Internet DRAFT - draft-ietf-ngtrans-isatap
draft-ietf-ngtrans-isatap
Network Working Group F. Templin
Internet-Draft Consultant
Expires: July 31, 2005 T. Gleeson
Cisco Systems K.K.
M. Talwar
D. Thaler
Microsoft Corporation
January 27, 2005
Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)
draft-ietf-ngtrans-isatap-24.txt
Status of this Memo
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of Section 3 of RFC 3667. By submitting this Internet-Draft, each
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
The Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) connects
IPv6 hosts/routers over IPv4 networks. ISATAP views the IPv4 network
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as a link layer for IPv6 and views other nodes on the network as
potential IPv6 hosts/routers. ISATAP supports an automatic tunneling
abstraction similar to the Non-Broadcast Multiple Access (NBMA)
model.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Domain of Applicability . . . . . . . . . . . . . . . . . . 4
5. Node Requirements . . . . . . . . . . . . . . . . . . . . . 4
6. Addressing Requirements . . . . . . . . . . . . . . . . . . 4
7. Automatic Tunneling . . . . . . . . . . . . . . . . . . . . 5
8. Neighbor Discovery for ISATAP Interfaces . . . . . . . . . . 7
9. Site Administration Considerations . . . . . . . . . . . . . 9
10. Summary of Impact on Routing . . . . . . . . . . . . . . . . 9
11. Security considerations . . . . . . . . . . . . . . . . . . 10
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . 11
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 11
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
14.1 Normative References . . . . . . . . . . . . . . . . . . 12
14.2 Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 13
A. Modified EUI-64 Addresses in the IANA Ethernet Address
Block . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
B. Changes since -22 . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . 16
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1. Introduction
This document specifies a simple mechanism called the Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP) that connects IPv6
hosts/routers over IPv4 networks. Dual-stack (IPv6/IPv4) nodes use
ISATAP to automatically tunnel IPv6 packets in IPv4, i.e., ISATAP
views the IPv4 network as a link layer for IPv6 and views other nodes
on the network as potential IPv6 hosts/routers.
ISATAP enables automatic tunneling whether global or private IPv4
addresses are used, and presents a Non-Broadcast Multiple Access
(NBMA) abstraction similar to [RFC2491][RFC2492][RFC2529][RFC3056].
The main objectives of this document are to: 1) describe the domain
of applicability, 2) specify addressing requirements, 3) specify
automatic tunneling using ISATAP, 4) specify the operation of IPv6
Neighbor Discovery over ISATAP interfaces, and 5) discuss Site
Administration, Security and IANA considerations.
2. 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
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.
3. Terminology
The terminology of [RFC2460][RFC2461] applies to this document. The
following additional terms are defined:
site:
a connected, self-contained, single administrative domain network
surrounded by zero or more border-filtering routers and containing
interior routers and links with their attached interfaces.
ISATAP node:
a node that implements the specifications in this document.
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ISATAP interface:
an ISATAP node's non-broadcast multi-access (NBMA) IPv6 interface
used for automatic tunneling of IPv6 packets in IPv4.
ISATAP interface identifier:
an IPv6 interface identifier with an embedded IPv4 address
constructed as specified in Section 6.1.
ISATAP address:
an IPv6 unicast address that matches an on-link prefix on an
ISATAP interface of the node, and includes an ISATAP interface
identifier.
locator:
an IPv4 address-to-interface mapping, i.e., a node's IPv4 address
and its associated interface.
locator set:
a set of locators associated with an ISATAP interface, where each
locator in the set belongs to the same site.
4. Domain of Applicability
The domain of applicability for this technical specification is
automatic tunneling of IPv6 packets in IPv4 for ISATAP nodes within
sites that observe the Security Considerations found in this
document, including host-to-router, router-to-host, and host-to-host
automatic tunneling in certain enterprise networks and 3GPP/3GPP2
wireless operator networks. (Other scenarios with sufficient trust
basis ensured by the mechanisms specified in this document also fall
within this domain of applicability.)
Extensions to the above domain of applicability (e.g., by combining
the mechanisms in this document with other technical specifications)
are out of scope.
