Network Working Group F. Templin
Internet-Draft S. Russert
Intended status: Informational I. Chakeres
Expires: August 5, 2007 S. Yi
Boeing Phantom Works
February 1, 2007
MANET Autoconfiguration
draft-templin-autoconf-dhcp-04.txt
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
Mobile Ad-hoc Networks (MANETs) consist of routers operating over
wireless channels and may or may not connect to other networks.
Routers in MANETs that connect to the Internet must have a way to
automatically provision globally routable and unique IP addresses/
prefixes. This document specifies mechanisms for MANET
autoconfiguration. Both IPv4 and IPv6 are discussed.
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1. Introduction
Mobile Ad-hoc Networks (MANETs) comprise links with asymmetric
reachability link characteristics (see: [RFC2461], Section 2.2) that
connect MANET Routers (MRs). MRs participate in a routing protocol
such that packets can be forwarded via multiple hops across the MANET
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, and may
contain other MANETs and/or fixed networks. MRs with hosts on
downstream-attached links that require global Internet access must
have a means to automatically provision global IP addresses/prefixes
and/or other configuration information.
Conceptually, MRs comprise a router entity and a host entity that are
connected via a virtual point-to-point VLAN (e.g., a loopback
interface) configured over an imaginary shared link for the MANET.
The imaginary shared link provides a conceptual model of a fully-
connected shared link to which all MRs attach, and has an associated
identifier (e.g., a prefix associated with the imaginary shared link)
that "names" the MANET. 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
Layer-3 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 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. Further information on the characteristics of MANETs can be
found in [RFC2501].
MANET Interface
a MANET router's attachment to a link within the MANET.
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 a host entity connected via a virtual point-to-
point VLAN (e.g., a loopback interface) configured over an
imaginary shared link for the MANET. An MR (and its downstream-
attached links) is a "site" unto itself, and a MANET is therefore
a "site-of-sites". 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.
MANET Local Address (MLA)
a Layer-3 unicast address/prefix configured by an MR that is used
for intra-MANET communications, i.e., routable only within the
scope of the MANET. For IPv6, Unique Local Addresses (ULAs)
[RFC4193][I-D.jelger-autoconf-mla] provide a natural MLA
mechanism.
Extended Router Advertisement/Solicitation (ERA/ERS)
an IP Router Advertisement/Solicitation (RA/RS) message [RFC1256]
[RFC2461] with an MLA source address and with destination address
set to an MLA or a site-scoped multicast address that spans the
MANET via a broadcast/multicast flooding mechanism (see:
Section 3.5). Unlike ordinary RA/RS messages, ERA/ERS messages
use a non-link-local source address and may travel multiple IP
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hops.
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 on each of its MANET interfaces. For IPv6,
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]). For IPv4,
MLAs are generated using a corresponding unique local address
configuration mechanism.
Each MR next engages in the routing protocol and discovers an
identifier for the MANET. The identifier could be an IP prefix, a
DNS Fully-Qualified Domain Name (FQDN), an IEEE MAC address, etc. but
in any case provides a name for the MANET. MRs can discover this
identifier by receiving ERAs that contain a prefix associated with
the imaginary shared link (see: Section 3.2), via an out-of-band
service discovery protocol, via information conveyed in the routing
protocol itself, or through some other means associated with the
particular link technology.
After a MR discovers an identifier for the MANET, the DHCP client
associated with its host function sends a DHCP DISCOVER (DHCPv4) or
Solicit (DHCPv6) request across the virtual interface 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 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 an MLA from the outgoing
MANET interface (i.e., the relay's upstream-attached interface) in
the 'giaddr' field and also includes the MLA in a DHCPv4 MLA option
(see: Section 3.4). If necessary to identify the downstream-attached
virtual interface, the relay also includes a link selection sub-
option [RFC3527] with an address from the prefix associated with the
MANET's imaginary shared link (if such a prefix is available).
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For DHCPv6, the MR's relay function writes an MLA from the outgoing
MANET interface in the "peer-address" field and also writes an
address from the prefix associated with the MANET's imaginary shared
link in the "link-address" field (if such 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 interface that
connects its host and router functions, i.e., the addresses are *not*
assigned on the upstream MANET interface. When prefixes are
delegated, the MR can assign and/or further sub-delegate the prefixes
to its downstream-attached links, including physical links and
virtual links of the MR itself. If the MANET uses a proactive
routing protocol, the MR advertises 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 (and not the upstream MANET interface) there is no
requirement for the MR to perform Duplicate Address Detection (DAD)
for global addresses on the MANET interface. 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 off-MANET destinations
using any of the MBRs as egress gateways. For MANETs in which MBRs
can advertise a 'default' route that propagates throughout the
routing protocol, the MR can send the IP packets without
encapsulation at the expense of extra TTL (IPv4) or Hop Limit (IPv6)
decrementation. For MANETs in which the routing protocol cannot
propagate a default route, the MR either: a) encapsulates IP packets
with an MLA for an MBR as the destination address in the outer header
(i.e., tunnels the packets to the MBR), or b) inserts an IPv4 source
routing header (likewise IPv6 routing header) to ensure that the
packets will be forwarded through an MBR.
3.2. MANET Border Router Operation
MBRs can send periodic and/or solicited ERAs associated with the
imaginary shared link for the MANET on their attached MANET links.
