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Network Working Group                                         F. TemplinRequest for Comments: 4214                                         NokiaCategory: Experimental                                        T. Gleeson                                                      Cisco Systems K.K.                                                               M. Talwar                                                               D. Thaler                                                   Microsoft Corporation                                                            October 2005Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)Status of This Memo   This memo defines an Experimental Protocol for the Internet   community.  It does not specify an Internet standard of any kind.   Discussion and suggestions for improvement are requested.   Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2005).IESG Note   The content of this RFC was at one time considered by the IETF, and   therefore it may resemble a current IETF work in progress or a   published IETF work.  This RFC is not a candidate for any level of   Internet Standard.  The IETF disclaims any knowledge of the fitness   of this RFC for any purpose, and in particular notes that the   decision to publish is not based on IETF review for such things as   security, congestion control or inappropriate interaction with   deployed protocols.  The RFC Editor has chosen to publish this   document at its discretion.  Readers of this RFC should exercise   caution in evaluating its value for implementation and deployment.   SeeRFC 3932 for more information.Abstract   The Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) connects   IPv6 hosts/routers over IPv4 networks.  ISATAP views the IPv4 network   as a link layer for IPv6 and views other nodes on the network as   potential IPv6 hosts/routers.  ISATAP supports an automatic tunneling   abstraction similar to the Non-Broadcast Multiple Access (NBMA)   model.Templin, et al.               Experimental                      [Page 1]

RFC 4214                         ISATAP                     October 20051.  Introduction   This document specifies a simple mechanism called the Intra-Site   Automatic Tunnel Addressing Protocol (ISATAP) that connects IPv6   hosts/routers over IPv4 networks.  Dual-stack (IPv6/IPv4) nodes use   ISATAP to automatically tunnel IPv6 packets in IPv4, i.e., ISATAP   views the IPv4 network as a link layer for IPv6 and views other nodes   on the network as potential IPv6 hosts/routers.   ISATAP enables automatic tunneling whether global or private IPv4   addresses are used, and presents a Non-Broadcast Multiple Access   (NBMA) abstraction similar to [RFC2491][RFC2492][RFC2529][RFC3056].   The main objectives of this document are to: 1) describe the domain   of applicability, 2) specify addressing requirements, 3) specify   automatic tunneling using ISATAP, 4) specify the operation of IPv6   Neighbor Discovery over ISATAP interfaces, and 5) discuss Site   Administration, Security, and IANA considerations.2.  Requirements   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this   document, are to be interpreted as described in [BCP14].   This document also uses internal conceptual variables to describe   protocol behavior and external variables that an implementation must   allow system administrators to change.  The specific variable names,   how their values change, and how their settings influence protocol   behavior are provided in order to demonstrate protocol behavior.  An   implementation is not required to have them in the exact form   described here, as long as its external behavior is consistent with   that described in this document.3.  Terminology   The terminology of [RFC2460][RFC2461] applies to this document.  The   following additional terms are defined:   ISATAP node:      A node that implements the specifications in this document.   ISATAP interface:      An ISATAP node's Non-Broadcast Multi-Access (NBMA) IPv6 interface,      used for automatic tunneling of IPv6 packets in IPv4.Templin, et al.               Experimental                      [Page 2]

RFC 4214                         ISATAP                     October 2005   ISATAP interface identifier:      An IPv6 interface identifier with an embedded IPv4 address      constructed as specified inSection 6.1.   ISATAP address:      An IPv6 unicast address that matches an on-link prefix on an      ISATAP interface of the node, and that includes an ISATAP      interface identifier.   locator:      An IPv4 address-to-interface mapping; i.e., a node's IPv4 address      and its associated interface.   locator set:      A set of locators associated with an ISATAP interface.  Each      locator in the set belongs to the same site.4.  Domain of Applicability   The domain of applicability for this technical specification is   automatic tunneling of IPv6 packets in IPv4 for ISATAP nodes within   sites that observe the security considerations found in this   document, including host-to-router, router-to-host, and host-to-host   automatic tunneling in certain enterprise networks and 3GPP/3GPP2   wireless operator networks.  (Other scenarios with a sufficient trust   basis ensured by the mechanisms specified in this document also fall   within this domain of applicability.)   Extensions to the above domain of applicability (e.g., by combining   the mechanisms in this document with those in other technical   specifications) are out of the scope of this document.5.  Node Requirements   ISATAP nodes observe the common functionality requirements for IPv6   nodes found in [NODEREQ] and the requirements for dual IP layer   operation found in ([MECH], Section 2).  They also implement the   additional features specified in this document.6.  Addressing Requirements6.1.  ISATAP Interface Identifiers   ISATAP interface identifiers are constructed in Modified EUI-64   format ([RFC3513], Section 2.5.1 andAppendix A) by concatenating the   24-bit IANA OUI (00-00-5E), the 8-bit hexadecimal value 0xFE, and a   32-bit IPv4 address in network byte order as follows:Templin, et al.               Experimental                      [Page 3]

