NGTRANS Working Group F. Templin Internet-Draft Nokia Expires: July 1, 2003 T. Gleeson Cisco Systems K.K. M. Talwar D. Thaler Microsoft Corporation December 31, 2002 Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) draft-ietf-ngtrans-isatap-09.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 July 1, 2003. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document specifies an Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) that connects IPv6 hosts and routers within IPv4 sites. ISATAP treats the site's IPv4 infrastructure as a link layer for IPv6 with no requirement for IPv4 multicast. ISATAP enables intra-site automatic IPv6-in-IPv4 tunneling whether globally assigned or private IPv4 addresses are used. Templin, et al. Expires July 1, 2003 [Page 1] Internet-Draft ISATAP December 2002 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Applicability Statement . . . . . . . . . . . . . . . . . . 3 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Basic IPv6 Operation on ISATAP Links . . . . . . . . . . . . 5 5.1 Interface Identifiers and Address Construction . . . . . . . 5 5.2 ISATAP Link/Interface Configuration . . . . . . . . . . . . 5 5.3 Dual Stack Operation and Address Configuration . . . . . . . 6 5.4 Tunneling Mechanisms . . . . . . . . . . . . . . . . . . . . 6 5.4.1 Encapsulation . . . . . . . . . . . . . . . . . . . . . . . 6 5.4.2 Tunnel MTU and Fragmentation . . . . . . . . . . . . . . . . 6 5.4.3 Handling IPv4 ICMP Errors . . . . . . . . . . . . . . . . . 7 5.4.4 Decapsulation . . . . . . . . . . . . . . . . . . . . . . . 7 5.4.5 Link-Local Addresses . . . . . . . . . . . . . . . . . . . . 7 5.4.6 Ingress Filtering . . . . . . . . . . . . . . . . . . . . . 7 6. Neighbor Discovery and Address Autoconfiguration . . . . . . 8 6.1 Address Resolution . . . . . . . . . . . . . . . . . . . . . 8 6.2 Address Autoconfiguration and Router Discovery . . . . . . . 9 6.2.1 Conceptual Data Structures . . . . . . . . . . . . . . . . . 9 6.2.2 Validity Checks for Router Advertisements . . . . . . . . . 10 6.2.3 Router Specification . . . . . . . . . . . . . . . . . . . . 10 6.2.4 Host Specification . . . . . . . . . . . . . . . . . . . . . 11 7. ISATAP Deployment Considerations . . . . . . . . . . . . . . 12 7.1 Host And Router Deployment Considerations . . . . . . . . . 12 7.2 Site Administration Considerations . . . . . . . . . . . . . 12 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 13 9. Security considerations . . . . . . . . . . . . . . . . . . 13 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 Normative References . . . . . . . . . . . . . . . . . . . . 14 Informative References . . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 16 A. Major Changes . . . . . . . . . . . . . . . . . . . . . . . 17 B. Rationale for Interface Identifier Construction . . . . . . 18 C. Dynamic Per-neighbor MTU Discovery . . . . . . . . . . . . . 19 Intellectual Property and Copyright Statements . . . . . . . 21 Templin, et al. Expires July 1, 2003 [Page 2] Internet-Draft ISATAP December 2002 1. Introduction This document presents a simple approach that enables incremental deployment of IPv6 [1] within IPv4-based [2] sites in a manner that is compatible with inter-domain tunneling mechanisms, e.g., RFC 3056 (6to4) [18]. We refer to this approach as the Intra-Site Automatic Tunnel Addressing Protocol (ISATAP). ISATAP allows dual-stack nodes that do not share a physical link with an IPv6 router to automatically tunnel packets to the IPv6 next-hop address through IPv4, i.e., the site's IPv4 infrastructure is treated as an link layer for IPv6. This document specifies details for the transmission of IPv6 packets over ISATAP links (i.e., automatic IPv6-in-IPv4 tunneling), including an interface identifier format that embeds an IPv4 address. This format supports IPv6 protocol mechanisms for address configuration as well as simple link-layer address mapping. Simple validity checks for received packets are given. Also specified in this document is the operation of IPv6 Neighbor Discovery for ISATAP. The document finally presents deployment and security considerations for ISATAP. 