NGTRANS Working Group F. Templin Internet-Draft Nokia Expires: June
13,19, 2003 T. Gleeson Cisco Systems K.K. M. Talwar D. Thaler Microsoft Corporation December 13,19, 2002 Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) draft-ietf-ngtrans-isatap-07.txtdraft-ietf-ngtrans-isatap-08.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 June 13,19, 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 is a transition mechanism that treats the site's IPv4 infrastructure as a Non-Broadcast Multiple Access (NBMA) 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Applicability Statement . . . . . . . . . . . . . . . . . . 3 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Transmission of IPv6 Packets on ISATAP Links . . . . . . . . 4 4.1 ISATAP Interface Identifier Construction . . . . . . . . . . 4 4.2 Stateless Autoconfiguration and Link-Local Addresses . . . . 5 4.3 ISATAP Link/Interface Configuration . . . . . . . . . . . . 5 4.4 Sending Rules and Address Mapping . . . . . . . . . . . . . 6 4.5 Validity Checks for Received Packets . . . . . . . . . . . . 6 4.6 Tunnel MTU and Fragmentation . . . . . . . . . . . . . . . . 6 5. Neighbor Discovery for ISATAP Links . . . . . . . . . . . . 9 5.1 Address Resolution . . . . . . . . . . . . . . . . . . . . . 9 5.2 Router and Prefix Discovery . . . . . . . . . . . . . . . . 10 5.2.1 Conceptual Data Structures . . . . . . . . . . . . . . . . . 10 5.2.2 Validity Checks for Router Advertisements . . . . . . . . . 11 5.2.3 Router Specification . . . . . . . . . . . . . . . . . . . . 12 5.2.4 Host Specification . . . . . . . . . . . . . . . . . . . . . 12 6. ISATAP Deployment Considerations . . . . . . . . . . . . . . 13 6.1 Host And Router Deployment Considerations . . . . . . . . . 13 6.2 Site Administration Considerations . . . . . . . . . . . . . 13 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . 14 8. Security considerations . . . . . . . . . . . . . . . . . . 14 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 Normative References . . . . . . . . . . . . . . . . . . . . 16 Informative References . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 17 A. Major Changes . . . . . . . . . . . . . . . . . . . . . . . 18 B. Rationale for Interface Identifier Construction Rules . . . 21 C. INTELLECTUAL PROPERTY . . . . . . . . . . . . . . . . . . . 22 Intellectual Property and Copyright Statements . . . . . . . 23 1. Introduction This document presents a simple approach that enables incremental deployment of IPv6  within IPv4-based  sites in a manner that is compatible with inter-domain transition mechanisms, e.g., RFC 3056 (6to4) .. We refer to this approach as the Intra-Site Automatic Tunnel Addressing Protocol, or ISATAP (pronounced: "ice-a-tap"). ISATAP allows dual-stack nodes that do not share a common 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 NBMA link layer. This document specifies details for the transmission of IPv6 packets over ISATAP links (i.e., automatic IPv6-in-IPv4 tunneling), including a new EUI-64 based interface identifier format  that embeds an IPv4 address. This format supports configuration of global, site-local and link-local addresses as specified in RFC 2462  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, as permitted for NBMA links by RFC 2461 . 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 an NBMA link layer 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  are used), but does not allow the virtual ISATAP link to span a Network Address Translator  o compatible with other NGTRANS mechanisms (e.g., 6to4 )) 3. Terminology The terminology of RFC 2460  applies to this document. The following additional terms are defined: link: same definition as . 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 prefix: a prefix used to configure an address on the ISATAP interface. This prefix is administratively assigned to the ISATAP link and MUST NOT be duplicated on native IPv6 links. ISATAP address: an IPv6 address with an ISATAP prefix and an ISATAP format interface identifier constructed as specified in section 4. 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. 