY use TCP
encapsulation for any IKE session to a peer that is configured to
support TCP encapsulation, although it is recommended that initiators
should only use TCP encapsulation when traffic over UDP is blocked.
Since the support of TCP encapsulation is a configured property, not
a negotiated one, it is recommended that if there are multiple IKE
endpoints representing a single peer (such as multiple machines with
different IP addresses when connecting by Fully-Qualified Domain
Name, or endpoints used with IKE redirection), all of the endpoints
equally support TCP encapsulation.
If TCP encapsulation is being used for a specific IKE SA, all
messages for that IKE SA and its Child SAs MUST be sent over a TCP
connection until the SA is deleted or MOBIKE is used to change the SA
endpoints and/or encapsulation protocol. See Section 8 for more
details on using MOBIKE to transition between encapsulation modes.
5.1. Recommended Fallback from UDP
Since UDP is the preferred method of transport for IKE messages,
implementations that use TCP encapsulation should have an algorithm
for deciding when to use TCP after determining that UDP is unusable.
If an initiator implementation has no prior knowledge about the
network it is on and the status of UDP on that network, it SHOULD
always attempt negotiate IKE over UDP first. IKEv2 defines how to
use retransmission timers with IKE messages, and IKE_SA_INIT messages
specifically [RFC7296]. Generally, this means that the
implementation will define a frequency of retransmission, and the
maximum number of retransmissions allowed before marking the IKE SA
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as failed. An implementation can attempt negotiation over TCP once
it has hit the maximum retransmissions over UDP, or slightly before
to reduce connection setup delays. It is recommended that the
initial message over UDP is retransmitted at least once before
falling back to TCP, unless the initiator knows beforehand that the
network is likely to block UDP.
6. Connection Establishment and Teardown
When the IKE initiator uses TCP encapsulation for its negotiation, it
will initiate a TCP connection to the responder using the configured
TCP port. The first bytes sent on the stream MUST be the stream
prefix value [Section 4]. After this prefix, encapsulated IKE
messages will negotiate the IKE SA and initial Child SA [RFC7296].
After this point, both encapsulated IKE Figure 1 and ESP Figure 2
messages will be sent over the TCP connection. The responder MUST
wait for the entire stream prefix to be received on the stream before
trying to parse out any IKE or ESP messages. The stream prefix is
sent only once, and only by the initiator.
In order to close an IKE session, either the initiator or responder
SHOULD gracefully tear down IKE SAs with DELETE payloads. Once all
SAs have been deleted, the initiator of the original connection
SHOULD close the TCP connection if it does not intend to use the
connection for another IKE session to the responder. If the
connection is left idle, and the responder needs to clean up
resources, the responder MAY close the TCP connection.
An unexpected FIN or a RST on the TCP connection may indicate either
a loss of connectivity, an attack, or some other error. If a DELETE
payload has not been sent, both sides SHOULD maintain the state for
their SAs for the standard lifetime or time-out period. The original
initiator (that is, the endpoint that initiated the TCP connection
and sent the first IKE_SA_INIT message) is responsible for re-
establishing the TCP connection if it is torn down for any unexpected
reason. Since new TCP connections may use different ports due to NAT
mappings or local port allocations changing, the responder MUST allow
packets for existing SAs to be received from new source ports.
A peer MUST discard a partially received message due to a broken
connection.
Whenever the initiator opens a new TCP connection to be used for an
existing IKE SA, it MUST send the stream prefix first, before any IKE
or ESP messages. This follows the same behavior as the initial TCP
connection.
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If the connection is being used to resume a previous IKE session, the
responder can recognize the session using either the IKE SPI from an
encapsulated IKE message or the ESP SPI from an encapsulated ESP
message. If the session had been fully established previously, it is
suggested that the initiator send an UPDATE_SA_ADDRESSES message if
MOBIKE is supported, or an INFORMATIONAL message (a keepalive)
otherwise. If either initiator or responder receives a stream that
cannot be parsed correctly (initiator stream missing the stream
prefix, or message frames not parsable as IKE or ESP messages), it
MUST close the TCP connection. If there is instead a syntax issue
within an IKE message, an implementation MUST send the INVALID_SYNTAX
notify payload and tear down the IKE session as ususal, rather than
tearing down the TCP connection directly.
