NGTRANS Working Group F. Templin
INTERNET-DRAFTInternet-Draft Nokia Expires: June 13, 2003 T. Gleeson Cisco Systems K.K. M. Talwar D. Thaler Microsoft Corporation Expires 31 April 2003 31 OctoberDecember 13, 2002 Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) draft-ietf-ngtrans-isatap-06.txtdraft-ietf-ngtrans-isatap-07.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. 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- DraftsInternet-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.txthttp:// 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, 2003. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document specifies thean Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) that connects IPv6 hosts and routers (nodes)within IPv4 sites. ISATAP is a transition mechanism that enables incremental deployment of IPv6 by treatingtreats the site's IPv4 infrastructure as a Non-Broadcast Multiple Access (NBMA) link layer for IPv6. ISATAP mechanisms use anIPv6 interface identifier format that embeds anwith no requirement for IPv4 address - thismulticast. ISATAP enables intra-site automatic IPv6-in-IPv4 tunneling within a site,whether the site usesglobally assigned or private IPv4 addresses. The new interface identifier format can be used with both local and global unicast IPv6 prefixes - this enables IPv6 routing both locally and globally. ISATAP mechanisms introduce no impact on routing table size and require no special IPv4 services (e.g., IPv4 multicast).addresses are used. 1. Introduction This document presents a simple approach that enables incremental deployment of IPv6  within IPv4-based  sites in a manner that is com- patiblecompatible with inter-domain transition mechanisms, e.g., [6TO4].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- stackdual-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 [EUI64]based interface identifier [ADDR][AGGR]format  that embeds an IPv4 address. This format supports configuration of global, site-local and link-local addresses as specified in [AUTO]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 [DISC].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 [PRIVATE] are used), but does not allow the virtual ISATAP link to span a Network Address Translator [NAT] - o compatible with other NGTRANS mechanisms (e.g., [6TO4])6to4 ) 3. Terminology The terminology of [IPv6]RFC 2460  applies to this document. The following additional terms are defined: link: same definition as [AUTO][DISC].. 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 IPv4tunneling. 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 tunnelingtunnels using the site's IPv4 infrastructure as an NBMA link layer. Automatic tunneling for ISATAP uses the same encapsulation, hop limit, IPv4 header con- struction, and decapsualtion specifications in [MECH, 3], i.e., IPv6 packets are automatically encapsulated in IPv4 using 'ip-protocol-41' as the payload type number. The specifications in [MECH, 3.2, 3.4] do not apply for ISATAP; instead: - The default link MTU SHOULD be set to the minimum IPv6 MTU of 1280 bytes [IPV6], unless specific configuration information is available. The Don't Fragment bit SHOULD NOT be set in the encapsulating IPv4 header. -IPv4 ICMP errors and ARP failures may be processed as link error notifications, as allowed by [DISC] SpecificRFC 2461 . The common tunneling mechanisms specified in Section 3 of RFC 2893  are used, with the following noted specific considerations for ISATAP links are given below: 4.1.and automatic tunnels: 4.1 ISATAP Interface Identifier Construction IPv6 unicast addresses [ADDR][AGGR] include a 64-bit interface iden- tifieridentifier field in "modified EUI-64 format", based on the IEEE EUI-64 [EUI64] specification. (Modified EUI-64 format inverts the sense of the 'u/l''u/ l' bit from its specification in [EUI64],, 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. 