NGTRANS Working Group F. Templin
INTERNET-DRAFT Nokia
T. Gleeson
Cisco Systems K.K.
M. Talwar
D. Thaler
Microsoft Corporation
Expires 31 April 2003 31 October 2002
Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)
draft-ietf-ngtrans-isatap-06.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
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Abstract
This document specifies the Intra-Site Automatic Tunnel Addressing
Protocol (ISATAP) that connects IPv6 hosts and routers (nodes) within
IPv4 sites. ISATAP is a transition mechanism that enables incremental
deployment of IPv6 by treating the site's IPv4 infrastructure as a
Non-Broadcast Multiple Access (NBMA) link layer for IPv6. ISATAP
mechanisms use an IPv6 interface identifier format that embeds an
IPv4 address - this enables automatic IPv6-in-IPv4 tunneling within a
site, whether the site uses globally assigned or private IPv4
addresses. The new interface identifier format can be used with both
local and global unicast IPv6 prefixes - this enables IPv6 routing
both locally and globally. ISATAP mechanisms introduce no impact on
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routing table size and require no special IPv4 services (e.g., IPv4
multicast).
1. Introduction
This document presents a simple approach that enables incremental
deployment of IPv6 within IPv4-based sites in a manner that is com-
patible with inter-domain transition mechanisms, e.g., [6TO4]. We
refer to this approach as the Intra-Site Automatic Tunnel Addressing
Protocol, or ISATAP (pronounced: "ice-a-tap"). ISATAP allows dual-
stack nodes that do not share a common link with an IPv6 router to
automatically tunnel packets to the IPv6 next-hop address through
IPv4, i.e., the site's IPv4 infrastructure is treated as an NBMA link
layer.
This document specifies details for the transmission of IPv6 packets
over ISATAP links (i.e., automatic IPv6-in-IPv4 tunneling), including
a new EUI-64 [EUI64] based interface identifier [ADDR][AGGR] format
that embeds an IPv4 address. This format supports configuration of
global, site-local and link-local addresses as specified in [AUTO] as
well as simple link-layer address mapping. Simple validity checks for
received packets are given. Also specified in this document is the
operation of IPv6 Neighbor Discovery for ISATAP, as permitted for
NBMA links by [DISC]. The document finally presents deployment and
security considerations for ISATAP.
2. Applicability Statement
ISATAP provides the following features:
- treats site's IPv4 infrastructure as an NBMA link layer using
automatic IPv6-in-IPv4 tunneling (i.e., no configured tunnel state)
- enables incremental deployment of IPv6 hosts within IPv4 sites with
no aggregation scaling issues at border gateways
- requires no special IPv4 services within the site (e.g., multicast)
- supports both stateless address autoconfiguration and manual
configuration
- supports networks that use non-globally unique IPv4 addresses (e.g.,
when private address allocations [PRIVATE] are used), but does not
allow the virtual ISATAP link to span a Network Address
Translator [NAT]
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- compatible with other NGTRANS mechanisms (e.g., [6TO4])
3. Terminology
The terminology of [IPv6] applies to this document. The following
additional terms are defined:
link:
same definition as [AUTO][DISC].
underlying link:
a link layer that supports IPv4 (for ISATAP), and MAY also support
IPv6 natively.
ISATAP link:
one or more underlying links used for IPv4 tunneling. The IPv4
network layer addresses of the underlying links are used as
link-layer addresses on the ISATAP link.
ISATAP interface:
a node's attachment to an ISATAP link.
ISATAP prefix:
a prefix used to configure an address on the ISATAP interface. This
prefix is administratively assigned to the ISATAP link and MUST NOT
be duplicated on native IPv6 links.
ISATAP address:
an IPv6 address with an ISATAP prefix and an ISATAP format interface
identifier constructed as specified in section 4.
ISATAP router:
an IPv6 node that has an ISATAP interface over which it forwards
packets not explicitly addressed to itself.
ISATAP host:
any node that has an ISATAP interface and is not an ISATAP router.