4. Transmission of IPv6 Packets on ISATAP Links ISATAP links transmit IPv6 packets via automatic tunnels using the site's IPv4 infrastructure as an NBMA link layer. IPv4 ICMP errors and ARP failures may be processed as link error notifications, as allowed by RFC 2461 . The common tunneling mechanisms specified in Section 3 of RFC 2893  are used, with the following noted specific considerations for ISATAP links and automatic tunnels: 4.1 ISATAP Interface Identifier Construction IPv6 unicast addresses  include a 64-bit interface identifier field in "modified EUI-64 format", based on the IEEE EUI-64  specification. (Modified EUI-64 format inverts the sense of the 'u/ l' bit from its specification in , i.e., 'u/l' = 0 indicates local-use.) ISATAP interface identifiers are constructed by prepending the 32-bit string '00-00-5E-FE' with an IPv4 address (see the following section for examples). Appendix B includes text explaining the rationale for this construction rule. 4.2 Stateless Autoconfiguration and Link-Local Addresses ISATAP addresses are unicast addresses that use ISATAP format interface identifiers as follows: | 64 bits | 32 bits | 32 bits | +------------------------------+---------------+----------------+ | link-local, site-local or | 0000:5EFE | IPv4 Address | | global unicast prefix | | of ISATAP link | +------------------------------+---------------+----------------+ Figure 1 Link-local, site-local, and global ISATAP addresses can be created exactly as specified in , (e.g., by auto-configuration  or manual configuration). For example, the IPv6 address: 3FFE:1A05:510:1111:0:5EFE:8CAD:8108 has a prefix of '3FFE:1A05:510:1111::/64' and an ISATAP format interface identifier with embedded IPv4 address: '18.104.22.168'. The address is alternately written as: 3FFE:1A05:510:1111:0:5EFE:22.214.171.124 The link-local and site-local variants (respectively) are: FE80::0:5EFE:126.96.36.199 FEC0::1111:0:5EFE:188.8.131.52 4.3 ISATAP Link/Interface Configuration An ISATAP link consists of one or 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. At least one link-layer address per each ISATAP router interface SHOULD be added to the Potential Routers List (see Section 5.2.1). 4.4 Sending Rules and Address Mapping The IPv6 next-hop address for packets sent on an ISATAP link MUST be an ISATAP address. Packets that do not satisfy this constraint MUST be discarded and an ICMPv6 destination unreachable indication with code 3 (Address Unreachable)  MUST be returned. No other sending rules are necessary. The procedure for mapping unicast addresses into link-layer addresses is to simply treat the last four octets of the ISATAP address as an IPv4 address (in network byte order). No multicast address mappings are specified. 4.5 Validity Checks for Received Packets Packets received on ISATAP interfaces MUST satisfy at least one (i.e., one or both) of the following validity checks: o the network-layer (IPv6) source address has a prefix configured on the ISATAP interface and an ISATAP-format interface identifier that embeds the link-layer (IPv4) source address, i.e., source is on-link o the link-layer (IPv4) source address is in the Potential Routers List (see Section 5.2.1), i.e., previous hop is an on-link ISATAP router Packets that do not satisfy at least one of the above checks are silently discarded. 4.6 Tunnel MTU and Fragmentation ISATAP interfaces implement automatic tunnels that may be configured over multiple underlying links with diverse MTUs. The ISATAP interface MTU (ISATAP_MTU) SHOULD be no larger thanset to the largest MTU of all underlying links (LINK_MTU),(LINK_MTU) minus 20120 bytes for IPv4 encapsulation.possible link-layer encapsulations (see note 1). The minimum value (ISATAP_MINMTU) MUST be at least 1280 bytes , but SHOULD be set to 1380 bytes (see note 1). The maximum value used for ISATAP_MTU SHOULD be 4140 bytes (see note2). The maximum receive unit (ISATAP_MRU) MUST be at least 4400 bytes.IPv6 path MTU discovery  is required for IPv6 interfaces that send packets larger than 1280 bytes. The following considerations for ISATAP interfaces are noted: o ISATAP encapsulators and decapsulators are IPv6 neighbors since they share a common link layer, i.e., the ISATAP link o ISATAP neighbors may be separated by multiple IPv4 hops requiring IPv4 path MTU discovery  to establish per-neighbor MTUs (NBR_MTU) o NBR_MTU information is stored as link-layer (IPv4) information (e.g., in the IPv4 path MTU discovery cache), thus it may not be visible to upper layers in all implementations o NBR_MTU information may not always be available for each neighbor due to finite storage limitations o IPv4 path MTU discovery delivers ICMPv4 "fragmentation needed" messages, but these cannot be translateddo not provide enough state for translation into ICMPv6 "packet too