draft-ietf-ngtrans-isatap-00.txt   draft-ietf-ngtrans-isatap-01.txt 
INTERNET-DRAFT Fred L. Templin INTERNET-DRAFT Fred L. Templin
SRI International SRI International
12 March 2001 17 May 2001
Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)
(Formerly: Connecting IPv6 Nodes within IPv4 Sites)
Copyright Notice Copyright Notice
Placeholder for ISOC copyright. Placeholder for ISOC copyright.
draft-ietf-ngtrans-isatap-00.txt draft-ietf-ngtrans-isatap-01.txt
Abstract Abstract
This document specifies a method for connecting IPv6 hosts and This document specifies an intra-site automatic tunneling protocol
routers (nodes) within predominantly IPv4-based sites. This method is (ISATAP) for connecting IPv6 hosts and routers (nodes) within
based on an IPv6-IPv4 compatibility aggregatable global unicast predominantly IPv4-based networks. This method is based on an IPv6
address format (described herein) that embeds the IPv4 address of a aggregatable global unicast address format (described herein) that
node within the EUI-64 format interface identifier of an IPv6 embeds the IPv4 address of a node within the EUI-64 format interface
address. This document assumes that, during the IPv4 to IPv6 co- identifier. This document assumes that, during the IPv4 to IPv6 co-
existence and transition phase, many sites will deploy IPv6 existence and transition phase, many sites will deploy IPv6
incrementally within their IPv4 interior routing domains; especially incrementally within their IPv4 interior routing domains; especially
those sites which have large and complex pre-existing IPv4 those sites which have large and complex pre-existing IPv4
infrastructures. Within such sites, the address format and methods infrastructures. Within such sites, the address format and methods
described in this document will enable IPv6 deployment for nodes that described in this document will enable IPv6 deployment for nodes that
do not share a common multiple access datalink with an IPv6 gateway do not share a common data link with an IPv6 gateway for their site.
within their site.
While other works in progress in the NGTRANS working group propose While other works in progress in the NGTRANS working group propose
mechanisms for assigning globally-unique IPv6 address prefixes to mechanisms for assigning globally-unique IPv6 address prefixes to
sites and methods for inter-domain routing between such sites, the sites and methods for inter-domain routing between such sites, the
approach outlined in this memo enables large-scale incremental approach outlined in this memo enables large-scale incremental
deployment of IPv6 for nodes within a site's pre-existing IPv4 deployment of IPv6 for nodes within a site's pre-existing IPv4
infrastructure without incurring aggregation scaling issues at the infrastructure without incurring aggregation scaling issues at the
border gateways nor requiring site-wide deployment of special IPv4 border gateways nor requiring site-wide deployment of special IPv4
services such as multicast. The approach proposed by this document services such as multicast. The approach proposed by this document
supports IPv6 routing within both the site-local and global IPv6 supports IPv6 routing within both the site-local and global IPv6
routing domains as well as automatic IPv6 in IPv4 tunneling across routing domains as well as automatic IPv6 in IPv4 tunneling across
portions of a site's IPv4 infrastructure which have no native IPv6 portions of a site's IPv4 infrastructure which have no native IPv6
support. Moreover, this approach supports automatic tunneling within support. Additionally, this approach supports automatic tunneling
sites which use non globally-unique IPv4 address assignments, such as within sites which use non globally-unique IPv4 address assignments,
when Network Address Translation [NAT] is used. such as when Network Address Translation [NAT] is used.
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
skipping to change at page 2, line 27 skipping to change at page 2, line 25
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
1. Introduction 1. Introduction
The IETF NGTRANS working group anticipates an heterogeneous IPv4/IPv6 The IETF NGTRANS working group anticipates an heterogeneous IPv4/IPv6
infrastructure in the near future and thus is chartered to develop infrastructure in the near future and thus is chartered to develop
mechanisms to support IPv4/IPv6 coexistence and transition toward mechanisms to support IPv4/IPv6 coexistence and transition toward
global IPv6 deployment. For the most part, existing NGTRANS global IPv6 deployment. For the most part, existing NGTRANS
approaches focus on inter-domain routing between IPv6 "islands" using approaches focus on inter-domain routing between IPv6 islands using
the existing global IPv4 backbone as transit. But, these islands may the existing global IPv4 backbone as transit. But, these islands may
themselves consist of complex heterogeneous IPv4/IPv6 networks (e.g. themselves comprise complex heterogeneous IPv4/IPv6 networks (e.g.
large academic or commercial campus "intranets") that require intra- large academic or commercial campus intranets) that require intra-
domain IPv4 to IPv6 transition mechanisms and strategies as well. In domain IPv4 to IPv6 transition mechanisms and strategies as well. In
order to address this requirement, this document presents a simple order to address this requirement, this document presents a simple
and scalable approach that enables incremental intra-site deployment and scalable approach that enables incremental deployment of IPv6
of IPv6 nodes within predominantly IPv4-based intranets. nodes within predominantly IPv4-based intranets. We refer to this
approach as the Intra-Site Automatic Tunnel Addressing Protocol, or
ISATAP (pronounced: "ice-a-tap").
The approach outlined in this document is based on a new aggregatable The ISATAP approach is based on an aggregatable global unicast
global unicast address format that carries a standard 64-bit IPv6 address format that carries a standard 64-bit IPv6 address prefix
address prefix [ADDR][AGGR] with a specially-constructed 64-bit EUI- [ADDR][AGGR] with a specially-constructed 64-bit EUI-64 Interface
64 Interface Identifier [EUI64]. The 64-bit address prefix used by Identifier [EUI64]. This address format is fully compatible with
this format is fully compatible with all existing and emerging prefix both native IPv6 and NGTRANS routing practices (e.g. [6to4],[6BONE]).
assignment and inter-domain routing practices (e.g. [6to4],[6BONE]). But, the interface identifier in an ISATAP address employs a special
But, the interface identifier employs a special construction using construction (using the IEEE Organizationally Unique Identifier (OUI)
the IEEE Organizationally Unique Identifier (OUI) reserved by the reserved by the Internet Assigned Numbers Authority [IANA]) that
Internet Assigned Numbers Authority [IANA] along with a "type" field encapsulates an IPv4 address suitable for automatic IPv6-in-IPv4 tun-
to indicate that the identifier encapsulates an IPv4 address suitable neling. Since tunneling occurs only within the site-level prefix of
for automatic intra-domain IPv6-in-IPv4 tunneling. As such, the the ISATAP address, the embedded IPv4 address NEED NOT be globally
embedded IPv4 address NEED NOT be globally unique; rather, it need unique; rather, it need only be topologically correct for (and unique
only be topologically correct for (and unique within) the context of within) the context of the site.
that site.
