NGTRANSNetwork Working Group F. Templin Internet-Draft Nokia Expires: July 4, 200218, 2003 T. Gleeson Cisco Systems K.K. M. Talwar D. Thaler Microsoft Corporation January 03, 200217, 2003 Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) draft-ietf-ngtrans-isatap-10.txtdraft-ietf-ngtrans-isatap-11.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on July 4, 2002.18, 2003. Copyright Notice Copyright (C) The Internet Society (2002).(2003). All Rights Reserved. Abstract This document specifies an Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) that connects IPv6 hosts and routers within IPv4 sites. ISATAP treats the site's IPv4 infrastructure as a link layer for IPv6 with no requirement for IPv4 multicast. ISATAP enables intra-site automatic IPv6-in-IPv4 tunneling whether globally assigned or private IPv4 addresses are used. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Applicability Statement . . . . . . . . . . . . . . . . . . . 3 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Non-Broadcast, Multiple Access (NBMA)Basic IPv6 Operation . . . . . . 4 5.1 Multicast . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.2 Interface Identifiers and Address Construction . . . . . . . 5 5.3 ISATAP Link/Interface Configuration . . . . . . . . . . . . 5 5.4 Link Layer Address Options .. . . . . . . . . . . . . . . . 64 6. Automatic Tunneling . . . . . . . . . . . . . . . . . . . . 6 6.1 Dual IP Layer Operation . . . . . . . . . . . . . . . . . . 6 6.2 Encapsulation . . . . . . . . . . . . . . . .. 5 7. Neighbor Discovery . . . . . . 6 6.3 Tunnel MTU and Fragmentation. . . . . . . . . . . . . . . . 7 6.4 Handling IPv4 ICMP Errors . . . . . . . . . . . . . . . . . 8 6.5 Local-Use IPv6 Unicast Addresses .8. Deployment Considerations . . . . . . . . . . . . . 8 6.6 Ingress Filtering. . . . . 10 9. IANA Considerations . . . . . . . . . . . . . . . . 8 7. Neighbor Discovery for ISATAP Links. . . . . 11 10. Security considerations . . . . . . . 8 7.1 Address Resolution. . . . . . . . . . . . 11 11. Acknowledgements . . . . . . . . . 9 7.2 Router and Prefix Discovery. . . . . . . . . . . . . . 12 Normative References . . 9 7.2.1 Conceptual Data Structures. . . . . . . . . . . . . . . . . 9 7.2.2 Validity Checks for Router Advertisements. . 12 Informative References . . . . . . . 10 7.2.3 Router Specification. . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . 11 7.2.4 Host Specification. . . . . . . . . . . . . . . 14 A. Major Changes . . . . . . 11 8. ISATAP Deployment Considerations. . . . . . . . . . . . . . 12 8.1 Host And Router Deployment Considerations. . . . 15 B. Rationale for Interface Identifier Construction . . . . . 12 8.2 Site Administration Considerations. . 17 C. Dynamic MTU Discovery . . . . . . . . . . . 12 9. IANA Considerations. . . . . . . . . 18 Intellectual Property and Copyright Statements . . . . . . . . . . . 13 10. Security considerations . . . . . . . . . . . . . . . . . . 13 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 Normative References . . . . . . . . . . . . . . . . . . . . 14 Informative References . . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 16 A. Major Changes . . . . . . . . . . . . . . . . . . . . . . . 17 B. Rationale for Interface Identifier Construction . . . . . . 18 C. Dynamic Per-neighbor MTU Discovery . . . . . . . . . . . . . 19 Intellectual Property and Copyright Statements . . . . . . . 2122 1. Introduction This document presents a simple approach called the Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) that enables incremental deployment of IPv6  within IPv4-basedIPv4  sites. We refer to this approach as the Intra-Site Automatic Tunnel Addressing Protocol (ISATAP).ISATAP allows dual-stack nodes that do not share a physical link with an IPv6 router to automatically tunnel packets to the IPv6 next-hop address through IPv4, i.e., the site's IPv4 infrastructure is treated as a link layer for IPv6. This document specifiesSpecific details for the operation of IPv6 and automatic tunneling over ISATAP links (i.e., automatic IPv6-in-IPv4 tunneling),are given, including an interface identifier format that embeds an IPv4 address. This format supports IPv6 protocol mechanisms foraddress configuration as well asand simple link-layer address mapping. Also specified in this documentis the operation of IPv6 Neighbor Discovery for ISATAP. The document finally presents deploymentand securitydeployment/security considerations. 