2. Applicability Statement ISATAP provides the following features: o treats site's IPv4 infrastructure as link layer for IPv6 using automatic IPv6-in-IPv4 tunneling (i.e., no configured tunnel state) o enables incremental deployment of IPv6 hosts within IPv4 sites with no aggregation scaling issues at border gateways o requires no special IPv4 services within the site (e.g., multicast) o supports both stateless address autoconfiguration and manual configuration o supports networks that use non-globally unique IPv4 addresses (e.g., when private address allocations [3] are used), but does not allow the virtual ISATAP link to span a Network Address Translator [4] o compatible with other NGTRANS mechanisms (e.g., 6to4 [18]) Templin, et al. Expires July 1, 2003 [Page 3] Internet-Draft ISATAP December 2002 3. 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 [5]. This document also makes use of 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 to demonstrate protocol behavior. An implementation is not required to have them in the exact form described here, so long as its external behavior is consistent with that described in this document. 4. Terminology The terminology of RFC 2460 [1] applies to this document. The following additional terms are defined: link; on-link: same definitions as ([6], section 2.1). underlying link: a link layer that supports IPv4 (for ISATAP), and MAY also support IPv6 natively. ISATAP link: one or more underlying links used for tunneling. The IPv4 network layer addresses of the underlying links are used as link-layer addresses on the ISATAP link. ISATAP interface: a node's attachment to an ISATAP link. ISATAP address: an on-link address on an ISATAP interface and with an interface identifier constructed as specified in Section 5.1 ISATAP router: an IPv6 node that has an ISATAP interface over which it forwards packets not explicitly addressed to itself. ISATAP host: any node that has an ISATAP interface and is not an ISATAP router. Templin, et al. Expires July 1, 2003 [Page 4] Internet-Draft ISATAP December 2002 5. Basic IPv6 Operation on ISATAP Links ISATAP links transmit IPv6 packets via automatic tunnels using the site's IPv4 infrastructure as a link layer for IPv6, i.e., the site's IPv4 infrastructure is treated as a Non-Broadcast, Multiple Access (NBMA) link layer. The following subsections outline basic operational details for IPv6 on ISATAP links: 5.1 Interface Identifiers and Address Construction (RFC2491 [7], section 5.1) requires companion documents to specify the exact mechanism for generating interface tokens (i.e., identifiers). Interface identifiers for ISATAP are compatible with the EUI-64 identifier format ([8], section 2.5.1), and are constructed by appending an IPv4 address on the ISATAP link to the 32-bit string '00-00-5E-FE'. (Appendix B includes non-normative text explaining the rationale for this construction rule.) Global and Local-use ISATAP addresses are constructed as follows: | 64 bits | 32 bits | 32 bits | +------------------------------+---------------+----------------+ | global or local-use unicast | 0000:5EFE | IPv4 Address | | prefix | | of ISATAP link | +------------------------------+---------------+----------------+ Figure 1 For example, the global unicast address: 3FFE:1A05:510:1111:0:5EFE:8CAD:8108 has a prefix of '3FFE:1A05:510:1111::/64' and an ISATAP interface identifier with embedded IPv4 address: '140.173.129.8'. The address is alternately written as: 3FFE:1A05:510:1111:0:5EFE:140.173.129.8 (Similar examples for local-use addresses are made obvious by the above and with reference to the IPv6 addressing architecture document.) 5.2 ISATAP Link/Interface Configuration ISATAP Link/Interface configuration is consistent with (RFC2491 [7], sections 5.1.1 and 5.1.2). Using the terminology of Section 4, an ISATAP link consists of one or Templin, et al. Expires July 1, 2003 [Page 5] Internet-Draft ISATAP December 2002 more underlying links that support IPv4 for tunneling within a site. ISATAP interfaces are configured over ISATAP links; each IPv4 address assigned to an underlying link is seen as a link-layer address for ISATAP. 5.3 Dual Stack Operation and Address Configuration ISATAP uses the same specification found in ([9], section 2). That is, ISATAP nodes implement "IPv6/IPv4" or "dual-stack" configurations and operate with both stacks enabled. Address configuration and DNS considerations are the same as for ([9], sections 2.1 and 2.2) 5.4 Tunneling Mechanisms The common tunneling mechanisms specified in ([9], sections 3.1 through 3.7) are used, with the following noted specific considerations: 5.4.1 Encapsulation The specification in ([9], section 3.1) is used. Additionally, the IPv6 next-hop address for packets sent on an ISATAP link MUST be an ISATAP address; other packets are discarded (i.e., not encapsulated) and an ICMPv6 destination unreachable indication with code 3 (Address Unreachable) [10] is returned to the source. 