For IPv6, MBRs can advertise prefixes in ERAs that MRs can consider
as an identifier for the MANET. 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
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Prefix Information Options to 0. (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.
For MANETs in which MRs cannot proactively advertise delegated
addresses/prefixes via the routing protocol, the MBR creates a tunnel
for each DHCP reply message it processes pertaining to address/prefix
delegation with the tunnel's destination address set to the MLA for
the MR encoded in the DHCPv4 MLA option or the DHCPv6 "peer-address"
field (see: Section 3.4). The MBR then creates entries in its IP
forwarding table that point to the tunnel for each delegated IP
address/prefix and relays the reply to the MLA for the MR.
For MANETs in which MRs will advertise delegated addresses/prefixes
via the routing protocol, tunneling from the MBR is not required
since standard IP routing within the MANET will direct packets to the
correct MR.
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 Cryptographically-
Generated Address (CGA) [RFC3972]) then propose the address to the
DHCP server. If the DHCP server determines that the self-generated
address is unique and can be assigned to MR's virtual interface
configured over the imaginary shared link, it will delegate the
address for the MR's use.
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
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
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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. Various IETF AUTOCONF working group proposals have
suggested similar mechanisms for address configuration.
8. Acknowledgements
The Naval Research Lab (NRL) Information Technology Division uses
DHCP in their MANET research testbeds. Many of the ideas on this
document originated from IETF AUTOCONF working group discussions on
various aspects of autoconfiguration for MANETs.
Thomas Henderson provided valuable input; Jinmei Tatuya reminded that
address duplication can occur when multiple mechanisms (i.e. manual
configuration, stateless and DHCP) are used within the same network.
9. References
9.1. 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.
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[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.
9.2. Informative References
[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-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.
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[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
Option for DHCPv4", RFC 3527, April 2003.
[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 and Duplicate Address Detection
IPv6 Neighbor Discovery (ND) and Duplicate Address Detection (DAD)
for MANETs is for further study.
In terms of ND, [RFC2461][RFC4291] require that a node configure a
link-local address on each of its IPv6-enabled interfaces, and 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 send RAs on MANET links at all, since
the MANET is a peering point between distinct sites and not the link
of a single site with a clear set of serving routers and dependent
end-hosts. In particular, since MANET interfaces configure MLAs
which already provide a statistically-unique identifier, link-local
addresses may be of little/no value on MANET interfaces and hence
strict enforcement of link-local address uniqueness may not be
necessary
In terms of DAD, pre-service DAD on a MANET link (such as specified
in [RFC2462]) would require either flooding the entire MANET or
somehow discovering a targeted region of the MANET on which a node
that configures a duplicate address resides and sending a directed
DAD message toward that region. But, the control message overhead
for such a MANET-wide DAD would be substantial and prone to false-
negatives due to packet loss. Note also that link-local addresses
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using Cryptographically Generated Addresses (CGAs) [RFC3972] provide
random generation only in 59 bits of the lower 64 bits of the IPv6
address, while MLAs using CGAs also use 40/56 bits of random
generation in the upper 64 bits of the IPv6 address. Since such MLAs
are highly unlikely to collide, pre-service DAD can be avoided and a
passive in-service DAD (e.g., one that monitors routing protocol
messages) can be used instead.
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
still be used to detect duplicates that were assigned via other
means, e.g., manual configuration.
Appendix B. IPv6 StateLess Address AutoConfiguration (SLAAC)
The use of StateLess Address AutoConfiguration (SLAAC) [RFC2462]
could be indicated by prefix information options in ERAs with the 'A'
bit set to 1. MRs that receive such ERAs could then self-generate an
address from the prefix and assign it to the virtual interface
configured over the imaginary shared link for the MANET, 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.
Appendix C. Change Log
Changed from -03 to -04:
o introduced conceptual "imaginary shared link" as a representation
for a MANET.
o discussion of autonomous system and site abstractions for MANETs
o discussion of autoconfiguration of CGAs
o new appendix on IPv6 StateLess Address AutoConfiguration
Changes from -02 to -03:
o updated terminology based on RFC2461 "asymmetric reachability"
link type; IETF67 MANET Autoconf wg discussions.
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o added new appendix on IPv6 Neighbor Discovery and Duplicate
Address Detection
o relaxed DHCP server deployment considerations allow DHCP servers
within the MANET itself
Changes from -01 to -02:
o minor updates for consistency with recent developments
Changes from -00 to -01:
o new text on DHCPv6 prefix delegation and multilink subnet
considerations.
o various editorial changes
Authors' Addresses
Fred L. Templin
Boeing Phantom Works
P.O. Box 3707 MC 7L-49
Seattle, WA 98124
USA
Email: fred.l.templin@boeing.com
Steven W. Russert
Boeing Phantom Works
P.O. Box 3707 MC 7L-49
Seattle, WA 98124
USA
Email: steven.w.russert@boeing.com
Ian D. Chakeres
Boeing Phantom Works
P.O. Box 3707 MC 7L-49
Seattle, WA 98124
USA
Email: ian.chakeres@gmail.com
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Seung Yi
Boeing Phantom Works
P.O. Box 3707 MC 7L-49
Seattle, WA 98124
USA
Email: seung.yi@boeing.com
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