2. Applicability Statement ISATAP provides the following features: o treats site's IPv4 infrastructure as a link layer for IPv6 using automatic IPv6-in-IPv4 tunneling (i.e., no configured tunnel state)o enables incremental deployment of IPv6 hosts within IPv4 sites with no aggregation scaling issues at border gateways o requires no special IPv4 services within the site (e.g., multicast) o supports both stateless address autoconfiguration and manual configuration o supports networks that use non-globally unique IPv4 addresses (e.g., when private address allocations  are used), but does not allow the virtual ISATAP link to span a Network Address Translator used) 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, on-link, off-link: same definitions 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. advertising ISATAP address: an on-linkinterface: same meaning as "advertising interface" in (, section 6.2.2). ISATAP address: an on-link address on an ISATAP interface and with an interface identifier constructed as specified in Section 5.2 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.5. Non-Broadcast, Multiple Access (NBMA)Basic IPv6 Operation ISATAP links transmit IPv6 packets via automatic tunnels using the site's IPv4 infrastructure as a link layer for IPv6, i.e., IPv6 treats the site's IPv4 infrastructure as a Non-Broadcast, Multiple Access (NBMA) link layer. RFC 2491  provides a general architecture for IPv6 over NBMA networks that forms the basis for companion documents such as the present.The following subsections present NBMAconsiderations for IPv6 on ISATAP links: 5.1 Multicast ISATAPlinks most closely meet the description for connectionless service found in the last paragraph of (, section 1), i.e., ISATAP addresses provide the sender with an NBMA destination address to which it can transmit packets whenever it desires. Thus, multicast emulation mechanismsare not required to support host-side operation of the IPv6 neighbor discovery protocol. 5.2noted: 5.1 Interface Identifiers and Address Construction (, section 5.1) requires companion documents to specify the exact mechanism for generatingUnicast Addresses ISATAP interface tokens (i.e., identifiers). Interfaceidentifiers for ISATAP are compatible with the EUI-64 identifieruse "modified EUI-64" format (,(, section 2.5.1),2.5.1) and are constructedformed by appending an IPv4 address on the ISATAP link to the 32-bit string '00-00-5E-FE'. (AppendixAppendix B includes non-normative text explaining therationale for this construction rule.) Globalrule. With reference to (, sections 2.5.4, 2.5.6), global and Local-uselocal-use ISATAP addresses are constructed as follows: | 64 bits | 32 bits | 32 bits | +------------------------------+---------------+----------------+ | global or local-use unicast | 0000:5EFE | IPv4 Address | | prefix | | of ISATAP link | +------------------------------+---------------+----------------+ Figure 1 For example, the global unicast address: 3FFE:1A05:510:1111:0:5EFE:8CAD:8108 has a prefix of '3FFE:1A05:510:1111::/64' and an ISATAP interface identifier with embedded IPv4 address: '22.214.171.124'. The address is alternately written as: 3FFE:1A05:510:1111:0:5EFE:126.96.36.199 Examples for local-use addresses are obvious from the above and with reference to (, section 2.5.6). 5.35.2 ISATAP Link/Interface Configuration ISATAP Link/Interface configuration is consistent with (, sections 5.1.1 and 5.1.2).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. 5.4At least one link-layer address per advertising ISATAP interface SHOULD be added to the Potential Routers List (see Section 7.3.1). 5.3 Link Layer Address Options (, section 5.2) requires companion documentsWith reference to specify the contents of(, section 5.2), when the [NTL], [STL], [NBMA Number][NTL] and [NBMA Subaddress][STL] fields forin an ISATAP link layer address options. For ISATAP links: o the [NTL] and [STL] fields MUST be zero ooption encode 0, the [NBMA Number] field encodes a 4-octet IPv4 address o the [NBMA Subaddress] field is omitted (, section 5.2) does NOT require companion documents to specify the valueaddress. 5.4 Multicast and Anycast As for [Length], i.e., the total length of the option in 8 octets. Senders may therefore set [Length] toany value between 1 and 255; when [Length]IPv6 interface, an ISATAP interface is greater than 1, receivers treat any bytes that follow the [NBMA Number]required to recognize certain IPv6 multicast and anycast addresses (, section 2.8). Mechanisms for sending multicast and anycast packets (e.g., ) are left as null-padding.future work. 6. Automatic Tunneling The common tunneling mechanisms specified in (,(, sections 2 and 3) are used, with the following noted specificconsiderations for ISATAP: 6.1 Dual IP Layer Operation ISATAP uses the same specification found in (,(, section 2). That is, ISATAP nodes provide complete IPv4 and IPv6 implementations and are able to send and receive both IPv4 and IPv6 packets. ISATAP nodes operate with both their IPv4 and IPv6 stacks enabled.Address configuration considerations are the same as for (, section 2.1). Additionally, ISATAP nodes require that IPv4 address configuration take place on at least one underlying link prior to IPv6 address configuration on an ISATAP link.and DNS considerations are the same as (,(, sections 2.2 and2.1 through 2.3). 