NGTRANS Working Group F. Templin Internet-Draft Nokia Expires:
June 19,July 1, 2003 T. Gleeson Cisco Systems K.K. M. Talwar D. Thaler Microsoft Corporation December 19,31, 2002 Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) draft-ietf-ngtrans-isatap-08.txtdraft-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 June 19,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 is a transition mechanism thattreats 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. TerminologyRequirements . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Transmission of IPv6 Packets on ISATAP LinksTerminology . . . . . . . . . . . . . . . . . . . . . . . . 4 4.15. Basic IPv6 Operation on ISATAP Interface Identifier ConstructionLinks . . . . . . . . . . 4 4.2 Stateless Autoconfiguration. . 5 5.1 Interface Identifiers and Link-Local AddressesAddress Construction . . . . . . . 5 4.35.2 ISATAP Link/Interface Configuration . . . . . . . . . . . . 5 4.4 Sending Rules5.3 Dual Stack Operation and Address MappingConfiguration . . . . . . . 6 5.4 Tunneling Mechanisms . . . . . . . . . . . . . . . . . . . . 6 4.5 Validity Checks for Received Packets5.4.1 Encapsulation . . . . . . . . . . . . . . . . . . . . . . . 6 18.104.22.168 Tunnel MTU and Fragmentation . . . . . . . . . . . . . . . . 6 5. Neighbor Discovery for ISATAP Links5.4.3 Handling IPv4 ICMP Errors . . . . . . . . . . . . 9 5.1 Address Resolution. . . . . 7 5.4.4 Decapsulation . . . . . . . . . . . . . . . . 9 5.2 Router and Prefix. . . . . . . 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 . . . . . . . . . . 10 5.2.1. . . . . . . . . . . 8 6.2 Address Autoconfiguration and Router Discovery . . . . . . . 9 6.2.1 Conceptual Data Structures . . . . . . . . . . . . . . . . . 10 5.2.29 6.2.2 Validity Checks for Router Advertisements . . . . . . . . . 11 5.2.310 6.2.3 Router Specification . . . . . . . . . . . . . . . . . . . . 12 5.2.410 6.2.4 Host Specification . . . . . . . . . . . . . . . . . . . . . 12 6.11 7. ISATAP Deployment Considerations . . . . . . . . . . . . . . 13 6.112 7.1 Host And Router Deployment Considerations . . . . . . . . . 13 6.212 7.2 Site Administration Considerations . . . . . . . . . . . . . 13 7.12 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 14 8.13 9. Security considerations . . . . . . . . . . . . . . . . . . 14 9.13 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 1514 Normative References . . . . . . . . . . . . . . . . . . . . 1614 Informative References . . . . . . . . . . . . . . . . . . . 1715 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 1716 A. Major Changes . . . . . . . . . . . . . . . . . . . . . . . 1817 B. Rationale for Interface Identifier Construction Rules . . . 21 C. INTELLECTUAL PROPERTY. . . . . . 18 C. Dynamic Per-neighbor MTU Discovery . . . . . . . . . . . . . 2219 Intellectual Property and Copyright Statements . . . . . . . 2321 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 transitiontunneling 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").Protocol (ISATAP). ISATAP allows dual-stack nodes that do not share a commonphysical 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 NBMAlink layer.layer for IPv6. 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 basedan interface identifier format that embeds an IPv4 address. This format supports IPv6 protocol mechanisms for address 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 .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 an NBMAlink 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  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. 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 . 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  applies to this document. The following additional terms are defined: link:link; on-link: same definitiondefinitions as .(, 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 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. ISATAPaddress: an IPv6on-link address withon an ISATAP prefixinterface and with an ISATAP formatinterface identifier constructed as specified in section 4.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. 