IPv6 Operations WG R. Graveman Internet-Draft RFG Security, LLC Expires: December 10, 2004 M. Parthasarathy Nokia P. Savola CSC/FUNET H. Tschofenig Siemens June 11, 2004 Using IPsec to Secure IPv6-over-IPv4 Tunnels draft-tschofenig-v6ops-secure-tunnels-00.txt Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 10, 2004. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This document gives guidance on securing IPv6-in-IPv4 tunnels using IPsec. No additional protocol extensions are described beyond those available with the revised IPsec framework. IKEv2 is extensively used as an authentication and key exchange protocol to cover address Graveman, et al. Expires December 10, 2004 [Page 1]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 configuration procedures, and the usage of the Extensible Authentication Procotol and NAT traversal capabilities is also described. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Threats and the Use of IPsec . . . . . . . . . . . . . . . . . 3 2.1 IPsec in Transport Mode . . . . . . . . . . . . . . . . . 4 2.2 IPsec in Tunnel Mode . . . . . . . . . . . . . . . . . . . 4 3. Scenarios and Overview . . . . . . . . . . . . . . . . . . . . 5 3.1 Router-to-Router Tunnels . . . . . . . . . . . . . . . . . 5 3.2 Site-to-Router/Router-to-Site Tunnels . . . . . . . . . . 5 3.3 Host-to-Host Tunnels . . . . . . . . . . . . . . . . . . . 7 4. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 7 5. IPsec Configuration Details . . . . . . . . . . . . . . . . . 9 5.1 IPsec Transport mode . . . . . . . . . . . . . . . . . . . 9 5.2 IPsec Tunnel mode . . . . . . . . . . . . . . . . . . . . 10 5.2.1 SPD for Host-to-Host Scenario . . . . . . . . . . . . 10 5.2.2 SPD for Host-to-Router scenario . . . . . . . . . . . 10 6. Dynamic Address Configuration . . . . . . . . . . . . . . . . 12 7. Extensible Authentication Support . . . . . . . . . . . . . . 13 8. NAT Traversal . . . . . . . . . . . . . . . . . . . . . . . . 15 9. Tunnel Endpoint Discovery . . . . . . . . . . . . . . . . . . 16 10. Example . . . . . . . . . . . . . . . . . . . . . . . . . . 17 11. Security Considerations . . . . . . . . . . . . . . . . . . 17 12. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . 18 13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 18 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 19 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 15.1 Normative References . . . . . . . . . . . . . . . . . . . . 19 15.2 Informative References . . . . . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 22 Intellectual Property and Copyright Statements . . . . . . . . 23 Graveman, et al. Expires December 10, 2004 [Page 2]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 1. Introduction The IPv6 operations (v6ops) working group has selected IPv6-in-IPv4 tunneling [I-D.ietf-v6ops-mech-v2] as one of the IPv6 transition mechanisms for IPv6 deployment. A number of threats have been identified with possible solutions to mitigate them [I-D.ietf-v6ops-mech-v2]. One of the solutions is the use of IPsec protected tunnels, but there is little detail on how IPsec would actually be used in an interoperable manner. This memo describes the use of IPsec in detail. First this document analyses the threats that can be addressed by IPsec. Next, this document discusses some of the assumptions made by this document for successful IPsec SA establishment. Then, it gives the details of IKE/IPsec exchange with packet formats and SPD entries. Finally, it discusses the usage of IPsec NAT-traversal mechanism that can be used with configured tunnels in some scenarios. 2. Threats and the Use of IPsec Following threats have been identified in [I-D.ietf-v6ops-mech-v2]: 1. IPv4 address of the encapsulating ("outer") packet can be spoofed. 2. IPv6 address of the encapsualted ("inner") packet can be spoofed. The reason for threat (1) is due to the lack of widespread deployment of IPv4 ingress filtering in the network. The reason for threat (2) is that the IPv6 packet is encapsulated in IPv4 and hence escapes IPv6 ingress filtering. [I-D.ietf-v6ops-mech-v2] specifies following strict address checks as mitigating measures. To mitigate threat (1), the decapsulator verifies that the IPv4 source address of the packet is the same as the address of the configured tunnel endpoint. The decapsulator may also implement IPv4 ingress filtering, i.e., checks whether the packet is received on the expected interface. To mitigate threat (2), the decapsulator verifies whether the inner IPv6 address is a valid IPv6 address and also applies IPv6 ingress filtering before accepting the IPv6 packet. This memo