6.2 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; other packets are discarded and an ICMPv6 destination unreachable indication with code 3 (Address Unreachable)  is returned to the source. 6.3 Tunnel MTU and Fragmentation The specification in (, section 3.2) is NOT used; the specification in this section is used instead.ISATAP usesautomatic tunnel interfaces thatmay be configured over multiple underlying links with diverse maximum transmission units (MTUs). The minimum MTU for IPv6 interfaces is 1280 bytes (, Section 5), but the following considerations apply for the MTU ofISATAP interfaces apply:interfaces: o Nearly all IPv4 nodes connect to physical links with MTUs of 1500 bytes or larger (e.g., Ethernet) o Sub-IPv4 layer encapsulations (e.g., VPN) may occur on some paths o Commonly-deployed VPNsVPN interfaces use an MTU of 1400 bytes UnlessTo maximize efficiency and minimize IPv4 fragmentation for the predominant deployment case, ISATAP interfaces that do not use a dynamic per-neighborMTU discovery mechanism is implemented, ISATAP interfaces MUST use an MTU (ISATAP_MTU) ofSHOULD set LinkMTU (, Section 6.3.2 ) to no more than 1380 bytes (1400 minus 20 bytes for IPv4 encapsulation) to maximize efficiency and minimize IPv4 fragmentation for the predominant deployment case. ISATAP_MTUencapsulation). LinkMTU MAY be set to alarger value when the encapsulator implementsvalues on ISATAP interfaces that use a dynamic per-neighborMTU discovery mechanism, but this value SHOULD NOT exceed the largest MTU of all underlying links (minus 20 bytes for IPv4 encapsulation).mechanism. Appendix C provides non-normative considerations for dynamic per-neighborMTU discovery. The network layer (IPv6) forwards packets of size ISATAP_MTU or smaller to the ISATAP interface. All other packets are dropped, and an ICMPv6 "packet too big" message with MTU = ISATAP_MTU is returned to the source . TheISATAP link layer encapsulates packets of size 1380 bytesor smaller with the Don't Fragment (DF) bit NOTnot set in the encapsualting IPv4 header. Nodes that configure ISATAP interfaces MUST have IPv4 reassembly buffers large enough to receive packets with the DF bit not set in the encapsulating IPv4 header. RFC 1122 , section 3.3.2 specifies that the Effective MTU to Receive (EMTU_R) for IPv4 nodes: "...MUST be greater than or equal to 576, SHOULD be either configurable or indefinite, and SHOULD be greater than or equal to the MTU of the connected network(s)". With reference to this specification, the EMTU_R for nodes that configure ISATAP interfaces MUST be greater than or equal to 1500 bytes (i.e., the predominant deployment case for connected IPv4 networks) and SHOULD be either configurable or indefinite. 6.4 Handling6.4 Handling IPv4 ICMP Errors The specification in (, section 3.4) MAY be used.IPv4 ICMP errors and ARP failures are otherwiseprocessed as link error notifications. 6.5 Local-Use IPv6 Unicast Addresses The specification in (,(, section 3.7) is NOTnot used. Instead, local use IPv6 unicast addresses are formed exactlyas specified in (, section 2.5.6).Section 5.1. 6.6 Ingress Filtering The specification in (,(, section 3.9) is used onused. In particular, ISATAP router interfaces. (ISATAP host interfaces silently discard anynodes that forward decapsulated packets receivedMUST be configured with a foreign IPv6 destination address, i.e., an address not configured on the local IPv6 stack.) Additionally, packets received on ISATAP host and router interfaces MUST satisfy at least one (i.e., one or both)list of the following validity checks: o the network-layer (IPv6) source address is an on-link ISATAP address with an interface identifier that embeds the link-layer (IPv4) source address o the link-layer (IPv4)source IPv4 address is in the Potential Routers List (see Section 7.2.1) Packetsprefixes that do not satisfy the above conditionsare silently discarded.acceptable. 7. Neighbor Discovery for ISATAP LinksRFC 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.)7.1 Address Resolution and Neighbor Unreachability Detection ISATAP addresses are resolved to link-layer addresses (IPv4) by a static computation, i.e., the last four octets are treated as an IPv4 address. Following static address resolution, ISATAPhosts SHOULD perform an initial reachability confirmation by sending unicast Neighbor Solicitations (NSs) and receiving a Neighbor Advertisement using the mechanisms specified in (,(, sections 7.2.2-7.2.8). (Note that implementations MAY omit the source/target link layer options in NS/ NA messages when unicast is used.) ISATAP hostsHosts SHOULD additionally perform Neighbor Unreachability Detection (NUD) as specified in (,(, section 7.3). ISATAP routersRouters MAY perform the above-specified reachability detection and NUD procedures, but this might not scale in all environments. All ISATAP nodes MUST send solicited neighbor advertisements (,(, section 7.2.4). 