Network Working Group F. Templin
Internet-Draft Boeing Phantom Works
Intended status: Informational February 20, 2007
Expires: August 24, 2007
MANET Autoconfiguration over Virtual Ethernets
draft-templin-autoconf-virtual-00.txt
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
Mobile Ad-hoc Networks (MANETs) consist of routers operating over
multihop wireless links, and may or may not connect to other networks
and/or the Internet. Routers in MANETs must have a way to
automatically provision local and global-use IP addresses/prefixes.
This document specifies mechanisms for MANET autoconfiguration that
view the MANET as a virtual ethernet. Both IPv4 and IPv6 are
discussed.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. MANET Autoconfiguration . . . . . . . . . . . . . . . . . . . 5
3.1. MANET Router (MR) Operation . . . . . . . . . . . . . . . 5
3.2. MANET Border Router Operation . . . . . . . . . . . . . . 8
3.3. DHCP Server Extensions . . . . . . . . . . . . . . . . . . 8
3.4. MLA Encapsulation . . . . . . . . . . . . . . . . . . . . 8
3.5. MANET Flooding . . . . . . . . . . . . . . . . . . . . . . 9
3.6. Self-Generated Addresses . . . . . . . . . . . . . . . . . 9
3.7. Changes to the Neighbor Discovery Model . . . . . . . . . 9
4. Operation with Multiple MBRs . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 10
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
10.1. Normative References . . . . . . . . . . . . . . . . . . . 11
10.2. Informative References . . . . . . . . . . . . . . . . . . 12
Appendix A. IPv6 Neighbor Discovery (ND) and Duplicate
Address Detection (DAD) . . . . . . . . . . . . . . . 13
Appendix B. IPv6 StateLess Address AutoConfiguration (SLAAC) . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . . . 15
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1. Introduction
Mobile Ad-hoc Networks (MANETs) comprise links with asymmetric
reachability characteristics (see: [RFC2461], Section 2.2) that
connect MANET Routers (MRs). MRs participate in a routing protocol
to discover routes for forwarding packets across the MANET using
multiple Layer-2 and/or Layer-3 hops if necessary. MANETs may
connect to other networks via MANET Border Routers (MBRs), and MRs
may be multiple IP hops away from their nearest MBR in some
scenarios. A MANET may be as large as an Autonomous System (AS) or
as small as an individual site. A MANET may contain other MANETs
and/or fixed networks, and a MANET may also be a smaller component of
a larger site. MRs with hosts on downstream-attached links must have
a means to automatically provision local and global-use IP addresses/
prefixes and/or other configuration information.
Conceptually, MRs comprise a router entity and (one or more) host
entity connected by a virtual point-to-point interface. The router
entity also connects to an imaginary shared link (i.e., a "virtual
ethernet") that connects all MRs in the MANET. For each MANET to
which they connect, MRs discover a list of MBRs that determines the
MANET's identity. An MR (and its downstream-attached links) is a
"site" unto itself, and a MANET is therefore a "site-of-sites".
MANETs that comprise homogeneous link types can configure the routing
protocol to operate as a sub-IP layer mechanism such that IP (i.e.,
Layer-3) sees the MANET as an ordinary shared link the same as for a
(bridged) campus LAN. In that case, a single IP hop is sufficient to
traverse the MANET.
MANETs that comprise heterogeneous link types must configure the
routing protocol to operate as a Layer-3 mechanism such that routing
protocol operation is based on MANET-local Addresses (MLAs) or other
identifiers that are unique within the MANET to avoid issues
associated with bridging media types with dissimilar Layer-2 address
formats and maximum transmission units (MTUs). In that case,
multiple IP hops may be necessary to traverse the MANET.
This document specifies mechanisms and operational practices for
MANET autoconfiguration. Operation using standard BOOTP/DHCP
[RFC0951][RFC2131][RFC3315][RFC3633] and neighbor discovery
[RFC0826][RFC1256][RFC2461][RFC2462] mechanisms is assumed unless
otherwise specified. Both IPv4 [RFC0791] and IPv6 [RFC2460] are
discussed.
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2. Terminology
The terminology in [I-D.ietf-autoconf-manetarch] and the normative
references apply; the following terms are defined within the scope of
this document:
Mobile Ad-hoc Network (MANET)
a connected network region that comprises MANET routers that
maintain a routing structure among themselves in a relatively
arbitrary fashion over links with asymmetric reachability
characteristics (see: [RFC2461], Section 2.2). MANETs may be
large as an Autonomous System (AS) or as small as an individual
site, and may also be a smaller component of a larger site. A
MANET router (and its downstream-attached links) is a "site" unto
itself, and a MANET is therefore a "site-of-sites". Further
information on the characteristics of MANETs can be found in
[RFC2501].