4. Transmission of IPv6 Packets on ISATAP Links
ISATAP links transmit IPv6 packets via automatic tunneling using the
site's IPv4 infrastructure as an NBMA link layer. Automatic tunneling
for ISATAP uses the same encapsulation, hop limit, IPv4 header con-
struction, and decapsualtion specifications in [MECH, 3], i.e., IPv6
packets are automatically encapsulated in IPv4 using 'ip-protocol-41'
as the payload type number. The specifications in [MECH, 3.2, 3.4] do
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not apply for ISATAP; instead:
- The default link MTU SHOULD be set to the minimum IPv6 MTU of
1280 bytes [IPV6], unless specific configuration information
is available. The Don't Fragment bit SHOULD NOT be set in the
encapsulating IPv4 header.
- IPv4 ICMP errors and ARP failures may be processed as
link error notifications, as allowed by [DISC]
Specific considerations for ISATAP links are given below:
4.1. ISATAP Interface Identifier Construction
IPv6 unicast addresses [ADDR][AGGR] include a 64-bit interface iden-
tifier field in "modified EUI-64 format", based on the IEEE EUI-64
[EUI64] specification. (Modified EUI-64 format inverts the sense of
the 'u/l' bit from its specification in [EUI64], i.e., 'u/l' = 0
indicates local-use.) ISATAP interface identifiers are constructed by
prepending the 32-bit string '00-00-5E-FE' with an IPv4 address (see
the following section for examples). Appendix B includes text
explaining the rationale for this construction rule.
4.2. Stateless Autoconfiguration and Link-Local Addresses
ISATAP addresses are unicast addresses [ADDR,2.5] that use ISATAP
format interface identifiers as follows:
| 64 bits | 32 bits | 32 bits |
+------------------------------+---------------+----------------+
| link-local, site-local or | 0000:5EFE | IPv4 Address |
| global unicast prefix | | of ISATAP link |
+------------------------------+---------------+----------------+
Link-local, site-local, and global ISATAP addresses can be created
exactly as specified in [ADDR], (e.g., by auto-configuration [AUTO]
or manual configuration). For example, the IPv6 address:
3FFE:1A05:510:1111:0:5EFE:8CAD:8108
has a prefix of '3FFE:1A05:510:1111::/64' and an ISATAP format inter-
face identifier with embedded IPv4 address: '140.173.129.8'. The
address is alternately written as:
3FFE:1A05:510:1111:0:5EFE:140.173.129.8
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The link-local and site-local variants (respectively) are:
FE80::0:5EFE:140.173.129.8
FEC0::1111:0:5EFE:140.173.129.8
4.3. ISATAP Link/Interface Configuration
A node configures an ISATAP link over one or more underlying IPv4
links, i.e., the ISATAP link MAY be configured over one or more link-
layer (IPv4) addresses. Each link-layer address 'V4ADDR_LINK' is used
to configure a link-local address 'FE80::0:5EFE:V4ADDR_LINK' on an
ISATAP interface. ISATAP interfaces MAY be assigned one per link-
layer address, or as a single interface for multiple link-layer
addresses.
In the former case, the address of each ISATAP interface SHOULD be
added to the Potential Routers List (see section 5.2.1). In the lat-
ter case, the interface will accept ISATAP packets addressed to any
of the IPv4 link-layer addresses, but will choose one as its primary
address, used for sourcing packets. Only this address need be repre-
sented in the Potential Routers List.
4.4. Sending Rules and Address Mapping
The IPv6 next-hop address for packets sent on an ISATAP link MUST be
an ISATAP address. Packets that do not satisfy this constraint MUST
be discarded and an ICMP destination unreachable indication with code
3 (Address Unreachable) [ICMPv6] MUST be returned. No other sending
rules are necessary.
The procedure for mapping unicast addresses into link-layer addresses
is to simply treat the last four octets of the ISATAP address as an
IPv4 address (in network byte order). No multicast address mappings
are specified.