proposes to use IPsec for providing stronger security in preventing these threats. IPsec can be used in two ways, in transport and tunnel mode. Graveman, et al. Expires December 10, 2004 [Page 3]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 2.1 IPsec in Transport Mode In transport mode, the IPsec security association (SA) is established to protect the traffic defined by (IPv4-source, IPv4-dest, protocol = 41). On receiving such an IPsec packet, the receiver first applies the IPsec transform (ESP) and then matches the packet against the inbound selectors associated with the SA to verify that the packet is appropriate for the SA via which it was received. The successful verification implies that the packet came from the right IPv4 endpoint as the SA is bound to the IPv4 source address. This prevents threat (1) but not the threat (2). IPsec in transport mode does not verify the contents of the payload itself where the IPv6 addresses are carried, that is, two nodes that are using IPsec transport mode to secure the tunnel can spoof the inner payload. The packet will be decapsulated successfully and accepted. The shortcoming can be mitigated by IPv6 ingress filtering i.e., check that the packet is arriving from the interface in the direction of the route towards the tunnel end-point, similar to a Strict Reverse Path Forwarding (RPF) check [RFC3704]. For performing ingress filtering, it is assumed that the tunnel is modelled as an interface and the traffic of the tunnel is protected using IPsec transport mode SA. 2.2 IPsec in Tunnel Mode In tunnel mode, the IPsec SA is established to protect the traffic defined by (IPv6-source, IPv6-destination). On receiving such an IPsec packet, the receiver first applies the IPsec transform (ESP) and then matches the packet against the inbound selectors associated with the SA to verify that the packet is appropriate for the SA via which it was received. The successful verification implies that the packet came from the right IPv6 endpoint as the SA is bound to the IPv6 source address. The IPv4 addresses may be spoofed and IPsec cannot detect it in this mode, that is, two nodes that are using IPsec tunnel mode to secure the tunnel with a common tunnel endpoint can spoof each other's IPv4 address. But, the packet will not be accepted by IPsec as the IPv6 address bound to the SA will not match the address in the spoofed packet. Thus, the outer address spoofing is irrelevant as long as the inner IPv6 packet can be verified to come from the right IPv6 endpoint. It may not be possible to always verify the IPv6 address -- for example with link-local addresses. The additional issues with Graveman, et al. Expires December 10, 2004 [Page 4]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 address verification are discussed in each of the scenarios section appropriately. 3. Scenarios and Overview There are roughly three kinds of scenarios: (generic) router-to-router tunnels, site-to-router/router-to-site tunnels (a generalization of host-to-router/router-to-host scenarios, respectively), and host-to-host tunnels. 3.1 Router-to-Router Tunnels IPv6/IPv4 hosts and routers can tunnel IPv6 datagrams over regions of IPv4 routing topology by encapsulating them within IPv4 packets. Tunneling can be used in a variety of ways. .--------. _----_ .--------. |v6-in-v4| _( IPv4 )_ |v6-in-v4| | Router | <======( Internet )=====> | Router | | A | (_ _) | B | '--------' '----' '--------' ^ IPsec tunnel between ^ | Router A and Router B | V V .--------. .-------. | End | | End | | Host | | Host | '--------' '--------' Figure 1: Router-to-Router Scenario IPv6/IPv4 routers interconnected by an IPv4 infrastructure can tunnel IPv6 packets between themselves. In this case, the tunnel spans one segment of the end-to-end path that the IPv6 packet takes. The source and destination addresses of the IPv6 packets traversing the tunnel could come from a wide range of IPv6 prefixes. It is not scalable to establish IPsec tunnel mode SAs for all such packets. Hence, IPsec transport mode SA is recommended for this scenario. IPv6 ingress filtering should be performed to mitigate the IPv6 address spoofing threat. A specific case of router-to-router tunnels, when one router resides at an end site, is described in the next section. 3.2 Site-to-Router/Router-to-Site Tunnels This is a generalization of site-to-router and router-to-site Graveman, et al. Expires December 10, 2004 [Page 5]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 tunneling, because the issues when connecting a whole site (using a router), and connecting a single host are roughly equal. _----_ .