Network Working Group F. Templin
Internet-Draft Nokia
Expires: September 25, 2003 T. Gleeson
Cisco Systems K.K.
M. Talwar
D. Thaler
Microsoft Corporation
March 27, 2003
Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)
draft-ietf-ngtrans-isatap-13.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on September 25, 2003.
Copyright Notice
Copyright (C) The Internet Society (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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Applicability Statement . . . . . . . . . . . . . . . . . . . 3
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Basic IPv6 Operation . . . . . . . . . . . . . . . . . . . . . 4
6. Automatic Tunneling . . . . . . . . . . . . . . . . . . . . . 5
7. Neighbor Discovery . . . . . . . . . . . . . . . . . . . . . . 6
8. Deployment Considerations . . . . . . . . . . . . . . . . . . 9
9. Site Administration Considerations . . . . . . . . . . . . . . 9
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
11. Security considerations . . . . . . . . . . . . . . . . . . . 10
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
Normative References . . . . . . . . . . . . . . . . . . . . . 11
Informative References . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 12
A. Major Changes . . . . . . . . . . . . . . . . . . . . . . . . 13
B. Rationale for Interface Identifier Construction . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . 17
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1. Introduction
This document presents a simple approach called the Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP) that enables
incremental deployment of IPv6 [RFC2460] within IPv4 [RFC0791] sites.
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.
Specific details for the operation of IPv6 and automatic tunneling
using ISATAP are given, including an interface identifier format that
embeds an IPv4 address. This format supports IPv6 address
configuration and simple link-layer address mapping. Also specified
is the operation of IPv6 Neighbor Discovery and deployment/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
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 and stateful autoconfiguration as well as
manual configuration
o supports networks that use non-globally unique IPv4 addresses
(e.g., when private address allocations [RFC1918] are used)
o compatible with other NGTRANS mechanisms (e.g., 6to4 [RFC3056])
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 [RFC2119].
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
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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 [RFC2460] applies to this document. The following
additional terms are defined:
link, on-link, off-link:
same definitions as ([RFC2461], section 2.1).
underlying link:
a link layer that supports IPv4 (for ISATAP), and MAY also support
IPv6 natively.
ISATAP interface:
an interface configured over one or more underling links.
advertising ISATAP interface:
same meaning as "advertising interface" in ([RFC2461], section
6.2.2).
ISATAP address:
an on-link address on an ISATAP interface and with an interface
identifier constructed as specified in Section 5.1
5. Basic IPv6 Operation
ISATAP interfaces automatically tunnel IPv6 packets 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. The mechanisms in [RFC2491] are used, with the following
noted exceptions for ISATAP:
5.1 Interface Identifiers and Unicast Addresses
ISATAP interface identifiers use "modified EUI-64" format ([ARCH],
section 2.5.1) and are formed by appending an IPv4 address assigned
to an underlying link to the 32-bit string '00-00-5E-FE'. Appendix B
includes non-normative rationale for this construction rule.
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IPv6 global and local-use ([ARCH], sections 2.5.4, 2.5.6) ISATAP
addresses are constructed as follows:
| 64 bits | 32 bits | 32 bits |
+------------------------------+---------------+----------------+
| global/local unicast prefix | 0000:5EFE | IPv4 Address |
+------------------------------+---------------+----------------+
5.2 ISATAP Interface Configuration
ISATAP interfaces are configured over one or more underlying links
that support IPv4 for tunneling within a site; each IPv4 address
assigned to an underlying link is seen as a link-layer address for
ISATAP.
5.3 Link Layer Address Options
With reference to ([RFC2491], section 5.2), when the [NTL] and [STL]
fields in an ISATAP link layer address option encode 0, the [NBMA
Number] field encodes a 4-octet IPv4 address.
5.4 Multicast and Anycast
ISATAP interfaces recognize an IPv6 node's required addresses
([ARCH], section 2.8), including certain multicast/anycast addresses.
Mechanisms for multicast/anycast emulation on ISATAP interfaces
(e.g., adaptations of MLD [RFC2710], PIM-SM [RFC2362], MARS
[RFC2022], etc.) are subject for future companion document(s).