MANET Interface
a MANET router's attachment to a link in the MANET.
virtual ethernet
an imaginary shared link that connects all MRs in a MANET. MRs
connect to this virtual ethernet via an interface configured over
underlying MANET interface(s) (see: Figure 1 and Figure 2). The
virtual ethernet interface encapsulates packets in an outer IP
header then sends them on an underlying MANET interface such that
only a single Layer 3 hop is necessary to traverse the MANET,
i.e., it views the MANET as a unified shared link.
MANET Router (MR)
a node that participates in a routing protocol over its MANET
interface(s) and forwards packets on behalf of its downstream-
attached nodes and other MRs. Conceptually, an MR comprises a
router entity and (one or more) host entity connected via a
virtual point-to-point interface, plus any other physical or
virtual interfaces connected to the router entity. For the
purpose of this specification, an MR's host entity configures a
DHCP client and its router entity configures a DHCP relay.
MANET Border Router (MBR)
an MR that connects the MANET to other networks. For the purpose
of this specification, MBRs are assumed to configure a DHCP relay
and/or a DHCP server.
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MANET Local Address (MLA)
a Layer-3 unicast address configured by an MR that is unique
within the MANET; it is used as an identifier for operating the
routing protocol and also as a locator for packet forwarding
within the scope of the MANET. For IPv6, Unique Local Addresses
(ULAs) [RFC4193][I-D.jelger-autoconf-mla] provide a natural MLA
mechanism.
3. MANET Autoconfiguration
The following sections specify autoconfiguration mechanisms and
operational practices that allow MRs to participate in the routing
protocol and obtain addresses/prefixes for Intra-MANET and global
Internet communications.
3.1. MANET Router (MR) Operation
Each MR configures MLAs used for operating the routing protocol
and/or for assignment on MANET interfaces. For IPv6 MANET
interfaces, MLAs are generated using Unique Local Addresses
[RFC4193][I-D.jelger-autoconf-mla] with interface identifiers that
are either managed for uniqueness (e.g., per [RFC4291], Appendix A)
or self-generated using a suitable random interface identifier
generation mechanism that is compatible with EUI-64 format (e.g.,
Cryptographically Generated Addresses (CGAs) [RFC3972], IPv6 privacy
addresses [I-D.ietf-ipv6-privacy-addrs-v2], etc.). For IPv4, MLAs
are generated using a corresponding unique local address
configuration mechanism. (Such a mechanism could be considered as a
site-scoped equivalent to IPv4 link-local addresses [RFC3927].)
The MR next engages in the routing protocol over its MANET interfaces
and discovers the set of MBRs that identify the virtual ethernet
associated with the MANET. The set of MBRs is discovered the same as
for the ISATAP Potential Router List (PRL) initialization procedure
[RFC4214]; if the set of MBRs is NULL, an alternate token (such as
the IEEE MAC address of an ordinary MR) can be used as an identifier
for the MANET.
For each MANET to which it attaches, the MR also configures a virtual
ethernet interface over the underlying MANET interfaces connected to
the MANET. The virtual ethernet interface presents an opaque view to
IP, and configures a link-local address that is assured to be unique
among the virtual ethernet interfaces of all MRs in the MANET. IP
packets sent via the virtual ethernet interface are encapsulated in
an outer IP header then submitted to ip_output() for transmission on
an underlying MANET interface.
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Figure 1 shows the protocol stack model for the virtual ethernet
output routine, and Figure 2 shows the virtual ethernet input
routine:
+---------------------------+ |
| ip_output() | |
+---------------------------+ |
| virtual_ethernet_output() |
| | p
| - select MANET intf | a
| - encapsulate in IP | c
| - send to MANET intf | k
| via ip_output() | e
+---------------------------+ t
| ip_output() | s
+---------------------------+
| MANET Interfaces 0 thru n | |
| MLA 0 | MLA 1 |...| MLA n | |
+-------+------ +...+-------+ v
Figure 1: virtual_ethernet_output()
+---------------------------+ ^
| ip_input() | |
+---------------------------+
| virtual_ethernet_input() | p
| | a
| - decapsulate packet | c
| - submit to ip_input() | k
+---------------------------+ e
| ip_input() | t
+---------------------------+ s
| MANET Interfaces 0 thru n |
| MLA 0 | MLA 1 |...| MLA n | |
+-------+------ +...+-------+ |
Figure 2: virtual_ethernet_input()
After the MR configures the virtual ethernet interface, it can
confirm reachability of MBRs and (in the case of IPv6) discover
prefixes associated with the MANET's virtual ethernet. It can
confirm reachability by sending/receiving neighbor discovery
messages, via information conveyed in the routing protocol itself, or
through some other means associated with the particular link
technology. For IPv6, prefixes can also be discovered through an
out-of-band service discovery protocol.