4. Transmission of5. Basic IPv6 PacketsOperation on ISATAP Links ISATAP links transmit IPv6 packets via automatic tunnels using the site's IPv4 infrastructure as an NBMAa link layer.layer for IPv6, i.e., the site's IPv4 ICMP errors and ARP failures may be processedinfrastructure is treated as a Non-Broadcast, Multiple Access (NBMA) link error notifications, as allowed by RFC 2461 .layer. The common tunneling mechanisms specified in Section 3 of RFC 2893  are used, with thefollowing noted specific considerationssubsections outline basic operational details for IPv6 on ISATAP links and automatic tunnels: 4.1 ISATAPlinks: 5.1 Interface IdentifierIdentifiers and Address Construction IPv6 unicast addresses  include a 64-bit(RFC2491 , section 5.1) requires companion documents to specify the exact mechanism for generating interface identifier field in "modified EUI-64 format", based ontokens (i.e., identifiers). Interface identifiers for ISATAP are compatible with the IEEE EUI-64  specification. (ModifiedEUI-64 identifier format inverts the sense of the 'u/ l' bit from its specification in , i.e., 'u/l' = 0 indicates local-use.) ISATAP interface identifiers(, section 2.5.1), and are constructed by prepending the 32-bit string '00-00-5E-FE' withappending an IPv4 address (seeon the following section for examples). AppendixISATAP link to the 32-bit string '00-00-5E-FE'. (Appendix B includes non-normative text explaining the rationale for this construction rule. 4.2 Stateless Autoconfigurationrule.) Global and Link-Local AddressesLocal-use ISATAP addresses are unicast addresses that use ISATAP format interface identifiersconstructed as follows: | 64 bits | 32 bits | 32 bits | +------------------------------+---------------+----------------+ | link-local, site-localglobal or local-use unicast | 0000:5EFE | IPv4 Address | | global unicastprefix | | 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 IPv6global unicast address: 3FFE:1A05:510:1111:0:5EFE:8CAD:8108 has a prefix of '3FFE:1A05:510:1111::/64' and an ISATAP formatinterface identifier with embedded IPv4 address: '22.214.171.124'. The address is alternately written as: 3FFE:1A05:510:1111:0:5EFE:126.96.36.199 The link-local(Similar examples for local-use addresses are made obvious by the above and site-local variants (respectively) are: FE80::0:5EFE:188.8.131.52 FEC0::1111:0:5EFE:184.108.40.206 4.3with reference to the IPv6 addressing architecture document.) 5.2 ISATAP Link/Interface Configuration AnISATAP Link/Interface configuration is consistent with (RFC2491 , sections 5.1.1 and 5.1.2). Using the terminology of Section 4, 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 each5.3 Dual Stack Operation and Address Configuration ISATAP router interface SHOULD be added touses the Potential Routers List (see Section 5.2.1). 4.4 Sending Rulessame specification found in (, section 2). That is, ISATAP nodes implement "IPv6/IPv4" or "dual-stack" configurations and operate with both stacks enabled. Address Mappingconfiguration and DNS considerations are the same as for (, sections 2.1 and 2.2) 5.4 Tunneling Mechanisms The common tunneling mechanisms specified in (, sections 3.1 through 3.7) are used, with the following noted specific considerations: 5.4.1 Encapsulation The specification in (, section 3.1) is used. Additionally, 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 beaddress; other packets are discarded (i.e., not encapsulated) 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 returned to simply treatthe last four octets ofsource. 5.4.2 Tunnel MTU and Fragmentation The specification in (, section 3.2) is NOT used; the specification in this section is used instead. ISATAP address as an IPv4 address (in network byte order). No multicast address mappings are specified. 4.5 Validity Checksuses automatic tunnel interfaces that may be configured over multiple underlying links with diverse maximum transmission units (MTUs). The minimum MTU for Received Packets Packets received on ISATAPIPv6 interfaces MUST satisfy at least one (i.e., one or both) ofis 1280 bytes (, Section 5), but the following validity checks: o the network-layer (IPv6) source address hasconsiderations apply when IPv4 is used as a prefix configuredlink 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 the ISATAP interface and an ISATAP-format interface identifier that embeds the link-layer (IPv4) source address, i.e., source is on-linksome paths o the link-layer (IPv4) source address is in the Potential Routers List (see Section 5.2.1), i.e., previous hop iscommonly-deployed VPNs use an on-link ISATAP router Packets that do not satisfy at least one of the above checks are silently discarded. 