This approach allows dual-stack nodes that do not share a common This approach allows dual-stack nodes that do not share a common
multiple access datalink with an IPv6 gateway to join the global IPv6 datalink with an IPv6 gateway to join the global IPv6 network by
network by automatically tunneling IPv6 messages through the IPv4 automatically tunneling IPv6 messages through the IPv4 routing
routing infrastructure within the site. Two methods for automatic infrastructure within their site. Two methods for automatic discovery
discovery of an off-link IPv6 gateway within the site are provided. of an off-link IPv6 gateway for ISATAP address autoconfiguration are
This approach allows large-scale intra-site deployment without incur- provided. This approach allows large-scale intra-site deployment
ring aggregation scaling issues at the border gateways, since only a without incurring aggregation scaling issues at the border gateways,
single IPv6 address prefix is used for the entire site. Finally, this since only a single IPv6 address prefix is used for the entire site.
approach supports intranets which use non-globally unique IPv4 Finally, this approach supports intranets which use non-globally
addresses, such as when private address allocations [PRIVATE] and/or unique IPv4 addresses, such as when private address allocations
Network Address Translation [NAT] are used; even when multiple levels [PRIVATE] and/or Network Address Translation [NAT] are used.
of NAT occur within a given site.
In the following sections, we present our proposed IPv6-IPv4 compati-
bility address format in detail. We further discuss technical con-
siderations for the application of IPv6-IPv4 compatibility addresses
to facilitate incremental deployment of IPv6 within predominantly
IPv4-based Intranets.
2. Changes 2. Changes
Major changes from version 01 to version 02: Major changes from version -00 to version -01:
- Revised draft to require *different* /64 prefixs 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.)
Major changes from version personal draft to NGTRANS WG version -00:
- Title change to provide higher-level description of field of - Title change to provide higher-level description of field of
use addressed by this draft. Removed other extraneous text. use addressed by this draft. Removed other extraneous text.
- Major new section on automatic discovery of off-link IPv6 routers - Major new section on automatic discovery of off-link IPv6 routers
when IPv6-IPv4 compatibility addresses are used. when IPv6-IPv4 compatibility addresses are used.
3. IPv6-IPv4 Compatibility Address Format 3. Terminology
In sections 3.1 and 3.2, we will motivate our proposed extensions of The terminology of [IPv6] applies to this document. Additionally, the
following terms are used extensively throughout this document:
ISATAP prefix:
Any globally aggregatable 64-bit IPv6 routing prefix (whether from a
native IPv6 assigned numbers authority or from a special-purpose numbering
scheme such as [6BONE][6TO4]) reserved by a local network administrator
specifically for ISATAP purposes. ISATAP prefixes are used to configure
ISATAP addresses ONLY; native IPv6 addresses SHOULD NOT be configured
using an ISATAP prefix.
ISATAP address:
An IPv6 address with an ISATAP prefix and having an IPv4 address
embedded in the interface identifier in the manner described in
section 4 below.
ISATAP pseudo-interface:
ISATAP encapsulation of IPv6 packets inside IPv4 packets occurs
at a point that is logically equivalent to an IPv6 interface,
with the link layer being the IPv4 unicast network. This point
is referred to as a pseudo-interface. An ISATAP pseudo-interface
is assigned an ISATAP address through address autoconfiguration.
ISATAP router:
An IPv6 router supporting an ISATAP pseudo-interface. It is normally
an interior router within an heterogeneous IPv6/IPv4 network.
ISATAP host:
An IPv6 host which has an ISATAP pseudo-interface.
4. ISATAP Address Format
In sections 4.1 and 4.2, we will motivate our proposed extensions of
the existing IEEE OUI reserved by IANA to support IEEE EUI-64 format the existing IEEE OUI reserved by IANA to support IEEE EUI-64 format
addresses. While these proposed extensions are necessary to support addresses. While these proposed extensions are intended support the
our IPv6-IPv4 compatibility address format, they also provide a flex- ISATAP address format, they also provide a flexible framework for
ible framework for future IANA use. Therefore, we believe the exten- future IANA use. Therefore, the extensions proposed in sections 4.1
sions proposed in sections 3.1 and 3.2 may provide beneficial future and 4.2 may provide beneficial future use to IANA beyond the scope of
use to the IANA beyond the scope of IPv6-IPv4 compatibility ISATAP addresses. We present the ISATAP address format itself in sec-
addresses. We present our IPv6-IPv4 compatibility address format pro- tions 4.3 and 4.4.
posal in sections 3.3 and 3.4 and conclude this section with some
notes on deployment considerations.
3.1. IEEE EUI-64 Interface Identifiers in IPv6 Addresses 4.1. IEEE EUI-64 Interface Identifiers in IPv6 Addresses
IPv6 aggregatable global and local-use unicast addresses [ADDR] IPv6 aggregatable global and local-use unicast addresses [ADDR]
include a 64-bit interface identifier in IEEE EUI-64 format [EUI64], include a 64-bit interface identifier in IEEE EUI-64 format [EUI64],
which is specified as the concatenation of a 24-bit company_id value which is specified as the concatenation of a 24-bit company_id value
(also known as the OUI) assigned by the IEEE Registration Authority (also known as the OUI) assigned by the IEEE Registration Authority
(IEEE/RAC) and a 40-bit extension identifier assigned by the organi- (IEEE/RAC) and a 40-bit extension identifier assigned by the address-
zation owning that OUI. IEEE EUI-64 interface identifiers are for- ing authority for that OUI. (Normally, the addressing authority is
matted as follows: the organization to which the IEEE has allocated the OUI). IEEE EUI-
64 interface identifiers are formatted as follows:
|0 1|1 3|3 4|4 6| |0 1|1 3|3 4|4 6|
|0 5|6 1|2 7|8 3| |0 5|6 1|2 7|8 3|
+----------------+----------------+----------------+----------------+ +----------------+----------------+----------------+----------------+
|ccccccugcccccccc|ccccccccmmmmmmmm|mmmmmmmmmmmmmmmm|mmmmmmmmmmmmmmmm| |ccccccugcccccccc|ccccccccmmmmmmmm|mmmmmmmmmmmmmmmm|mmmmmmmmmmmmmmmm|
+----------------+----------------+----------------+----------------+ +----------------+----------------+----------------+----------------+
Where 'c' are the company-specific bits of the OUI, 'u' is the Where 'c' are the company-specific bits of the OUI, 'u' is the
universal/local bit, 'g' is the individual/group bit and 'm' are the universal/local bit, 'g' is the individual/group bit and 'm' are the
extension identifier bits. (NOTE: [ADDR] specifies that the 'u' bit extension identifier bits. (NOTE: [ADDR] specifies that the 'u' bit
is inverted from its normal sense in the IEEE context; therefore u=1 is inverted from its normal sense in the IEEE context; therefore u=1
indicates global scope and u=0 indicates local scope). indicates global scope and u=0 indicates local scope).