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After the MR discovers MBRs, it can configure addresses/prefixes
according to either DHCP or IPv6 Stateless Address AutoConfiguration
(SLAAC) (but see Appendix B for further consideration on SLAAC).
When DHCP is used, the DHCP client associated with its host function
forwards a DHCP DISCOVER (DHCPv4) or Solicit (DHCPv6) request to the
DHCP relay associated with its router function to request global IP
address and/or prefix delegations (see also: Section 3.6). The relay
function then forwards the request to one or more MBRs, to other
known DHCP servers, or to a site-scoped "All-DHCP-Servers" multicast
address.
For DHCPv4, the MR's relay function writes the virtual ethernet
interface's link-local address in the 'giaddr' field and also
includes the address in a DHCPv4 MLA option (see: Section 3.4). If
necessary to identify the MR's downstream-attached host function, the
relay also includes a link selection sub-option [RFC3527] with an
address from the prefix associated with the virtual ethernet (if a
prefix is available).
For DHCPv6, the MR's relay function writes the virtual ethernet
interface's link-local address in the "peer-address" field and also
writes an address from the prefix associated with the virtual
ethernet in the "link-address" field (if a prefix is available). The
MR can also use DHCP prefix delegation [RFC3633] to obtain prefixes
for further sub-delegation to nodes on its downstream-attached links.
The DHCP request will elicit a DHCP reply from a server with IP
address/prefix delegations. When addresses are delegated, the MR
assigns the resulting addresses to the virtual point-to-point
interface that connects its host and router functions, i.e., the
addresses are *not* assigned on the virtual ethernet interface or an
underlying MANET interface. When prefixes are delegated, the MR can
assign and/or further sub-delegate the prefixes to its downstream-
attached links. If the MANET uses a proactive routing protocol, the
MR can advertise the delegated addresses/prefixes into the routing
protocol during the duration of the delegation lifetimes.
The DHCP server ensures unique IP address/prefix delegations. By
assigning global IP addresses/prefixes only on downstream-attached
interfaces there is no requirement for the MR to perform Duplicate
Address Detection (DAD) over its virtual ethernet or MANET
interfaces. See Appendix A for further DAD considerations.
After the MR configures global IP addresses/prefixes, it can send IP
packets with global IP source addresses to on- and off-MANET
destinations. Packets can be sent to off-MANET destinations either
by using any available MBRs as egress gateways or by selecting
specific MBRs on a per-packet basis; the packets are transmitted over
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the virtual ethernet interface with an MLA for an MBR as the
destination address in the outer header.
3.2. MANET Border Router Operation
MBRs send standard IP neighbor discovery messages on their virtual
ethernet interfaces which (for IPv6 RAs) can include prefixes
associated with the MANET's virtual ethernet. When stateful
configuration is desired, such prefixes should be advertised as not
to be used for on-link determination or StateLess Address
AutoConfiguration (SLAAC) [RFC2462] by setting the 'A', 'L' bits in
Prefix Information Options to 0. (But, see: Appendix B for further
considerations on using SLAAC for MANET Autoconfiguration.)
MBRs act as BOOTP/DHCP relays and/or servers for a MR's DHCP
requests/replies. For DHCPv4, when a MBR acting as a relay forwards
a DHCP request that includes an MLA option, it writes its own address
in the 'giaddr' field, i.e., it overwrites the value that was written
into 'giaddr' by the MR's relay function.
3.3. DHCP Server Extensions
No MANET autoconfiguration-specific extensions are required for
DHCPv6 servers.
DHCPv4 servers examine DHCPv4 requests for a DHCPv4 MLA option (see:
Section 3.4). If a DHCPv4 MLA option is present, the DHCPv4 server
copies the option into the corresponding DHCPv4 reply message(s).
3.4. MLA Encapsulation
For DHCPv6, the MLA is encoded directly in the "peer-address" field
of DHCPv6 requests/replies.