5. Node Requirements
ISATAP nodes observe the common functionality requirements for IPv6
nodes found in [NODEREQ] and the requirements for dual IP layer
operation found in ([MECH], section 2). They also implement the
additional features specified in this document.
6. Addressing Requirements
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6.1 ISATAP Interface Identifiers
ISATAP interface identifiers are constructed in Modified EUI-64
format ([RFC3513], section 2.5.1 and appendix A) by concatenating the
24-bit IANA OUI (00-00-5E), the 8-bit hexadecimal value 0xFE, and a
32-bit IPv4 address in network byte order as follows:
|0 1|1 3|3 6|
|0 5|6 1|2 3|
+----------------+----------------+--------------------------------+
|000000ug00000000|0101111011111110|mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm|
+----------------+----------------+--------------------------------+
When the IPv4 address is known to be globally unique, the "u" bit
(universal/local) is set to 1; otherwise, the "u" bit is set to 0.
"g" is the individual/group bit, and "m" are the bits of the IPv4
address.
6.2 ISATAP Interface Address Configuration
Each ISATAP interface configures a set of locators consisting of IPv4
address-to-interface mappings from a single site, i.e., an ISATAP
interface's locator set MUST NOT span multiple sites.
When an IPv4 address is removed from an interface, the corresponding
locator SHOULD be removed from its associated locator set(s). When a
new IPv4 address is assigned to an interface, the corresponding
locator MAY be added to the appropriate locator set(s).
ISATAP interfaces form ISATAP interface identifiers from IPv4
addresses in their locator set and use them to create link-local
ISATAP addresses ([RFC2462], section 5.3).
6.3 Multicast/Anycast
It is not possible to assume the general availability of wide-area
IPv4 multicast, so (unlike 6over4 [RFC2529]) ISATAP must assume only
unicast capability in its underlying IPv4 carrier network. Support
for IPv6 multicast over ISATAP interfaces is not described in this
document.
Similarly, support for Reserved IPv6 Subnet Anycast Addresses is not
described in this document.
7. Automatic Tunneling
ISATAP interfaces use the basic tunneling mechanisms specified in
([MECH], section 3). The following additional specifications are
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also used:
7.1 Encapsulation
ISATAP addresses are mapped to a link-layer address by a static
computation, i.e., the last four octets are treated as an IPv4
address.
7.2 Handling IPv4 ICMP Errors
ISATAP interfaces SHOULD process ARP failures and persistent ICMPv4
errors as link-specific information indicating that a path to a
neighbor may have failed ([RFC2461], section 7.3.3).
7.3 Decapsulation
The specification in ([MECH], section 3.6) is used. Additionally,
when an ISATAP node receives an IPv4 protocol 41 datagram that does
not belong to a configured tunnel interface, it determines whether
the packet's IPv4 destination address and arrival interface match a
locator configured in an ISATAP interface's locator set.
If an ISATAP interface that configures a matching locator is found,
the decapsulator MUST verify that the packet's IPv4 source address is
correct for the encapsulated IPv6 source address. The IPv4 source
address is correct if:
o the IPv6 source address is an ISATAP address that embeds the IPv4
source address in its interface identifier, or:
o the IPv4 source address is a member of the Potential Router List
(see: section 8.1).
Packets for which the IPv4 source address is incorrect for this
ISATAP interface are checked to determine whether they belong to
another tunnel interface.
7.4 Link-Local Addresses
ISATAP interfaces use link local addresses constructed as specified
in section 6 of this document.
7.5 Neighbor Discovery over Tunnels
ISATAP interfaces use the specifications for neighbor discovery found
in section 8 of this document.
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8. Neighbor Discovery for ISATAP Interfaces
ISATAP interfaces use the neighbor discovery mechanisms specified in
[RFC2461] and also implement the following specifications:
8.1 Conceptual Model Of A Host
To the list of Conceptual Data Structures ([RFC2461], section 5.1),
ISATAP interfaces add:
Potential Router List
A set of entries about potential routers; used to support router
and prefix discovery. Each entry ("PRL(i)") has an associated
timer ("TIMER(i)"), and an IPv4 address ("V4ADDR(i)") that
represents a router's advertising ISATAP interface.
