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Versions: 00 01 02 03 04 draft-ietf-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
   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 October 27, 2016.

Copyright Notice

   Copyright (c) 2016 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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   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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