---------. IPsec _----_ IPsec .-------. _( IPv6 )_ |v6-in-v4 | Tunnel _( IPv4 )_ Tunnel | V4/V6 | ( Internet )<--->| Router |<=======( Internet )=======>| Site B | (_ _) | A | (_ _) '--------' '----' '---------' '----' ^ | V .--------. | Native | | IPv6 | | node | '--------' Figure 2: Router-to-Site Scenario IPv6/IPv4 routers can tunnel IPv6 packets to their final destination IPv6/IPv4 host. This tunnel spans only the last segment of the end-to-end path. This is the same as the Site-to-Router case. +---------------------+ | IPv6 Network | | | .--------. _----_ | .--------. | | V6/V4 | _( IPv4 )_ | |v6-in-v4| | | Site B |<====( Internet )==========>| Router | | '--------' (_ _) | | A | | '----' | '--------' | IPsec tunnel between | ^ | V6 Site and Router A | | | | V | | .-------. | | | V6 | | | | Host | | | '--------' | +---------------------+ Figure 3: Site-to-Router Scenario IPv6/IPv4 hosts can tunnel IPv6 packets to an intermediary IPv6/IPv4 router that is reachable via an IPv4 infrastructure. This type of tunnel spans the first segment of the packet's end-to-end path. Graveman, et al. Expires December 10, 2004 [Page 6]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 In this case, the host(s) originate the packet with source address coming from a well known prefix whereas the destination address could be any node on the internet. In this case, the IPsec tunnel mode SA can be bound to the prefix that was allocated to the router at Site B and router A can verify that the source address of the packet matches the prefix. Site B will not be able to do a similar verification for the packets it receives. This may be quite reasonable for most of the deployment cases, for example, the ISP allocating a /48 to a customer. The CPE (where the tunnel is terminated) "trusts" (in a weak sense) the ISP's router and the ISP's router can verify that the Site B is the only one that can originate packets within the /48. IPsec tunnel mode SA is recommended for this case, though similar amount of protection can be obtained with transport mode SA with strict ingress filtering as well. 3.3 Host-to-Host Tunnels .--------. _----_ .--------. | V6/V4 | _( IPv4 )_ | V6/V4 | | Host | <======( Internet )=====> | Host | | A | (_ _) | B | '--------' '----' '--------' IPsec tunnel between Host A and Host B Figure 4: Host-to-Host Scenario IPv6/IPv4 hosts that are interconnected by an IPv4 infrastructure can tunnel IPv6 packets between themselves. In this case, the tunnel spans the entire end-to-end path that the packet takes. In this case, the source and the destination IPv6 address are known a priori. A tunnel mode SA can be bound to the specific address. The address verification prevents IPv6 address spoofing completely. 4. Assumptions Throughout this document we make a few assumptions which are briefly listed here. The following documents are used as a basis: o Revised 'Security Architecture for the Internet Protocol' as described in [I-D.ietf-ipsec-rfc2401bis]. o IKEv2 as described in [I-D.ietf-ipsec-ikev2] and the accompagning documents for cipher suites and cryptgraphic algorithms (see [I-D.ietf-ipsec-ikev2-algorithms], [I-D.ietf-ipsec-ikev2-iana] and [I-D.ietf-ipsec-ui-suites]). Graveman, et al. Expires December 10, 2004 [Page 7]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 o 'IP Encapsulating Security Payload (ESP)' as described in [I-D.ietf-ipsec-esp-v3] o 'UDP Encapsulation of IPsec Packets' as described in [I-D.ietf-ipsec-udp-encaps] for the purpose of NAT traversal. Please note that we do not consider the usage of the IP Authentication Header (AH) [I-D.ietf-ipsec-rfc2402bis] since Section 3.2 of [I-D.ietf-ipsec-rfc2401bis] specifies that IPsec implementations MUST implement ESP and MAY implement AH with the reasoning that ESP provides security services (such as integrity protection without confidentiality protection using 'NULL' encryption) which are comparable with AH. Furthermore, we focus on IKEv2 since [I-D.ietf-ipsec-rfc2401bis] assumes use of IKEv2 as a key and security association management system and not IKEv1 with its extensions. The decision to focus on IKEv2 and newer IPsec documents is based on the premise that doing so allows using "mixed-mode" transforms as described below. This is useful for Transport mode SAs. Some implementations might, however, support these SAs already, at least using manual configuration. XXX TBD: the issue may be revisited, and/or "legacy" considerations added in an Appendix, etc. In supporting IPv4/IPv6 transition the following functionality described in section 5.1.2 of [I-D.ietf-ipsec-rfc2401bis] is particularly useful: " o IPsec allows the IP version of