5.4.2 Tunnel MTU and Fragmentation The specification in ([9], section 3.2) is NOT used; the specification in this section is used instead. ISATAP uses automatic tunnel interfaces that may be configured over multiple underlying links with diverse maximum transmission units (MTUs). The minimum MTU for IPv6 interfaces is 1280 bytes ([1], Section 5), but the following considerations apply when IPv4 is used as a link layer for IPv6: o nearly all IPv4 nodes accept unfragmented packets up to 1500 bytes o sub-IPv4 layer encapsulations (e.g., VPN) may occur on some paths o commonly-deployed VPNs use an MTU of 1400 bytes Thus, ISATAP interfaces SHOULD use an MTU (ISATAP_MTU) of 1380 bytes (1400 minus 20 bytes for IPv4 encapsulation) to maximize efficiency and minimize IPv4 fragmentation. ISATAP_MTU MAY be set to larger values when the encapsulator uses Templin, et al. Expires July 1, 2003 [Page 6] Internet-Draft ISATAP December 2002 dynamic per-neighbor MTU discovery. When larger values are used, ISATAP_MTU SHOULD NOT exceed the maximum MTU of all underlying links minus 20 bytes for link layer encapsulation. (Appendix C provides non-normative considerations for dynamic per-neighbor MTU discovery.) As with ordinary IPv6 interfaces, the network layer (IPv6) forwards packets of size ISATAP_MTU or smaller to the ISATAP interface. All other packets are dropped, and an ICMPv6 "packet too big" message with MTU = ISATAP_MTU is returned to the source [11]. ISATAP interfaces send all packets of size 1380 bytes or smaller with the Don't Fragment (DF) bit NOT set in the encapsualting IPv4 header. 5.4.3 Handling IPv4 ICMP Errors The specification in ([9], section 3.4) MAY be used. IPv4 ICMP errors and ARP failures are otherwise processed as link error notifications. 5.4.4 Decapsulation The specification in ([9], section 3.6) is used. 5.4.5 Link-Local Addresses The specification in ([9], section 3.7) is NOT used. Instead, link-local addresses are formed by appending an interface identifier, as defined in Section 5.1, to the prefix FE80::/64. 5.4.6 Ingress Filtering The network layer (IPv6) destination address of a packet received on an ISATAP interface is either local (i.e., matches an address configured on the local IPv6 stack) or foreign. The decapsulator MUST be configured with a list of IPv4 address prefixes that are acceptable, i.e., an ingress filter list (default deny all). For packets with foreign network layer (IPv6) destination addresses, the link layer (IPv4) source address MUST be explicitly allowed by ingress filtering. Packets that do not satisfy this condition are silently discarded. Additionally, all packets (whether foreign or local) MUST satisfy at least one (i.e., one or both) of the following validity checks: o the network-layer (IPv6) source address is an on-link ISATAP address with an interface identifier that embeds the link-layer (IPv4) source address Templin, et al. Expires July 1, 2003 [Page 7] Internet-Draft ISATAP December 2002 o the link-layer (IPv4) source address is in the Potential Routers List (see Section 6.2.1) Packets that do not satisfy the above conditions are silently discarded. 6. Neighbor Discovery and Address Autoconfiguration RFC 2491 [7] provides a general architecture for IPv6 over NBMA networks, including multicast mechanisms to support host-side operation of the IPv6 neighbor discovery protocol. ISATAP links most closely meet the description for connectionless service found in the last paragraph of ([7], section 1), i.e., ISATAP addresses provide the sender with an NBMA destination address to which it can transmit packets whenever it desires. Thus, the RFC 2491 multicast mechanisms are not required for address resolution and not otherwise implemented on ISATAP links due to traffic scaling considerations (i.e., ISATAP links are unicast-only). RFC 2461 [6] provides the following guidelines for non-broadcast multiple access (NBMA) link support: "Redirect, Neighbor Unreachability Detection and next-hop determination should be implemented as described in this document. Address resolution and the mechanism for delivering Router Solicitations and Advertisements on NBMA links is not specified in this document." ISATAP links SHOULD implement Redirect, Neighbor Unreachability Detection, and next-hop determination exactly as specified in [6]. Address resolution and the mechanisms for delivering Router Solicitations and Advertisements on ISATAP links use the specifications found in this document. 