An initiator SHOULD only open one TCP connection per IKE SA, over
which it sends all of the corresponding IKE and ESP messages. This
helps ensure that any firewall or NAT mappings allocated for the TCP
connection apply to all of the traffic associated with the IKE SA
equally.
A responder SHOULD at any given time send packets for an IKE SA and
its Child SAs over only one TCP connection. It SHOULD choose the TCP
connection on which it last received a valid and decryptable IKE or
ESP message. In order to be considered valid for choosing a TCP
connection, an IKE message successfully decrypt and be authenticated,
not be a retransmission of a previously received message, and be
within the expected window for IKE message IDs. Similarly, an ESP
message must pass authentication checks and be decrypted, not be a
replay of a previous message.
Since a connection may be broken and a new connection re-established
by the initiator without the responder being aware, a responder
SHOULD accept receiving IKE and ESP messages on both old and new
connections until the old connection is closed by the initiator. A
responder MAY close a TCP connection that it perceives as idle and
extraneous (one previously used for IKE and ESP messages that has
been replaced by a new connection).
Multiple IKE SAs MUST NOT share a single TCP connection.
7. Interaction with NAT Detection Payloads
When negotiating over UDP port 500, IKE_SA_INIT packets include
NAT_DETECTION_SOURCE_IP and NAT_DETECTION_DESTINATION_IP payloads to
determine if UDP encapsulation of IPsec packets should be used.
These payloads contain SHA-1 digests of the SPIs, IP addresses, and
ports. IKE_SA_INIT packets sent on a TCP connection SHOULD include
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these payloads, and SHOULD use the applicable TCP ports when creating
and checking the SHA-1 digests.
If a NAT is detected due to the SHA-1 digests not matching the
expected values, no change should be made for encapsulation of
subsequent IKE or ESP packets, since TCP encapsulation inherently
supports NAT traversal. Implementations MAY use the information that
a NAT is present to influence keep-alive timer values.
If a NAT is detected, implementations need to handle transport mode
TCP and UDP packet checksum fixup as defined for UDP encapsulation
[RFC3948].
8. Using MOBIKE with TCP encapsulation
When an IKE session that has negotiated MOBIKE [RFC4555] is
transitioning between networks, the initiator of the transition may
switch between using TCP encapsulation, UDP encapsulation, or no
encapsulation. Implementations that implement both MOBIKE and TCP
encapsulation MUST support dynamically enabling and disabling TCP
encapsulation as interfaces change.
When a MOBIKE-enabled initiator changes networks, the
UPDATE_SA_ADDRESSES notification SHOULD be sent out first over UDP
before attempting over TCP. If there is a response to the
UPDATE_SA_ADDRESSES notification sent over UDP, then the ESP packets
should be sent directly over IP or over UDP port 4500 (depending on
if a NAT was detected), regardless of if a connection on a previous
network was using TCP encapsulation. Similarly, if the responder
only responds to the UPDATE_SA_ADDRESSES notification over TCP, then
the ESP packets should be sent over the TCP connection, regardless of
if a connection on a previous network did not use TCP encapsulation.
9. Using IKE Message Fragmentation with TCP encapsulation
IKE Message Fragmentation [RFC7383] is not required when using TCP
encapsulation, since a TCP stream already handles the fragmentation
of its contents across packets. Since fragmentation is redundant in
this case, implementations might choose to not negotiate IKE
fragmentation. Even if fragmentation is negotiated, an
implementation SHOULD NOT send fragments when going over a TCP
connection, although it MUST support receiving fragements.
If an implementation supports both MOBIKE and IKE fragmentation, it
SHOULD negotiate IKE fragmentation over a TCP encapsulated session in
case the session switches to UDP encapsulation on another network.
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10. Considerations for Keep-alives and DPD
Encapsulating IKE and IPsec inside of a TCP connection can impact the
strategy that implementations use to detect peer liveness and to
maintain middlebox port mappings. Peer liveness should be checked
using IKE Informational packets [RFC7296].