7.2 Duplicate Address Detection Duplicate Address Detection (, section 5.4) is not required for ISATAP addresses, since duplicate address detection is assumed already performed for the IPv4 addresses from which they derive. 7.3 Router and Prefix Discovery Since NBMA multicast emulation mechanisms are not used,ISATAP nodes will typically not receive unsolicited multicast Router Advertisements. Thus, alternateAdvertisements, unicast mechanisms are required andas specified below: 188.8.131.52.1 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 structuresstructure "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 bean "advertising interface"),advertising ISATAP interface, and is used to construct the ISATAPlink-local ISATAP address for that interface. The following sections specify the process for initializing the PRL: When a node enables an ISATAP link, it firstdiscovers IPv4 addresses for the PRL. The addresses SHOULDMAY be established by a DHCPv4  option for ISATAP (option code TBD), bymanual configuration, or byan unspecified alternate method (e.g., DHCPv4 vendor-specific option). When no other mechanisms are available, a DNS fully-qualified domain name (FQDN)  established by an out-of-band method (e.g., DHCPv4, manual configuration, etc.) MAY be used. In this case, theThe FQDN is resolved into IPv4 addresses for the PRLthrough a static host file, a site-specific name service, or byquerying an IPv4-baseda DNS server. Unspecifiedserver within the site, or an unspecified alternate methods for domain name resolution may also be used.method. The following notes apply: 1. Site administrators maintain a list of IPv4 addresses representing advertising ISATAP routerinterfaces and make them available via one or more of the mechanisms described above. 2. There are no mandatory rules for the selection of a FQDN, but administrators are encouraged to use the convention "isatap.domainname" (e.g., isatap.example.com).manual configuration MUST be supported. 3. After initialization, nodes periodically re-initialize the PRL (after(e.g., after ResolveInterval). When DNS is used, client DNSresolvers use the IPv4 transport to resolve the names and follow the cache invalidation procedures in  when the DNS time-to-live expires. 7.2.2 Validity Checks fortransport. 7.3.2 Validation of Router Advertisements A node MUST silently discard any Router AdvertisementMessages The specification in (, section 6.1.2) is used. Additionally, received RA messages it receivesthat do not satisfy both the validity checkscontain Prefix Information options and/or encode non-zero values in (,the Cur Hop Limit, Router Lifetime, Reachable Time, or Retrans Timer fields (see: , section 6.1.2) and4.2) MUST satisfy the following additionalvalidity check for ISATAP: o the network-layer (IPv6) source address is an ISATAP address and embeds an IPv4 address from the PRL 184.108.40.206.3 Router Specification AdvertisingRouters with advertising ISATAP interfaces of routersbehave the same as advertising interfacesdescribed in (,(, section 6.2). However, periodic unsolicited multicast Router Advertisements are not used, thus the "interval timer" associated with advertising interfaces is not used for that purpose. When an ISATAP router receives a valid Router Solicitation on an advertisingAdvertising ISATAP interface, it replies with a unicast Router Advertisementinterfaces send RA messages to the address of the node which sent the Router Solicitation. The source address of the Router Advertisement isa link-localnode's unicast address associated with the interface. This MAY be the sameaddress, 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 (,permitted by (, section 6.2.7) is desired. 220.127.116.11.6). 7.3.4 Host Specification 18.104.22.168 Sending Router Solicitations All entries in the PRL are assumed to represent active advertising ISATAP routersinterfaces within the site, i.e., the PRL provides trust basis only; not reachability detection. ISATAP nodes SHOULD use stateful configuration to assign IPv6 prefixes and default router information. When stateful configuration is not available, hosts MAYHosts periodically solicit information from one or more entries in the PRL ("PRL(i)") by sending unicast Router Solicitation (RS) messages using thePRL(i)'s IPv4 address ("V4ADDR_PRL(i)") and associated timer in("TIMER(i)"). The manner of selecting a PRL(i) for solicitation and/or deprecating a previously-selected PRL(i) is outside the entry.scope of this specification. Hosts add the following variable to support the solicitation process: MinRouterSolicitInterval Minimum time between sending Router Solicitations to any router.Solicitations. Default and suggested minimum: 15min. When a PRL(i) is selected, the host sets its associated timerTIMER(i) 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.delay. Solicitation consists of sending Router SolicitationsRS messages to the ISATAP link-local address constructed from the entry's IPv4 address,V4ADDR_PRL(i), i.e., they are sent to 'FE80::0:5EFE:V4ADDR_PRL(i)' instead of 'All-Routers multicast'.'All-Routers-multicast'. They are otherwise sent exactly as in (,(, section 6.3.7). 