--- 1/draft-ietf-ipsecme-tcp-encaps-01.txt 2016-08-17 11:15:51.817490218 -0700 +++ 2/draft-ietf-ipsecme-tcp-encaps-02.txt 2016-08-17 11:15:51.857491222 -0700 @@ -1,48 +1,48 @@ Network T. Pauly Internet-Draft Apple Inc. Intended status: Standards Track S. Touati -Expires: January 8, 2017 Ericsson +Expires: February 18, 2017 Ericsson R. Mantha Cisco Systems - July 7, 2016 + August 17, 2016 - TCP Encapsulation of IKE and IPSec Packets - draft-ietf-ipsecme-tcp-encaps-01 + TCP Encapsulation of IKE and IPsec Packets + draft-ietf-ipsecme-tcp-encaps-02 Abstract - This document describes a method to transport IKE and IPSec packets + 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 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. + 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 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 January 8, 2017. + This Internet-Draft will expire on February 18, 2017. 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 @@ -69,142 +69,152 @@ 9. Using IKE Message Fragmentation with TCP encapsulation . . . 9 10. Considerations for Keep-alives and DPD . . . . . . . . . . . 9 11. Middlebox Considerations . . . . . . . . . . . . . . . . . . 10 12. Performance Considerations . . . . . . . . . . . . . . . . . 10 12.1. TCP-in-TCP . . . . . . . . . . . . . . . . . . . . . . . 10 12.2. Added Reliability for Unreliable Protocols . . . . . . . 11 12.3. Quality of Service Markings . . . . . . . . . . . . . . 11 12.4. Maximum Segment Size . . . . . . . . . . . . . . . . . . 11 13. Security Considerations . . . . . . . . . . . . . . . . . . . 11 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 - 15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 + 15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 16. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 16.1. Normative References . . . . . . . . . . . . . . . . . . 12 16.2. Informative References . . . . . . . . . . . . . . . . . 12 Appendix A. Using TCP encapsulation with TLS . . . . . . . . . . 13 Appendix B. Example exchanges of TCP Encapsulation with TLS . . 14 B.1. Establishing an IKE session . . . . . . . . . . . . . . . 14 B.2. Deleting an IKE session . . . . . . . . . . . . . . . . . 16 B.3. Re-establishing an IKE session . . . . . . . . . . . . . 17 B.4. Using MOBIKE between UDP and TCP Encapsulation . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 1. Introduction - IKEv2 [RFC7296] is a protocol for establishing IPSec tunnels, using + 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 network middleboxes that filter traffic on public hotspots block all - UDP traffic, including IKE and IPSec, but allow TCP connections + 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 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. + 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. + 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: + 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]. + 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 [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 solutions include: + Some previous alternatives include: 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. + 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. + 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. + 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 + further encapsulate the stream of IKE and IPsec packets. See Appendix A for a detailed discussion. 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. + allocated for IPsec NAT Traversal. - Since TCP encapsulation of IKE and IPSec packets adds overhead and + 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 - In order to encapsulate IKE 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 IKE message. Otherwise, the contents comprise an ESP message. + 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). @@ -218,25 +228,25 @@ | Non-ESP Marker | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ IKE 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 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. + 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 | @@ -252,33 +262,38 @@ 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 + 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 - TCP streams, since the bytes 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. + 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 be at the start of the Initiator's IKE and ESP message stream within - the added protocol layer [Appendix A]. + 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 @@ -293,23 +308,22 @@ 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. No packets should be sent - over UDP or direct ESP for the IKE SA or its Child SAs while using - TCP encapsulation. + endpoints and/or encapsulation protocol. See Section 8 for more + details on using MOBIKE to transition between encapsulation modes. 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. @@ -352,82 +366,79 @@ 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. + 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 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. 8. Using MOBIKE with TCP encapsulation When an IKE 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 IKE negotiation, which may be different - when an IKE 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. + 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 MAY choose to not fragment when going over a TCP connection. 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. 10. Considerations for Keep-alives and DPD - Encapsulating IKE and IPSec inside of a TCP connection can impact the + 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 + 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 + 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 @@ -444,21 +455,21 @@ 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 + 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. 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- @@ -488,30 +499,37 @@ 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 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 + 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. @@ -600,21 +618,21 @@ 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 + 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 -------------------