8.2 Router and Prefix Discovery - Router Specification
Advertising ISATAP interfaces send Solicited Router Advertisement
messages as specified in ([RFC2461], section 6.2.6) except that the
messages are sent directly to the soliciting node, i.e., they might
not be received by other nodes on the link.
8.3 Router and Prefix Discovery - Host Specification
The Host Specification in ([RFC2461], section 6.3) is used. ISATAP
interfaces add the following specifications:
8.3.1 Host Variables
To the list of host variables ([RFC2461], section 6.3.2), ISATAP
interfaces add:
PrlRefreshInterval
Time in seconds between successive refreshments of the PRL after
initialization. The designated value of all 1's (0xffffffff)
represents infinity.
Default: 3600 seconds
MinRouterSolicitInterval
Minimum time in seconds between successive solicitations of the
same advertising ISATAP interface. The designated value of all
1's (0xffffffff) represents infinity.
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8.3.2 Potential Router List Initialization
ISATAP nodes initialize an ISATAP interface's PRL with IPv4 addresses
discovered via manual configuration, a DNS fully-qualified domain
name (FQDN) [RFC1035], a DHCPv4 option, a DHCPv4 vendor-specific
option, or an unspecified alternate method. FQDNs are established
via manual configuration or an unspecified alternate method. FQDNs
are resolved into IPv4 addresses through a static host file lookup,
querying the DNS service, querying a site-specific name service, or
an unspecified alternate method.
After initializing an ISATAP interface's PRL, if the PRL is empty the
node SHOULD disable the interface. Otherwise, the node sets a timer
for the interface to PrlRefreshInterval seconds and re-initializes
the interface's PRL as specified above when the timer expires. When
an FQDN is used, and when it is resolved via a service that includes
TTLs with the IPv4 addresses returned (e.g., DNS 'A' resource records
[RFC1035]), the timer SHOULD be set to the minimum of
PrlRefreshInterval and the minimum TTL returned. (Zero-valued TTLs
are interpreted to mean that the PRL is re-initialized before each
Router Solicitation event - see: section 8.3.4).
8.3.3 Processing Received Router Advertisements
To the list of checks for validating Router Advertisement messages
([RFC2461], section 6.1.1), ISATAP interfaces add:
o IP Source Address is a link-local ISATAP address that embeds
V4ADDR(i) for some PRL(i).
Valid Router Advertisements received on an ISATAP interface are
processed as specified in ([RFC2461], section 6.3.4).
8.3.4 Sending Router Solicitations
To the list of events after which Router Solicitation messages may be
sent ([RFC2461], section 6.3.7), ISATAP interfaces add:
o TIMER(i) for some PRL(i) expires.
Since unsolicited Router Advertisements may be incomplete and/or
absent, ISATAP nodes MAY schedule periodic Router Solicitation events
for certain PRL(i)'s by setting the corresponding TIMER(i).
When periodic Router Solicitation events are scheduled, the node
SHOULD set TIMER(i) such that the next event will refresh remaining
lifetimes stored for PRL(i) before they expire, including the Router
Lifetime, Valid Lifetimes received in Prefix Information Options, and
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Route Lifetimes received in Route Information Options [DEFLT].
TIMER(i) MUST be set to no less than MinRouterSolicitInterval seconds
where MinRouterSolicitInterval is configurable for the node, or for a
specific PRL(i), with a conservative default value (e.g., 2 minutes).
When TIMER(i) expires, the node sends Router Solicitation messages as
specified in ([RFC2461], section 6.3.7) except that the messages are
sent directly to PRL(i), i.e., they might not be received by other
routers. While the node continues to require periodic Router
Solicitation events for PRL(i), and while PRL(i) continues to act as
a router, the node resets TIMER(i) after each expiration event as
described above.
8.4 Neighbor Unreachability Detection
Hosts SHOULD perform Neighbor Unreachability Detection ([RFC2461],
section 7.3). Routers MAY perform neighbor unreachability detection,
but this might not scale in all environments.
After address resolution, hosts SHOULD perform an initial
reachability confirmation by sending Neighbor Solicitation message(s)
and receiving a Neighbor Advertisement message. Routers MAY perform
this initial reachability confirmation, but this might not scale in
all environments.