22.214.171.124 Processing Router Advertisements Hosts process received Router AdvertisementsRA messages exactly as in (,(, section 6.3.4). Hosts additionally reset6.3.4) and (, section 5.5.3) except that, when an RA message contains an MTU option, hosts SHOULD NOT copy the timer associated withoption's value into the V4ADDR_PRL(i) embedded inISATAP interface LinkMTU. Instead, when the ISATAP link layer implements a per-neighbor path MTU cache, hosts SHOULD copy the MTU option's value into the cache entry for the router that sent the RA message (see: Appendix C). When the network-layer source address in each solicited Router Advertisement received. The timeran RA message is an ISATAP address that embeds V4ADDR_PRL(i) for some PRL(i) selected for solicitation, hosts additionally reset to either 0.5 * (theTIMER(i). Let "MIN_LIFETIME" be the minimum value in the router lifetime or valid lifetime of any on-linkprefixes receivedadvertised in the advertisement) or MinRouterSolicitInterval; whicheverRA message. Then, TIMER(i) is longer.reset to: MAX((0.5 * MIN_LIFETIME), MinRouterSolicitInterval) 8. ISATAPDeployment Considerations 8.1 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 supportboth a native IPv6,IPv6 and alsoISATAP (over IPv4).interface over the same physical link. 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 advertising ISATAP interface(s) SHOULD be added (either automatically or manually) to the site's address records for advertising ISATAP routerinterfaces. 8.2 Site Administration Considerations The following considerations are noted for sites that deploy ISATAP: o ISATAP links are administratively defined by a set of routeradvertising ISATAP interfaces and set of nodes which discover those interface and server addressesaddresses. Thus, ISATAP links are defined by administrative (not physical) boundaries. o ISATAP hostsHosts and routers that use ISATAP can be deployed in an ad-hoc and independentfashion. In particular, ISATAPhosts can be deployed with little/no advanced knowledge of existing ISATAProuters, and ISATAProuters can deployed with no reconfiguration requirements for hosts. o When stateful autoconfiguration is not available, ISATAP nodes MAY periodically send unicast Router Solicitations to and receive unicast Router Advertisements from to one or more members of the potential router list. A well-deployed stateful autoconfiguration service within the site can minimize and/or eliminate the need for periodic solicitation. oISATAP nodes periodically refresh the entries on the PRL. Responsible site administration can reduce the control traffic. At a minimum, administrators SHOULD ensure that dynamically advertised information for the site's PRL is well maintained. 9. IANA Considerations A DHCPv4 option code for ISATAP (TBD)  is requested in may be requested in the event that the IESG recommendsthis document for(or a derivative thereof) is moved to standards track. 10. Security considerations Site administrators are advised that, inISATAP site border routers and firewalls MUST implement IPv6 ingress filtering and MUST NOT allow packets with site-local source and/or destination addresses (i.e., addresses with prefix FEC0::/10) to enter or leave the site. In addition to possible attacks against IPv6, security attacks against IPv4 MUSTmust also be considered. Responsible IPv4 site security management is strongly encouraged.In particular, border gateways SHOULDrouters and firewalls MUST implement filtering to detect spoofedIPv4 source addresses at a minimum; ip-protocol-41ingress filtering SHOULD also be implemented. Ifand ip-protocol-41 filtering. Even with IPv4 source address filtering is not correctly implemented, theand IPv6 ingress filtering, reflection attacks can originate from nodes within an ISATAP validity checks will not be effective in preventingsite that spoof IPv6 source address spoofing. If filteringaddresses. Security mechanisms for ip-protocol-41 is not correctly implemented, IPv6 source address spoofing is clearly possible, but this canreflection attack mitigation (e.g., , , etc.) SHOULD be eliminated if both IPv4used in routers with advertising ISATAP interfaces. At a minimum, ISATAP site border gateways MUST log potential source address filtering, and the ISATAP validity checks are implemented.spoofing cases. (RFC 2461 ),, section 126.96.36.199.2) implies that nodes trust received Router Advertisements they receiveAdvertisement (RA) messages 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 Advertisementsan additional validation check for 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. TheRA messages (see: Section 7.3.2). ISATAP address format doesaddresses do 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 issueis the same for NAT'd addresses.)especially true when private address allocations  are used.) 11. 