6.1 Address Resolution ISATAP addresses are resolved to link-layer addresses (IPv4) by a static computation, i.e., the last four octets are treated as an IPv4 address. ([7], section 5.2) requires companion documents to specify the format for link layer address options, however, link layer address options are not needed for address resolution in ISATAP. Thus, no format is specified and the following specification from ([9], section 3.8) applies: "This means that a sender of Neighbor Discovery packets * SHOULD NOT include Source Link Layer Address options or Target Link Layer Address options on the tunnel link. Templin, et al. Expires July 1, 2003 [Page 8] Internet-Draft ISATAP December 2002 * MUST silently ignore any received SLLA or TLLA options on the tunnel link." Following static address resolution, ISATAP hosts SHOULD implement the reachability confirmation specifications in [6], sections 7.2.2-7.2.8 that apply when unicast Neighbor Solicitations (NS) are used. ISATAP hosts SHOULD additionally perform Neighbor Unreachability Detection (NUD) as specified in (RFC 2461 [6], section 7.3). ISATAP routers MAY perform the above-specified reachability detection and NUD procedures, but this might not scale in all environments. All ISATAP nodes MUST send solicited neighbor advertisements ([6], section 7.2.4). ISATAP links disable Duplicate Address Detection, as permitted by ([12], section 4). 6.2 Address Autoconfiguration and Router Discovery Since NBMA multicast emulation mechanisms are not used on ISATAP links, nodes will not receive unsolicited multicast Router Advertisements. (RFC 2462 [12], section 5.5.2) requires that hosts use stateful autoconfiguration (i.e., DHCPv6 [13]) in the absence of Router Advertisements. When statelful autoconfiguration is not available, nodes use alternate mechanisms (described below) for router and prefix discovery. 6.2.1 Conceptual Data Structures ISATAP nodes use the conceptual data structures Prefix List and Default Router List exactly as in ([6], section 5.1). ISATAP links add two new conceptual data structures "Potential Router List" and "Stateful Autoconfiguration Server List". A Potential Router List (PRL) and Stateful Autoconfiguration Server List (SASL) is associated with every ISATAP link. The PRL provides a trust basis for router validation (see security considerations). Each entry in the PRL has an IPv4 address and an associated timer. The IPv4 address represents a router's ISATAP interface (likely to be an "advertising interface"), and is used to construct the ISATAP link-local address for that interface. Similarly, each entry in the SASL has an IPv4 address and associated timer. The IPv4 address represents a DHCPv6 server attached to the ISATAP link, and is used to construct the ISATAP link-local address for that DHCPv6 server. When a node enables an ISATAP link, it first discovers IPv4 addresses for the PRL and SASL. The addresses MAY be established by a DHCPv4 Templin, et al. Expires July 1, 2003 [Page 9] Internet-Draft ISATAP December 2002 [14] option for ISATAP (option code TBD), by manual configuration, or by an unspecified alternative method (e.g., DHCPv4 vendor-specific option; DNS ([19]) fully-qualified domain names). When DNS fully-qualified domain names are used, IPv4 addresses for the PRL and SASL are discovered through a static host file or by querying an IPv4-based DNS server to resolve the domain names into address records (e.g., DNS 'A' resource records) containing IPv4 addresses. Unspecified alternative methods for domain name resolution may also be used. The following notes apply when DNS fully-qualified domain names are used: 1. Site administrators maintain domain names and IPv4 addresses for the PRL and SASL for the site's ISATAP service, e.g., as address records in the site's name service. Administrators may also advertise the domain names in a DHCPv4 option for ISATAP. 2. There are no mandatory rules for the selection of domain names, but administrators are encouraged to use the convention "(list_name).isatap.domainname" (e.g., prl.isatap.example.com). 3. After initialization, nodes periodically re-initialize the PRL and SASL, e.g., once per hour. When DNS is used, client DNS resolvers use the IPv4 transport to resolve the names and follow the cache invalidation procedures in [19] when the DNS time-to-live expires. 