In order to support encapsulation of legacy IEEE EUI-48 (24-bit) In order to support encapsulation of legacy IEEE EUI-48 (24-bit)
extension identifier values, [EUI64] specifies that the first two extension identifier values, [EUI64] specifies that the first two
octets of the EUI-64 40-bit extension identifier (bits 24 through 39 octets of the EUI-64 40-bit extension identifier (bits 24 through 39
of the EUI-64 address itself) SHALL BE 0xFFFE if the extension iden- of the EUI-64 address itself) SHALL BE 0xFFFE if the extension iden-
tifier encapsulates an EUI-48 value. [EUI64] further specifies that tifier encapsulates an EUI-48 value. [EUI64] further specifies that
the first two octets of the extension identifier SHALL NOT be 0xFFFF, the first two octets of the extension identifier SHALL NOT be 0xFFFF,
as this value is reserved by the IEEE/RAC. However, all other 40-bit since this value is reserved by the IEEE/RAC. However, all other 40-
extension identifier values are available for assignment by the bit extension identifier values are available for assignment by the
addressing authority responsible for a given OUI. OUI addressing authority.
3.2. An EUI-64 Interface Identifier Format for IANA 4.2. An EUI-64 Interface Identifier Format for IANA
The IANA owns IEEE OUI: 0x00005E (also written as: 00-00-5E), and The IANA owns IEEE OUI: 00-00-5E, and [IANA] specifies EUI-48 format
[IANA] specifies EUI-48 format (24-bit) interface identifier assign- (24-bit) interface identifier assignments within that OUI. But,
ments within that OUI. But, [IANA] does not specify how these legacy [IANA] does not specify how these legacy EUI-48 assignments will be
EUI-48 assignments will be written in EUI-64 format, nor does it written in EUI-64 format, nor does it specify a format for future
specify a format for future 40-bit extension identifier assignments. 40-bit extension identifier assignments. We propose the following
We propose the following format for EUI-64 addresses within IANA's format for EUI-64 addresses within IANA's OUI reservation:
OUI reservation:
|0 2|2 3|3 3|4 6| |0 2|2 3|3 3|4 6|
|0 3|4 1|2 9|0 3| |0 3|4 1|2 9|0 3|
+------------------------+--------+--------+------------------------+ +------------------------+--------+--------+------------------------+
| OUI ("00-00-5E"+u+g) | TYPE | TSE | TSD | | OUI ("00-00-5E"+u+g) | TYPE | TSE | TSD |
+------------------------+--------+--------+------------------------+ +------------------------+--------+--------+------------------------+
Where the fields are: Where the fields are:
OUI IANA's OUI: 00-00-5E with 'u' and 'g' bits (3 octets) OUI IANA's OUI: 00-00-5E with 'u' and 'g' bits (3 octets)
skipping to change at page 5, line 32 skipping to change at page 6, line 15
TYPE (TSE, TSD) Interpretation TYPE (TSE, TSD) Interpretation
---- ------------------------- ---- -------------------------
0x00-0xFD RESERVED for future IANA use 0x00-0xFD RESERVED for future IANA use
0xFE (TSE, TSD) together contain an embedded IPv4 address 0xFE (TSE, TSD) together contain an embedded IPv4 address
0xFF TSD is interpreted based on TSE as follows: 0xFF TSD is interpreted based on TSE as follows:
TSE TSD Interpretation TSE TSD Interpretation
--- ------------------ --- ------------------
0x00-0xFD RESERVED for future IANA use 0x00-0xFD RESERVED for future IANA use
0xFE TSD contains 24-bit EUI-48 intf identif- 0xFE TSD contains 24-bit EUI-48 intf id
ier
0xFF RESERVED by IEEE/RAC 0xFF RESERVED by IEEE/RAC
Essentially, if TYPE=0xFE, TSE is treated as an extension of TSD. If Essentially, if TYPE=0xFE, TSE is treated as an extension of TSD. If
TYPE=0xFF, TSE is treated as an extension of TYPE. Other values for TYPE=0xFF, TSE is treated as an extension of TYPE. Other values for
TYPE (and hence, other interpretations of TSE, TSD) are reserved for TYPE (and hence, other interpretations of TSE, TSD) are reserved for
future IANA use. This format conforms to all requirements specified future IANA use. This format conforms to all requirements specified
in [EUI64] and supports encapsulation of EUI-48 interface identifiers in [EUI64] and supports encapsulation of EUI-48 interface identifiers
in the manner described by that document. For example, an existing in the manner described by that document. For example, an existing
IANA EUI-48 format multicast address such as: IANA EUI-48 format multicast address such as:
01-00-5E-01-02-03 01-00-5E-01-02-03
would be written in the IANA EUI-64 format as: would be written in the IANA EUI-64 format as:
01-00-5E-FF-FE-01-02-03 01-00-5E-FF-FE-01-02-03
But, this proposed format also provides a special TYPE (0xFE) for But, this proposed format also provides a special TYPE (0xFE) for
embedding IPv4 addresses within the IANA 40-bit extension identifier. embedding IPv4 addresses within the IANA 40-bit extension identifier.
This special TYPE forms the basis for the ISATAP address format as
described in the following sections.