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.  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. Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", draft-ietf-ipngwg-addr-arch-v3-11 (work in progress), October 2002.  Armitage, G., Schulter, P., Jork, M. and G. Harter, "IPv6 over Non-Broadcast Multiple Access (NBMA) networks", RFC 2491, January 1999.  Gilligan, R. and E. Nordmark, "Basic Transition Mechanisms for IPv6 Hosts and Routers", 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.  McCann, J., Deering, Thomson, S. and J. Mogul, "Path MTU Discovery for IP version 6", RFC 1981, August 1996.  Braden, R., "Requirements for Internet Hosts - Communication Layers", STD 3,T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 1122, October 1989. 2462, December 1998.  Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.  Thomson, S. Savola, P., "Security Considerations for 6to4", draft-savola-ngtrans-6to4-security-01 (work in progress), March 2002.  Bellovin, S., Leech, M. and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. Taylor, "ICMP Traceback Messages", draft-ietf-itrace-03 (work in progress), January 2003.  Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, November 1990.  Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, September 1981.  Baker, F., "Requirements for IP Version 4 Routers", RFC 1812, June 1995.  Droms, McCann, J., Deering, S. and J. Mogul, "Path MTU Discovery for IP version 6", RFC 1981, August 1996.  Braden, R., "Dynamic Host Configuration Protocol"Requirements for IPv6 (DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress), November 2002.Internet Hosts - Communication Layers", STD 3, RFC 1122, October 1989. Informative References  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G. and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, February 1996.  Carpenter, B. and K. Moore, "Connection of IPv6 Domains via IPv4 Clouds", RFC 3056, February 2001.  Thaler, D., "Support for Multicast over 6to4 Networks", draft-ietf-ngtrans-6to4-multicast-01 (work in progress), July 2002.  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.  Jacobson, V., Braden, B. and D. Borman, "TCP Extensions for High Performance", RFC 1323, May 1992.  Templin, F., "Neighbor Affiliation Protocol for IPv6-over-(foo)-over-IPv4", draft-templin-v6v4-ndisc-01 (work in progress), November 2002. 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 10 to version 11: o Added multicast/anycast subsection o Revised PRL initialization o Updated neighbor discovery, security consideration sections o Updated MTU section changes from version 09 to version 10: o Rearranged/revised sections 5, 6, 7 o updated MTU section changes from version 08 to version 09: o Added stateful autoconfiguration mechanism o Normative references to RFC 2491, RFC 2462 o Moved non-normative MTU text to appendix C changes from version 07 to version 08: o updated MTU section changes from version 06 to version 07: o clarified address resolution, Neighbor Unreachability Detection o specified MTU/MRU requirements changes from earlier versions to version 06: o Addressed operational issues identified in 05 based on discussion between co-authors o Clarified ambiguous text per comments from Hannu Flinck; Jason Goldschmidt o Moved historical text in section 4.1 to Appendix B in response to comments from Pekka Savola o Identified operational issues for anticipated deployment scenarios o Included reference to Quang Nguyen work Appendix B. Rationale for Interface Identifier Construction ISATAP specifies an EUI64-format address construction for the Organizationally-Unique Identifier (OUI) owned by the Internet Assigned Numbers Authority (IANA). This format (given below) is used to construct both native EUI64 addresses for general use and modified EUI-64 format interface identifiers for IPv6 unicast addresses: |0 2|2 3|3 3|4 6| |0 3|4 1|2 9|0 3| +------------------------+--------+--------+------------------------+ | OUI ("00-00-5E"+u+g) | TYPE | TSE | TSD | +------------------------+--------+--------+------------------------+ Where the fields are: OUI IANA's OUI: 00-00-5E with 'u' and 'g' bits (3 octets) TYPE Type field; specifies use of (TSE, TSD) (1 octet) TSE Type-Specific Extension (1 octet) TSD Type-Specific Data (3 octets) And the following interpretations are specified based on TYPE: TYPE (TSE, TSD) Interpretation ---- ------------------------- 0x00-0xFD RESERVED for future IANA use 0xFE (TSE, TSD) together contain an embedded IPv4 address 0xFF TSD is interpreted based on TSE as follows: TSE TSD Interpretation --- ------------------ 0x00-0xFD RESERVED for future IANA use 0xFE TSD contains 24-bit EUI-48 intf id 0xFF RESERVED by IEEE/RAC Figure 2Thus, 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. Dynamic Per-neighborMTU Discovery ISATAP encapsulators and decapsulators are IPv6 neighbors that may be separated