6.2.2 Validity Checks for Router Advertisements A node MUST silently discard any Router Advertisement messages it receives that do not satisfy both the validity checks in ([6], section 6.1.2) and the following additional validity check for ISATAP: o the network-layer (IPv6) source address is an ISATAP address and embeds an IPv4 address from the PRL 6.2.3 Router Specification Advertising ISATAP interfaces of routers behave the same as advertising interfaces described in ([6], section 6.2). However, periodic unsolicited multicast Router Advertisements are not used, thus the "interval timer" associated with advertising interfaces is not used for that purpose. When an ISATAP router receives a valid Router Solicitation on an Templin, et al. Expires July 1, 2003 [Page 10] Internet-Draft ISATAP December 2002 advertising ISATAP interface, it replies with a unicast Router Advertisement to the address of the node which sent the Router Solicitation. The source address of the Router Advertisement is a link-local unicast address associated with the interface. This MAY be the same as the destination address of the Router Solicitation. ISATAP routers MAY engage in the solicitation process described under Host Specification below, e.g., if Router Advertisement consistency verification ([6], section 6.2.7) is desired. 6.2.4 Host Specification All entries in the PRL are assumed to represent active ISATAP routers within the site, i.e., the PRL provides trust basis only; not reachability detection. When stateful autoconfiguration is available (i.e., when the SASL is non-null and at least one DHCPv6 server is reachable), hosts may send unicast messages directly to the DHCPv6 server as specified in ([13], section 1.1). Hosts SHOULD attempt stateful autoconfiguration for each entry in the SASL (i.e., until an attempt succeeds) before concluding that stateful autoconfiguration is unavailable. When stateful autoconfiguration is unavailable, hosts MAY periodically solicit information from one or more entries in the PRL ("PRL(i)") by sending unicast Router Solicitation messages using the IPv4 address ("V4ADDR_PRL(i)") and associated timer in the entry. Hosts add the following variable to support the solicitation process: MinRouterSolicitInterval Minimum time between sending Router Solicitations to any router. Default and suggested minimum 800,000 milliseconds (15min). When a PRL(i) is selected, the host sets its associated timer to MinRouterSolicitInterval and initiates solicitation following a short delay as in ([6], section 6.3.7). The manner of choosing particular routers in the PRL for solicitation is outside the scope of this specification. The solicitation process repeats when the associated timer expires. Solicitation consists of sending Router Solicitations to the ISATAP link-local address constructed from the entry's IPv4 address, i.e., they are sent to 'FE80::0:5EFE:V4ADDR_PRL(i)' instead of 'All-Routers multicast'. They are otherwise sent exactly as in ([6], section 6.3.7). Hosts process received Router Advertisements exactly as in ([6], section 6.3.4). Hosts additionally reset the timer associated with the V4ADDR_PRL(i) embedded in the network-layer source address in each solicited Router Advertisement received. The timer is reset to Templin, et al. Expires July 1, 2003 [Page 11] Internet-Draft ISATAP December 2002 either 0.5 * (the minimum value in the router lifetime or valid lifetime of any on-link prefixes received in the advertisement) or MinRouterSolicitInterval; whichever is longer. 7. ISATAP Deployment Considerations 7.1 Host And Router Deployment Considerations For hosts, if an underlying link supports both IPv4 (over which ISATAP is implemented) and also supports IPv6 natively, then ISATAP MAY be enabled if the native IPv6 layer does not receive Router Advertisements (i.e., does not have connection with an IPv6 router). After a non-link-local address has been configured and a default router acquired on the native link, the host SHOULD discontinue the router solicitation process described in the host specification and allow existing ISATAP address configurations to expire as specified in ([6], section 5.3) and ([12], section 5.5.4). Any ISATAP addresses added to the DNS for this host should also be removed. In this way, ISATAP use will gradually diminish as IPv6 routers are widely deployed throughout the site. Routers MAY configure an interface to simultaneously support both native IPv6, and also ISATAP (over IPv4). Routing will operate as usual between these two domains. Note that the prefixes used on the ISATAP and native IPv6 interfaces will be distinct. The IPv4 address(es) configured on a router's ISATAP interface(s) SHOULD be added (either automatically or manually) to the site's address records for ISATAP router interfaces. 