In general, TCP port mappings are maintained by NATs longers than UDP
port mappings, so IPsec ESP NAT keep-alives [RFC3948] SHOULD NOT be
sent when using TCP encapsulation. Any implementation using TCP
encapsulation MUST silently drop incoming NAT keep-alive packets, and
not treat them as errors. NAT keep-alive packets over a TCP
encapsulated IPsec connection will be sent with a length value of 1
byte, whose value is 0xFF [Figure 2].
Note that depending on the configuration of TCP and TLS on the
connection, TCP keep-alives [RFC1122] and TLS keep-alives [RFC6520]
may be used. These MUST NOT be used as indications of IKE peer
liveness.
11. Middlebox Considerations
Many security networking devices such as Firewalls or Intrusion
Prevention Systems, network optimization/acceleration devices and
Network Address Translation (NAT) devices keep the state of sessions
that traverse through them.
These devices commonly track the transport layer and/or the
application layer data to drop traffic that is anomalous or malicious
in nature.
A network device that monitors up to the application layer will
commonly expect to see HTTP traffic within a TCP socket running over
port 80, if non-HTTP traffic is seen (such as TCP encapsulated IKE),
this could be dropped by the security device.
A network device that monitors the transport layer will track the
state of TCP sessions, such as TCP sequence numbers. TCP
encapsulation of IKE should therefore use standard TCP behaviors to
avoid being dropped by middleboxes.
12. Performance Considerations
Several aspects of TCP encapsulation for IKE and IPsec packets may
negatively impact the performance of connections within the tunnel.
Implementations should be aware of these and take these into
consideration when determining when to use TCP encapsulation.
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12.1. TCP-in-TCP
If the outer connection between IKE peers is over TCP, inner TCP
connections may suffer effects from using TCP within TCP. In
particular, the inner TCP's round-trip-time estimation will be
affected by the burstiness of the outer TCP. This will make loss-
recovery of the inner TCP traffic less reactive and more prone to
spurious retransmission timeouts.
12.2. Added Reliability for Unreliable Protocols
Since ESP is an unreliable protocol, transmitting ESP packets over a
TCP connection will change the fundamental behavior of the packets.
Some application-level protocols that prefer packet loss to delay
(such as Voice over IP or other real-time protocols) may be
negatively impacted if their packets are retransmitted by the TCP
connection due to packet loss.
12.3. Quality of Service Markings
Quality of Service (QoS) markings, such as DSCP and Traffic Class,
should be used with care on TCP connections used for encapsulation.
Individual packets SHOULD NOT use different markings than the rest of
the connection, since packets with different priorities may be routed
differently and cause unnecessary delays in the connection.
12.4. Maximum Segment Size
A TCP connection used for IKE encapsulation SHOULD negotiate its
maximum segment size (MSS) in order to avoid unnecessary
fragmentation of packets.
13. Security Considerations
IKE responders that support TCP encapsulation may become vulnerable
to new Denial-of-Service (DoS) attacks that are specific to TCP, such
as SYN-flooding attacks. Responders should be aware of this
additional attack-surface.
Responders should be careful to ensure that the stream prefix
"IKETCP" uniquely identifies streams using the TCP encapsulation
protocol. The prefix was chosen to not overlap with the start of any
known valid protocol over TCP, but implementations should make sure
to validate this assumption in order to avoid unexpected processing
of TCP connections.
Attackers may be able to disrupt the TCP connection by sending
spurious RST packets. Due to this, implementations SHOULD make sure
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that IKE session state persists even if the underlying TCP connection
is torn down.
If MOBIKE is being used, all of the security considerations outlined
for MOBIKE apply [[RFC4555]].
Similarly to MOBIKE, TCP encapsulation requires a responder to handle
changing of source address and port due to network or connection
disruption. The successful delivery of valid IKE or ESP messages
over a new TCP connection is used by the responder to determine where
to send subsequent responses. If an attacker is able to send packets
on a new TCP connection that pass the validation checks of the
responder, it can influence which path future packets take. For this
reason, the validation of messages on the responder must include
decryption, authentication, and replay checks.