This special TYPE forms the basis for our IPv6-IPv4 compatibility 4.3. ISATAP Address Construction
aggregatable global unicast address format proposal as described in
the following sections.
3.3. IPv6-IPv4 Compatibility Address Construction
Using the proposed IANA-specific method for interface identifier con- Using the proposed IANA-specific method for interface identifier con-
struction discussed in sections 3.1 and 3.2 (with TYPE=0xFE), and struction discussed in sections 4.1 and 4.2 (with TYPE=0xFE), and
with reference to [ADDR], we can construct IPv6-IPv4 compatibility with reference to [ADDR], we can construct an ISATAP address as fol-
aggregatable global unicast addresses. Using this methodology, we lows:
propose an IPv6 address format with embedded IPv4 address in the
EUI-64 interface identifier. The following diagram shows the con-
struction:
| 3| 13 | 8 | 24 | 16 | 8 | 8 | 8 | 8 | 32 bits | | 3| 13 | 8 | 24 | 16 | 8 | 8 | 8 | 8 | 32 bits |
+--+-----+---+--------+--------+---+---+---+---+---+---+---+----+ +--+-----+---+--------+--------+---+---+---+---+---+---+---+----+
|FP| TLA |RES| NLA | SLA | 0x| 0x| 0x| 0x| IPv4 Address | |FP| TLA |RES| NLA | SLA | 0x| 0x| 0x| 0x| IPv4 Address |
| | ID | | ID | ID | 02| 00| 5E| FE| of Endpoint | | | ID | | ID | ID | 00| 00| 5E| FE| of Endpoint |
+--+-----+---+--------+--------+--------------------------------+ +--+-----+---+--------+--------+--------------------------------+
(NOTE: the least significant octet of the OUI in the interface iden- (NOTE: since ISATAP address interface identifiers are interpreted
tifier is 0x02 instead of 0x00 since u=1 for global scope.) only within the local scope of the /64 ISATAP prefix, we set the u/l
bit in the least significant octet of the OUI to '0' to indicate
local scope.)
By way of example, an existing node with IPv4 address 140.173.129.8 By way of example, an existing node with IPv4 address 140.173.129.8
might be assigned an IPv6 64-bit prefix of 3FFE:1a05:510:200::/64. We might be assigned an IPv6 64-bit prefix of 3FFE:1a05:510:200::/64. We
can then construct an IPv6-IPv4 compatibility aggregatable global can then construct an ISATAP address for this node as:
unicast address for this node as:
3FFE:1a05:510:200:0200:5EFE:8CAD:8108 3FFE:1a05:510:200:0:5EFE:8CAD:8108
or (perhaps more appropriately) written as the alternative form for or (perhaps more appropriately) written as the alternative form for
an IPv6 address with embedded IPv4 address found in [ADDR]: an IPv6 address with embedded IPv4 address found in [ADDR]:
3FFE:1a05:510:200:0200:5EFE:140.173.129.8 3FFE:1a05:510:200:0:5EFE:140.173.129.8
Similarly, we can construct the link-local and site-local variants Similarly, we can construct the link-local and site-local variants
(respectively) of the IPv6-IPv4 compatibility address as: (respectively) of the ISATAP address as:
FE80::0200:5EFE:140.173.129.8 FE80::0:5EFE:140.173.129.8
FEC0::200:0200:5EFE:140.173.129.8 FEC0::200:0:5EFE:140.173.129.8
3.4. Advantages 4.4. Advantages
By embedding an IPv4 address in the interface identifier portion of By embedding an IPv4 address in the interface identifier portion of
an IPv6 address as described in section 3.3, we can construct aggre- an IPv6 address as described in section 4.3, we can construct aggre-
gatable global unicast IPv6 addresses that can either be routed gatable global unicast IPv6 addresses that can either be routed glo-
globally via the IPv6 infrastructure or automatically tunneled bally via the IPv6 infrastructure or automatically tunneled locally
locally across portions of a site's IPv4 infrastructure which have no across portions of a site's IPv4 infrastructure which have no native
native IPv6 routing support. Thus the addressing scheme supports IPv6 support. Additionally, a node with an ISATAP address could act
heterogeneous IPv6/IPv4 infrastructures in transition with incremen- as a gateway for nodes with native IPv6 addresses with which it
tal deployment of IPv6 at the site level. Additionally, a node with shares a common physical link, since the ISATAP node could automati-
such an IPv6-IPv4 compatibility address could act as a gateway for cally tunnel messages across a site's IPv4 domain on behalf of the
nodes with native IPv6 addresses connected to the same link, since it native IPv6 nodes. An example would be deployment of IPv6 on some
could automatically tunnel messages across a site's IPv4 domain to subset of the hosts attached to a workgroup's LAN. In this case, one
reach a border IPv6 gateway for the site on behalf of such native host could configure an ISATAP address and act as a gateway for other
IPv6 nodes. An example would be deployment of IPv6 on some subset of hosts on the LAN which use native IPv6 addresses.
the hosts attached to a workgroup's Ethernet LAN. In this case, one
host would receive an IPv6-IPv4 compatibility address and act as a
gateway for the other hosts which receive native IPv6 addresses.
An additional advantage for our proposed method of embedding an IPv4 An additional advantage for our proposed method of embedding an IPv4
address in the interface identifier portion of an IPv6 address not address in the interface identifier portion of an IPv6 address not
found in other approaches such as [6TO4] is that large numbers of found in other approaches such as [6TO4] is that large numbers of
IPv6-IPv4 compatibility addresses could be assigned within a common ISATAP addresses could be assigned within a common IPv6 routing pre-
IPv6 routing prefix, thus providing maximal aggregation at the border fix, thus providing maximal aggregation at the border gateways. For
gateways. For example, the single 64-bit IPv6 prefix: example, the single 64-bit IPv6 prefix:
3FFE:1a05:510:2412::/64 3FFE:1a05:510:2412::/64
could include literally millions of nodes with IPv6-IPv4 compatibil- could include literally millions of nodes with ISATAP addresses.
ity addresses. This feature would allow a "sparse mode" IPv6 deploy-
ment such as the deployment of sparse populations of IPv6 hosts on This feature would allow a "sparse mode" IPv6 deployment such as the
large numbers of independent links throughout a large corporate deployment of sparse populations of IPv6 hosts on large numbers of
Intranet. independent links throughout a large corporate Intranet.