7.2 Site Administration Considerations The following considerations are noted for sites that deploy ISATAP: o ISATAP links are administratively defined by a set of router interfaces, a set of stateful autoconfiguration servers, and set of nodes which discover those interface and server addresses Thus, ISATAP links are defined by administrative (not physical) boundaries. o ISATAP hosts and routers can be deployed in an ad-hoc and independent fashion. In particular, ISATAP hosts can be deployed with little/no advanced knowledge of existing ISATAP routers, and ISATAP routers can deployed with no reconfiguration requirements for hosts. o When stateful autoconfiguration is not available, ISATAP nodes MAY periodically send unicast Router Solicitations to and receive unicast Router Advertisements from to one or more members of the Templin, et al. Expires July 1, 2003 [Page 12] Internet-Draft ISATAP December 2002 potential router list. A well-deployed stateful autoconfiguration service within the site can minimize and/or eliminate the need for periodic solicitation. o ISATAP nodes periodically refresh the entries on the PRL and SASL. Responsible site administration can reduce the control traffic. At a minimum, administrators SHOULD ensure that dynamically advertised information for the site's PRL and SASL are well maintained. 8. IANA Considerations A DHCPv4 option code for ISATAP (TBD) [20] is requested in the event that the IESG recommends this document for standards track. 9. Security considerations Site administrators are advised that, in addition to possible attacks against IPv6, security attacks against IPv4 MUST also be considered. Responsible IPv4 site security management is strongly encouraged. In particular, border gateways SHOULD implement filtering to detect spoofed IPv4 source addresses at a minimum; ip-protocol-41 filtering SHOULD also be implemented. If IPv4 source address filtering is not correctly implemented, the ISATAP validity checks will not be effective in preventing IPv6 source address spoofing. If filtering for ip-protocol-41 is not correctly implemented, IPv6 source address spoofing is clearly possible, but this can be eliminated if both IPv4 source address filtering, and the ISATAP validity checks are implemented. (RFC 2461 [6]), section 6.1.2 implies that nodes trust Router Advertisements they receive from on-link routers, as indicated by a value of 255 in the IPv6 'hop-limit' field. Since this field is not decremented when ip-protocol-41 packets traverse multiple IPv4 hops ([9], section 3), ISATAP links require a different trust model. In particular, ONLY those Router Advertisements received from a member of the Potential Routers List are trusted; all others are silently discarded. This trust model is predicated on IPv4 source address filtering, as described above. The ISATAP address format does not support privacy extensions for stateless address autoconfiguration [21]. However, since the ISATAP interface identifier is derived from the node's IPv4 address, ISATAP Templin, et al. Expires July 1, 2003 [Page 13] Internet-Draft ISATAP December 2002 addresses do not have the same level of privacy concerns as IPv6 addresses that use an interface identifier derived from the MAC address. (This issue is the same for NAT'd addresses.) 10. Acknowledgements Some of the ideas presented in this draft were derived from work at SRI with internal funds and contractual support. Government sponsors who supported the work include Monica Farah-Stapleton and Russell Langan from U.S. Army CECOM ASEO, and Dr. Allen Moshfegh from U.S. Office of Naval Research. Within SRI, Dr. Mike Frankel, J. Peter Marcotullio, Lou Rodriguez, and Dr. Ambatipudi Sastry supported the work and helped foster early interest. The following peer reviewers are acknowledged for taking the time to review a pre-release of this document and provide input: Jim Bound, Rich Draves, Cyndi Jung, Ambatipudi Sastry, Aaron Schrader, Ole Troan, Vlad Yasevich. The authors acknowledge members of the NGTRANS community who have made significant contributions to this effort, including Rich Draves, Alain Durand, Nathan Lutchansky, Karen Nielsen, Art Shelest, Margaret Wasserman, and Brian Zill. The authors also wish to acknowledge the work of Quang Nguyen [22] 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. Normative References [1] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [2] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. [3] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G. and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, February 