the encapsulating header to be different from that of the inner header. " The IPsec framework does not allow IKEv1/IKEv2 to be used to create tunnels which do not experience cryptographic protection although this functionality might be useful in some environments. IKEv2 would then migrate into a secure signaling protocol for tunnel establishment (without implementing data traffic protection) in a fashion similar to the 'IPv6 Tunnel Broker with the Tunnel Setup Protocol (TSP)' [I-D.blanchet-v6ops-tunnelbroker-tsp] protocol proposal. Section 4.2 of [I-D.ietf-ipsec-rfc2401bis], however, prohibits this functionality by stating: Graveman, et al. Expires December 10, 2004 [Page 8]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 " A compliant implementation MUST NOT allow instantiation of an ESP SA that employs both NULL encryption and no integrity algorithm. " Regarding the usage of the Explicit Congestion Notification (ECN), it appears that the ECN bits in the IPv4 and IPv6 headers have exactly the same semantics, so the bits just need to be copied from the outer IPv4 header to the inner IPv6 header on tunnel exit. 5. IPsec Configuration Details This section describes details about the IPsec tunnel establishment for protection of IPv4/IPv6 data traffic. 5.1 IPsec Transport mode This is typically used in Router-to-Router scenario. The following SPD entries assume that there are two routers Router1 and Router2, whose tunnel endpoint's IPv4 address is denoted by IPV4-TEP1 and IPV4-TEP2 respectively. Router1's SPD OUT : IF SRC = IPV4-TEP1 && DST = IPV4-TEP2 && protocol = 41 THEN USE ESP TRANSPORT MODE SA Router1's SPD IN: IF SRC = IPV4-TEP2 && DST = IPV4-TEP1 && protocol = 41 THEN USE ESP TRANSPORT MODE SA Router2's SPD OUT: IF SRC = IPV4-TEP2 && DST = IPV4-TEP1 && protocol = 41 THEN USE ESP TRANSPORT MODE SA Router2's SPD IN: IF SRC = IPV4-TEP1 && DST = IPV4-TEP2 && protocol = 41 THEN USE ESP TRANSPORT MODE SA The IDci and IDcr payloads of IKEv1 carry the IPv4-TEP1, IPV4-TEP2 and protocol value 41 as phase 2 identities. With IKEv2, the traffic selectors are used to carry the same information. Graveman, et al. Expires December 10, 2004 [Page 9]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 5.2 IPsec Tunnel mode 5.2.1 SPD for Host-to-Host Scenario The following SPD entries assume that there are two hosts Host1 and Host2, whose IPv6 addresses are denoted by IPV6-EP1 and IPV6-EP2 and IPV4 addresses of the tunnel endpoints are denoted by IPV4-TEP1 and IPV4-TEP2 respectively. Host1's SPD OUT : IF SRC = IPV6-EP1 && DST = IPV6-EP2 THEN USE ESP TUNNEL MODE SA: outer source = IPv4-TEP1 outer dest = IPV4-TEP2 Host1's SPD IN: IF SRC = IPV4-EP2 && DST = IPV6-EP1 THEN USE ESP TUNNEL MODE SA outer source = IPV4-TEP2 outer dest = IPV4-TEP1 Host2's SPD OUT: IF SRC = IPV4-EP2 && DST = IPV6-EP1 THEN USE ESP TUNNEL MODE SA outer source = IPV4-TEP2 outer dest = IPV4-TEP1 Host2's SPD IN: IF SRC = IPV6-EP1 && DST = IPV6-EP2 THEN USE ESP TUNNEL MODE SA: outer source = IPv4-TEP1 outer dest = IPV4-TEP2 The IDci and IDcr payloads of IKEv1 carry the IPV6-EP1 and IPV6-TEP2 as phase 2 identities. With IKEv2, the traffic selectors are used to carry the same information. 5.2.2 SPD for Host-to-Router scenario The following SPD entries assume that the host has the IPv6 address IPV6-EP1 and the tunnel end points of the host and router are IPV4-TEP1 and IPV4-TEP2 respectively. If the tunnel is between a router and a CPE device where the router has allocated a IPV6-PREF/48 Graveman, et al. Expires December 10, 2004 [Page 10]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 to the CPE device, the corresponding SPD entries can be derived by substituting IPV6-EP1 by IPV6-PREF/48. Host's SPD OUT: IF SRC = IPV6-EP1 && DST = any THEN use ESP TUNNEL MODE SA outer source = IPV4-TEP1 outer dest = IPV4-TEP2 Host's SPD IN: IF SRC = any && DST = IPV6-EP1 THEN use ESP TUNNEL MODE SA outer source = IPV4-TEP1 outer dest = IPV4-TEP2 Router's SPD OUT: IF SRC = any && DST = IPV6-EP1 THEN use ESP TUNNEL MODE SA outer source = IPV4-TEP1 outer dest = IPV4-TEP2 Router's SPD IN: IF SRC = IPV6-EP1 && DST = any THEN use ESP TUNNEL MODE SA outer source = IPV4-TEP1 outer dest = IPV4-TEP2 The IDci and IDcr payloads of IKEv1 carry the IPV6-EP1 and ID_IPV6_ADDR_RANGE or ID_IPV6_ADDR_SUBNET as its phase 2 identity. The starting address is zero IP address and the end address is all ones for ID_IPV6_ADDR_RANGE. The starting address is zero IP address and the end address is all zeroes for ID_IPV6_ADDR_SUBNET. With IKEv2, the traffic selectors are used to carry the same information. To describe the packet format the following acronyms