For DHCPv4, a new DHCPv4 option [RFC2132] called the 'MLA option' is
required to encode an MLA for DHCP transactions that will traverse a
MBR, i.e., so that the MBR has a MANET-relevant address to direct
DHCPv4 replies to the correct MR, which may be multiple Layer-3 hops
away. The format of the DHCPv4 MLA option is given below:
Code Len Ether Type MLA
+-----+-----+-----+-----+-----+-----+---
| TBD | n | type | a1 | a2 | ...
+-----+-----+-----+-----+-----+-----+---
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Code
a one-octet field that identifies the option type (see:
Section 5).
Len
a one-octet field that encodes the remaining option length.
Ether Type
a type value from the IANA "ethernet-numbers" registry.
MLA
a variable-length MANET Local Address (MLA).
3.5. MANET Flooding
When multicast service discovery is required, Layer-3 MANETs that
implement this specification must use a MANET flooding mechanism
(e.g., Simplified Multicast Forwarding (SMF) [I-D.ietf-manet-smf]) so
that site-scoped multicast messages can be propagated across multiple
Layer-3 hops.
3.6. Self-Generated Addresses
MR's can self-generate an address (e.g., an IPv6 CGA [RFC3972], an
IPv6 privacy address [I-D.ietf-ipv6-privacy-addrs-v2], etc.) then
propose the address to the DHCP server. If the DHCP server
determines that the self-generated address is unique, it will
delegate the address for the MR's use.
3.7. Changes to the Neighbor Discovery Model
Ordinary link-scoped neighbor discovery messages work as-normal over
the virtual ethernet interface, so ND operation requires no changes
to the standard IP neighbor discovery protocols specified in
[RFC1256][RFC2461].
4. Operation with Multiple MBRs
For a set of MANETs and MBRs that attach to the same backbone
network, MRs can retain their global IP address/prefix delegations as
they move if the backbone network participates with the MBRs and MRs
in a localized mobility management scheme, e.g., see:
[I-D.templin-autoconf-netlmm-dhcp].
For a set of MBRs that attach to different backbone networks and/or
serve different global IP prefixes from within the same network, MRs
must configure new global IP addresses/prefixes as they change
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between different MBRs unless inter-MBR tunnels and routing protocol
exchanges are supported, e.g., see:
[I-D.templin-autoconf-netlmm-dhcp], Appendix A.
Global mobility management mechanisms for MRs that configure new
global IP addresses/prefixes as they move between different MBRs are
beyond the scope of this document.
5. IANA Considerations
A new DHCP option code is requested for the DHCP MLA Option in the
IANA "bootp-dhcp-parameters" registry.
6. Security Considerations
Threats relating to MANET routing protocols also apply to this
document.
7. Related Work
Telcordia has proposed DHCP-related solutions for the CECOM MOSAIC
program. The virtual ethernet model was proposed by Quang Nguyen
under the guidance of Dr. Lixia Zhang. Various IETF AUTOCONF working
group proposals have suggested similar mechanisms.
8. Contributors
Steve Russert (steven.w.russert@boeing.com), Ian Chakeres
(ian.chakeres@gmail.com) and Seung Yi (seung.yi@boeing.com)
contributed text and numerous change suggestions for "MANET
Autoconfiguration" [I-D.templin-autoconf-dhcp] from which this
document was derived.
9. Acknowledgements
The following individuals gave direct and/or indirect input that was
essential to the work: Jari Arkko, Emmanuel Bacelli, James Bound,
Thomas Clausen, Joe Macker, Thomas Henderson, Bob Hinden, Thomas
Narten, Alexandru Petrescu, Jinmei Tatuya, Dave Thaler, and others in
the IETF AUTOCONF and MANET working groups. Many others have
provided guidance over the course of many years.
The Naval Research Lab (NRL) Information Technology Division uses
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DHCP in their MANET research testbeds.
10. References
10.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37,
RFC 826, November 1982.
[RFC0951] Croft, B. and J. Gilmore, "Bootstrap Protocol", RFC 951,
September 1985.
[RFC1256] Deering, S., "ICMP Router Discovery Messages", RFC 1256,
September 1991.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, 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.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC4214] Templin, F., Gleeson, T., Talwar, M., and D. Thaler,
"Intra-Site Automatic Tunnel Addressing Protocol
(ISATAP)", RFC 4214, October 2005.
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10.2. Informative References
[I-D.ietf-autoconf-manetarch]
Chakeres, I., "Mobile Ad hoc Network Architecture",
draft-ietf-autoconf-manetarch-00 (work in progress),
February 2007.