by multiple link layer (IPv4) forwarding hops. When ISATAP_MTU isan encapsulator's interface configures a LinkMTU (, Section 6.3.2) value larger than 1380 bytes, the encapsulator must implementa dynamic link layer (IPv4) mechanism is required to discover per-neighbor path MTUs. The following text gives non-normative considerations for dynamic MTU discovery. IPv4 path MTU discovery  relies on uses ICMPv4 "fragmentation needed" messages, but these generally do not provide enough information for stateless translation intoto 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 ismay be inadequate and can result in black holes that are difficult to diagnose . The ISATAP encapsulator may implement an alternate. Alternate methods for determining per-neighbor MTUs should be used when RFC 1191 path MTU discovery mechanism, e.g.,is deemed inadequate. In any method, the encapsulator uses periodic and/or on-demand probing of the IPv4 path to the decapsulator. Probing consists of sending packets larger than 1380 bytes to the neighbor and receiving positive confirmation of receipt. TwoThe following three methods are possible: In the first method,1. Encapsulator-driven - the encapsulator does NOT setperiodically sends probe packets with the DF bit set in the IPv4 header of probe packets. In this case, the encapsulator must have a priori knowledge of the decapsulator's reassembly buffer sizeand should havewaits for a priori knowledge of the decapsulator's link MTU. This method haspositive acknowledgement from the advantagedecapsulator that the probe packets will be delivered even ifwas received 2. Decapsulator-driven - the network performs fragmentation, thus ordinary dataencapsulator sends all packets may be used for probing resultingwith the DF bit NOT set in greater efficiency. Disadvantages for this method include: o special mechanisms required on both encapsulatorthe IPv4 header unless and until the decapsulator o extra state required on bothsends a "Fragmentation Experienced" indication(s) 3. Hybrid - the encapsulator and decapsulator o complex protocol signalling between encapsulatorengage in a dialogue and decapsulator o possible extended periods of network fragmentation Inuse "intelligent" probing to monitor the path MTU These methods are discussed in detail in the second (and preferred)following subsections: C.1 Encapsulator-driven Method In this method, the encapsulator sets the DF bit in the IPv4 header of probe packets. Probe packets may be sent either when the encapsulator's link layer forwards a large data packet to the decapsulator (i.e., on-demand) or when the path MTU for the decapsulator has not been verified for some time (i.e., periodic). IPv6 Neighbor Solicitation (NS) or ICMPv6 ECHO_REQUEST packets with padding bytes added shouldcould be used for this purpose, since successful delivery results in a positive acknowledgement that the probe succeeded, i.e., in the form ofsucceeded vis-a-vis a Neighbor Advertisement (NA)response from the decapsulator. SettingWhile the DF bit prevents the network from fragmentingdecapsulator is being probed, the packets and protects decapsulators from receivingencapsulator maintains a queue of packets that might overrunhave the IPv4 reassembly buffer. Additionally, special mechanisms and state are needed only ondecapsulator as the encapsulator, andIPv6 next-hop address. The queue should be large enough to buffer the (delay*bandwidth) product for the round-trip time (RTT) to the decapsulator. If the probe succeeds, packets in the queue that are no complex protocol signalling betweenlarger than the encapsulatorprobe size are sent to the decapsulator. If the probe fails, packets larger than the last known successful probe are dropped and an ICMPv6 "packet too big" message returned to the sender . This method has the advantage that the decapsulator need not implement any special mechanisms, since standard IPv6 request/ response mechanisms are used. Additionally, the encapsulator is required.assured that any packets that are too large for the decapsulator to receive will be dropped by the network. Disadvantages for this method include the fact that probe packets do not carry data and thus consume network resources. Additionally, packet queues may become large on Long, Fat Networks (LFNs) (see: RFC 1323 ). C.2 Decapsulator-driven Method In eitherthis method, implementations may choose to couplethe probing processencapsulator sends all packets with neighbor cache management procedures (, section 7), e.g. to maintain timers, state variables and/orthe DF bit NOT set in the IPv4 header with the expectation that the decapsulator will send a queue of"Fragmentation Experienced" indication if the IPv4 network fragments packets. In other words, the decapsulator simply sends all packets waitingthat are no larger than LinkMTU unless and until it receives "Fragmentation Experienced" messages from the decapsulator. The decapsulator can use