22.214.171.124 Stateless Autoconfiguration and Link-Local Addresses ISATAP addresses are unicast addresses [ADDR,2.5]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 [ADDR],, (e.g., by auto-configuration [AUTO] 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 inter- faceinterface identifier with embedded IPv4 address: '126.96.36.199'. The address is alternately written as: 3FFE:1A05:510:1111:0:5EFE:188.8.131.52 The link-local and site-local variants (respectively) are: FE80::0:5EFE:184.108.40.206 FEC0::1111:0:5EFE:220.127.116.11 18.104.22.168 ISATAP Link/Interface Configuration A node configures anAn ISATAP link overconsists of one or more underlying links that support IPv4 links, i.e., thefor tunneling within a site. ISATAP link MAY beinterfaces are configured over one or more link- layer (IPv4) addresses. Each link-layerISATAP links; each IPv4 address 'V4ADDR_LINK' is usedassigned to configure a link-local address 'FE80::0:5EFE:V4ADDR_LINK' onan ISATAP interface. ISATAP interfaces MAY be assigned one per link- layer address, orunderlying link is seen as a single interfacelink-layer address for multipleISATAP. At least one link-layer addresses. In the former case, theaddress ofper each ISATAP router interface SHOULD be added to the Potential Routers List (see sectionSection 5.2.1). In the lat- ter case, the interface will accept ISATAP packets addressed to any of the IPv4 link-layer addresses, but will choose one as its primary address, used for sourcing packets. Only this address need be repre- sented in the Potential Routers List. 22.214.171.124 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 ICMPICMPv6 destination unreachable indication with code 3 (Address Unreachable) [ICMPv6] 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. 126.96.36.199 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 than the largest MTU of all underlying links (LINK_MTU), minus 20 bytes for IPv4 encapsulation. 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 note 2). 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 translated 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 packetization and network (IPv6) layer implementations view ISATAP interfaces as ordinary IPv6 interfaces with a single MTU (ISATAP_MTU). Such implementations forward only those IPv6 packets of size ISATAP_MTU or smaller to the ISATAP interface. 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 the ISATAP 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 employ the following algorithm at the link layer to determine when to perform IPv6-in-IPv4 encapsulation and when to return an IPv6 ICMP "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 - 20 and packet is larger than ISATAP_MINMTU Send IPv6 ICMP "packet too big" with MTU = MAX(NBR_MTU - 20, ISATAP_MINMTU) Drop packet else Encapsulate but do not set the Don't Fragment flag in the IPv4 header endif else if packet is larger than LINK_MTU - 20 and packet is larger than ISATAP_MINMTU Send IPv6 ICMP "packet too big" with MTU = ISATAP_MINMTU Drop packet else if IPv6 neighbor is an IPv4 neighbor on the underlying link, or packet is less than or == ISATAP_MINMTU</t> Encapsulate but do not set the Don't Fragment flag in the IPv4 hdr else send ICMPv6 "packet too big" with MTU = ISATAP_MINMTU Drop packet endif endif endif Figure 2 NOTES: 1. Nearly all IPv4 routers can forward 1500 byte packets without fragmentation. However, sub-IPv4 layer encapsulation (e.g., for VPNs) may occur on some paths. Commonly-deployed VPNs use an MTU of 1400 bytes, thus 1380 bytes SHOULD be used as ISATAP_MINMTU. 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 of 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. 4140 is the RECOMMENDED maximum value for ISATAP_MTU, since: * 4140 bytes makes efficient use of common larger-than- ethernet MTUs in the link-layer (IPv4) source address isinternet (e.g., FDDI) * Locally-generated ICMPv6 "packet too big" messages are likely to advertise an "active" memberMTU of 1380, resulting in at most three fragments and limiting loss probability 3. Implementations MAY cache recently-sent IPv6 packets to provide state for translating ICMPv4 "fragmentation needed" messages into ICMPv6 "packet too big" messages. Such implementations MAY set the Potential Routers List (see section 5.2), i.e., previous hop is an on-link ISATAP router actively being used byDF flag in the node PacketsIPv4 header in the above algorithm for packets that do not satisfywill be retained in the cache at least one ofas long as the above checks are silently discarded.round-trip time (RTT) between the encapsulator and decapsulator. 5. Neighbor Discovery for ISATAP Links Section 3.2 of [DISC] ("Supported Link Types")RFC 2461  provides the following guidelines for non-broadcast multiple access (NBMA) link support: "Redirect, Neighbor Unreachability Detection and next-hop determi- nationdetermination 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 docu- ment."document." ISATAP links SHOULD implement Redirect, Neighbor Unreachability Detection, and next-hop determination exactly as specified in [DISC].. Address resolution and the mechanisms for delivering Router Solicita- tionsSolicitations and Advertisements for ISATAP links are not specified by [DISC];; instead, they are specified in this document. (Note that these mechanisms MAY potentially apply to other types of NBMA links in the future.) 