1996. [4] Egevang, K. and P. Francis, "The IP Network Address Translator (NAT)", RFC 1631, May 1994. [5] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [6] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery Templin, et al. Expires July 1, 2003 [Page 14] Internet-Draft ISATAP December 2002 for IP Version 6 (IPv6)", RFC 2461, December 1998. [7] Armitage, G., Schulter, P., Jork, M. and G. Harter, "IPv6 over Non-Broadcast Multiple Access (NBMA) networks", RFC 2491, January 1999. [8] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", draft-ietf-ipngwg-addr-arch-v3-11 (work in progress), October 2002. [9] Gilligan, R. and E. Nordmark, "Basic Transition Mechanisms for IPv6 Hosts and Routers", draft-ietf-ngtrans-mech-v2-01 (work in progress), November 2002. [10] Conta, A. and S. Deering, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 2463, December 1998. [11] McCann, J., Deering, S. and J. Mogul, "Path MTU Discovery for IP version 6", RFC 1981, August 1996. [12] Thomson, S. and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. [13] Droms, R., "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress), November 2002. [14] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [15] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, November 1990. [16] Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, September 1981. [17] Baker, F., "Requirements for IP Version 4 Routers", RFC 1812, June 1995. Informative References [18] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via IPv4 Clouds", RFC 3056, February 2001. [19] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987. Templin, et al. Expires July 1, 2003 [Page 15] Internet-Draft ISATAP December 2002 [20] Droms, R., "Procedures and IANA Guidelines for Definition of New DHCP Options and Message Types", BCP 43, RFC 2939, September 2000. [21] Narten, T. and R. Draves, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001. [22] Nguyen, Q., "http://irl.cs.ucla.edu/vet/report.ps", spring 1998. [23] Lahey, K., "TCP Problems with Path MTU Discovery", RFC 2923, September 2000. Authors' Addresses Fred L. Templin Nokia 313 Fairchild Drive Mountain View, CA 94110 US Phone: +1 650 625 2331 EMail: ftemplin@iprg.nokia.com Tim Gleeson Cisco Systems K.K. Shinjuku Mitsu 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 Templin, et al. Expires July 1, 2003 [Page 16] Internet-Draft ISATAP December 2002 Dave Thaler Microsoft Corporation One Microsoft Way Redmond, WA 98052-6399 US Phone: +1 425 703 8835 EMail: dthaler@microsoft.com Appendix A. Major Changes changes from version 08 to version 09: o Added stateful autoconfiguration mechanism o Normative references to RFC 2491, RFC 2462 o Moved non-normative MTU text to appendix C changes from version 07 to version 08: o updated MTU section changes from version 06 to version 07: o clarified address resolution, Neighbor Unreachability Detection o specified MTU/MRU requirements changes from earlier versions to version 06: o Addressed operational issues identified in 05 based on discussion between co-authors o Clarified ambiguous text per comments from Hannu Flinck; Jason Goldschmidt o Moved historical text in section 4.1 to Appendix B in response to comments from Pekka Savola o Identified operational issues for anticipated deployment scenarios o Included reference to Quang Nguyen work Templin, et al. Expires July 1, 2003 [Page 17] Internet-Draft ISATAP December 2002 Appendix B. Rationale for Interface Identifier Construction ISATAP specifies an EUI64-format address construction for the Organizationally-Unique Identifier (OUI) owned by the Internet Assigned Numbers Authority (IANA). This format (given below) is used to construct both native EUI64 addresses for general use and modified EUI-64 format interface identifiers for IPv6 unicast addresses: |0 2|2 3|3 3|4 6| |0 3|4 1|2 9|0 3| +------------------------+--------+--------+------------------------+ | OUI ("00-00-5E"+u+g) | TYPE | TSE | TSD | +------------------------+--------+--------+------------------------+ Where the fields are: OUI IANA's OUI: 00-00-5E with 'u' and 'g' bits (3 octets) TYPE Type field; specifies use of (TSE, TSD) (1 octet) TSE Type-Specific Extension (1 octet) TSD Type-Specific Data (3 octets) And the following interpretations are specified based on TYPE: TYPE (TSE, TSD) Interpretation ---- ------------------------- 0x00-0xFD RESERVED for future IANA use 0xFE (TSE, TSD) together contain an embedded IPv4 address 0xFF TSD is interpreted based on TSE as follows: TSE TSD Interpretation --- ------------------ 0x00-0xFD RESERVED for future IANA use 0xFE TSD contains 24-bit EUI-48 intf id 0xFF RESERVED by IEEE/RAC Figure 2 Thus, if TYPE=0xFE, TSE is an extension of TSD. If TYPE=0xFF, TSE is an extension of TYPE. Other values for TYPE (thus, other interpretations of TSE, TSD) are reserved for future IANA use. The above specification is compatible with all aspects of EUI64, including support for encapsulating legacy EUI-48 interface identifiers (e.g., an IANA EUI-48 format multicast address such as: '01-00-5E-01-02-03' is encapsulated as: '01-00-5E-FF-FE-01-02-03'). Templin, et al. Expires July 1, 2003 [Page 18] Internet-Draft ISATAP December 2002 But, the specification also provides a special TYPE (0xFE) to indicate an IPv4 address is embedded. Thus, when the first four octets of an IPv6 interface identifier are: '00-00-5E-FE' (note: the 'u/l' bit MUST be 0) the interface identifier is said to be in "ISATAP format" and the next four octets embed an IPv4 address encoded in network byte order. Appendix C. Dynamic Per-neighbor MTU Discovery ISATAP encapsulators and decapsulators are IPv6 neighbors that may be separated by multiple link layer (IPv4) forwarding hops. When ISATAP_MTU is larger than 1380 bytes, the encapsulator must implement a dynamic link layer mechanism to discover per-neighbor MTUs. IPv4 path MTU discovery [15] relies on ICMPv4 "fragmentation needed" messages, but these do not provide enough information for stateless translation into ICMPv6 "packet too big" messages (see: RFC 792 [16] and RFC 1812 [17], section 4.3.2.3). Additionally, ICMPv4 "fragmentation needed" messages can be spoofed, filtered, or not sent at all by some forwarding nodes. Thus, IPv4 Path MTU discovery used alone is inadequate and can result in black holes that are difficult to diagnose [23]. The ISATAP encapsulator may implement an alternate per-neighbor MTU discovery mechanism, e.g., periodic and/or on-demand probing of the IPv4 path to the decapsulator. Probing consists of sending packets larger than 1380 bytes with the DF bit set in the IPv4 header. Neighbor Solicitation (NS) packets with padding bytes added should be used for this purpose, since successful delivery results in a positive acknowledgement that the probe succeeded, i.e., in the form of a Neighbor Advertisement (NA) from the decapsulator. (NB: Setting the DF bit prevents decapsulators from receiving probe packets that would overrun the receive buffer on an underlying link, thus no maximum receive unit (MRU) is required.) Implementations may choose to couple the probing process with neighbor cache management procedures ([6], section 7), e.g. to maintain timers, state variables and/or a queue of packets waiting for probes to complete. Packets retained on the queue are forwarded when probes succeed, and provide state for sending ICMPv6 "packet too big" messages to the source when probes fail. Implementations may choose to store per-neighbor MTU information in the IPv4 path MTU discovery cache, in the ISATAP link layer's private data structures, etc. ICMPv4 "fragmentation needed" messages may result when a link restriction is encountered but may also come from denial of service attacks. Implementations should treat ICMPv4 "fragmentation needed" Templin, et al. Expires July 1, 2003 [Page 19] Internet-Draft ISATAP December 2002 messages as "tentative" negative acknowledgments and apply heuristics to determine when to suspect an actual link restriction and when to ignore the messages. IPv6 packets lost due actual link restrictions are perceived as lost due to congestion by the original source, but robust implementations minimize instances of such packet loss without ICMPv6 "packet too big" messages returned to the sender. Templin, et al. Expires July 1, 2003 [Page 20] Internet-Draft ISATAP December 2002 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property 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; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication 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 implementors or users of this specification can be obtained from the IETF Secretariat. 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However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assignees. Templin, et al. Expires July 1, 2003 [Page 21] Internet-Draft ISATAP December 2002 This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS 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. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Templin, et al. Expires July 1, 2003 [Page 22]