9. Site Administration Considerations
Site administrators maintain a Potential Router List (PRL) of IPv4
addresses representing advertising ISATAP interfaces of routers.
The PRL is commonly maintained as an FQDN for the ISATAP service in
the site's name service (see: section 8.3.2). There are no mandatory
rules for the selection of the FQDN, but site administrators are
encouraged to use the convention "isatap.domainname" (e.g.,
isatap.example.com).
When the site's name service includes TTLs with the IPv4 addresses
returned, site administrators SHOULD configure the TTLs with
conservative values to minimize control traffic.
10. Summary of Impact on Routing
As stated in Section 4, this document focuses on connectivity to
hosts. Router-to-router protocols which rely on the use of multicast
will not work over an ISATAP link, but this is not required for
ISATAP's domain of applicability. For router-to-host communication,
the impact on Neighbor Discovery/Router Discovery is covered in
Section 8.
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Finally, there is no impact on existing routing protocols outside of
the ISATAP link, as any arbitrary prefix can be used, as with most
other link-layer protocols.
11. Security considerations
Implementors should be aware that, in addition to possible attacks
against IPv6, security attacks against IPv4 must also be considered.
Use of IP security at both IPv4 and IPv6 levels should nevertheless
be avoided, for efficiency reasons. For example, if IPv6 is running
encrypted, encryption of IPv4 would be redundant except if traffic
analysis is felt to be a threat. If IPv6 is running authenticated,
then authentication of IPv4 will add little. Conversely, IPv4
security will not protect IPv6 traffic once it leaves the ISATAP
domain. Therefore, implementing IPv6 security is required even if
IPv4 security is available.
There is a possible spoofing attack in which an attacker outside the
IPv4 site spoofs an IPv6 source address which appears to be an
on-link ISATAP address, and encapsulates it to an ISATAP node. Since
an ISATAP link spans an entire IPv4 site, restricting access to the
link can be achieved by restricting access to the site, i.e., by
having site border routers implement IPv4 ingress filtering and
ip-protocol-41 filtering.
Another possible spoofing attack involves spurious ip-protocol-41
packets injected from within an ISATAP link by a node pretending to
be a router. The Potential Router List (PRL) provides a list of IPv4
addresses representing advertising ISATAP interfaces of routers that
hosts use in filtering decisions. Site administrators should ensure
that the PRL is kept up to date, and that the resolution mechanism
(see: section 9) cannot be subverted. ISATAP SHOULD NOT be used when
the PRL is empty (see: section 8.3.2).
ISATAP has unique characteristics that do not exist in other
tunneling solutions such as 6to4 [RFC3056] and result in avoiding
most security issues that exist in those protocols. Unlike such
protocols, ISATAP is only to be used within a site with border
routers which filter ip-protocol-41 packets, as noted above. This
reduces the scope of spoofing attacks to other attackers inside the
site. Also unlike such protocols, ISATAP will not accept packets
from arbitrary routers, only from routers in the Potential Router
List it knows, as noted above. This avoids spoofing attacks that
would otherwise be possible by an attacker pretending to be a router,
but relies on the security of the PRL resolution method used.
Together, these characteristics mean that spoofing an IPv6 source
address requires either spoofing the IPv4 address embedded in an
ISATAP address, or spoofing an IPv4 address in the PRL. This is
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hence no worse than IPv4 without ISATAP in this respect.
The threats associated with IPv6 Neighbor Discovery are described in
[RFC3756].
The use of temporary addresses [RFC3041] and Cryptographically
Generated Addresses [CGA] on ISATAP interfaces is outside the scope
of this specification.
12. IANA Considerations
The IANA is requested to specify the format for Modified EUI-64
address construction ([RFC3513], Appendix A) in the IANA Ethernet
Address Block. The text in Appendix B of this document is offered as
an example specification. The current version of the IANA registry
for Ether Types can be accessed at:
http://www.iana.org/assignments/ethernet-numbers
13. Acknowledgments
The ideas in this document are not original, and the authors
acknowledge the original architects. Portions of this work were
sponsored through U.S. government contracts and internal projects at
SRI International and Nokia. Government sponsors include Monica
Farah-Stapleton and Russell Langan (U.S. Army CECOM ASEO), and Dr.
