Internet DRAFT - draft-pauly-ipsecme-tcp-encaps
draft-pauly-ipsecme-tcp-encaps
Network T. Pauly
Internet-Draft Apple Inc.
Intended status: Standards Track S. Touati
Expires: October 27, 2016 Ericsson
R. Mantha
Cisco Systems
April 25, 2016
TCP Encapsulation of IKEv2 and IPSec Packets
draft-pauly-ipsecme-tcp-encaps-04
Abstract
This document describes a method to transport IKEv2 and IPSec packets
over a TCP connection for traversing network middleboxes that may
block IKEv2 negotiation over UDP. This method, referred to as TCP
encapsulation, involves sending all packets for tunnel establishment
as well as tunneled packets 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
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
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This Internet-Draft will expire on October 27, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Provisions Relating to IETF Documents
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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 IKEv2 Header Format . . . . . . . . . . 5
3.2. TCP-Encapsulated ESP Header Format . . . . . . . . . . . 6
4. TCP-Encapsulated Stream Prefix . . . . . . . . . . . . . . . 6
5. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Connection Establishment and Teardown . . . . . . . . . . . . 7
7. Interaction with NAT Detection Payloads . . . . . . . . . . . 8
8. Using MOBIKE with TCP encapsulation . . . . . . . . . . . . . 8
9. Using IKEv2 Message Fragmentation with TCP encapsulation . . 9
10. Considerations for Keep-alives and DPD . . . . . . . . . . . 9
11. Middlebox Considerations . . . . . . . . . . . . . . . . . . 9
12. Performance Considerations . . . . . . . . . . . . . . . . . 10
12.1. TCP-in-TCP . . . . . . . . . . . . . . . . . . . . . . . 10
12.2. Added Reliability for Unreliable Protocols . . . . . . . 10
12.3. Quality of Service Markings . . . . . . . . . . . . . . 10
12.4. Maximum Segment Size . . . . . . . . . . . . . . . . . . 10
13. Security Considerations . . . . . . . . . . . . . . . . . . . 11
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
16.1. Normative References . . . . . . . . . . . . . . . . . . 11
16.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Using TCP encapsulation with TLS . . . . . . . . . . 12
Appendix B. Example exchanges of TCP Encapsulation with TLS . . 13
B.1. Establishing an IKEv2 session . . . . . . . . . . . . . . 13
B.2. Deleting an IKEv2 session . . . . . . . . . . . . . . . . 15
B.3. Re-establishing an IKEv2 session . . . . . . . . . . . . 16
B.4. Using MOBIKE between UDP and TCP Encapsulation . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
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 its data traffic. Many network
middleboxes that filter traffic on public hotspots block all UDP
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traffic, including IKEv2 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 IKEv2 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, IKEv2 negotiations begin over UDP port 500.
If no NAT is detected between the initiator and the receiver,
then subsequent IKEv2 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 IKEv2 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 IKEv2 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 IKEv2
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 IKEv2 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 IKEv2 and
ESP message within streams, and to provide guidelines for how to
configure and use TCP encapsulation.
Some previous solutions 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.
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 IKEv2
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.
o Optionally, an extra framing protocol to use on top of TCP to
further encapsulate the stream of IKEv2 and IPSec packets. See
Appendix A for a detailed discussion.
This document leaves the selection of TCP ports up to
implementations. It's suggested to use TCP port 4500, which is
allocated for IPSec NAT Traversal.
Since TCP encapsulation of IKEv2 and IPSec packets adds overhead and
has potential performance trade-offs compared to direct or UDP-
encapsulated tunnels (as described in Performance Considerations,
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Section 12), when possible, implementations SHOULD prefer IKEv2
direct or UDP encapsulated tunnels over TCP encapsulated tunnels.
3. TCP-Encapsulated Header Formats
In order to encapsulate IKEv2 and ESP messages within a TCP stream, a
16-bit length field precedes every message. If the first 32-bits of
the message are zeros (a Non-ESP Marker), then the contents comprise
an IKEv2 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).
3.1. TCP-Encapsulated IKEv2 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ IKEv2 header [RFC7296] ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
The IKE header is preceded by a 16-bit length field in network byte
order that specifies the length of the IKE packet within the TCP
stream. As with IKEv2 over UDP port 4500, a zeroed 32-bit Non-ESP
Marker is inserted before the start of the IKEv2 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.