RFC 4214                         ISATAP                     October 2005   |0              1|1              3|3                              6|   |0              5|6              1|2                              3|   +----------------+----------------+--------------------------------+   |000000ug00000000|0101111011111110|mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm|   +----------------+----------------+--------------------------------+   When the IPv4 address is known to be globally unique, the "u" bit   (universal/local) is set to 1; otherwise, the "u" bit is set to 0.   "g" is the individual/group bit, and "m" are the bits of the IPv4   address.6.2.  ISATAP Interface Address Configuration   Each ISATAP interface configures a set of locators consisting of IPv4   address-to-interface mappings from a single site; i.e., an ISATAP   interface's locator set MUST NOT span multiple sites.   When an IPv4 address is removed from an interface, the corresponding   locator SHOULD be removed from its associated locator set(s).  When a   new IPv4 address is assigned to an interface, the corresponding   locator MAY be added to the appropriate locator set(s).   ISATAP interfaces form ISATAP interface identifiers from IPv4   addresses in their locator set and use them to create link-local   ISATAP addresses ([RFC2462], Section 5.3).6.3.  Multicast/Anycast   It is not possible to assume the general availability of wide-area   IPv4 multicast, so (unlike 6over4 [RFC2529]) ISATAP must assume that   its underlying IPv4 carrier network only has unicast capability.   Support for IPv6 multicast over ISATAP interfaces is not described in   this document.   Similarly, support for Reserved IPv6 Subnet Anycast Addresses is not   described in this document.7.  Automatic Tunneling   ISATAP interfaces use the basic tunneling mechanisms specified in   ([MECH], Section 3).  The following sub-sections describe additional   specifications.7.1.  Encapsulation   ISATAP addresses are mapped to a link-layer address by a static   computation; i.e., the last four octets are treated as an IPv4   address.Templin, et al.               Experimental                      [Page 4]

RFC 4214                         ISATAP                     October 20057.2.  Handling ICMPv4 Errors   ISATAP interfaces SHOULD process ARP failures and persistent ICMPv4   errors as link-specific information indicating that a path to a   neighbor may have failed ([RFC2461], Section 7.3.3).7.3.  Decapsulation   The specification in ([MECH], Section 3.6) is used.  Additionally,   when an ISATAP node receives an IPv4 protocol 41 datagram that does   not belong to a configured tunnel interface, it determines whether   the packet's IPv4 destination address and arrival interface match a   locator configured in an ISATAP interface's locator set.   If an ISATAP interface that configures a matching locator is found,   the decapsulator MUST verify that the packet's IPv4 source address is   correct for the encapsulated IPv6 source address.  The IPv4 source   address is correct if:      -  the IPv6 source address is an ISATAP address that embeds the         IPv4 source address in its interface identifier, or      -  the IPv4 source address is a member of the Potential Router         List (seeSection 8.1).   Packets for which the IPv4 source address is incorrect for this   ISATAP interface are checked to determine whether they belong to   another tunnel interface.7.4.  Link-Local Addresses   ISATAP interfaces use link-local addresses constructed as specified   inSection 6 of this document.7.5.  Neighbor Discovery over Tunnels   ISATAP interfaces use the specifications for neighbor discovery found   in the following section of this document.8.  Neighbor Discovery for ISATAP Interfaces   ISATAP interfaces use the neighbor discovery mechanisms specified in   [RFC2461].  The following sub-sections describe specifications that   are also implemented.Templin, et al.               Experimental                      [Page 5]