4.5. Validity Checks for Received Packets
Packets received on ISATAP interfaces MUST satisfy at least one
(i.e., one or both) of the following validity checks:
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- the network-layer (IPv6) source address has a prefix configured on
the ISATAP interface and an ISATAP-format interface identifier that
embeds the link-layer (IPv4) source address, i.e., source is on-link
- the link-layer (IPv4) source address is an "active" member of
the Potential Routers List (see section 5.2), i.e., previous
hop is an on-link ISATAP router actively being used by the node
Packets that do not satisfy at least one of the above checks are
silently discarded.
5. Neighbor Discovery for ISATAP Links
Section 3.2 of [DISC] ("Supported Link Types") provides the following
guidelines for non-broadcast multiple access (NBMA) link support:
"Redirect, Neighbor Unreachability Detection and next-hop determi-
nation should be implemented as described in this document. Address
resolution and the mechanism for delivering Router Solicitations
and Advertisements on NBMA links is not specified in this docu-
ment."
ISATAP links SHOULD implement Redirect, Neighbor Unreachability
Detection, and next-hop determination exactly as specified in [DISC].
Address resolution and the mechanisms for delivering Router Solicita-
tions and Advertisements for ISATAP links are not specified by
[DISC]; instead, they are specified in this document. (Note that
these mechanisms MAY potentially apply to other types of NBMA links
in the future.)
5.1. Address Resolution
Protocol addresses (IPv6) in ISATAP are resolved to link-layer
addresses (IPv4) by a static computation, i.e., the last four octets
are treated as an IPv4 address.
ISATAP nodes SHOULD perform Neighbor Unreachability Detection (NUD)
as specified in [DISC, 7.3], and MUST send solicited neighbor adver-
tisements as specified in [DISC, 7.2.4].
The link-layer address option used in [DISC] is not needed. Link-
layer address options SHOULD NOT be sent in any Neighbor Discovery
packets, and MUST be silently ignored in any received Neighbor Dis-
covery packets.
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5.2. Router and Prefix Discovery
Since the site's IPv4 infrastructure is treated as an NBMA link
layer, unsolicited Router Advertisements do not provide sufficient
means for router discovery on ISATAP links. Thus, alternate mecha-
nisms are required and specified below:
5.2.1. Conceptual Data Structures
ISATAP nodes use the conceptual data structures Prefix List and
Default Router List exactly as specified in [DISC,5.1]. ISATAP links
add a new conceptual data structure "Potential Router List" and the
following new configuration variable:
ResolveInterval Time between name service resolutions.
Default and suggested minimum: 1hr
A Potential Router List (PRL) is associated with every ISATAP link.
The PRL provides context for router discovery and a trust basis for
router validation (see security considerations). Each entry in the
PRL has an IPv4 address and an associated timer used for polling. 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.
When a node enables an ISATAP link, it initializes the Potential
Router List (PRL) for that link. Unless other information is avail-
able (e.g., manual address configuration, a vendor-specific DHCP
option, etc.) the following method (similar to the [SIP, 1.4.2] pro-
cedure) SHOULD be used:
1. The site administrator maintains address records for ISATAP
router interfaces, and makes these available in the site's
name service. Nodes attempt to find one or more addresses
for the PRL by querying the name service.
2. There are no mandatory rules on the selection of domain name
to be used within a site for this purpose, but administrators
are encouraged to use the "isatap.domainname" convention
(e.g., isatap.example.com), as specified in [RFC2219]. Nodes
can construct this domain name by prepending the label "isatap"
to their parent domain name, which is established by other
means. Nodes then query this domain name for address records
(e.g., DNS 'A' resource records), and initialize the PRL with
the IPv4 addresses in the replies.
3. After initialization, nodes periodically repeat the above
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procedure ResolveInterval to update the PRL with any IPv4
addresses added/deleted since the previous iteration. When
DNS is used, nodes MUST follow the procedures in [RFC1035]
regarding cache invalidation when the DNS time-to-live expires.
5.2.2. Validation of Router Advertisement Messages
A node MUST silently discard any received Router Advertisement mes-
sages that do not satisfy the validity checks in [DISC,6.1.2] as well
as the following additional validity check for ISATAP:
- the network-layer (IPv6) source address is derived from
an IPv4 address in the PRL
5.2.3. Router Specification
Advertising ISATAP interfaces of routers behave the same as advertis-
ing interfaces described in [DISC,6.2]. However, periodic unsolicited
multicast Router Advertisements are not required, thus the "interval
timer" associated with advertising interfaces is not used for that
purpose.