A final important advantage is that this method supports both sites A final important advantage is that this method supports both sites
that use globally unique IPv4 address assignments and those that use that use globally unique IPv4 address assignments and those that use
non-globally unique IPv4 addresses, such as when private address non-globally unique IPv4 addresses, such as when private address
assignments and/or Network Address Translation are used. By way of assignments and/or Network Address Translation are used. By way of
analogy to the US Postal system, inter-domain transition approaches analogy to the US Postal system, inter-domain transition approaches
such as [6TO4] provide means for routing messages "cross-country" to such as [6TO4] provide means for routing messages "cross-country" to
the "street address" of a distant site while the approach outlined in the "street address" of a distant site while the approach outlined in
this document provides localized routing information to reach a this document provides localized routing information to reach a
specific (mailstop, apartment number, post office box, etc) WITHIN specific (mailstop, apartment number, post office box, etc) WITHIN
that site. Thus, the site-level routing information need not have that site. Thus, the site-level routing information need not have
relevance outside the scope of that site. relevance outside the scope of that site.
3.5. Deployment Considerations 5. ISATAP Deployment Considerations
IPv6-IPv4 compatibility addresses should only be used by nodes which
do not share a common multiple access datalink with an IPv6 router
for their site. But, there are numerous cases in which such "iso-
lated" nodes may occur within an heterogeneous IPv6/IPv4 Intranet.
Two such examples are:
- A researcher wishes to run IPv6 on his existing IPv4-based works-
tation. One or more IPv6 routers are configured within the
researchers site, but the network administrators have not yet con-
figured an IPv6 router for the LAN that connects the researcher's
workstation.
- A network administrator within a large corporate network wishes ISATAP addresses should only be used by nodes which do not share a
to configure IPv6 on the existing IPv4 subnets under their jurisd- common datalink with a native IPv6 router. At least one ISATAP router
iction, but these subnets are separated from the IPv6 border gate- must be configured within the site which advertises an
way for the corporation by other IPv4 subnets which are not ready administratively- assigned ISATAP prefix in response to an Rtsol mes-
for IPv6 deployment. sage from an off-link host. Such off-link hosts will configure an
ISATAP pseudo-interface and assign it an address using the ISATAP
prefix it receives in an Rtadv message solicited from an ISATAP
router.
In both examples, intra-site IPv6-in-IPv4 tunneling can be used to Following ISATAP address configuration, ISATAP hosts automatically
span the "gaps" in IPv6 coverage. The IPv6-IPv4 compatibility address and transparently communicate the IPv4 address of their *own* end of
format described in the previous subsections provides a means for the ISATAP tunnel to any ISATAP host or router which uses the same
isolated nodes to automatically and transparently communicate the ISATAP prefix. While nodes may optionally use stateful configuration
IPv4 address of their *own* end of the tunnel to an off-link IPv6 to set an ISATAP prefix and a "default" route that points to an ISA-
gateway. While such nodes may optionally use stateful configuration TAP router, a greatly preferred alternative is to provide for
to set a "default" route that points to the off-link gateway, a automatic intra-site IPv6 router discovery and stateless address
greatly preferred alternative is to provide for automatic intra-site autoconfiguration [DISCUSS]. The following section presents a means
IPv6 router discovery and stateless address autoconfiguration [DIS- for the automatic discovery of ISATAP routers.
CUSS]. The following section presents a means for the automatic
discovery of off-link IPv6 routers.
4. Automatic Discovery of Off-link IPv6 Routers 5.1. Automatic Discovery of ISATAP Routers
As described in [AUTO], a node that does not share a common multiple As described in [AUTO], a node that does not share a common multiple
access datalink with an IPv6 router will NOT receive unsolicited access datalink with an IPv6 router will NOT receive unsolicited
Router Advertisements (Rtadv's), nor will Router Solicitations Router Advertisements (Rtadv's), nor will Router Solicitations
(Rtsol's) from that node reach an IPv6 router on the local link. (Rtsol's) from that node reach an IPv6 router on the local link. But,
Hence, a means for off-link IPv6 router discovery is required. We the node may still be able to connect to the global IPv6 Internet if
present the following procedure for a node to initiate off-link IPv6 an ISATAP router for the site exists. Hence, a means for ISATAP
router discovery (and for an off-link IPv6 router to respond) when router discovery is required. We present the following procedure for
IPv6-IPv4 compatibility addresses are used: a node to initiate ISATAP router discovery (and for an ISATAP router
to respond) when an on-link IPv6 router is not available:
- The node constructs an IPv6-IPv4 compatibility link local address - The node constructs an ISATAP link local address for itself
for itself (as described in section 3.) as: (as described in section 4.) as:
FE80::0200:5EFE:V4ADDR_NODE FE80::0:5EFE:V4ADDR_NODE
- The node discovers the IPv4 address for an off-link IPv6 router - The node discovers the IPv4 address for an ISATAP router
as: V4ADDR_RTR (**) as: V4ADDR_RTR (**)
- The node sends an Rtsol to the IPv6 "all-routers-multicast" address - The node sends an Rtsol to the IPv6 "all-routers-multicast" address
tunneled through the IPv4 infrastructure to the off-link IPv6 router's tunneled through the IPv4 infrastructure to the ISATAP router's
IPv4 address. The addresses used in the IPv6 and IPv4 headers are: IPv4 address. The addresses used in the IPv6 and IPv4 headers are:
ipv6_src: FE80::0200:5EFE:V4ADDR_NODE ipv6_src: FE80::0:5EFE:V4ADDR_NODE
ipv6_dst: FF02::2 ipv6_dst: FF02::2
ipv4_src: V4ADDR_NODE ipv4_src: V4ADDR_NODE
ipv4_dst: V4ADDR_RTR ipv4_dst: V4ADDR_RTR
- Upon receiving the tunneled Rtsol, the off-link IPv6 router sends - Upon receiving the tunneled Rtsol, the ISATAP router sends