big" messages. Thus, encapsulated packets MUST be sent with the DF flag in the IPv4 header NOT set unless additional state is maintained in the encapsulator (see note 3) Traditional packetizationmessages (see: RFC 792  and network (IPv6) layer implementations viewRFC 1812 , section 184.108.40.206). IPv6 sees the ISATAP interfacesinterface as an ordinary IPv6 interfacesinterface with a singlefixed MTU (ISATAP_MTU). Such implementations forward(ISATAP_MTU), i.e., only those IPv6 packets of size ISATAP_MTU or smaller to the ISATAP interface.are accepted. All other packets are dropped, and an IPv6 ICMP "packet too big" message with MTU = ISATAP_MTU is returned. Modified packetization and network (IPv6) layer implementations MAY look into theISATAP link layer for per-neighbor MTU information. When available, this information supersedes ISATAP_MTU in determining whether to forward the packet or return an ICMPv6 "packet too big" (see above). For IPv6 packets forwarded to the ISATAP interface, all implementations employinterfaces SHOULD implement the following link-layer algorithm at the link layerto determine when to perform IPv6-in-IPv4 encapsulation and when to return an IPv6 ICMPICMPv6 "packet too big" message: Determine per-neighbor LINK_MTU; NBR_MTU, e.g., by consulting IPv4 forwarding table and/or IPv4 path MTU discovery cache, then: if NBR_MTU information exists if packet is larger than NBR_MTU - 20120 and packet is larger than ISATAP_MINMTU Send IPv6 ICMP "packet too big" with MTU = MAX(NBR_MTU - 20,120, ISATAP_MINMTU) Drop packet else if packet is larger than ISATAP_MINMTU Encapsulate and set the Don't Fragment flag in the IPv4 header else Encapsulate but do not set the Don't Fragment flag in the IPv4 header endif endif else if packet is larger than LINK_MTU - 20120 and packet is larger than ISATAP_MINMTU Send IPv6 ICMP "packet too big" with MTU = ISATAP_MINMTU Drop packet else if IPv6 neighbor is also an IPv4 neighbor on the underlying link, or packet is less than or == ISATAP_MINMTU</t>ISATAP_MINMTU Encapsulate but do not set the Don't Fragment flag in the IPv4 hdrheader else send ICMPv6 "packet too big" with MTU = ISATAP_MINMTU Drop packet endif endif endif Figure 2= ISATAP_MINMTU Drop packet endif endif endif Figure 2 Encapsulators MAY maintain per-neighbor MTU (NBR_MTU) values by periodically probing the IPv4 path, e.g., by sending packets larger than ISATAP_MINMTU with the DF bit set in the IPv4 header. Large data packets and/or Neighbor Solicitation (NS) packets with padding bytes added (up to a total length of ISATAP_MTU) may be used for this purpose. (NS packets are preferred, since successful delivery results in a positive acknowledgement from the decapsulator.) When probing, implementations SHOULD maintain state for translating ICMPv4 "fragmentation needed" messages into ICMPv6 "packet too big" messages for at least the round-trip time (RTT) between the encapsulator and decapsulator (see note 3). Implementations SHOULD repeat the polling process within REACHABLE_TIME (, section 10) to detect link MTU restrictions. NOTES: 1. Nearly all IPv4 routers can forward 1500 byte packets without fragmentation.ISATAP requires 20 bytes for link-layer (IPv4) encapsulation. However, sub-IPv4 layer encapsulation (e.g., for VPNs) may occur on some paths. Commonly-deployed VPNs on Ethernet use an MTU of 1400 bytes, thus 1380100 bytes SHOULD be used as ISATAP_MINMTU.(1500 minums 1400) are reserverd for sub-IPv4 layer encapsulation. 2. TCP adapts to an overestimated MSS by reducing the segment size based on IPv6 "packet too big" messages (, section 5.4), thus setting ISATAP_MTU to the largest MTU ofNearly all underlying links would optimize performance for asymmetric paths. SCTP (, section 7.3) and other packetization layers (, section 5.5), perform upper-layer fragmentation based on IPv6 "packet too big" messages, which may result in unacceptable loss when the initial MTU estimate is too large. 4140IPv4 routers can forward 1500 byte packets without fragmentation. Thus, 1380 bytes (1500 minus 100 minus 20) is theRECOMMENDED maximum value for ISATAP_MTU, since: * 4140 bytes makes efficient use of common larger-than- ethernet MTUs in the internet (e.g., FDDI) * Locally-generated ICMPv6 "packet too big" messages are likely to advertise an MTU of 1380, resulting in at most three fragments and limiting loss probabilityas ISATAP_MINMTU. 