When an ISATAP router receives a valid Router Solicitation on an
advertising ISATAP interface, it replies with a unicast Router Adver-
tisement to the address of the node which sent the Router Solicita-
tion. 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 polling process described under Host Specification
below (e.g. if Router Advertisement consistency verification
[DISC,6.2.7] is desired), but this is not required.
5.2.4. Host Specification
Hosts periodically poll 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 polling process:
MinRouterSolicitInterval
Minimum time between sending Router Solicitations
to any router. Default and suggested minimum: 15min
When a PRL(i) is selected for polling, the host sets its associated
timer to MinRouterSolicitInterval and initiates polling following a
short delay as for initial solicitations [ND,6.3.7]), and when the
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associated timer expires.
Polling 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 mul-
ticast'. They are otherwise sent in the same manner described in
[DISC,6.3.7].
When the host receives a valid Router Advertisement (i.e., one that
satisfies the validity checks in sections 4.5 and 5.2.2) it is pro-
cesses in the same manner described in [DISC,6.3.4]. The host addi-
tionally resets the timer associated with the V4ADDR_PRL(i) embedded
in the network-layer source address in the Router Advertisement. The
timer is reset to either 0.5 * (the minimum value in the router life-
time or valid lifetime of any on-link prefixes advertised) or Min-
RouterSolicitInterval; whichever is longer.
6. ISATAP Deployment Considerations
6.1. Host And Router Deployment Considerations
For hosts, if an underlying link supports both IPv4 (over which ISA-
TAP is implemented) and also supports IPv6 natively, then ISATAP MAY
be enabled if the native IPv6 layer does not receive Router Adver-
tisements (i.e., does not have connection with an IPv6 router). After
a non-link-local address has been configured and a default router
acquired on the native link, the host SHOULD discontinue the 'Router
Polling Process' process specified in section 5.2.4 and allow exist-
ing ISATAP address configurations to expire as specified in
[DISC,5.3][AUTO,5.5.4]. Any ISATAP addresses added to the DNS for
this host should also be removed. In this way, ISATAP use will gradu-
ally diminish as IPv6 routers are widely deployed throughout the
site.
Routers MAY configure an interface to simultaneously support both
native IPv6, and also ISATAP (over IPv4). Routing will operate as
usual between these two domains. Note that the prefixes used on the
ISATAP and native IPv6 interfaces will be distinct. The IPv4
address(es) configured on a router's ISATAP interface(s) SHOULD be
added (either automatically or manually) to the site's address
records for ISATAP router interfaces (see section 5.2.1).
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6.2. Site Administration Considerations
The following considerations are noted for sites that deploy ISATAP:
- ISATAP links are administratively defined by a set of router
interfaces, and set of nodes which have those interface addresses
in their potential router lists. Thus, ISATAP links are defined by
administrative (not physical) boundaries.
- 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.
- ISATAP nodes periodically send Router Solicitations to all entries
in the Potential Router List. Worst-case control traffic is on the
order of (M x N), where 'M' is the number of routers in the Potential
Router List and 'N' is the total number of nodes on the ISATAP link.
The MinRouterSolicitInterval ([5.2.4]) bounds control traffic for
large numbers of nodes even in worst-case scenarios.
- ISATAP nodes periodically refresh the entries on the PRL, typically
by polling the DNS. Responsible site administration can reduce the
control traffic. At a minimum, administrators SHOULD ensure that
the site's address records for ISATAP router interfaces (see
section 5.2.1) are well maintained.
7. IANA considerations
Appendix B offers one possible specification for managing the IEEE
OUI assigned to IANA for EUI-64 interface identifier construction.
This specification is made freely available to IANA for any purpose
they may find useful.
8. Security considerations
Site administrators are advised that, in addition to possible attacks
against IPv6, security attacks against IPv4 MUST also be considered.