a unicast Rtadv to the unicast address of the node which sent the a unicast Rtadv to the unicast address of the node which sent the
Rtsol; again, by tunneling the Rtadv through IPv4. The addresses Rtsol; again, by tunneling the Rtadv through IPv4. The addresses
used in the IPv6 and IPv4 headers are: used in the IPv6 and IPv4 headers are:
ipv6_src: FE80::0200:5EFE:V4ADDR_RTR ipv6_src: FE80::0:5EFE:V4ADDR_RTR
ipv6_dst: FE80::0200:5EFE:V4ADDR_NODE ipv6_dst: FE80::0:5EFE:V4ADDR_NODE
ipv4_src: V4ADDR_RTR ipv4_src: V4ADDR_RTR
ipv4_dst: V4ADDR_NODE ipv4_dst: V4ADDR_NODE
- Upon receiving the Rtsol, the originating node performs address - Upon receiving the Rtsol, the originating node performs address
autoconfiguration as described in [AUTO] and constructs: autoconfiguration as described in [AUTO] and constructs:
- a fully-qualified IPv6-IPv4 compatibility address for use as - a fully-qualified ISATAP address for use as the source address
the source address for IPv6 packets for an ISATAP pseudo-interface
- a default route that points to the off-link IPv6 router's - a default route that points to the ISATAP router
IPv6-IPv4 compatibility link-local address
Note (**) that the above procedure assumes a means for discovering Note (**) that the above procedure assumes a means for discovering
V4ADDR_RTR. We present two alternative methods for the automatic V4ADDR_RTR. We present two alternative methods for the automatic
discovery of V4ADDR_RTR: discovery of V4ADDR_RTR:
4.1. DNS Well-Known Service Name 5.2. DNS Well-Known Service Name
The first method for discovering V4ADDR_RTR employs a new DNS Well- The first method for discovering V4ADDR_RTR employs a new DNS Well-
Known Service (WKS) name [DNS1,DNS2]. With the establishment of a new Known Service (WKS) name [DNS1,DNS2]. With the establishment of a new
well-known service name (e.g. "V6V4GW"), administrators could publish well-known service name (e.g. "ISATAPGW"), administrators could pub-
the IPv4 address of a gateway which implementations could use to lish the IPv4 address of a gateway which implementations could use to
discover V4ADDR_RTR. This method has the advantage that it can be discover V4ADDR_RTR. This method has the advantage that it can be
deployed immediately using existing mechanisms. However, it requires deployed immediately using existing mechanisms. However, it requires
name service lookups and may not always provide the optimum name service lookups and may not always provide the optimum
V4ADDR_RTR resolution for isolated hosts which use IPv6-IPv4 compati- V4ADDR_RTR resolution for isolated hosts if multiple ISATAP routers
bility addresses. are available.
4.2. IPv4 Anycast for Intra-domain IPv6 router 5.3. IPv4 Anycast for ISATAP routers
[6TO4ANY] proposes an IPv4 anycast prefix for 6to4 relay routers. [6TO4ANY] proposes an IPv4 anycast prefix for 6to4 relay routers.
The proposal suggests an IPv4 prefix assignment 'x.x.x.0/nn' ('nn' is The proposal suggests an IPv4 prefix assignment 'x.x.x.0/nn' ('nn' is
currently proposed as 16) where the single address 'x.x.x.1' is currently proposed as 16) where the single address 'x.x.x.1' is
assigned as the "6to4 IPv6 relay anycast address". We propose analo- assigned as the "6to4 IPv6 relay anycast address". We propose analo-
gous assignments for the purpose of an "IPv6-IPv4 compatibility gous assignments for the purpose of an "ISATAP router anycast
router anycast address". (Whether the reservation of a second /32 address". (Whether the reservation of a second /32 assignment from
assignment from the 6to4 IPv4 anycast prefix proposed in [6TO4ANY] the 6to4 IPv4 anycast prefix proposed in [6TO4ANY] would be possible,
would be possible, or a separate prefix assignment would be required or a separate prefix assignment would be required is a matter of
is a matter of debate and TBD.) debate and TBD.)
Any IPv6 router capable of providing an IPv6-IPv4 compatibility ISATAP routers would advertise the ISATAP router anycast prefix via
address-based tunnel endpoint as described in the previous sections
would advertise the IPv6-IPv4 compatibility router anycast prefix via
the intra-domain IPv4 routing infrastructure. Isolated IPv6 nodes the intra-domain IPv4 routing infrastructure. Isolated IPv6 nodes
would then use the IPv6-IPv4 compatibility router anycast address as would then use the ISATAP router anycast address as the V4ADDR_RTR
the V4ADDR_RTR IPv4 destination for off-link Rtsol's. This approach IPv4 destination for off-link Rtsol's. This approach has the signifi-
has the significant advantages that: cant advantages that:
- implementations could hard-code the well-known V6V4Compat - implementations could hard-code the well-known ISATAP
anycast address, thus avoiding service discovery via DNS anycast address, thus avoiding service discovery via DNS
- an optimum path to an off-link IPv6 router would be ensured - an optimum path to an ISATAP router would be ensured
by intra-domain IPv4 routing by intra-domain IPv4 routing
As described above, the IPv4 anycast method for locating intra-domain As described above, the IPv4 anycast method for locating ISATAP
routers that support IPv6-IPv4 compatibility address-based tunneling routers provides significant functional advantages over the DNS
provides significant functional advantages over the DNS approach, approach, while the DNS approach can be implemented immediately pend-
while the DNS approach can be implemented immediately pending the ing the registration of a WKS name with IANA. While either method
registration of a WKS name with IANA. While either method will work, will work, the decision of which to push for standardization is TBD
the decision of which to push for standardization is TBD pending dis- pending discussion at upcoming NGTRANS WG meetings.
cussion at upcoming NGTRANS WG meetings.
5. Sending Rules and Routing Considerations
The sending rule for a host or router that sends an IPv6 packet to an
IPv6-IPv4 compatibility destination address is simple and direct:
"If the 64-bit IPv6 prefix of the IPv6-IPv4 compatibility
destination address matches the 64-bit IPv6 prefix of one of my
network interfaces, tunnel the packet through IPv4 - else, route
the packet through IPv6."
From the above rule, a sender that does NOT have an interface which
shares a common 64-bit routing prefix with the packet's IPv6-IPv4
compatibility destination address simply sends the packet to the
next-hop gateway determined by an ordinary IPv6 routing table lookup.