6. Automatic Tunneling
The common tunneling mechanisms specified in ([MECH], sections 2 and
3) are used, with the following noted considerations for ISATAP:
6.1 Tunnel MTU and Fragmentation
ISATAP automatic tunnel interfaces may be configured over multiple
underlying links with diverse maximum transmission units (MTUs). The
minimum MTU for IPv6 interfaces is 1280 bytes ([RFC2460], Section 5),
but the following considerations apply for ISATAP 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
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o Commonly-deployed VPN interfaces use an MTU of 1400 bytes
To maximize efficiency and minimize IPv4 fragmentation for the
predominant deployment case, the ISATAP interface MTU, or "LinkMTU"
(see: [RFC2461], Section 6.3.2), SHOULD be set to no more than 1380
bytes (1400 minus 20 bytes for IPv4 encapsulation). LinkMTU MAY be
set to larger values when a dynamic link layer MTU discovery
mechanism is used or when a static MTU assignment is used and
additional fragmentation in the site's IPv4 network is deemed
acceptable.
When a dynamic IPv4 MTU discovery mechanism is not used, the ISATAP
interface encapsulates IPv6 packets with the Don't Fragment (DF) bit
not set in the encapsualting IPv4 header.
6.2 Handling IPv4 ICMP Errors
ARP failures and persistent ICMPv4 errors SHOULD be processed as
link-specific information indicating that a path to a neighbor has
failed ([RFC2461], section 7.3.3).
6.3 Local-Use IPv6 Unicast Addresses
The specification in ([MECH], section 3.7) is not used; the
specification in Section 5.1 is used instead.
7. Neighbor Discovery
The specification in ([MECH], section 3.8) applies only to configured
tunnels. [RFC2461] 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 interfaces SHOULD implement Redirect, Neighbor Unreachability
Detection, and next-hop determination exactly as specified in
[RFC2461]. Address resolution and the mechanisms for delivering
Router Solicitations and Advertisements are not specified by
[RFC2461]; instead, they are specified in the following sections of
this document.
7.1 Address Resolution and Neighbor Unreachability Detection
ISATAP addresses are resolved to link-layer (IPv4) addresses by a
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static computation, i.e., the last four octets are treated as an IPv4
address.
Hosts SHOULD perform an initial reachability confirmation by sending
Neighbor Solicitation (NS) message(s) and receiving a Neighbor
Advertisement (NA) message as specified in ([RFC2461], section 7.2).
Unless otherwise specified in a future document, solicitations are
sent to the target's unicast address.
Hosts SHOULD additionally perform Neighbor Unreachability Detection
(NUD) as specified in ([RFC2461], section 7.3). Routers MAY perform
these reachability confirmation and NUD procedures, but this might
not scale in all environments.
All ISATAP nodes MUST send solicited neighbor advertisements
([RFC2461], section 7.2.4).
7.2 Duplicate Address Detection
Duplicate Address Detection ([RFC2462], 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
The following sections describe mechanisms to support the router and
prefix discovery process ([RFC2461], section 6):
7.3.1 Conceptual Data Structures
ISATAP nodes use the conceptual data structures Prefix List and
Default Router List exactly as in ([RFC2461], section 5.1). ISATAP
adds a new conceptual data structure "Potential Router List" (PRL)
and the following new configuration variable:
PrlRefreshInterval
Time in seconds between successive refreshments of the PRL after
initialization. SHOULD be no less than 3,600 seconds.
Default: 3,600 seconds
A PRL is associated with every ISATAP interface. Each entry in the
PRL ("PRL(i)") has an IPv4 address ("V4ADDR(i)") that represents an
advertising ISATAP interface and an associated timer ("TIMER(i)").
When a node enables an ISATAP interface, it initializes the PRL with
IPv4 addresses. The addresses MAY be discovered via a DHCPv4
[RFC2131] option for ISATAP, manual configuration, or an unspecified
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alternate method (e.g., DHCPv4 vendor-specific option).
When no other mechanisms are available, a DNS fully-qualified domain
name (FQDN) [RFC1035] established by an out-of-band method (e.g.,
DHCPv4, manual configuration, etc.) MAY be used. The FQDN is resolved
into IPv4 addresses for the PRL through a static host file, a
site-specific name service, querying a DNS server within the site, or
an unspecified alternate method. There are no mandatory rules for the
selection of a FQDN, but manual configuration MUST be supported. When
DNS is used, client resolvers use the IPv4 transport.