188.8.131.52 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 nodeshosts 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 [DISC, 7.3],(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 adver- tisements as specified in [DISC, 7.2.4]. The link-layer address option used in [DISC] is not needed. Link- layeradvertisements (, 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 any Neighbor Discovery packets,NS/NA messages and MUST be silently ignored in anyreceived Neighbor Dis- covery packets. 5.2.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 mecha- nismsmechanisms are required and specified below: 184.108.40.206.2.1 Conceptual Data Structures ISATAP nodes use the conceptual data structures Prefix List and Default Router List exactly as specifiedin [DISC,5.1].(, 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 context for router discovery anda trust basis for router validation (see security considerations). Each entry in the PRL has an IPv4 address and an associated timer used for polling.timer. The IPv4 address represents a router's ISATAP interface (likely to be an "advertising interface"), and is used to construct the ISATAP link- locallink-local address for that interface. The following sections specify the process for initializing the PRL: When a node enables an ISATAP link, it initializesfirst discovers a DNS (RFC 1035 ) fully-qualified domain name for the Potential Router List (PRL)site's ISATAP service. The domain name MAY be established by a DHCPv4  option for that link. Unless other informationISATAP (option code TBD, see IANA Considerations), by manual configuration, or by an unspecified alternative method. The DHCPv4 option for ISATAP is avail- able (e.g.,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 address configuration, a vendor-specific DHCP option, etc.)config or by querying the following method (similarname service to resolving the [SIP, 1.4.2] pro- cedure) SHOULD be used: 1. The site administrator maintainsdomain 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 router interfaces,service and makes these availablea list of IPv4 addresses representing ISATAP router interfaces (normally as address records in the site's name service. Nodes attempt to find one or more addresses for the PRL by queryingservice). Administrators may also advertise the domain name service.in a DHCPv4 option for ISATAP. 2. There are no mandatory rules onfor the selection of domain name to be used withina site for this purpose,domain name, but administrators are encouraged to use the "isatap.domainname"convention "isatap.domainname" (e.g., isatap.example.com), as specified in [RFC2219]. Nodes can construct this domain name by prepending the label "isatap" to their parent domain name, which is established by other means. Nodes then query this domain name for address records (e.g., DNS 'A' resource records), and initialize the PRL with the IPv4 addresses in the replies.isatap.example.com). 3. After initialization, nodes periodically repeat the above procedure ResolveInterval to updatere-initialize the PRL with any IPv4 addresses added/deleted since the previous iteration.(after ResolveInterval). When DNS is used, nodes MUST follow the procedures in [RFC1035] regardingcache invalidation procedures in  when the DNS time-to-live expires. 5.2.2. Validation of5.2.2 Validity Checks for Router Advertisement MessagesAdvertisements A node MUST silently discard any receivedRouter Advertisement mes- sagesmessages it receives that do not satisfy both the validity checks in [DISC,6.1.2] as well as(, section 6.1.2) and the following additional validity check for ISATAP: -o the network-layer (IPv6) source address is derived froman ISATAP address and embeds an IPv4 address infrom the PRL 220.127.116.11.2.3 Router Specification Advertising ISATAP interfaces of routers behave the same as advertis- ingadvertising interfaces described in [DISC,6.2].(, 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 Adver- tisementAdvertisement to the address of the node which sent the Router Solicita- tion.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 pollingsolicitation process described under Host Specification below (e.g.below, e.g., if Router Advertisement consistency verification [DISC,6.2.7] is desired), but this(, section 6.2.7) is not required. 