3. Implementations MAY cache recently-sent IPv6 packets to provide state for translatingICMPv4 "fragmentation needed" messages into ICMPv6 "packet too big" messages. Such implementations MAY set the DF flag in the IPv4 header in the above algorithm for packets that willcan be retainedinjected by malicious nodes, but this same problem exists in the cache at least as long as the round-trip time (RTT) between the encapsulatorIPv4. Using Neighbor Solicitation messages for probing and decapsulator.receiving a positive acknowledgement from a trusted decapsulator MAY help encapsulators recognize spoofed ICMPv4 "fragmentation needed" messages. 5. Neighbor Discovery for ISATAP Links Section 3.2 of RFC 2461  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 . Address resolution and the mechanisms for delivering Router Solicitations and Advertisements for ISATAP links are not specified by ; instead, they are specified in this document. (Note that these mechanisms MAY potentially apply to other types of NBMA links in the future.) 5.1 Address Resolution Protocol addresses (IPv6) in ISATAP are resolved to link-layer addresses (IPv4) by a static computation, i.e., the last four octets are treated as an IPv4 address. ISATAP hosts SHOULD enhance the static address resolution computation with a unicast Neighbor Solicitation(NS)/Neighbor Advertisement(NA) exchange to ensure IPv6 level reachability of the neighbor and also SHOULD perform Neighbor Unreachability Detection (NUD) as specified in (RFC 2461 , section 7.3). ISATAP routers MAY implement the enhanced address resolution and NUD, but this might not scale in all environments. All ISATAP nodes MUST send solicited neighbor advertisements (, section 7.2.4). Link-layer address options (, section 4.6.1) for this specification MUST have Length = 1 and a six-octet interface identifier consisting of two zero octets followed by a four-octet IPv4 address. Options of this form SHOULD NOT be sent in NS/NA messages and MUST be silently ignored in received NS/NA messages. 5.2 Router and Prefix Discovery Since the site's IPv4 infrastructure is treated as an NBMA link layer, unsolicited Router Advertisements do not provide sufficient means for router discovery on ISATAP links. Thus, alternate mechanisms are required and specified below: 5.2.1 Conceptual Data Structures ISATAP nodes use the conceptual data structures Prefix List and Default Router List exactly as in (, section 5.1). ISATAP links add a new conceptual data structure "Potential Router List" and the following new configuration variable: ResolveInterval Time between name service resolutions. Default and suggested minimum: 1hr A Potential Router List (PRL) 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. The following sections specify the process for initializing the PRL: When a node enables an ISATAP link, it first discovers a DNS (RFC 1035 )) fully-qualified domain name for the site's ISATAP service. The domain name MAY be established by a DHCPv4  option for ISATAP (option code TBD, see IANA Considerations), by manual configuration, or by an unspecified alternative method. The DHCPv4 option for ISATAP is implemented exactly as in RFC 3361  with the following noted exceptions: o the DHCP option code for ISATAP (TBD) is used o the encoding byte MUST be 0, i.e.; only FQDNs are accepted o if multiple domain names occur, only the first is used Next, the node initializes the link's PRL with IPv4 addresses associated with the domain name discovered above. IPv4 addresses are discovered through manual config or by querying the name service to resolving the domain name into address records (e.g., DNS 'A' resource records) containing IPv4 addresses. Unspecified alternative methods may also be used. Notes: 1. Site administrators maintain a domain name for the ISATAP service and a list of IPv4 addresses representing ISATAP router interfaces (normally as address records in the site's name service). Administrators may also advertise the domain name in a DHCPv4 option for ISATAP. 2. There are no mandatory rules for the selection of a domain name, but administrators are encouraged to use the convention "isatap.domainname" (e.g., isatap.example.com). 3. After initialization, nodes periodically re-initialize the PRL (after ResolveInterval). When DNS is used, nodes MUST follow the cache invalidation procedures in  when the DNS time-to-live expires. 