14. IANA Considerations
This memo includes no request to IANA.
TCP port 4500 is already allocated to IPsec. This port MAY be used
for the protocol described in this document, but implementations MAY
prefer to use other ports based on local policy.
15. Acknowledgments
The authors would like to acknowledge the input and advice of Stuart
Cheshire, Delziel Fernandes, Yoav Nir, Christoph Paasch, Yaron
Sheffer, David Schinazi, Graham Bartlett, Byju Pularikkal, March Wu,
Kingwel Xie, Valery Smyslov, Jun Hu, and Tero Kivinen. Special
thanks to Eric Kinnear for his implementation work.
16. References
16.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <http://www.rfc-editor.org/info/rfc7296>.
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16.2. Informative References
[I-D.nir-ipsecme-ike-tcp]
Nir, Y., "A TCP transport for the Internet Key Exchange",
draft-nir-ipsecme-ike-tcp-01 (work in progress), July
2012.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<http://www.rfc-editor.org/info/rfc1122>.
[RFC2817] Khare, R. and S. Lawrence, "Upgrading to TLS Within
HTTP/1.1", RFC 2817, DOI 10.17487/RFC2817, May 2000,
<http://www.rfc-editor.org/info/rfc2817>.
[RFC3948] Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
Stenberg, "UDP Encapsulation of IPsec ESP Packets",
RFC 3948, DOI 10.17487/RFC3948, January 2005,
<http://www.rfc-editor.org/info/rfc3948>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<http://www.rfc-editor.org/info/rfc4303>.
[RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol
(MOBIKE)", RFC 4555, DOI 10.17487/RFC4555, June 2006,
<http://www.rfc-editor.org/info/rfc4555>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[RFC6520] Seggelmann, R., Tuexen, M., and M. Williams, "Transport
Layer Security (TLS) and Datagram Transport Layer Security
(DTLS) Heartbeat Extension", RFC 6520,
DOI 10.17487/RFC6520, February 2012,
<http://www.rfc-editor.org/info/rfc6520>.
[RFC7383] Smyslov, V., "Internet Key Exchange Protocol Version 2
(IKEv2) Message Fragmentation", RFC 7383,
DOI 10.17487/RFC7383, November 2014,
<http://www.rfc-editor.org/info/rfc7383>.
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Appendix A. Using TCP encapsulation with TLS
This section provides recommendations on the support of TLS with the
TCP encapsulation.
When using TCP encapsulation, implementations may choose to use TLS
[RFC5246], to be able to traverse middle-boxes, which may block non
HTTP traffic.
If a web proxy is applied to the ports for the TCP connection, and
TLS is being used, the initiator can send an HTTP CONNECT message to
establish a tunnel through the proxy [RFC2817].
The use of TLS should be configurable on the peers. The responder
may expect to read encapsulated IKE and ESP packets directly from the
TCP connection, or it may expect to read them from a stream of TLS
data packets. The initiator should be pre-configured to use TLS or
not when communicating with a given port on the responder.
When new TCP connections are re-established due to a broken
connection, TLS must be re-negotiated. TLS Session Resumption is
recommended to improve efficiency in this case.
The security of the IKE session is entirely derived from the IKE
negotiation and key establishment and not from the TLS session (which
in this context is only used for encapsulation purposes), therefore
when TLS is used on the TCP connection, both the initiator and
responder SHOULD allow the NULL cipher to be selected for performance
reasons.
Implementations should be aware that the use of TLS introduces
another layer of overhead requiring more bytes to transmit a given
IKE and IPsec packet. For this reason, direct ESP, UDP
encapsulation, or TCP encapsulation without TLS should be preferred
in situations in which TLS is not required in order to traverse
middle-boxes.