Allen Moshfegh (U.S. Office of Naval Research). SRI International
sponsors include Dr. Mike Frankel, J. Peter Marcotullio, Lou
Rodriguez, and Dr. Ambatipudi Sastry.
The following are acknowledged for providing peer review input: Jim
Bound, Rich Draves, Cyndi Jung, Ambatipudi Sastry, Aaron Schrader,
Ole Troan, Vlad Yasevich.
The following are acknowledged for their significant contributions:
Alain Durand, Hannu Flinck, Jason Goldschmidt, Nathan Lutchansky,
Karen Nielsen, Mohan Parthasarathy, Chirayu Patel, Art Shelest,
Markku Savela, Pekka Savola, Margaret Wasserman, Brian Zill.
The authors acknowledge the work of Quang Nguyen on "Virtual
Ethernet" 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.
14. References
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14.1 Normative References
[MECH] Gilligan, R. and E. Nordmark, "Basic Transition Mechanisms
for IPv6 Hosts and Routers",
Internet-Draft draft-ietf-v6ops-mech-v2-00, February 2003.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[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.
[RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513, April 2003.
14.2 Informative References
[CGA] Aura, T., "Cryptographically Generated Addresses (CGA)",
Internet-Draft draft-ietf-send-cga, April 2004.
[DEFLT] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes",
Internet-Draft draft-ietf-ipv6-router-selection-06.txt,
October 2003.
[NODEREQ] Loughney, J., "IPv6 Node Requirements",
Internet-Draft draft-ietf-ipv6-node-requirements, August
2004.
[RFC2491] Armitage, G., Schulter, P., Jork, M. and G. Harter, "IPv6
over Non-Broadcast Multiple Access (NBMA) networks",
RFC 2491, January 1999.
[RFC2492] Armitage, G., Schulter, P. and M. Jork, "IPv6 over ATM
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Networks", RFC 2492, January 1999.
[RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529, March 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.
[RFC3756] Nikander, P., Kempf, J. and E. Nordmark, "IPv6 Neighbor
Discovery (ND) Trust Models and Threats", RFC 3756, May
2004.
Authors' Addresses
Fred L. Templin
Consultant
Email: fltemplin@acm.org
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
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Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
US
Phone: +1 425 703 8835
Email: dthaler@microsoft.com
Appendix A. Modified EUI-64 Addresses in the IANA Ethernet Address
Block
Modified EUI-64 addresses ([RFC3513], section 2.5.1 and Appendix A)
in the IANA Ethernet Address Block are formed by concatenating the
24-bit IANA OUI (00-00-5E) with a 40-bit extension identifier and
inverting the "u" bit, i.e., the "u" bit is set to one (1) to
indicate universal scope and it is set to zero (0) to indicate local
scope.
Modified EUI-64 addresses have the following appearance in memory
(bits transmitted right-to-left within octets, octets transmitted
left-to-right):
0 23 63
| OUI | extension identifier |
000000ug00000000 01011110xxxxxxxx xxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxx
When the first two octets of the extension identifier encode the
hexadecimal value 0xFFFE, the remainder of the extension identifier
encodes a 24-bit vendor-supplied id as follows:
0 23 39 63
| OUI | 0xFFFE | vendor-supplied id |
000000ug00000000 0101111011111111 11111110xxxxxxxx xxxxxxxxxxxxxxxx
When the first octet of the extension identifier encodes the
hexadecimal value 0xFE, the remainder of the extension identifier
encodes a 32-bit IPv4 address as follows:
0 23 31 63
| OUI | 0xFE | IPv4 address |
000000ug00000000 0101111011111110 xxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxx
Appendix B. Changes since -22
NOTE: This section to be removed before publication as an RFC.
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o added definition for the term "site"
o added new section on summary of impact on routing
o added 6to4 comparision paragraph in Security Considerations
o clarified security considerations statement on possible spoofing
attacks from a node outside the site
o added "ISATAP SHOULD NOT be used when the PRL is empty" to section
8.3.2 and security considerations
o mentioned Nokia internal project work under acknowledgements
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Templin, et al. Expires July 31, 2005 [Page 16]
Internet-Draft ISATAP January 2005
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Templin, et al. Expires July 31, 2005 [Page 17]