4.6 TunnelMTU and Fragmentationof 1400 bytes Thus, ISATAP interfaces implement automatic tunnels that may be configured over multiple underlying links with diverse MTUs. The ISATAP interfaceSHOULD use an MTU (ISATAP_MTU) SHOULDof 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 dynamic per-neighbor MTU discovery. When larger values are used, ISATAP_MTU SHOULD NOT exceed the largestmaximum MTU of all underlying links (LINK_MTU)minus 12020 bytes for 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 2). IPv6 path MTU discovery  is requiredlink layer encapsulation. (Appendix C provides non-normative considerations for dynamic per-neighbor MTU discovery.) As with ordinary IPv6 interfaces that sendinterfaces, the network layer (IPv6) forwards packets larger than 1280 bytes. The following considerations forof size ISATAP_MTU or smaller to the ISATAP interfacesinterface. All other packets are noted: o ISATAP encapsulatorsdropped, 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 pathan ICMPv6 "packet too big" message with MTU discovery = ISATAP_MTU is returned 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 do not provide enough state for translation into ICMPv6 "packet too big" messages (see: RFC 792  and RFC 1812 , section 220.127.116.11). IPv6 seesthe source . ISATAP interface as an ordinary IPv6 interface with a fixed MTU (ISATAP_MTU), i.e., only those IPv6interfaces send all packets of size ISATAP_MTU1380 bytes or smaller are accepted. All other packets are dropped, and an IPv6 ICMP "packet too big" messagewith MTU = ISATAP_MTU is returned. ISATAP interfaces SHOULD implement the following link-layer algorithm to determine when to perform IPv6-in-IPv4 encapsulation and when to return an ICMPv6 "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 - 120 and packet is larger than ISATAP_MINMTU Send IPv6 ICMP "packet too big" with MTU = MAX(NBR_MTU - 120, ISATAP_MINMTU) Drop packet else if packet is larger than ISATAP_MINMTU Encapsulate and setthe Don't Fragment flag(DF) bit NOT set in the encapsualting IPv4 header else Encapsulate but do not set the Don't Fragment flagheader. 5.4.3 Handling IPv4 ICMP Errors The specification in the(, section 3.4) MAY be used. IPv4 header endif endif else if packet is larger than LINK_MTU - 120ICMP errors and packetARP failures are otherwise processed as link error notifications. 5.4.4 Decapsulation The specification in (, section 3.6) is larger than ISATAP_MINMTU Send IPv6 ICMP "packet too big" with MTU = ISATAP_MINMTU Drop packet else if IPv6 neighborused. 5.4.5 Link-Local Addresses The specification in (, section 3.7) is alsoNOT used. Instead, link-local addresses are formed by appending an IPv4 neighbor oninterface identifier, as defined in Section 5.1, to the underlying link, orprefix FE80::/64. 5.4.6 Ingress Filtering The network layer (IPv6) destination address of a packet received on an ISATAP interface is less than or == ISATAP_MINMTU Encapsulate but do not set the Don't Fragment flag ineither local (i.e., matches an address configured on the IPv4 header else send ICMPv6 "packet too big"local IPv6 stack) or foreign. The decapsulator MUST be configured with MTU = ISATAP_MINMTU Drop packet endif endif endif Figure 2 Encapsulators MAY maintain per-neighbor MTU (NBR_MTU) values by periodically probing thea list of IPv4 path, e.g., by sendingaddress prefixes that are acceptable, i.e., an ingress filter list (default deny all). For packets larger than ISATAP_MINMTUwith foreign network layer (IPv6) destination addresses, 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) maylink layer (IPv4) source address MUST be used forexplicitly allowed by ingress filtering. Packets that do not satisfy this purpose. (NS packetscondition 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 forsilently discarded. Additionally, all packets (whether foreign or local) MUST satisfy at least one (i.e., one or both) of the round-trip time (RTT) betweenfollowing validity checks: o the encapsulator and decapsulatornetwork-layer (IPv6) source address is an on-link ISATAP address with an interface identifier that embeds the link-layer (IPv4) source address o the link-layer (IPv4) source address is in the Potential Routers List (see note 3). Implementations SHOULD repeatSection 6.2.1) Packets that do not satisfy the above conditions are silently discarded. 6. Neighbor Discovery and Address Autoconfiguration RFC 2491  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 polling process within REACHABLE_TIMEdescription for connectionless service found in the last paragraph of (, section 10) to detect link MTU restrictions. NOTES: 1.1), i.e., 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 useaddresses provide the sender with an MTU of 1400 bytes, thus 100 bytes (1500 minums 1400) are reserverd for sub-IPv4 layer encapsulation. 