RFC 4214                         ISATAP                     October 20058.1.  Conceptual Model of a Host   To the list of Conceptual Data Structures ([RFC2461], Section 5.1),   ISATAP interfaces add the following:      Potential Router List (PRL)      A set of entries about potential routers; used to support router      and prefix discovery.  Each entry ("PRL(i)") has an associated      timer ("TIMER(i)"), and an IPv4 address ("V4ADDR(i)") that      represents a router's advertising ISATAP interface.8.2.  Router and Prefix Discovery - Router Specification   Advertising ISATAP interfaces send Solicited Router Advertisement   messages as specified in ([RFC2461], Section 6.2.6) except that the   messages are sent directly to the soliciting node; i.e., they might   not be received by other nodes on the link.8.3.  Router and Prefix Discovery - Host Specification   The Host Specification in ([RFC2461], Section 6.3) is used.  The   following sub-sections describe specifications added by ISATAP   interfaces.8.3.1.  Host Variables   To the list of host variables ([RFC2461], Section 6.3.2), ISATAP   interfaces add the following:   PrlRefreshInterval      Time in seconds between successive refreshments of the PRL after      initialization.  The designated value of all ones (0xffffffff)      represents infinity.      Default: 3600 seconds   MinRouterSolicitInterval      Minimum time in seconds between successive solicitations of the      same advertising ISATAP interface.  The designated value of all      ones (0xffffffff) represents infinity.8.3.2.  Potential Router List Initialization   ISATAP nodes initialize an ISATAP interface's PRL with IPv4 addresses   discovered via manual configuration, a DNS Fully Qualified Domain   Name (FQDN) [STD13], a DHCPv4 option, a DHCPv4 vendor-specific   option, or an unspecified alternate method.  FQDNs are established   via manual configuration or an unspecified alternate method.  FQDNs   are resolved into IPv4 addresses through a static host file lookup,Templin, et al.               Experimental                      [Page 6]

RFC 4214                         ISATAP                     October 2005   querying the DNS service, querying a site-specific name service, or   with an unspecified alternate method.   After initializing an ISATAP interface's PRL, the node sets a timer   for the interface to PrlRefreshInterval seconds and re-initializes   the interface's PRL as specified above when the timer expires.  When   an FQDN is used, and when it is resolved via a service that includes   TTLs with the IPv4 addresses returned (e.g., DNS 'A' resource records   [STD13]), the timer SHOULD be set to the minimum of   PrlRefreshInterval and the minimum TTL returned.  (Zero-valued TTLs   are interpreted to mean that the PRL is re-initialized before each   Router Solicitation event; seeSection 8.3.4.)8.3.3.  Processing Received Router Advertisements   To the list of checks for validating Router Advertisement messages   ([RFC2461], Section 6.1.1), ISATAP interfaces add the following:      -  IP Source Address is a link-local ISATAP address that embeds         V4ADDR(i) for some PRL(i).   Valid Router Advertisements received on an ISATAP interface are   processed as specified in ([RFC2461], Section 6.3.4).8.3.4.  Sending Router Solicitations   To the list of events after which Router Solicitation messages may be   sent ([RFC2461], Section 6.3.7), ISATAP interfaces add the following:      -  TIMER(i) for some PRL(i) expires.   Since unsolicited Router Advertisements may be incomplete and/or   absent, ISATAP nodes MAY schedule periodic Router Solicitation events   for certain PRL(i)s by setting the corresponding TIMER(i).   When periodic Router Solicitation events are scheduled, the node   SHOULD set TIMER(i) so that the next event will refresh remaining   lifetimes stored for PRL(i) before they expire, including the Router   Lifetime, Valid Lifetimes received in Prefix Information Options, and   Route Lifetimes received in Route Information Options [DEFLT].   TIMER(i) MUST be set to no less than MinRouterSolicitInterval seconds   where MinRouterSolicitInterval is configurable for the node, or for a   specific PRL(i), with a conservative default value (e.g., 2 minutes).   When TIMER(i) expires, the node sends Router Solicitation messages as   specified in ([RFC2461], Section 6.3.7) except that the messages are   sent directly to PRL(i); i.e., they might not be received by other   routers.  While the node continues to require periodic RouterTemplin, et al.               Experimental                      [Page 7]