are used throughout this document: o IPV4-TEP1 and IPV4-TEP2 denote the IPv4 address of the tunnel endpoints. o IPV6-EP1 and IPV6-EP2 denote the IPv6 address of the two IPv6 endpoints of the communication. Graveman, et al. Expires December 10, 2004 [Page 11]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 The packet format is the same for both transport mode and tunnel mode as shown in Figure 10. IPv4 header (source = IPV4-TEP1, destination = IPV4-TEP2) ESP header IPv6 header (source = IPV6-EP1, destination = IPV6-EP2) Figure 10: Packet Format for transport and tunnel mode This type of layering may not be valid with [RFC2401] since, with a strict definition, IP does not meet the definition of a "higher layer protocol" being the next protocol after an IP header. With [I-D.ietf-ipsec-rfc2401bis] the definition about the "next layer protocol" was explicitly expanded and hence this type of layering is valid. 6. Dynamic Address Configuration With the exchange of protected configuration payloads, IKEv2 is able to provide the IKEv2 peer with DHCP-like information payloads. These configuration payloads are exchanged between the IKEv2 initiator and the responder with the help of the CFG_REQUEST/CFG_REPLY and CFG_SET/ CFG_ACK payloads. The former is used to request information and the latter allows to push configuration data. Configuration information (e.g., a temporary address) can be carried in any request to create a CHILD_SA by including a CP payload. These configuration payloads are primiarly used for bootstrapping the IKEv2 peer. Although these payloads are extensible they are not used as a generic purpose management. The following example exchange illustrates the usage of configuration payloads: Graveman, et al. Expires December 10, 2004 [Page 12]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 Initiator Responder ------------- -------------- HDR, SAi1, KEi, Ni --> <-- HDR(A,0), N(COOKIE) HDR(A,0), N(COOKIE), SAi1, KEi, Ni --> <-- HDR, SAr1, KEr, Nr,[CERTREQ] HDR, SK {IDi, [CERT,] [CERTREQ,] [IDr,] AUTH, CP(CFG_REQUEST), SAi2, TSi, TSr} --> <-- HDR, SK {IDr, [CERT,] AUTH, CP(CFG_REPLY), SAr2, TSi, TSr} Figure 11: IKEv2 Configuration payload payload exchange The example message exchange shown in Figure 11 shows IKEv2 with a denial of service protection enabled exchange and a CFG_REQUEST in message 5 and the corresponding response in message 6. The content of these payloads, for example, contains (as given in Section 2.19 of [I-D.ietf-ipsec-ikev2]): CP(CFG_REQUEST)= INTERNAL_ADDRESS(0.0.0.0) INTERNAL_NETMASK(0.0.0.0) INTERNAL_DNS(0.0.0.0) TSi = (0, 0-65536,0.0.0.0-255.255.255.255) TSr = (0, 0-65536,0.0.0.0-255.255.255.255) CP(CFG_REPLY)= INTERNAL_ADDRESS(10.168.219.202) INTERNAL_NETMASK(255.255.255.0) INTERNAL_SUBNET(10.168.219.0/255.255.255.0) TSi = (0, 0-65536,10.168.219.202-10.168.219.202) TSr = (0, 0-65536,10.168.219.0-10.168.219.255) 7. Extensible Authentication Support In addition to the authentication mechanisms provided in IKEv2 the Extensible Authentication Protocol (EAP) [I-D.ietf-eap-rfc2284bis] is included which provides some flexibility for authentication mechanisms. Figure 13 shows an example IKEv2 exchange with EAP support. The usage of EAP offers two interesting features: Graveman, et al. Expires December 10, 2004 [Page 13]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 o User authentication is terminated at a different entity other than the IKEv2 responder. This allows users' security credentials to be kept in a central place (e.g., AAA server) and to terminate the EAP method at this entity instead at the IKEv2 responder. Authorization can also be executed at the same entity. o A number of authentication and key exchange protocols are supported via EAP method (such as EAP-AKA, EAP-SIM, SRP, etc.). Each EAP methods provides its own properties and usage environment. This provides a certain degree of flexibility. Note that IKEv2 with EAP authentication still requires public key based authentication of the IKEv2 responder outside the EAP authentication. In most deployments this requires a server-side public-key based authentication to protect the EAP exchange with a uni-lateral authenticated tunnel. With the extensions proposed in [I-D.eronen-ipsec-ikev2-eap-auth] only EAP authentication is used by omitting the IKEv2 responder authentication. Please note that Section 3.16 of [I-D.ietf-ipsec-ikev2] indicates that the EAP Identity-Request/Identity-Response payload SHOULD NOT be used. The IDr payload (message 3 in Figure 13) carries this identity instead. As a consequence active user identity confidentiality for the IKEv2 initiator is not provided. Special