2. Nearly all IPv4 routersNBMA destination address to which it can forward 1500 bytetransmit packets without fragmentation.whenever it desires. Thus, 1380 bytes (1500 minus 100 minus 20) is RECOMMENDED as ISATAP_MINMTU. 3. ICMPv4 "fragmentation needed" messages can be injected by malicious nodes, but this same problem exists in IPv4. Using Neighbor Solicitation messagesthe RFC 2491 multicast mechanisms are not required for probingaddress resolution and receiving a positive acknowledgement from a trusted decapsulator MAY help encapsulators recognize spoofed ICMPv4 "fragmentation needed" messages. 5. Neighbor Discovery fornot otherwise implemented on ISATAP Links Section 3.2 oflinks due to traffic scaling considerations (i.e., ISATAP links are unicast-only). 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 foron ISATAP links are not specified by ; instead, they are specifieduse the specifications found in this document. (Note that these mechanisms MAY potentially apply to other types of NBMA links in the future.) 5.16.1 Address Resolution Protocol addresses (IPv6) inISATAP addresses 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(, section 5.2) requires companion documents to specify the staticformat for link layer address options, however, link layer address options are not needed for address resolution computation within ISATAP. Thus, no format is specified and the following specification from (, section 3.8) applies: "This means that a unicast Neighbor Solicitation(NS)/Neighbor Advertisement(NA) exchange to ensure IPv6 level reachabilitysender of Neighbor Discovery packets * SHOULD NOT include Source Link Layer Address options or Target Link Layer Address options on the neighbor and alsotunnel link. * 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 , 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 ,, section 7.3). ISATAP routers MAY implementperform the enhanced address resolutionabove-specified reachability detection and NUD,NUD procedures, 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 followedISATAP links disable Duplicate Address Detection, as permitted by a four-octet IPv4 address. Options of this form SHOULD NOT be sent in NS/NA messages(, section 4). 6.2 Address Autoconfiguration and MUST be silently ignored in received NS/NA messages. 5.2Router and PrefixDiscovery Since the site's IPv4 infrastructure is treated as anNBMA link layer, unsolicited Router Advertisements domulticast emulation mechanisms are not provide sufficient means for router discoveryused on ISATAP links. Thus,links, nodes will not receive unsolicited multicast Router Advertisements. (RFC 2462 , section 5.5.2) requires that hosts use stateful autoconfiguration (i.e., DHCPv6 ) in the absence of Router Advertisements. When statelful autoconfiguration is not available, nodes use alternate mechanisms are required(described below) for router and specified below: 5.2.1prefix discovery. 6.2.1 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 atwo new conceptual data structurestructures "Potential Router List" and the following new configuration variable: ResolveInterval Time between name service resolutions. Default and suggested minimum: 1hr"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 following sections specifyIPv4 address represents a DHCPv6 server attached to the process for initializingISATAP link, and is used to construct the PRL:ISATAP link-local address for that DHCPv6 server. When a node enables an ISATAP link, it first discovers a DNS (RFC 1035 ) fully-qualified domain nameIPv4 addresses for the site's ISATAP service.PRL and SASL. The domain nameaddresses MAY be established by a DHCPv4  option for ISATAP (option code TBD, see IANA Considerations),TBD), by manual configuration, or by an unspecified alternative method. Themethod (e.g., 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 multiplevendor-specific option; DNS () fully-qualified domain names occur, only the first is used Next, the node initializes the link's PRL with IPv4 addresses associated with thenames). When DNS fully-qualified domain name discovered above.names are used, IPv4 addresses for the PRL and SASL are discovered through manual configa static host file or by querying the name servicean IPv4-based DNS server to resolvingresolve the domain namenames into address records (e.g., DNS 'A' resource records) containing IPv4 addresses. Unspecified alternative methods for domain name resolution may also be used. Notes:The following notes apply when DNS fully-qualified domain names are used: 1. Site administrators maintain adomain name for the ISATAP servicenames and a list ofIPv4 addresses representingfor the PRL and SASL for the site's ISATAP router interfaces (normallyservice, e.g., as address records in the site's name service).service. Administrators may also advertise the domain namenames in a DHCPv4 option for ISATAP. 