RFC 4214                         ISATAP                     October 2005   Solicitation events for PRL(i), and while PRL(i) continues to act as   a router, the node resets TIMER(i) after each expiration event as   described above.8.4.  Neighbor Unreachability Detection   Hosts SHOULD perform Neighbor Unreachability Detection ([RFC2461],   Section 7.3).  Routers MAY perform neighbor unreachability detection,   but this might not scale in all environments.   After address resolution, hosts SHOULD perform an initial   reachability confirmation by sending Neighbor Solicitation messages   and receiving a Neighbor Advertisement message.  Routers MAY perform   this initial reachability confirmation, but this might not scale in   all environments.9.  Site Administration Considerations   Site administrators maintain a Potential Router List (PRL) of IPv4   addresses representing advertising ISATAP interfaces of routers.   The PRL is commonly maintained as an FQDN for the ISATAP service in   the site's name service (seeSection 8.3.2).  There are no mandatory   rules for the selection of the FQDN, but site administrators are   encouraged to use the convention "isatap.domainname" (e.g.,   isatap.example.com).   When the site's name service includes TTLs with the IPv4 addresses   returned, site administrators SHOULD configure the TTLs with   conservative values to minimize control traffic.10.  Security Considerations   Implementors should be aware that, in addition to possible attacks   against IPv6, security attacks against IPv4 must also be considered.   Use of IP security at both IPv4 and IPv6 levels should nevertheless   be avoided, for efficiency reasons.  For example, if IPv6 is running   encrypted, encryption of IPv4 would be redundant unless traffic   analysis is felt to be a threat.  If IPv6 is running authenticated,   then authentication of IPv4 will add little.  Conversely, IPv4   security will not protect IPv6 traffic once it leaves the ISATAP   domain.  Therefore, implementing IPv6 security is required even if   IPv4 security is available.   The threats associated with IPv6 Neighbor Discovery are described in   [RFC3756].Templin, et al.               Experimental                      [Page 8]

RFC 4214                         ISATAP                     October 2005   There is a possible spoofing attack in which spurious ip-protocol-41   packets are injected into an ISATAP link from outside.  Since an   ISATAP link spans an entire IPv4 site, restricting access to the link   can be achieved by restricting access to the site; i.e., by having   site border routers implement IPv4 ingress filtering and ip-   protocol-41 filtering.   Another possible spoofing attack involves spurious ip-protocol-41   packets injected from within an ISATAP link by a node pretending to   be a router.  The Potential Router List (PRL) provides a list of IPv4   addresses representing advertising ISATAP interfaces of routers that   hosts use in filtering decisions.  Site administrators should ensure   that the PRL is kept up to date, and that the resolution mechanism   (seeSection 9) cannot be subverted.   The use of temporary addresses [RFC3041] and Cryptographically   Generated Addresses [CGA] on ISATAP interfaces is outside the scope   of this specification.11.  IANA Considerations   The IANA has specified the format for Modified EUI-64 address   construction ([RFC3513], Appendix A) in the IANA Ethernet Address   Block.  The text inAppendix A of this document has been offered as   an example specification.  The current version of the IANA registry   for Ether Types can be accessed at:http://www.iana.org/assignments/ethernet-numbers12.  Acknowledgements   The ideas in this document are not original, and the authors   acknowledge the original architects.  Portions of this work were   sponsored through SRI International internal projects and government   contracts.  Government sponsors include Monica Farah-Stapleton and   Russell Langan (U.S. Army CECOM ASEO), and Dr. Allen Moshfegh (U.S.   Office of Naval Research).  SRI International sponsors include Dr.   Mike Frankel, J. Peter Marcotullio, Lou Rodriguez, and Dr. Ambatipudi   Sastry.   The following are acknowledged for providing peer review input: Jim   Bound, Rich Draves, Cyndi Jung, Ambatipudi Sastry, Aaron Schrader,   Ole Troan, and Vlad Yasevich.   The following are acknowledged for their significant contributions:   Alain Durand, Hannu Flinck, Jason Goldschmidt, Nathan Lutchansky,   Karen Nielsen, Mohan Parthasarathy, Chirayu Patel, Art Shelest,   Markku Savela, Pekka Savola, Margaret Wasserman, and Brian Zill.Templin, et al.               Experimental                      [Page 9]

RFC 4214                         ISATAP                     October 2005   The authors acknowledge the work of Quang Nguyen on "Virtual   Ethernet", under the guidance of Dr. Lixia Zhang, that proposed very   similar ideas to those that appear in this document.  This work was   first brought to the authors' attention on September 20, 2002.Templin, et al.               Experimental                     [Page 10]