5.2.4.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 pollsolicit 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 pollingsolicitation process: MinRouterSolicitInterval Minimum time between sending Router Solicitations to any router. Default and suggested minimum: 15min When a PRL(i) is selected for polling,selected, the host sets its associated timer to MinRouterSolicitInterval and initiates pollingsolicitation following a short delay as for initial solicitations [ND,6.3.7]), andin (, section 6.3.7). The solicitation process repeats when the associated timer expires. PollingSolicitation consists of sending Router Solicitations to the ISATAP link- locallink-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 mul- ticast'.multicast'. They are otherwise sent exactly as in the same manner described in [DISC,6.3.7]. When the host receives a valid Router Advertisement (i.e., one that satisfies the validity checks in sections 4.5 and 5.2.2) it is pro- cesses in the same manner described(, section 6.3.7). Hosts process received Router Advertisements exactly as in [DISC,6.3.4]. The host addi- tionally resets(, section 6.3.4). Hosts additionally reset the timer associated with the V4ADDR_PRL(i) embedded in the network-layer source address in theeach received Router Advertisement. The timer is reset to either 0.5 * (the minimum value in the router life- timelifetime or valid lifetime of any on-link prefixes advertised) or Min- RouterSolicitInterval;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 18.104.22.168 Host And Router Deployment Considerations For hosts, if an underlying link supports both IPv4 (over which ISA- TAPISATAP is implemented) and also supports IPv6 natively, then ISATAP MAY be enabled if the native IPv6 layer does not receive Router Adver- tisementsAdvertisements (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 Polling Process'router solicitation process specifieddescribed in section 5.2.4the host specification and allow exist- ingexisting ISATAP address configurations to expire as specified in [DISC,5.3][AUTO,5.5.4].(, 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 gradu- allygradually 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 (see section 5.2.1). 6.2.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 all entries in the Potential Router List. Worst-case control traffic is on the order of (M x N), where 'M' is the numberone or more members of routers inthe Potentialpotential router list. When Router List and 'N' isAdvertisements (RAs) are received, the total number of nodes onRouter Lifetime value provides a timer for the ISATAP link. The MinRouterSolicitInterval ([5.2.4]) bounds control trafficnext RS to be sent. Worst-case is for large numberssmall values of nodes even in worst-case scenarios. -Router Lifetime which is bounded by MinRouterSolicitInterval. o ISATAP nodes periodically refresh the entries on the PRL, typically by pollingquerying 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 (see section 5.2.1)are well maintained. 7. IANA considerationsConsiderations A DHCPv4 option assignment for ISATAP is requested, as outlined in the procedures found in RFC 2939 , section 3. Appendix B offers one possibleproposes 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 [6OVER4,9]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 in section 4.7will 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 elimi- natedeliminated if both IPv4 source address filtering, and the ISATAP validity checks in section 4.7are implemented. [DISC,6.1.2](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-41ip-protocol-41 packets traverse multiple IPv4 hops [MECH,3.3],(, 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 (see section 5.2.2).discarded. This trust model is predicated on IPv4 source address filter- ing,filtering, as described above. The ISATAP address format does not support privacy extensions for stateless address autoconfiguration [PRIVACY].. 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 Mar- cotullio,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 [VET] 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. Finally, the authors recognize that ideas similar to those in this document may have already been presented by others and wish to acknowledge any other such contributions.Normative References [ADDR] 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.,R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 2373, July 1998. (Pending approval of "addr-arch-v3"). [AGGR] Hinden., R, O'Dell, M., Hinden, R. and S. Deering, S.,"An IPv6 Aggregatable Global Unicast Address Format", RFC 2374, July 1998. [AUTO] IEEE, "http://standards.ieee.org/regauth/oui/tutorials/ EUI64.html", March 1997.  