purpose EAP methods must be used instead if this features is desired. Figure 13 shows an example IKEv2 message exchange with EAP-AKA as an EAP method. Note that the interaction between the IKEv2 responder and the AAA infrastructure is not shown. Graveman, et al. Expires December 10, 2004 [Page 14]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 Initiator Responder ------------- -------------- HDR, SAi1, KEi, Ni --> <-- HDR, SAr1, KEr, Nr, [CERTREQ] HDR, SK {IDi, [CERTREQ,] [IDr,] SAi2, TSi, TSr} --> <-- HDR, SK {IDr, [CERT,] AUTH, EAP-Request/AKA-Challenge (AT_RAND, AT_AUTN, AT_MAC) } HDR, SK {EAP-Response/AKA-Challenge(AT_RES, AT_MAC)} --> <-- HDR, SK {EAP-Success, AUTH} HDR, SK { AUTH } --> <-- HDR, SK { SAr2, TSi, TSr } Figure 13: EAP usage in IKEv2 with EAP-AKA EAP will typically be used with a backend AAA server which raises some security concerns. See [I-D.ietf-eap-keying] for a more complete discussion of these security issues. When a backend server is used, there are actually two authentication exchanges: the EAP method between the client and the AAA server, and another authentication between the AAA server and IKEv2 gateway. The AAA server authenticates the client using the selected EAP method, and they establish a session key. The AAA server then sends this key to the IKEv2 gateway over a connection authenticated using e.g. IPsec or TLS. The protocol used between the IKEv2 responder and the AAA server could be, for instance, Diameter or RADIUS [RFC3579]. RADIUS and Diameter are able to carry EAP payloads as described in [RFC3579] and in [I-D.ietf-aaa-eap], respectively. 8. NAT Traversal Network address (and port) translation devices are commonly found in today's networks. A detailed description of the problem of IPsec protected data traffic traversing a NAT including requirements are discussed in [RFC3715]. IKEv2 can detect the presence of a NAT automatically by sending an Informational exchange with NAT_DETECTION_SOURCE_IP and NAT_DETECTION_DESTINATION_IP payloads before establishing an IPsec SA. These payloads are processed the same way as in the initial Graveman, et al. Expires December 10, 2004 [Page 15]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 IKE_SA_INIT exchange. Once a NAT is detected and both end points support IPsec NAT traversal extensions UDP encapsulation can be enabled. More details about UDP encapsulation of IPsec protected IP packets can be found in [I-D.ietf-ipsec-udp-encaps]. For IPv6-over-IPv4 tunneling, NAT traversal is interesting for two reasons: 1. One of the tunnel endpoints is often behind a NAT, and configured tunneling, using protocol 41, is not guaranteed to traverse the NAT. Hence, using IPsec tunnels would enable one to both set-up a secure tunnel, and set-up a tunnel where it might not always be possible without other tunneling mechanisms. 2. Using NAT traversal allows the outer address to change without having to renegotiate the SAs. This could be very beneficial for a crude form of mobility, and in scenarios the NAT changes the IP addresses frequently. However, as the outer address may change, this might introduce new security issues, and using tunnel mode would be most appropriate. XXX: can you force the use of NAT traversal so that you don't need to renegotiate SAs even if you aren't behind a NAT -- could be useful for MOBIKE applications. 9. Tunnel Endpoint Discovery The IKEv2 initiator needs to know the address of the IKEv2 responder for IKEv2 signaling. A number of ways can be used to provide the initiator with this information, for example: o Using off-band mechanisms, e.g., from the ISP's web page. o Using DNS to look up a service name by appending it to the DNS search path provided by DHCPv4 (e.g. "tunnel-service.example.com"). o Using a DHCP option. o Using a pre-configured or pre-determined IPv4 anycast address. o Using other, unspecified or proprietary methods such as TED (see [I-D.fluhrer-ted]). For the purpose of this document it is assumed that this address can be obtained somehow. Once the address has been learned, it is Graveman, et al. Expires December 10, 2004 [Page 16]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 configured as the tunnel end-point for the configured IPv6-over-IPv4 tunnel. 