Appendix B. Example exchanges of TCP Encapsulation with TLS
B.1. Establishing an IKE session
Client Server
---------- ----------
1) -------------------- TCP Connection -------------------
(IP_I:Port_I -> IP_R:TCP443 or TCP4500)
TcpSyn ---------->
<---------- TcpSyn,Ack
TcpAck ---------->
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2) --------------------- TLS Session ---------------------
ClientHello ---------->
ServerHello
Certificate*
ServerKeyExchange*
<---------- ServerHelloDone
ClientKeyExchange
CertificateVerify*
[ChangeCipherSpec]
Finished ---------->
[ChangeCipherSpec]
<---------- Finished
3) ---------------------- Stream Prefix --------------------
"IKETCP" ---------->
4) ----------------------- IKE Session ---------------------
Length + Non-ESP Marker ---------->
IKE_SA_INIT
HDR, SAi1, KEi, Ni,
[N(NAT_DETECTION_*_IP)]
<------ Length + Non-ESP Marker
IKE_SA_INIT
HDR, SAr1, KEr, Nr,
[N(NAT_DETECTION_*_IP)]
Length + Non-ESP Marker ---------->
first IKE_AUTH
HDR, SK {IDi, [CERTREQ]
CP(CFG_REQUEST), IDr,
SAi2, TSi, TSr, ...}
<------ Length + Non-ESP Marker
first IKE_AUTH
HDR, SK {IDr, [CERT], AUTH,
EAP, SAr2, TSi, TSr}
Length + Non-ESP Marker ---------->
IKE_AUTH + EAP
repeat 1..N times
<------ Length + Non-ESP Marker
IKE_AUTH + EAP
Length + Non-ESP Marker ---------->
final IKE_AUTH
HDR, SK {AUTH}
<------ Length + Non-ESP Marker
final IKE_AUTH
HDR, SK {AUTH, CP(CFG_REPLY),
SA, TSi, TSr, ...}
----------------- IKE Tunnel Established ----------------
Length + ESP frame ---------->
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Figure 4
1. Client establishes a TCP connection with the server on port 443
or 4500.
2. Client initiates TLS handshake. During TLS handshake, the
server SHOULD NOT request the client's' certificate, since
authentication is handled as part of IKE negotiation.
3. Client send the Stream Prefix for TCP encapsulated IKE
[Section 4] traffic to signal the beginning of IKE negotation.
4. Client and server establish an IKE connection. This example
shows EAP-based authentication, although any authentication
type may be used.
B.2. Deleting an IKE session
Client Server
---------- ----------
1) ----------------------- IKE Session ---------------------
Length + Non-ESP Marker ---------->
INFORMATIONAL
HDR, SK {[N,] [D,]
[CP,] ...}
<------ Length + Non-ESP Marker
INFORMATIONAL
HDR, SK {[N,] [D,]
[CP], ...}
2) --------------------- TLS Session ---------------------
close_notify ---------->
<---------- close_notify
3) -------------------- TCP Connection -------------------
TcpFin ---------->
<---------- Ack
<---------- TcpFin
Ack ---------->
--------------------- Tunnel Deleted -------------------
Figure 5
1. Client and server exchange INFORMATIONAL messages to notify IKE
SA deletion.
2. Client and server negotiate TLS session deletion using TLS
CLOSE_NOTIFY.
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3. The TCP connection is torn down.
The deletion of the IKE SA should lead to the disposal of the
underlying TLS and TCP state.
B.3. Re-establishing an IKE session
Client Server
---------- ----------
1) -------------------- TCP Connection -------------------
(IP_I:Port_I -> IP_R:TCP443 or TCP4500)
TcpSyn ---------->
<---------- TcpSyn,Ack
TcpAck ---------->
2) --------------------- TLS Session ---------------------
ClientHello ---------->
<---------- ServerHello
[ChangeCipherSpec]
Finished
[ChangeCipherSpec] ---------->
Finished
3) ---------------------- Stream Prefix --------------------
"IKETCP" ---------->
4) <---------------------> IKE/ESP flow <------------------>
Length + ESP frame ---------->
Figure 6
1. If a previous TCP connection was broken (for example, due to a
RST), the client is responsible for re-initiating the TCP
connection. The initiator's address and port (IP_I and Port_I)
may be different from the previous connection's address and
port.