In short, when a sending node does not have an interface which shares
a common 64-bit (site-level) routing prefix with an IPv6-IPv4 compa-
tibility destination address, the sending rule is identical to that
for a native IPv6 destination address. This decision is independent
of whether the sender has an IPv6-IPv4 compatibility address itself,
or whether the sender even comprises a dual-stack configuration.
Indeed, the sender can simply be a native IPv6 node with no legacy
IPv4 support.
When a sender has an interface which shares a common 64-bit routing
prefix with an IPv6-IPv4 compatibility destination address, however,
the sender must assume that the destination is NOT directly reachable
at the datalink level - even though the shared site-level routing
prefix implies otherwise. Instead, if the sender comprises a dual-
stack configuration, it should automatically tunnel the IPv6 packet
(via IPv6-in-IPv4 tunneling as described in [MECH]) to the IPv4
address embedded within the IPv6-IPv4 compatibility destination
address' interface identifier. If the sender is an IPv6-only node
that DOES NOT comprise a dual-stack configuration, however, it has no
means for automatically tunneling the packet via IPv4. In this case:
- If the sender is the host that originates the packet, it should
send the packet to a router that lists the 64-bit prefix in its
router advertisements. If no such router exists, the sender should
drop the packet and return a "No route to host" error indication
to the originating application.
- If the sender is a router that forwards the packet, it should drop
the packet and send an ICMPv6 "Destination Unreachable" message to
the source
By implication, the scheme breaks down if a packet with an IPv6-IPv4
compatibility destination address reaches an IPv6-only router that
has an interface which shares a common 64-bit routing prefix with the
destination address. Additional mechanisms to address this issue
might be possible, such as allowing dual-stack routers to advertise
96-bit prefixes which incorporate the special 32-bit EUI-64 interface
identifier prefix: 0200:5EFE. A sender could then interpret such an
advertisement to mean that the advertising router comprises a dual
stack and is capable of intra-site IPv6-in-IPv4 tunneling. But a
reasonable argument could be made to the effect that:
"By the time IPv6-only routers begin to proliferate throughout a
site, nodes within the site should no longer be using IPv6-IPv4
compatibility addresses."
In fact, the advent of IPv6-only routers within a site would serve as
a strong indication that the site is no longer a predominantly IPv4-
based infrastructure in transition, but rather that the transition is
either complete or nearly complete. Therefore, IPv6-IPv4 compatibil-
ity addresses should no longer be used.
6. Address Selection
Other works in progress ([6TO4] and [SELECT]) have begun to explore
the subject of address selection when multiple IPv6 destination
address alternatives are available. These address selection policies
deal with the 64-bit IPv6 routing prefix and thus can be applied
independently of whether/not the destination address alternatives are
constructed as described in this document. However, in order to
ensure efficient routing within the destination's site, we propose
the following simple "second-tier" address selection policy for deal-
ing with IPv6-IPv4 compatibility addresses:
"If multiple alternatives remain after address selection has been 6. Sending Rules and Routing Considerations
applied on the 64-bit routing prefixes, and if at least one of the
remaining alternatives is constructed with a native IPv6 interface
identifier (one that does NOT contain an embedded IPv4 address as
described in this document), select a native IPv6 address. Other-
wise, select an IPv6-IPv4 compatible address."
This policy decision is in keeping with the concept that NGTRANS Since each node will be assigned an ISATAP prefix which is adminis-
transition mechanisms should remain in place ONLY as long as needed tratively reserved for use ONLY by ISATAP nodes, no special sending
and should be disabled as soon as native IPv6 mechanisms become rules are needed. In particular, correspondent nodes that share a
available. common ISATAP prefix will always exchange messages using their ISATAP
pseudo-interfaces, whereas nodes that do not share a common ISATAP
prefix will always exchange messages via standard IPv6 routing. When
sending a message on an ISATAP pseudo-interface, an implementation
SHOULD verify that the IPv6 destination address employs the ISATAP
address construction rules described in section 4 in order to detect
mis-configured addresses. No other sending rules are necessary.
7. Automatic Deprecation 7. Address Selection
IPv6-IPv4 compatibility addresses constructed in the manner described No special address selection rules are necessary.
in this document are intended for use only by nodes which do not
receive router advertisements due to not sharing a common multiple
access datalink with an IPv6 router. When router advertisements
become available (such as when an IPv6 router is deployed on a common
multiple access datalink shared by the node), the node should discon-
tinue use of its IPv6-IPv4 compatibility address and adopt a normal
aggregatable global IPv4 unicast address using address auto-
configuration [AUTO] for a prefix discovered through normal router
discovery [DISC] means. In this way, IPv6-IPv4 compatibility
addresses will gradually (and automatically) disappear as IPv6
routers become widely deployed within a site.
8. Multicast Considerations 8. Automatic Deprecation
Other works in progress are currently investigating IPv4-mapped mul- ISATAP addresses are intended for use only by nodes which do not
ticast addressing issues. The address format discussed in this docu- receive native IPv6 Rtadv's due to not sharing a common datalink with
ment is expected to be compatible with those emerging approaches. an IPv6 router. When native IPv6 Rtadv's become available (such as
when an IPv6 router is deployed on a node's datalink), the node
should construct a non-ISATAP aggregatable global IPv6 unicast
address using address auto-configuration [AUTO] for a non-ISATAP IPv6
prefix discovered through normal means [DISC]. After the node's
native IPv6 address is populated in the DNS, the node should eventu-
ally cease sending Rtsol's to the ISATAP router and discontinue use
of its ISATAP pseudo-interface. In this way, ISATAP addresses will
gradually (and automatically) disappear as IPv6 routers are widely
deployed within sites.
9. Relation to other works in progress 9. Multicast Considerations
The IPv6-IPv4 compatibility address format and routing policy deci- Other works in progress [6TO4MULTI] are currently investigating mul-
sions presented in this draft evolved from SRI contractual works out- ticast addressing issues for [6TO4]. The address format discussed in
side the scope of the NGTRANS working group. Additionally, the this document is expected to be compatible with those emerging
mechanisms presented in this draft were developed by the author with approaches.
no prior knowledge of the activities in NGTRANS. The author recog-
nizes that other works in progress seek to address very similar
IPv4-IPv6 transition issues as those targeted by this draft. However,
the approach described in this draft presents a number of unique
advantages for NGTRANS that supplement the other works in progress.