10. Example TBD: Full-fledged example 11. Security Considerations When you run IPv6-in-IPv4 tunnels (unsecured) over the Internet, it is possible to "inject" packets in the tunnel by spoofing the source address (data plane security), or if the tunnel is signalled somehow (e.g., some messages where you authenticate to the server, so that you would get a static v6 prefix), someone might be able to spoof the signalling (control plane security). To add security to both, the protocol for tunnel setup and to the data traffic, the IPsec framework plays an important role. IKEv2 is a signaling protocol with optional Denial of Service protection which authenticates both end points (with different identifities) and establishes two types of security associations (CHILD-SAs and IKE-SA). The authentication mechanisms are very flexible due to the built-in support for symmetric and asymmetric cryptography (or even a combination of both) and the Extensible Authentication Protocol support (as desribed in Figure 13). The IKE-SA is used to secure most of the IKEv2 message exchange. In particular the CHILD-SA exchange, Informational exchanges (such as the dead-peer detection mechanisms used for liveness checks) and the exchange of configuration messages are secured. The CHILD-SA exchange leads to the establishment of a IPsec tunnel and the creation of SAD and SPD entries. As a summary, IKEv2 provides a secure signaling protocol for establishing, maintaining and deleting an IPsec tunnel. IPsec, with the Encapsulating Security Payload (ESP), offers integrity and data origin authentication, confidentiality, with optional (at the discretion of the receiver) anti-replay features. The usage of confidentity-only is discouraged. ESP furthermore provides limited traffic flow confidentality. IPsec provides access control mechanisms through the distribution of keys and also through the usage of policies dictated by the Security Policy Database (SPD). Furthermore, through the usage of EAP and the backend AAA infrastructure it is possible to enforce additional authorization mechanisms (at the user level) at entities other than the tunnel end points. Graveman, et al. Expires December 10, 2004 [Page 17]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 The NAT traversal mechanism provided by IKEv2 introduces some weaknesses into IKEv2 and IPsec. These issues are discussed in more detail in [I-D.ietf-ipsec-ikev2]. Please note that the usage of IPsec for the scenarios described in Figure 3, Figure 2 and Figure 1 does not aim to protect the end-to-end communication. It protects just the tunnel part. It is still possible for an IPv6 endpoint that is not attached to the IPsec tunnel to spoof packets. 12. Open Issues This section lists some open issues that will be resolved in future versions of this document. o More considerations of IKEv1 might be useful. o Discussion of 'Use of IPsec Transport Mode for Dynamic Routing' [I-D.touch-ipsec-vpn] would be appropriate. o A more detailed description of the address configuration mechanism would be helpful. The configuration example with CFG_REQUEST/ CFG_REPLY payloads should contain IPv6 addresses. o The full-fledged example of Section 10 is still missing. o Some notes on the implications of mobility interworking are still missing. o Discuss the use of link-local etc. messages with Tunnel mode SAs -- i.e., how many SAs will be needed (and how they are negotiated) if link-local messages will be present as well? o The "Site-to-Router" scenarios separation is a bit weak -- any better ideas how to categorize these would be appreciated. o Better discussion of when transport/tunnel mode SAs make more sense would probably be useful. 13. Contributors Please note that the authors are listed in alphabetical order. Suresh Satapati also participated in the discussions. Graveman, et al. Expires December 10, 2004 [Page 18]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 14. Acknowledgments The authors would like to thank Stephen Kent and Michael Richardson for their comments. We would like to thank Pasi Eronen for his text contributions. 15. References 15.1 Normative References [I-D.ietf-eap-rfc2284bis] Blunk, L., Vollbrecht, J., Aboba, B., Carlson, J. and H. Levkowetz, "Extensible Authentication Protocol (EAP)", draft-ietf-eap-rfc2284bis-07 (work in progress), December 2003. [I-D.ietf-ipsec-esp-v3] Kent, S., "IP Encapsulating Security Payload (ESP)", draft-ietf-ipsec-esp-v3-08 (work in progress), March 2004, <reference.I-D.ietf-ipsec-esp-v3.xml>. [I-D.ietf-ipsec-ikev2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", draft-ietf-ipsec-ikev2-13 (work in progress), March 2004, <reference.I-D.ietf-ipsec-ikev2.xml>. [I-D.ietf-ipsec-ikev2-algorithms] Schiller, J., "Cryptographic Algorithms for use in the Internet Key Exchange Version 2", draft-ietf-ipsec-ikev2-algorithms-04 (work in progress), September 2003, <reference.I-D.ietf-ipsec-ikev2-algorithms.xml>. [I-D.ietf-ipsec-rfc2401bis] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", draft-ietf-ipsec-rfc2401bis-01 (work