[I-D.ietf-ipv6-privacy-addrs-v2]
Narten, T., "Privacy Extensions for Stateless Address
Autoconfiguration in IPv6",
draft-ietf-ipv6-privacy-addrs-v2-05 (work in progress),
October 2006.
[I-D.ietf-manet-smf]
Macker, J., "Simplified Multicast Forwarding for MANET",
draft-ietf-manet-smf-03 (work in progress), October 2006.
[I-D.jelger-autoconf-mla]
Jelger, C., "MANET Local IPv6 Addresses",
draft-jelger-autoconf-mla-01 (work in progress),
October 2006.
[I-D.templin-autoconf-dhcp]
Templin, F., "MANET Autoconfiguration",
draft-templin-autoconf-dhcp-05 (work in progress),
February 2007.
[I-D.templin-autoconf-netlmm-dhcp]
Templin, F., "Network Localized Mobility Management using
DHCP", draft-templin-autoconf-netlmm-dhcp-04 (work in
progress), October 2006.
[I-D.thaler-autoconf-multisubnet-manets]
Thaler, D., "Multi-Subnet MANETs",
draft-thaler-autoconf-multisubnet-manets-00 (work in
progress), February 2006.
[I-D.thaler-intarea-multilink-subnet-issues]
Thaler, D., "Issues With Protocols Proposing Multilink
Subnets", draft-thaler-intarea-multilink-subnet-issues-00
(work in progress), March 2006.
[RFC2501] Corson, M. and J. Macker, "Mobile Ad hoc Networking
(MANET): Routing Protocol Performance Issues and
Evaluation Considerations", RFC 2501, January 1999.
[RFC3527] Kinnear, K., Stapp, M., Johnson, R., and J. Kumarasamy,
"Link Selection sub-option for the Relay Agent Information
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Option for DHCPv4", RFC 3527, April 2003.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927,
May 2005.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
Appendix A. IPv6 Neighbor Discovery (ND) and Duplicate Address
Detection (DAD)
In terms of ND, existing standards [RFC2461][RFC4291] require that a
node configure a link-local address on each of its IPv6-enabled
interfaces, but the primary requirement for link-locals seems to be
for the purpose of uniquely identifying routers on the link. But, it
is for further study as to whether MRs should even send RAs on MANET
interfaces at all, since the MANET interface view of the MANET is as
a multilink peering point between distinct sites and not a unified
link. It is therefore also for further study as to whether MANET
interfaces should configure link local addresses at all.
In terms of DAD, pre-service DAD for an MLA assigned on a MANET
interface (such as specified in [RFC2462]) would require either
flooding the entire MANET or somehow discovering a link in the MANET
on which a node that configures a duplicate address is attached, and
performing a (remote) DAD exchange on that link. But, the control
message overhead for such a MANET-wide DAD would be substantial and
prone to false-negatives due to packet loss and node mobility. An
alternative to pre-service DAD is to autoconfigure pseudo-random MLAs
on MANET interfaces and employ a passive in-service DAD (e.g., one
that monitors routing protocol messages for duplicate assignments).
Pseudo-random link-local addresses can be generated with mechanisms
such as CGAs, IPv6 privacy addresses, etc., but ULAs provide an
additional 40/56 pseudo-random bits in the IPv6 address prefix.
Statistical properties can assure uniqueness for the MLAs assigned on
a MR's MANET interfaces, and careful operational practices can assure
uniqueness for the global addresses/prefixes assigned on a MR's
downstream-attached links (since the DHCP server assures unique
assignments). However, a passive in-service DAD mechanism should
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still be used to detect duplicates that were assigned via other
means, e.g., manual configuration.
Appendix B. IPv6 StateLess Address AutoConfiguration (SLAAC)
For IPv6, the use of StateLess Address AutoConfiguration (SLAAC)
[RFC2462] could be indicated by prefix information options in
neighbor discovery messages with the 'A' bit set to 1. MRs that
receive such messages could then self-generate an address from the
prefix and assign it to the virtual point-to-point interface
associated with the MANET's virtual ethernet, then use a passive in-
service DAD approach to detect duplicates within the MANET. But, if
the MANET partitions, DAD might not be able to monitor the routing
exchanges occurring in other partitions and address duplication could
result. Further study on DAD implications for SLAAC is required.
Author's Address
Fred L. Templin
Boeing Phantom Works
P.O. Box 3707 MC 7L-49
Seattle, WA 98124
USA
Email: fred.l.templin@boeing.com
Templin Expires August 24, 2007 [Page 14]
Internet-Draft MANET Autoconfiguration (Virtual) February 2007
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