After initialization, nodes periodically refresh the PRL (i.e., using
one or more of the methods described above) after PrlRefreshInterval.
7.3.2 Validation of Router Advertisements Messages
The specification in ([RFC2461], section 6.1.2) is used.
Additionally, received RA messages that contain Prefix Information
options and/or encode non-zero values in the Cur Hop Limit, Router
Lifetime, Reachable Time, or Retrans Timer fields (see: [RFC2461],
section 4.2) MUST satisfy the following validity check for ISATAP:
o the network-layer (IPv6) source address is an ISATAP address and
embeds V4ADDR(i) for some PRL(i)
7.3.3 Router Specification
Routers with advertising ISATAP interfaces behave the same as
described in ([RFC2461], section 6.2). As permitted by ([RFC2461],
section 6.2.6), advertising ISATAP interfaces SHOULD send unicast RA
messages to a soliciting host's unicast address when the
solicitation's source address is not the unspecified address.
7.3.4 Host Specification
Hosts behave the same as described in ([RFC2461], section 6.3) and
([RFC2462], section 5.5) with the following additional considerations
for ISATAP:
7.3.4.1 Soliciting Router Advertisements
Hosts solicit Router Advertisements (RAs) by sending Router
Solicitations (RSs) to advertising ISATAP interfaces in the PRL. The
manner of selecting PRL(i)'s for solicitation is up to the
implementation. Hosts add the following variable to support the
solicitation process:
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MinRouterSolicitInterval
Minimum time in seconds between successive solicitations of the
same advertising ISATAP interface. SHOULD be no less than 900
seconds.
Default: 900 seconds
RS messages use a link-local unicast address from the ISATAP
interface as the IPv6 source address. Unless otherwise specified in a
future document, RS messages use the link-local ISATAP address
constructed from V4ADDR(i) for the PRL(i) being solicited as the IPv6
destination address.
7.3.4.2 Router Advertisement Processing
When the source address of an RA message is an ISATAP address that
embeds V4ADDR(i) for some PRL(i), hosts reset TIMER(i) to schedule
the next solicitation event (see: Section 7.3.4.1). Let
"MIN_LIFETIME" be the minimum value in the router lifetime or the
lifetime(s) encoded in options included in the RA message. Then,
TIMER(i) is reset as follows:
TIMER(i) = MAX((0.5 * MIN_LIFETIME), MinRouterSolicitInterval)
7.3.4.3 Stateful Autoconfiguration
If stateful autoconfiguration is invoked ([RFC2462], sections 5.5.2,
5.5.3), the "ALL_DHCP_Relay_Agents_and_Servers" multicast address
([DHCPV6], section 5.1) is resolved to the link-local ISATAP address
constructed from V4ADDR(i) for some PRL(i).
8. Deployment Considerations
Hosts may enable ISATAP, e.g., when native IPv6 service is
unavailable. When native IPv6 service is acquired, hosts SHOULD
discontinue the ISATAP router solicitation process (Section 7.3.4)
and/or allow associated state to expire (see: [RFC2461], section 5.3
and [RFC2462], section 5.5.4). Any associated addresses added to the
DNS should also be removed.
Routers MAY configure both native IPv6 and ISATAP interfaces over the
same physical link. The prefixes used on each interface will be
distinct, and normal IPv6 routing between the interfaces may occur.
9. Site Administration Considerations
ISATAP sites are administratively defined by a set of advertising
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interfaces and set of nodes that solicit those interfaces. Thus,
ISATAP sites are defined by administrative (not physical) boundaries.
Site administrators maintain a list of IPv4 addresses representing
advertising ISATAP interfaces and make them available via one or more
of the mechanisms described in Section 7.3.1. Responsible
administration can reduce control traffic overhead.
10. IANA Considerations
Modifications to the IANA "ethernet-numbers" registry (e.g., based on
text in Appendix B) are requested.
11. Security considerations
ISATAP site border routers and firewalls MUST implement IPv6 and IPv4
ingress filtering, including ip-protocol-41 filtering. Packets with
local-use source and/or destination addresses MUST NOT be forwarded
outside of the site.
Even with IPv4 and IPv6 ingress filtering, reflection attacks can
originate from compromised nodes within an ISATAP site that spoof
IPv6 source addresses. Security mechanisms for reflection attack
mitigation SHOULD be used in routers with advertising ISATAP
interfaces. At a minimum, border gateways SHOULD log potential source
address spoofing cases.