5.2.2 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 (, 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 5.2.3 Router Specification Advertising ISATAP interfaces of routers behave the same as advertising interfaces described in (, section 6.2). However, periodic unsolicited multicast Router Advertisements are not required, 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 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 (, section 6.2.7) is desired. 5.2.4 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. Hosts 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: 15min When a PRL(i) is selected, the host sets its associated timer to MinRouterSolicitInterval and initiates solicitation following a short delay as in (, section 6.3.7). 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 (, section 6.3.7). Hosts process received Router Advertisements exactly as in (, section 6.3.4). Hosts additionally reset the timer associated with the V4ADDR_PRL(i) embedded in the network-layer source address in each received Router Advertisement. The timer is reset to either 0.5 * (the minimum value in the router lifetime or valid lifetime of any on-link prefixes advertised) or MinRouterSolicitInterval; whichever is longer. (, section 6.3.4) includes the following specification: "To limit the storage needed for the Default Router List, a host MAY choose not to store all of the router addresses discovered via advertisements. However, a host MUST retain at least two addresses and SHOULD retain more." The router solicitation process for ISATAP nodes is analogous to choosing which router addresses to store as in the above text. ISATAP nodes may wish to consider the control traffic overhead of this process when choosing how many routers to solict. The manner of choosing particular routers in the PRL for solicitation is outside the scope of this specification. 6. ISATAP Deployment Considerations 6.1 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 (, section 5.3) and (, 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. 6.2 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, and set of nodes which have those interface addresses in their potential router lists. 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 ISATAP nodes periodically send Router Solicitations (RS) to one or more members of the potential router list. When Router Advertisements (RAs) are received, the Router Lifetime value provides a timer for the next RS to be sent. Worst-case is for small values of Router Lifetime which is bounded by MinRouterSolicitInterval. o ISATAP nodes periodically refresh the entries on the PRL, typically by querying the DNS. Responsible site administration can reduce the control traffic. At a minimum, administrators SHOULD ensure that the site's address records for ISATAP router interfaces are well maintained. 7. IANA Considerations A DHCPv4 option assignment for ISATAP is requested, as outlined in the procedures found in RFC 2939 ,, section 3. Appendix B proposes a specification for managing the IEEE OUI assigned to IANA for EUI-64 interface identifier construction. This specification is made freely available to IANA for any purpose they may find useful. 8. Security considerations Site administrators are advised that, in addition to possible attacks against IPv6, security attacks against IPv4 MUST also be considered. Many security considerations in RFC 2529 ,, section 9 apply also to ISATAP. 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 ), 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 (, 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 .. However, since the ISATAP interface identifier is derived from the node's IPv4 address, ISATAP 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.) 9. 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  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  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998.  Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.  Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 2373, July 1998.  Hinden, R. and S. Deering, "An IPv6 Aggregatable Global Unicast Address Format", RFC 2374, July 1998.  IEEE, "http://standards.ieee.org/regauth/oui/tutorials/ EUI64.html", March 1997.  Thomson, S. and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998.  Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998.  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G. and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, February 1996.  Egevang, K. and P. Francis, "The IP Network Address Translator (NAT)", RFC 1631, May 1994.  Gilligan, R. and E. Nordmark, "Transition Mechanisms for IPv6 Hosts and Routers", RFC 2893, August 2000.  