2. In ClientHello TLS message, the client SHOULD send the Session
ID it received in the previous TLS handshake if available. It
is up to the server to perform either an abbreviated handshake
or full handshake based on the session ID match.
3. After TCP and TLS are complete, the client sends the Stream
Prefix for TCP encapsulated IKE traffic [Section 4].
4. The IKE and ESP packet flow can resume. If MOBIKE is being
used, the initiator SHOULD send UPDATE_SA_ADDRESSES.
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B.4. Using MOBIKE between UDP and TCP Encapsulation
Client Server
---------- ----------
(IP_I1:UDP500 -> IP_R:UDP500)
1) ----------------- IKE_SA_INIT Exchange -----------------
(IP_I1:UDP4500 -> IP_R:UDP4500)
Non-ESP Marker ----------->
Intial IKE_AUTH
HDR, SK { IDi, CERT, AUTH,
CP(CFG_REQUEST),
SAi2, TSi, TSr,
N(MOBIKE_SUPPORTED) }
<----------- Non-ESP Marker
Initial IKE_AUTH
HDR, SK { IDr, CERT, AUTH,
EAP, SAr2, TSi, TSr,
N(MOBIKE_SUPPORTED) }
<---------------- IKE tunnel establishment ------------->
2) ------------ MOBIKE Attempt on new network --------------
(IP_I2:UDP4500 -> IP_R:UDP4500)
Non-ESP Marker ----------->
INFORMATIONAL
HDR, SK { N(UPDATE_SA_ADDRESSES),
N(NAT_DETECTION_SOURCE_IP),
N(NAT_DETECTION_DESTINATION_IP) }
3) -------------------- TCP Connection -------------------
(IP_I2:PORT_I -> IP_R:TCP443 or TCP4500)
TcpSyn ----------->
<----------- TcpSyn,Ack
TcpAck ----------->
4) --------------------- TLS Session ---------------------
ClientHello ----------->
ServerHello
Certificate*
ServerKeyExchange*
<----------- ServerHelloDone
ClientKeyExchange
CertificateVerify*
[ChangeCipherSpec]
Finished ----------->
[ChangeCipherSpec]
<----------- Finished
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5) ---------------------- Stream Prefix --------------------
"IKETCP" ---------->
6) ----------------------- IKE Session ---------------------
Length + Non-ESP Marker ----------->
INFORMATIONAL (Same as step 2)
HDR, SK { N(UPDATE_SA_ADDRESSES),
N(NAT_DETECTION_SOURCE_IP),
N(NAT_DETECTION_DESTINATION_IP) }
<------- Length + Non-ESP Marker
HDR, SK { N(NAT_DETECTION_SOURCE_IP),
N(NAT_DETECTION_DESTINATION_IP) }
7) <----------------- IKE/ESP data flow ------------------->
Figure 7
1. During the IKE_SA_INIT exchange, the client and server exchange
MOBIKE_SUPPORTED notify payloads to indicate support for
MOBIKE.
2. The client changes its point of attachment to the network, and
receives a new IP address. The client attempts to re-establish
the IKE session using the UPDATE_SA_ADDRESSES notify payload,
but the server does not respond because the network blocks UDP
traffic.
3. The client brings up a TCP connection to the server in order to
use TCP encapsulation.
4. The client initiates and TLS handshake with the server.
5. The client sends the Stream Prefix for TCP encapsulated IKE
traffic [Section 4].
6. The client sends the UPDATE_SA_ADDRESSES notify payload on the
TCP encapsulated connection. Note that this IKE message is the
same as the one sent over UDP in step 2, and should have the
same message ID and contents.
7. The IKE and ESP packet flow can resume.
Authors' Addresses
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Tommy Pauly
Apple Inc.
1 Infinite Loop
Cupertino, California 95014
US
Email: tpauly@apple.com
Samy Touati
Ericsson
300 Holger Way
San Jose, California 95134
US
Email: samy.touati@ericsson.com
Ravi Mantha
Cisco Systems
SEZ, Embassy Tech Village
Panathur, Bangalore 560 037
India
Email: ramantha@cisco.com
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