RFC 4214                         ISATAP                     October 2005Appendix A.  Modified EUI-64 Addresses in the IANA Ethernet Address             Block   Modified EUI-64 addresses ([RFC3513], Section 2.5.1 andAppendix A)   in the IANA Ethernet Address Block are formed by concatenating the   24-bit IANA OUI (00-00-5E) with a 40-bit extension identifier and   inverting the "u" bit; i.e., the "u" bit is set to one (1) to   indicate universal scope and set to zero (0) to indicate local scope.   Modified EUI-64 addresses have the following appearance in memory   (bits transmitted right-to-left within octets, octets transmitted   left-to-right):   0                       23                                        63   |        OUI            |            extension identifier         |   000000ug00000000 01011110xxxxxxxx xxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxx   When the first two octets of the extension identifier encode the   hexadecimal value 0xFFFE, the remainder of the extension identifier   encodes a 24-bit vendor-supplied id as follows:   0                       23               39                       63   |        OUI            |     0xFFFE     |   vendor-supplied id   |   000000ug00000000 0101111011111111 11111110xxxxxxxx xxxxxxxxxxxxxxxx   When the first octet of the extension identifier encodes the   hexadecimal value 0xFE, the remainder of the extension identifier   encodes a 32-bit IPv4 address as follows:   0                       23      31                                63   |        OUI            |  0xFE |           IPv4 address          |   000000ug00000000 0101111011111110 xxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxNormative References   [BCP14]    Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [STD13]    Mockapetris, P., "Domain names - implementation and              specification", STD 13,RFC 1035, November 1987.   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6              (IPv6) Specification",RFC 2460, December 1998.   [RFC2461]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor              Discovery for IP Version 6 (IPv6)",RFC 2461, December              1998.Templin, et al.               Experimental                     [Page 11]

RFC 4214                         ISATAP                     October 2005   [RFC2462]  Thomson, S. and T. Narten, "IPv6 Stateless Address              Autoconfiguration",RFC 2462, December 1998.   [RFC3513]  Hinden, R. and S. Deering, "Internet Protocol Version 6              (IPv6) Addressing Architecture",RFC 3513, April 2003.   [MECH]     Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms              for IPv6 Hosts and Routers",RFC 4213, October 2005.Informative References   [RFC2491]  Armitage, G., Schulter, P., Jork, M., and G. Harter, "IPv6              over Non-Broadcast Multiple Access (NBMA) networks",RFC2491, January 1999.   [RFC2492]  Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM              Networks",RFC 2492, January 1999.   [RFC2529]  Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4              Domains without Explicit Tunnels",RFC 2529, March 1999.   [RFC3041]  Narten, T. and R. Draves, "Privacy Extensions for              Stateless Address Autoconfiguration in IPv6",RFC 3041,              January 2001.   [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains              via IPv4 Clouds",RFC 3056, February 2001.   [RFC3756]  Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor              Discovery (ND) Trust Models and Threats",RFC 3756, May              2004.   [CGA]      Aura, T., "Cryptographically Generated Addresses (CGA)",RFC 3972, March 2005.   [DEFLT]    Draves, R. and D. Thaler, "Default Router Preferences and              More-Specific Routes", Work in Progress, December 2003.   [NODEREQ]  Loughney, J., Ed.,"IPv6 Node Requirements", Work in              Progress, May 2004.Templin, et al.               Experimental                     [Page 12]

RFC 4214                         ISATAP                     October 2005Authors' Addresses   Fred L. Templin   Nokia   313 Fairchild Drive   Mountain View, CA  94110   US   EMail: fltemplin@acm.org   Tim Gleeson   Cisco Systems K.K.   Shinjuku Mitsui Building   2-1-1 Nishishinjuku, Shinjuku-ku   Tokyo  163-0409   Japan   EMail: tgleeson@cisco.com   Mohit Talwar   Microsoft Corporation   One Microsoft Way   Redmond, WA  98052-6399   US   Phone: +1 425 705 3131   EMail: mohitt@microsoft.com   Dave Thaler   Microsoft Corporation   One Microsoft Way   Redmond, WA  98052-6399   US   Phone: +1 425 703 8835   EMail: dthaler@microsoft.comTemplin, et al.               Experimental                     [Page 13]

RFC 4214                         ISATAP                     October 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 78 and at www.rfc-editor.org/copyright.html, and   except as set forth therein, the authors retain all their rights.   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.Intellectual Property   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 inBCP 78 andBCP 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 athttp://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.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Templin, et al.               Experimental                     [Page 14]