2. There are no mandatory rules for the selection of adomain name,names, but administrators are encouraged to use the convention "isatap.domainname""(list_name).isatap.domainname" (e.g., isatap.example.com).prl.isatap.example.com). 3. After initialization, nodes periodically re-initialize the PRL (after ResolveInterval).and SASL, e.g., once per hour. When DNS is used, nodes MUSTclient DNS resolvers use the IPv4 transport to resolve the names and follow the cache invalidation procedures in  when the DNS time-to-live expires. 18.104.22.168.2 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 22.214.171.124.3 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,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 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. 126.96.36.199.4 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 (, 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: 15minminimum 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 (,(, 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 (,(, 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 solicitationnetwork-layer source address in each solicited Router Advertisement received. The timer is outsidereset to either 0.5 * (the minimum value in the scoperouter lifetime or valid lifetime of this specification. 6.any on-link prefixes received in the advertisement) or MinRouterSolicitInterval; whichever is longer. 7. ISATAP Deployment Considerations 6.17.1 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. 6.27.2 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 havediscover those interface and server 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 When stateful autoconfiguration is not available, ISATAP nodes MAY periodically send unicast Router Solicitations (RS)to and receive unicast Router Advertisements from to one or more members of the potential router list. When Router Advertisements (RAs) are received,A well-deployed stateful autoconfiguration service within the Router Lifetime value provides a timer forsite can minimize and/or eliminate the next RS to be sent. Worst-case isneed for small values of Router Lifetime which is bounded by MinRouterSolicitInterval.periodic solicitation. o ISATAP nodes periodically refresh the entries on the PRL, typically by querying the DNS.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 address records for ISATAP router interfacesPRL and SASL are well maintained. 7.8. IANA Considerations A DHCPv4 option assignmentcode for ISATAP (TBD)  is requested, as outlinedrequested in the procedures found in RFC 2939 , section 3. Appendix B proposes a specification for managingevent that the IEEE OUI assigned to IANA for EUI-64 interface identifier construction. This specification is made freely available to IANAIESG recommends this document for any purpose they may find useful. 8.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. 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.) 9.10. 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  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.brought to the authors' attention on September 20, 2002. Normative References  Deering, S. and W. Simpson, "Neighbor Discovery for IPR. Hinden, "Internet Protocol, Version 6 (IPv6)",(IPv6) Specification", RFC 2461,2460, December 1998.  Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.  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.  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.  Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998.  Armitage, G., Schulter, P., Jork, M. and G. Harter, "IPv6 over Non-Broadcast Multiple Access (NBMA) networks", RFC 2491, January 1999.  Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", draft-ietf-ipngwg-addr-arch-v3-11 (work in progress), October 2002.  Gilligan, R. and E. Nordmark, "Transition"Basic Transition Mechanisms for IPv6 Hosts and Routers", RFC 2893, August 2000. draft-ietf-ngtrans-mech-v2-01 (work in progress), November 2002.  