(Most specifically, advantages for incremental deployment of IPv6
nodes at the intra-domain level.)
10. IANA considerations 10. IANA considerations
In order to support the EUI-64 address form described in this docu- In order to support the EUI-64 address form described in this docu-
ment, we propose that IANA adopt the EUI-64 Interface Identifier for- ment, we propose that IANA adopt the EUI-64 Interface Identifier for-
mat specified in section 3.2 for the existing 00-00-5E OUI owned by mat specified in section 4.2 for the existing 00-00-5E OUI owned by
IANA. No other actions are required by the IANA. IANA. No other actions are required by the IANA.
11. Security considerations 11. Security considerations
The IPv6-IPv4 compatibility address format does not support privacy The ISATAP address format does not support privacy extensions for
extensions for stateless address autoconfiguration [PRIVACY]. How- stateless address autoconfiguration [PRIVACY]. However, such privacy
ever, such privacy extensions are intended primarily to avoid reveal- extensions are intended primarily to avoid revealing one's MAC
ing one's MAC address, and the IPv6-IPv4 compatibility address format address, and the ISATAP address format described in this document
described in this document accomplishes this same goal. accomplishes this same goal.
Additional security issues are called out in [6TO4] and probably Additional security issues are called out in [6TO4] and probably
apply here as well. apply here as well.
12. Implementation status 12. Implementation status
The author has implemented the mechanisms described in this draft The author has implemented the mechanisms described in this draft
through modifications to the FreeBSD 3.2-RELEASE [FBSD] operating through modifications to the FreeBSD 3.2-RELEASE [FBSD] operating
system with the INRIA [INRIA] IPv6 distribution. These modifications system with the INRIA [INRIA] IPv6 distribution. A Linux implementa-
implement the sending rules and routing considerations as described tion is planned for the June, 2001 timeframe.
in section 5. The source code is not yet ready for public distribu-
tion, but the author would be happy to discuss details with
interested parties.
Additionally, Windows XP RC1 will implement elements of the mechanism Additionally, Windows XP RC1 will implement elements of the mechanism
proposed in this paper. proposed in this paper.
Acknowledgements Acknowledgements
The ideas presented in this draft were derived from SRI contractual The original ideas presented in this draft were derived from SRI con-
work. The author recognizes that ideas similar to those in this tractual work. The author recognizes that ideas similar to those in
document may have already been presented by others and wishes to ack- this document may have already been presented by others and wishes to
nowledge any other such authors. The author also wishes to ack- acknowledge any other such authors. The author also wishes to ack-
nowledge the government contract administrators who sponsored the nowledge the government contract administrators who sponsored the
projects from which these works derived as well as his SRI colleagues projects from which these works derived as well as his SRI colleagues
with whom he has discussed and reviewed this work, including Dr. Mike with whom he has discussed and reviewed this work, including Monica
Frankel, J. Peter Marcotullio, Lou Rodriguez, and Dr. Ambatipudi Sas- Farah-Stapleton, Dr. Mike Frankel, J. Peter Marcotullio, Lou Rodri-
try. guez, and Dr. Ambatipudi Sastry.
The author acknowledges discussions with Alain Durand and Keith Moore The author acknowledges valuable input from numerous members of the
during the IETF 48 conference in Pittsburgh, PA. which helped NGTRANS community which has helped guide the direction of the draft.
motivate ideas on restructuring this document from the first version. The list of contributors is too long to enumerate, but the input from
the community has been vital to the draft's evolution. Alain Durand
deserves special mention for contributing the title of this draft and
the ISATAP acronym.
The author further wishes to provide special acknowledgement to Dave The author finally wishes to provide special acknowledgement to Dave
Thaler, Art Shelest, and their colleagues at Microsoft Research for Thaler, Art Shelest, Richard Draves, and others at Microsoft Research
their ideas on automatic discovery of off-link IPv6 routers. Much of for their ideas on automatic discovery of off-link IPv6 routers. Much
the text in that section derives directly from discussions with Dave, of the text in section on deployment considerations derives directly
Art and others. from discussions with Dave, Art, Rich and others.
References References
[AGGR] Hinden., R, O'Dell, M., and Deering, S., "An IPv6 [AGGR] Hinden., R, O'Dell, M., and Deering, S., "An IPv6
Aggregatable Global Unicast Address Format", Aggregatable Global Unicast Address Format",
RFC 2374, July 1998. RFC 2374, July 1998.
[ADDR] Hinden, R., and S. Deering, "IP Version 6 Addressing [ADDR] Hinden, R., and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998. Architecture", RFC 2373, July 1998.
skipping to change at page 15, line 37 skipping to change at page 13, line 45
[IPV6] Deering, S., and R. Hinden, "Internet Protocol, Version 6 [IPV6] Deering, S., and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460 (IPv6) Specification", RFC 2460
[6TO4] Carpenter, B., and K. Moore, "Connection of IPv6 Domains [6TO4] Carpenter, B., and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001. via IPv4 Clouds", RFC 3056, February 2001.
[6TO4ANY] Huitema, C., "An anycast prefix for 6to4 relay routers", [6TO4ANY] Huitema, C., "An anycast prefix for 6to4 relay routers",
draft-ietf-ngtrans-6to4anycsat-02.txt (work in progress) draft-ietf-ngtrans-6to4anycsat-02.txt (work in progress)
[6TO4MULTI] Thaler, D., "Support for Multicsat over 6to4 Networks",
draft-ietf-ngtrans-6to4-multicast-00.txt (work in pro-
gress)
[MECH] Gilligan, R., and E. Nordmark, "Transition Mechanisms for [MECH] Gilligan, R., and E. Nordmark, "Transition Mechanisms for
IPv6 Hosts and Routers", RFC 2893, August 2000. IPv6 Hosts and Routers", RFC 2893, August 2000.
[SELECT] Draves, R., Default Address Selection for IPv6, draft- [SELECT] Draves, R., Default Address Selection for IPv6, draft-
ietf- ietf-
ipngwg-default-addr-select-00.txt (work in progress) ipngwg-default-addr-select-00.txt (work in progress)
[FBSD] http://www.freebsd.org [FBSD] http://www.freebsd.org
[INRIA] ftp://ftp.inria.fr/network/ipv6/ [INRIA] ftp://ftp.inria.fr/network/ipv6/
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