IPv6 Router Advertisement (RA) messages with an MTU option as the means for probesboth reporting fragmentation and informing the encapsulator of a new MTU value to complete. Packets retained onuse. This method has the queuedistinct advantages that the data packets themselves are forwarded whenused as probes succeed,and provide stateno queueing on the encapsulator is necessary. Additionally, fewer packets will be lost since the decapsulator will quite often be able to reassemble packets fragmented by the network. The primary disadvantage is that, using the current specifications, the encapsulator has no way of knowing whether a particular decapsulator implements the "fragmentation experienced" signalling capability. However, the "fragmentation experienced" indication can be trivially implemented in an application on the decapsulator that uses the Berkeley Packet Filter (aka, libpcap) to listen for sendingfragmented packets from encapsulators. When fragmented packets arrive, the application sends IPv6 RA messages with an MTU option to inform the encapsulator that fragmentation has been experienced and a new value for the neighbor's MTU should be used. The application additionally sends ICMPv6 "packet too big" messages to the original source when probes fail. Implementations may choosea fragmented packet is not correctly reassembled. This function need not be built into the decapsulator's operating system and can be added as an after-market feature. Finally, simply adding an extra bit in the RA message header (, section 4.2) would provide a means for the decapsulator to store per-neighborinform the encapsulator that dynamic MTU informationdiscovery is supported. C.3 Hybrid Method In this method, the encapsulator and decapsulator engage in a "neighbor affiliation" protocol to negotiate link-layer parameters such as MTU. (See:  for an example of such an approach.) This approach has the IPv4 path MTU discovery cache, inadvantage that bi-directional links are used and both ends of the ISATAPlink layer's private data structures, etc. Additional notes: 1. Per-neighbor MTUs may vary dynamically due to fluctuations inhave unambiguous knowledge that the IPv4 forwarding path and/or multipath routing (e.g., when QoS routingother end implements the protocol. However, the signalling protocol between the endpoints is usedcomplicated and additional state is required in both the IPv4 network). For such neighbors, encapsulators should detect a "losing battle"encapsulator and reducedecapsultor. C.4 Summary In summary, the per-neighbor MTU size to no more than 1380 bytes. 2. When not probing, encapsulators may send packets to a neighbor with MTU greater than 1380 bytes eitherdecapsulator-based approach in Appendix C.2 has distinct efficiency advantages over methods that engage the encapsulator. Additionally, probing methods which use IPv4 encapsulation with the DF bit NOT set or not set. When the DF bit is set, undetected packet lossmay occur inuse LinkMTU values for the network ifISATAP link that exceed the neighbor'sunderlying link MTU decreases. When the DF bitsize. Experimental verification is NOT set, undetectedcalled for which may eventually result in a recommendation for proposed standard. C.5 Additional Notes o In all methods, some packet loss is less likely butdue to link/buffer restrictions may occur eitherwith no ICMPv6 "packet too big" message returned to the sender. Unenlightened senders will interpret such loss as loss due to congestion, which may result in longer convergence to the network or atactual path MTU. Enlightened senders will interpret the neighbor's reassembly buffer. 3.loss as loss due to link/buffer restrictions and immediately reduce their MTU estimate. o To avoid denial-of-service attacks that would cause superfluous probing based on counting down/up by small increments, plateau tables (e.g., , section 7) should be used when the actual MTU value is indeterminant. o ICMPv4 "fragmentation needed" messages may result when a link restriction is encountered but may also come from denial of service attacks. Implementations should treat ICMPv4 "fragmentation needed" messages as "tentative" negative acknowledgments and apply heuristics to determine when to suspect an actual link restriction and when to ignore the messages. IPv6 packets lost due actual link restrictions are perceived as lost due to congestion by the original source, but robust implementations minimize instances of such packet loss without ICMPv6 "packet too big" messages returned to the sender. o Nodes that connect to the Internet are expected to be able to reassemble or discard IPv4 packets up to 64KB in length when the DF bit is not set in the encapsulating IPv4 header. Nodes that cannot reassemble or discard maximum-length IPv4 packets are vulnerable to attacks such as the "ping-of-death". 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. 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