Conta, A. and S. Deering, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 2463, December 1998.  Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, September 1981.  Baker, F., "Requirements for IP Version 4 Routers", RFC 1812, June 1995.  McCann, J., Deering, S. and J. Mogul, "Path MTU Discovery for IP version 6", RFC 1981, August 1996.  Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, November 1990.  Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and V. Paxson, "Stream Control Transmission Protocol", RFC 2960, October 2000.  Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.  Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCP-for-IPv4) Option for Session Initiation Protocol (SIP) Servers", RFC 3361, August 2002. Informative References  Carpenter, B. and K. Moore, "Connection of IPv6 Domains via IPv4 Clouds", RFC 3056, February 2001.  Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 Domains without Explicit Tunnels", RFC 2529, March 1999.  Narten, T. and R. Draves, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001.  Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987.  Droms, R., "Procedures and IANA Guidelines for Definition of New DHCP Options and Message Types", BCP 43, RFC 2939, September 2000.  Nguyen, Q., "http://irl.cs.ucla.edu/vet/report.ps", spring 1998. Authors' Addresses Fred L. Templin Nokia 313 Fairchild Drive Mountain View, CA 94110 US Phone: +1 650 625 2331 EMail: email@example.com Tim Gleeson Cisco Systems K.K. Shinjuku Mitsu Building 2-1-1 Nishishinjuku, Shinjuku-ku Tokyo 163-0409 Japan EMail: firstname.lastname@example.org Mohit Talwar Microsoft Corporation One Microsoft Way Redmond, WA> 98052-6399 US Phone: +1 425 705 3131 EMail: email@example.com Dave Thaler Microsoft Corporation One Microsoft Way Redmond, WA 98052-6399 US Phone: +1 425 703 8835 EMail: firstname.lastname@example.org Appendix A. Major Changes 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 version 05 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 changes from version 04 to version 05: 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 SRI IPR statement and contact information o Included reference to Quang Nguyen work changes from version 03 to version 04: o Re-wrote section on Potential Router List initialization to reference existing precedence in other documents o several minor wording changes based on feedback from the community changes from version 02 to version 03: o Added contributing co-authors o RSs are now sent to unicast addresses rather than all-routers-multicast o Brought draft into better alignment with other IPv6 standards-track documents o Added applicability statement changes from version 01 to version 02: o Cleaned up text and tightened up terminology o Changed "IPv6 destination address" to "IPv6 next-hop address" under "sending rules" o Changed definition of ISATAP prefix to include link and site-local o Changed language in sections 4 and 5 changes from version 00 to version 01: o Revised draft to require different /64 prefixes for ISATAP addresses and native IPv6 addresses. Thus, a node's ISATAP interface is assigned a /64 prefix that is distinct from the prefixes assigned to any other interfaces attached to the node - be they physical or logical interfaces. This approach eliminates ISATAP-specific sending rules presented in earlier draft versions. o Changed sense of 'u/l' bit in the ISATAP address interface identifier to indicate "local scope", since ISATAP interface identifiers are unique only within the scope of the ISATAP prefix. (See section 4.) changes from personal draft to version 00: o Title change to provide higher-level description of field of use addressed by this draft. Removed other extraneous text. o Major new section on automatic discovery of off-link IPv6 routers when IPv6-IPv4 compatibility addresses are used. Appendix B. Rationale for Interface Identifier Construction Rules 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 use in 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 interpretation 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 3 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'). 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. INTELLECTUAL PROPERTY SRI International has notified the IETF of IPR considerations for some aspects of this specification. For more information consult the online list of claimed rights. 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