in progress), January 2004, <reference.I-D.ietf-ipsec-rfc2401bis.xml>. [I-D.ietf-ipsec-udp-encaps] Huttunen, A., "UDP Encapsulation of IPsec Packets", draft-ietf-ipsec-udp-encaps-08 (work in progress), February 2004, <reference.I-D.ietf-ipsec-udp-encaps.xml>. [I-D.ietf-ipsec-ui-suites] Hoffman, P., "Cryptographic Suites for IPsec", draft-ietf-ipsec-ui-suites-04 (work in progress), August Graveman, et al. Expires December 10, 2004 [Page 19]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 2003, <reference.I-D.ietf-ipsec-ui-suites.xml>. [I-D.ietf-v6ops-mech-v2] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms for IPv6 Hosts and Routers", draft-ietf-v6ops-mech-v2-02 (work in progress), February 2004, <reference.I-D.ietf-v6ops-mech-v2.xml>. 15.2 Informative References [I-D.bellovin-useipsec] Bellovin, S., "Guidelines for Mandating the Use of IPsec", draft-bellovin-useipsec-03 (work in progress), March 2004, <reference.I-D.bellovin-useipsec.xml>. [I-D.blanchet-v6ops-tunnelbroker-tsp] Blanchet, M., "IPv6 Tunnel Broker with the Tunnel Setup Protocol(TSP)", draft-blanchet-v6ops-tunnelbroker-tsp-00 (work in progress), February 2004, <reference.I-D.blanchet-v6ops-tunnelbroker-tsp.xml>. [I-D.dupont-ikev2-addrmgmt] Dupont, F., "Address Management for IKE version 2", draft-dupont-ikev2-addrmgmt-04 (work in progress), February 2004, <reference.I-D.dupont-ikev2-addrmgmt.xml>. [I-D.eronen-ipsec-ikev2-eap-auth] Eronen, P., "Extension for EAP Authentication in IKEv2", draft-eronen-ipsec-ikev2-eap-auth-00 (work in progress), February 2004, <reference.I-D.eronen-ipsec-ikev2-eap-auth.xml>. [I-D.fluhrer-ted] Fluhrer, S., "Tunnel Endpoint Discovery", draft-fluhrer-ted-00 (work in progress), November 2001, <reference.I-D.fluhrer-ted.xml>. [I-D.ietf-aaa-eap] Eronen, P., Hiller, T. and G. Zorn, "Diameter Extensible Authentication Protocol (EAP) Application", draft-ietf-aaa-eap-03 (work in progress), October 2003. [I-D.ietf-eap-keying] Aboba, B., Simon, D., Arkko, J. and H. Levkowetz, "EAP Key Management Framework", draft-ietf-eap-keying-01 (work in progress), October 2003. [I-D.ietf-ipsec-ikev2-iana] Graveman, et al. Expires December 10, 2004 [Page 20]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 Richardson, M., "Initial IANA registry contents", draft-ietf-ipsec-ikev2-iana-01 (work in progress), January 2004, <reference.I-D.ietf-ipsec-ikev2-iana.xml>. [I-D.ietf-ipsec-rfc2402bis] Kent, S., "IP Authentication Header", draft-ietf-ipsec-rfc2402bis-07 (work in progress), March 2004, <reference.I-D.ietf-ipsec-rfc2402bis.xml>. [I-D.ietf-pana-ipsec] Parthasarathy, M., "PANA enabling IPsec based Access Control", draft-ietf-pana-ipsec-02 (work in progress), February 2004, <reference.I-D.ietf-pana-ipsec.xml>. [I-D.kivinen-mobike-design] Kivinen, T., "Design of the MOBIKE protocol", draft-kivinen-mobike-design-00 (work in progress), March 2004, <reference.I-D.kivinen-mobike-design.xml>. [I-D.touch-ipsec-vpn] Touch, J., Eggert, L. and Y. Wang, "Use of IPsec Transport Mode for Dynamic Routing", draft-touch-ipsec-vpn-07 (work in progress), March 2004, <reference.I-D.touch-ipsec-vpn.xml>. [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, November 1998, <reference.RFC.2401.xml>. [RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address Translator (NAT) Terminology and Considerations", RFC 2663, August 1999, <reference.RFC.2663.xml>. [RFC2865] Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000. [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial In User Service) Support For Extensible Authentication Protocol (EAP)", RFC 3579, September 2003. [RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed Networks", BCP 84, RFC 3704, March 2004, <reference.RFC.3704.xml>. [RFC3715] Aboba, B. and W. Dixon, "IPsec-Network Address Translation (NAT) Compatibility Requirements", RFC 3715, March 2004, <reference.RFC.3715.xml>. Graveman, et al. Expires December 10, 2004 [Page 21]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 Authors' Addresses Richard Graveman RFG Security, LLC 15 Park Avenue Morristown, New Jersey 07960 USA EMail: rfg@acm.org Mohan Parthasarathy Nokia 313 Fairchild Drive Mountain View CA-94043 USA EMail: mohanp@sbcglobal.net Pekka Savola CSC/FUNET Espoo Finnland EMail: psavola@funet.fi Hannes Tschofenig Siemens Otto-Hahn-Ring 6 Munich, Bayern 81739 Germany EMail: Hannes.Tschofenig@siemens.com Graveman, et al. Expires December 10, 2004 [Page 22]
Internet-Draft Using IPsec to Secure v6-over-v4 Tunnels June 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2004). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Graveman, et al. Expires December 10, 2004 [Page 23]