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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.
o Length (2 octets, unsigned integer) - Length of the ESP packet
including the Length Field.
4. TCP-Encapsulated Stream Prefix
Each TCP stream used for IKEv2 and IPSec encapsulation MUST begin
with a fixed sequence of five bytes as a magic value, containing the
characters "IKEv2" as ASCII values. This allows peers to
differentiate this protocol from other protocols that may be run over
TCP streams, since the value does 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 TCP stream.
0 1 2 3 4
+------+------+------+------+------+
| 0x69 | 0x6b | 0x65 | 0x76 | 0x32 |
+------+------+------+------+------+
Figure 3
5. Applicability
TCP encapsulation is applicable only when it has been configured to
be used with specific IKEv2 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 IKEv2 sessions. Initiators MAY use
TCP encapsulation for any IKEv2 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.
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Any specific IKE SA, along with its Child SAs, is either TCP
encapsulated or not. A mix of TCP and UDP encapsulation for a single
SA is not allowed.
6. Connection Establishment and Teardown
When the IKEv2 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
IKEv2 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.
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 MUST
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.
The streams of data sent over any TCP connection used for this
protocol MUST begin with the stream prefix value followed by a
complete message, which is either an encapsulated IKE or ESP message.
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, it MUST close the TCP connection.
Multiple TCP connections between the initiator and the responder are
allowed, but their use must take into account the initiator
capabilities and the deployment model such as to connect to multiple
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gateways handling different ESP SAs when deployed in a high
availability model. It is also possible to negotiate multiple IKE
SAs over the same TCP connection.
The processing of the TCP packets is the same whether its within a
single or multiple TCP connections.
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
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 IKEv2 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.
8. Using MOBIKE with TCP encapsulation
When an IKEv2 session is transitioned between networks using MOBIKE
[RFC4555], 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.
The encapsulation method of ESP packets MUST always match the
encapsulation method of the IKEv2 negotiation, which may be different
when an IKEv2 endpoint changes networks. 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.
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9. Using IKEv2 Message Fragmentation with TCP encapsulation
IKEv2 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 IKEv2
fragmentation. Even if fragmentation is negotiated, an
implementation MAY choose to not fragment when going over a TCP
connection.
If an implementation supports both MOBIKE and IKEv2 fragmentation, it
SHOULD negotiate IKEv2 fragmentation over a TCP encapsulated session
in case the session switches to UDP encapsulation on another network.
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 IKEv2 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 IKEv2 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
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port 80, if non-HTTP traffic is seen (such as TCP encapsulated
IKEv2), 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 IKEv2 should therefore use standard TCP behaviors to
avoid being dropped by middleboxes.
12. Performance Considerations
Several aspects of TCP encapsulation for IKEv2 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.
12.1. TCP-in-TCP
If the outer connection between IKEv2 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 IKEv2 encapsulation SHOULD negotiate its
maximum segment size (MSS) in order to avoid unnecessary
fragmentation of packets.
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13. Security Considerations
IKEv2 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.
Attackers may be able to disrupt the TCP connection by sending
spurious RST packets. Due to this, implementations SHOULD make sure
that IKE session state persists even if the underlying TCP connection
is torn down.
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
and Kingwel Xie. 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>.
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.
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[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>.
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.
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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 IKEv2 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 IKEv2 session is entirely derived from the IKVEv2
negotiation and key establishment, therefore When TLS is used on the
TCP connection, both the initiator and responder MUST allow for the
NULL cipher to be selected.
Implementations must be aware that the use of TLS introduces another
layer of overhead requiring more bytes to transmit a given IKEv2 and
IPSec packet.