Thomson, S.,S. and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. [DISC] Narten, T., Nordmark, E.,E. and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998. [EUI64] IEEE, "Guidelines Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G. and E. Lear, "Address Allocation for 64-bit Global Identifier (EUI-64) Registration Authority", http://standards.ieee.org/regauth/oui/tutori- als/EUI64.html, March 1997. [ICMPv6]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. [IPV4] Postel, McCann, J., "Internet Protocol", RFC 791. [IPV6]Deering, S., and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460. [MECH] Gilligan, R.,S. and E. Nordmark, "Transition MechanismsJ. Mogul, "Path MTU Discovery for IPv6 Hosts and Routers",IP version 6", RFC 2893,1981, August 2000. [NAT] Egevang, K.,1996.  Mogul, J. and P. Francis, "The IP Network Address Translator (NAT)",S. Deering, "Path MTU discovery", RFC 1631, May 1994. [PRIVATE] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,1191, November 1990.  Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and E. Lear, "Address Allocation for Private Internets",V. Paxson, "Stream Control Transmission Protocol", RFC 1918, February 1996. [SIP] Handley, M.,2960, October 2000.  Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.  Schulzrinne, H., Schooler, E., and J. Rosenberg, "SIP:"Dynamic Host Configuration Protocol (DHCP-for-IPv4) Option for Session Initiation Protocol",Protocol (SIP) Servers", RFC 2543, March 1999.3361, August 2002. Informative References [6OVER4] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 Domains without Explicit Tunnels", RFC 2529. [6TO4] Carpenter, B., andK. Moore, "Connection of IPv6 Domains via IPv4 Clouds", RFC 3056, February 2001. [IANA] Reynolds, J., Carpenter, B. and J. Postel, "Assigned Numbers", STD 2, USC/Information Sciences Institute, October 1994. [PRIVACY]C. Jung, "Transmission of IPv6 over IPv4 Domains without Explicit Tunnels", RFC 2529, March 1999.  Narten, T.,T. and R. Draves, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001. [RFC1035] Mockapetris, P., "Domain Namesnames - Implementationimplementation and Specification",specification", STD 13, RFC 1035, November 1987. [RFC2219] Hamilton, M., Droms, R., "Procedures and R. Wright, "Use of DNS AliasesIANA Guidelines for Network Services",Definition of New DHCP Options and Message Types", BCP 43, RFC 2219 (BCP), October 1997. [VET]2939, September 2000.  Nguyen, Quang, "Virtual Ethernet: A New Approach to IPv6 Transition", http://irl.cs.ucla.edu/vet/report.ps, MS Project Report, SpringQ., "http://irl.cs.ucla.edu/vet/report.ps", spring 1998. AuthorsAuthors' Addresses Fred L. Templin Nokia 313 Fairchild Drive Mountain View, CA, USACA 94110 US Phone: (650)-625-2331 Email:+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:163-0409 Japan EMail: firstname.lastname@example.org Mohit Talwar Microsoft Corporation One Microsoft Way Redmond, WAWA> 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:Appendix A. Major Changes 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.terminology o Changed "IPv6 destination address" to "IPv6 next-hop address" under "sending rules".rules" o Changed definition of ISATAP prefix to include link and site-local.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:Appendix B. Rationale for Interface Identifier Construction Rules ISATAP specifies an [EUI64]-formatEUI64-format address construction for the Orga- nizationally-UniqueOrganizationally-Unique Identifier (OUI) owned by the Internet Assigned Numbers Authority [IANA].(IANA). This format (given below) is used to con- structconstruct both native [EUI64]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 (hence,(thus, other interpreta- tionsinterpretations of TSE, TSD) are reserved for future IANA use. The above specification is compatible with all aspects of [EUI64],EUI64, including support for encapsulating legacy EUI-48 interface identi- fiersidentifiers (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 indi- cateindicate an IPv4 address is embedded. Thus, when the first four octets of a [ADDR]-compatiblean 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. 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