Many security considerations in [6OVER4,9] 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
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validity checks in section 4.7 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 elimi-
nated if both IPv4 source address filtering, and the validity checks
in section 4.7 are implemented.
[DISC,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 [MECH,3.3], ISATAP
links require a different trust model. In particular, ONLY those
Router Advertisements received from a member of the Potential Routers
List are trusted; all others are silently discarded (see section
5.2.2). This trust model is predicated on IPv4 source address filter-
ing, as described above.
The ISATAP address format does not support privacy extensions for
stateless address autoconfiguration [PRIVACY]. However, since the
ISATAP interface identifier is derived from the node's IPv4 address,
ISATAP addresses do not have the same level of privacy concerns as
IPv6 addresses that use an interface identifier derived from the MAC
address.
Acknowledgements
Some of the ideas presented in this draft were derived from work at
SRI with internal funds and contractual support. Government sponsors
who supported the work include Monica Farah-Stapleton and Russell
Langan from U.S. Army CECOM ASEO, and Dr. Allen Moshfegh from U.S.
Office of Naval Research. Within SRI, Dr. Mike Frankel, J. Peter Mar-
cotullio, 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, Art Shelest, Margaret Wasserman, and
Brian Zill.
The authors wish to acknowledge the work of Quang Nguyen [VET] under
the guidance of Dr. Lixia Zhang that proposed very similar ideas to
those that appear in this document. This work was first brought to
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the authors' attention on September 20, 2002.
Finally, the authors recognize that ideas similar to those in this
document may have already been presented by others and wish to
acknowledge any other such contributions.
Normative References
[ADDR] Hinden, R., and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998. (Pending approval
of "addr-arch-v3").
[AGGR] Hinden., R, O'Dell, M., and Deering, S., "An IPv6
Aggregatable Global Unicast Address Format",
RFC 2374, July 1998.
[AUTO] Thomson, S., and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[DISC] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998.
[EUI64] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
Registration Authority",
http://standards.ieee.org/regauth/oui/tutori-
als/EUI64.html,
March 1997.
[ICMPv6] Conta, A. and S. Deering, "Internet Control Message
Protocol (ICMPv6) for the Internet Protocol Version 6
(IPv6) Specification", RFC 2463, December 1998.
[IPV4] Postel, J., "Internet Protocol", RFC 791.
[IPV6] Deering, S., and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460.
[MECH] Gilligan, R., and E. Nordmark, "Transition Mechanisms for
IPv6 Hosts and Routers", RFC 2893, August 2000.
[NAT] Egevang, K., and P. Francis, "The IP Network Address
Translator (NAT)", RFC 1631, May 1994.
[PRIVATE] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
and E. Lear, "Address Allocation for Private Internets",
RFC 1918, February 1996.
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[SIP] Handley, M., Schulzrinne, H., Schooler, E., and
J. Rosenberg, "SIP: Session Initiation Protocol",
RFC 2543, March 1999.
Informative References
[6OVER4] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529.
[6TO4] Carpenter, B., and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[IANA] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2,
USC/Information Sciences Institute, October 1994.
[PRIVACY] Narten, T., R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041,
January 2001.
[RFC1035] Mockapetris, P., "Domain Names - Implementation and
Specification", RFC 1035, November 1987.
[RFC2219] Hamilton, M., and R. Wright, "Use of DNS Aliases for
Network Services", RFC 2219 (BCP), October 1997.
[VET] Nguyen, Quang, "Virtual Ethernet: A New Approach to
IPv6 Transition", http://irl.cs.ucla.edu/vet/report.ps,
MS Project Report, Spring 1998.
Authors Addresses
Fred L. Templin
Nokia
313 Fairchild Drive
Mountain View, CA, USA
Phone: (650)-625-2331
Email: ftemplin@iprg.nokia.com
Tim Gleeson
Cisco Systems K.K.