ISATAP addresses do not support privacy extensions for stateless
address autoconfiguration [RFC3041]. 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 is especially true when private address allocations
[RFC1918] are used.)
12. 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
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Troan, Vlad Yasevich.
The authors acknowledge members of the NGTRANS community who have
made significant contributions to this effort, including Rich Draves,
Alain Durand, Nathan Lutchansky, Karen Nielsen, Art Shelest, Margaret
Wasserman, and Brian Zill.
The authors also wish to acknowledge the work of Quang Nguyen [VET]
under the guidance of Dr. Lixia Zhang that proposed very similar
ideas to those that appear in this document. This work was first
brought to the authors' attention on September 20, 2002.
Normative References
[ARCH] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", draft-ietf-ipngwg-addr-arch-v3-11 (work in
progress), October 2002.
[MECH] Gilligan, R. and E. Nordmark, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", draft-ietf-v6ops-mech-v2-00
(work in progress), February 2003.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2461] Narten, T., Nordmark, E. and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December
1998.
[RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[RFC2463] Conta, A. and S. Deering, "Internet Control Message
Protocol (ICMPv6) for the Internet Protocol Version 6
(IPv6) Specification", RFC 2463, December 1998.
[RFC2491] Armitage, G., Schulter, P., Jork, M. and G. Harter, "IPv6
over Non-Broadcast Multiple Access (NBMA) networks", RFC
2491, January 1999.
Informative References
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[DHCPV6] Droms, R., "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress),
November 2002.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G. and
E. Lear, "Address Allocation for Private Internets", BCP
5, RFC 1918, February 1996.
[RFC2022] Armitage, G., "Support for Multicast over UNI 3.0/3.1
based ATM Networks", RFC 2022, November 1996.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
[RFC2362] Estrin, D., Farinacci, D., Helmy, A., Thaler, D., Deering,
S., Handley, M. and V. Jacobson, "Protocol Independent
Multicast-Sparse Mode (PIM-SM): Protocol Specification",
RFC 2362, June 1998.
[RFC2710] Deering, S., Fenner, W. and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710, October
1999.
[RFC3041] Narten, T. and R. Draves, "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6", RFC 3041,
January 2001.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[VET] Nguyen, Q., "http://irl.cs.ucla.edu/vet/report.ps", spring
1998.
Authors' Addresses
Fred L. Templin
Nokia
313 Fairchild Drive
Mountain View, CA 94110
US
Phone: +1 650 625 2331
EMail: ftemplin@iprg.nokia.com
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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
One Microsoft Way
Redmond, WA> 98052-6399
US
Phone: +1 425 705 3131
EMail: mohitt@microsoft.com
Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
US
Phone: +1 425 703 8835
EMail: dthaler@microsoft.com
Appendix A. Major Changes
changes from version 12 to version 13:
o Added comments from co-authors
o Text cleanup; removed extraneous text
o Revised ISATAP interface/link terminology
o Returned to using symbolic reference names
o Revised MTU section; moved non-normative MTU text to seperate
document
changes from earlier versions to version 12:
o Added multicast/anycast subsection
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o Revised PRL initialization
o Updated neighbor discovery, security consideration sections
o Rearranged/revised sections 5, 6, 7
o Added stateful autoconfiguration mechanism
o Normative references to RFC 2491, RFC 2462
o Moved non-normative MTU text to appendix C
o clarified address resolution, Neighbor Unreachability Detection
o specified MTU/MRU requirements
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
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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
Thus, if TYPE=0xFE, TSE is an extension of TSD. If TYPE=0xFF, TSE is
an extension of TYPE. Other values for TYPE (thus, other
interpretations of TSE, TSD) are reserved for future IANA use.
The above specification is compatible with all aspects of EUI64,
including support for encapsulating legacy EUI-48 interface
identifiers (e.g., an IANA EUI-48 format multicast address such as:
'01-00-5E-01-02-03' is encapsulated as: '01-00-5E-FF-FE-01-02-03').
But, the specification also provides a special TYPE (0xFE) to
indicate an IPv4 address is embedded. Thus, when the first four
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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.
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Internet-Draft ISATAP March 2003
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