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.  Thomson, S. and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998.  Droms, R., "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress), November 2002.  Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.  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, "StreamPostel, J., "Internet Control TransmissionMessage Protocol", STD 5, RFC 2960, October 2000.792, September 1981.  Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.  Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCP-for-IPv4) OptionBaker, F., "Requirements for Session Initiation Protocol (SIP) Servers",IP Version 4 Routers", RFC 3361, August 2002.1812, June 1995. 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",Clouds", RFC 3041, January3056, February 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.  Narten, T. and R. Draves, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001.  Nguyen, Q., "http://irl.cs.ucla.edu/vet/report.ps", spring 1998.  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: firstname.lastname@example.org Tim Gleeson Cisco Systems K.K. Shinjuku Mitsu Building 2-1-1 Nishishinjuku, Shinjuku-ku Tokyo 163-0409 Japan EMail: email@example.com Mohit Talwar Microsoft Corporation One Microsoft Way Redmond, WA> 98052-6399 US Phone: +1 425 705 3131 EMail: firstname.lastname@example.org Dave Thaler Microsoft Corporation One Microsoft Way Redmond, WA 98052-6399 US Phone: +1 425 703 8835 EMail: email@example.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 version 05earlier 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 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 draft4.1 to version 00: o Title changeAppendix B in response to provide higher-level description of field of use addressed by this draft. Removed other extraneous text.comments from Pekka Savola o Major new section on automatic discovery of off-link IPv6 routers when IPv6-IPv4 compatibility addresses are used.Identified operational issues for anticipated deployment scenarios o Included reference to Quang Nguyen work Appendix B. Rationale for Interface Identifier Construction RulesISATAP 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 inIPv6 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 interpretationuse 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 32 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 providesspecification 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  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  and RFC 1812 , section 188.8.131.52). 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 . 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 special TYPE (0xFE) to indicateNeighbor Advertisement (NA) from the decapsulator. (NB: Setting the DF bit prevents decapsulators from receiving probe packets that would overrun the receive buffer on an IPv4 addressunderlying link, thus no maximum receive unit (MRU) is embedded. Thus, whenrequired.) Implementations may choose to couple the first four octetsprobing process with neighbor cache management procedures (, section 7), e.g. to maintain timers, state variables and/or a queue of an IPv6 interface identifier are: '00-00-5E-FE' (note:packets waiting for probes to complete. Packets retained on the 'u/l' bit MUST be 0)queue are forwarded when probes succeed, and provide state for sending ICMPv6 "packet too big" messages to the interface identifier is saidsource when probes fail. Implementations may choose to bestore per-neighbor MTU information in "ISATAP format" andthe next four octets embed anIPv4 address encodedpath MTU discovery cache, in network byte order. Appendix C. INTELLECTUAL PROPERTY SRI International has notifiedthe IETF of IPR considerations for some aspectsISATAP 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 this specification. For more information consultservice attacks. Implementations should treat ICMPv4 "fragmentation needed" messages as "tentative" negative acknowledgments and apply heuristics to determine when to suspect an actual link restriction and when to ignore the online listmessages. IPv6 packets lost due actual link restrictions are perceived as lost due to congestion by the original source, but robust implementations minimize instances of claimed rights.such packet loss without ICMPv6 "packet too big" messages returned to the sender. 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. 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