Shinjuku Mitsu Building
2-1-1 Nishishinjuku, Shinjuku-ku
Tokyo 163-0409, JAPAN
email: tgleeson@cisco.com
Mohit Talwar
Microsoft Corporation
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One Microsoft Way
Redmond, WA 98052-6399
Phone: +1 425 705 3131
EMail: mohitt@microsoft.com
Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
Phone: +1 425 703 8835
EMail: dthaler@microsoft.com
APPENDIX A: Major Changes
changes from version 05 to version 06:
- Addressed operational issues identified in 05 based on
discussion between co-authors
- Clarified ambiguous text per comments from Hannu Flinck;
Jason Goldschmidt
changes from version 04 to version 05:
- Moved historical text in section 4.1 to Appendix B in
response to comments from Pekka Savola
- Identified operational issues for anticipated deployment
scenarios
- Included SRI IPR statement and contact information
- Included reference to Quang Nguyen work
changes from version 03 to version 04:
- Re-wrote section on Potential Router List initialization to
reference existing precedence in other documents
- several minor wording changes based on feedback from the
community
changes from version 02 to version 03:
- Added contributing co-authors
- RSs are now sent to unicast addresses rather than all-routers-multicast
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- Brought draft into better alignment with other IPv6
standards-track documents
- Added applicability statement
changes from version 01 to version 02:
- Cleaned up text and tightened up terminology. Changed "IPv6 destination
address" to "IPv6 next-hop address" under "sending rules". Changed
definition of ISATAP prefix to include link and site-local. Changed
language in sections 4 and 5
changes from version 00 to version 01:
- 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.
- Changed sense of 'u/l' bit in the ISATAP address interface
identifier to indicate "local scope", since ISATAP interface
identifiers are unique only within the scope of the ISATAP
prefix. (See section 4.)
changes from personal draft to version 00:
- Title change to provide higher-level description of field of
use addressed by this draft. Removed other extraneous text.
- Major new section on automatic discovery of off-link IPv6 routers
when IPv6-IPv4 compatibility addresses are used.
APPENDIX B: Rationale for Interface Identifier Construction Rules
ISATAP specifies an [EUI64]-format address construction for the Orga-
nizationally-Unique Identifier (OUI) owned by the Internet Assigned
Numbers Authority [IANA]. This format (given below) is used to con-
struct both native [EUI64] addresses for general use and modified
EUI-64 format interface identifiers for use in IPv6 unicast
addresses:
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|0 2|2 3|3 3|4 6|
|0 3|4 1|2 9|0 3|
+------------------------+--------+--------+------------------------+
| OUI ("00-00-5E"+u+g) | TYPE | TSE | TSD |
+------------------------+--------+--------+------------------------+
Where the fields are:
OUI IANA's OUI: 00-00-5E with 'u' and 'g' bits (3 octets)
TYPE Type field; specifies interpretation of (TSE, TSD) (1 octet)
TSE Type-Specific Extension (1 octet)
TSD Type-Specific Data (3 octets)
And the following interpretations are specified based on TYPE:
TYPE (TSE, TSD) Interpretation
---- -------------------------
0x00-0xFD RESERVED for future IANA use
0xFE (TSE, TSD) together contain an embedded IPv4 address
0xFF TSD is interpreted based on TSE as follows:
TSE TSD Interpretation
--- ------------------
0x00-0xFD RESERVED for future IANA use
0xFE TSD contains 24-bit EUI-48 intf id
0xFF RESERVED by IEEE/RAC
Thus, if TYPE=0xFE, TSE is an extension of TSD. If TYPE=0xFF, TSE is
an extension of TYPE. Other values for TYPE (hence, other interpreta-
tions 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 identi-
fiers (e.g., an IANA EUI-48 format multicast address such as:
'01-00-5E-01-02-03' is encapsulated as: '01-00-5E-FF-FE-01-02-03').
But, the specification also provides a special TYPE (0xFE) to indi-
cate an IPv4 address is embedded. Thus, when the first four octets of
a [ADDR]-compatible 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.
INTELLECTUAL PROPERTY
SRI International has notified the IETF of IPR considerations for
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INTERNET-DRAFT ISATAP 31 October 2002
some aspects of this specification. For more information consult the
online list of claimed rights.
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