Appendix B. Example exchanges of TCP Encapsulation with TLS
B.1. Establishing an IKEv2 session
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Client Server
---------- ----------
-------------------- TCP Connection -------------------
1) (IP_I:Port_I -> IP_R:TCP443 or TCP4500)
TcpSyn ---------->
<---------- TcpSyn,Ack
TcpAck ---------->
--------------------- TLS Session ---------------------
2) ClientHello ---------->
ServerHello
Certificate*
ServerKeyExchange*
<---------- ServerHelloDone
ClientKeyExchange
CertificateVerify*
[ChangeCipherSpec]
Finished ---------->
[ChangeCipherSpec]
<---------- Finished
---------------------- IKEv2 Session --------------------
3) IKE_SA_INIT ---------->
HDR, SAi1, KEi, Ni,
[N(NAT_DETECTION_*_IP)]
<---------- IKE_SA_INIT
HDR, SAr1, KEr, Nr,
[N(NAT_DETECTION_*_IP)]
first IKE_AUTH ---------->
HDR, SK {IDi, [CERTREQ]
CP(CFG_REQUEST), IDr,
SAi2, TSi, TSr, ...}
<---------- first IKE_AUTH
HDR, SK {IDr, [CERT], AUTH,
EAP, SAr2, TSi, TSr}
EAP ---------->
repeat 1..N times
<---------- EAP
final IKE_AUTH ---------->
HDR, SK {AUTH}
<---------- final IKE_AUTH
HDR, SK {AUTH, CP(CFG_REPLY),
SA, TSi, TSr, ...}
-------------- IKEv2 Tunnel Established -------------
Figure 4
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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 IKEv2 negotiation.
3. Client and server establish an IKEv2 connection. This example
shows EAP-based authentication, although any authentication
type may be used.
B.2. Deleting an IKEv2 session
Client Server
---------- ----------
---------------------- IKEv2 Session --------------------
1) INFORMATIONAL ---------->
HDR, SK {[N,] [D,]
[CP,] ...}
<---------- INFORMATIONAL
HDR, SK {[N,] [D,]
[CP], ...}
--------------------- TLS Session ---------------------
2) close_notify ---------->
<---------- close_notify
-------------------- TCP Connection -------------------
3) 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.
3. The TCP connection is torn down.
Unless the TCP connection and/or TLS session are being used for
multiple IKE SAs, the deletion of the IKE SA should lead to the
disposal of the underlying TLS and TCP state.
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B.3. Re-establishing an IKEv2 session
Client Server
---------- ----------
-------------------- TCP Connection -------------------
1) (IP_I:Port_I -> IP_R:TCP443 or TCP4500)
TcpSyn ---------->
<---------- TcpSyn,Ack
TcpAck ---------->
--------------------- TLS Session ---------------------
2) ClientHello ---------->
<---------- ServerHello
[ChangeCipherSpec]
Finished
[ChangeCipherSpec] ---------->
Finished
3) <--------------------> IKEv2/ESP flow <----------------->
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 IKEv2 and ESP packet flow
can resume. If MOBIKE is being used, the initiator SHOULD send
UPDATE_SA_ADDRESSES.
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)
Intial IKE_AUTH ----------->
HDR, SK { IDi, CERT, AUTH,
CP(CFG_REQUEST),
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SAi2, TSi, TSr,
N(MOBIKE_SUPPORTED) }
<----------- Initial IKE_AUTH
HDR, SK { IDr, CERT, AUTH,
EAP, SAr2, TSi, TSr,
N(MOBIKE_SUPPORTED) }
<--------------- IKEv2 tunnel establishment ------------>
2) ------------ MOBIKE Attempt on new network --------------
(IP_I2:UDP4500 -> IP_R:UDP4500)
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
5) ---------------------- IKEv2 Session --------------------
INFORMATIONAL ----------->
HDR, SK { N(UPDATE_SA_ADDRESSES),
N(NAT_DETECTION_SOURCE_IP),
N(NAT_DETECTION_DESTINATION_IP) }
<----------- INFORMATIONAL
HDR, SK { N(NAT_DETECTION_SOURCE_IP),
N(NAT_DETECTION_DESTINATION_IP) }
6) <---------------- IKEv2/ESP data flow ------------------>
Figure 7
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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 IKEv2 session using the UPDATE_SA_ADDRESSES notify payload,
but the server does not respond because the network blocks UDP
traffic.
3. The client beings 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 UPDATE_SA_ADDRESSES notify payload on the
TCP encapsulated connection.
6. The IKEv2 and ESP packet flow can resume.
Authors' Addresses
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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