Network Working Group F. Templin
Internet-Draft S. Russert
Intended status: Informational I. Chakeres
Expires: April 26, 2007 S. Yi
Boeing Phantom Works
October 23, 2006
MANET Autoconfiguration using DHCP
draft-templin-autoconf-dhcp-02.txt
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Copyright (C) The Internet Society (2006).
Abstract
Mobile Ad-hoc Networks (MANETs) comprise MANET routers and their
attached devices, and connect to the global Internet via one or more
MANET gateways. MANET routers that require global Internet access
must have a way to automatically configure globally routable and
unique IP addresses/prefixes. This document specifies mechanisms for
MANET autoconfiguration (AUTOCONF) based on the Dynamic Host
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Configuration Protocol (DHCP). Solutions for both IPv4 and IPv6 are
given.
1. Introduction
Mobile Ad-hoc Networks (MANETs) comprise MANET Routers (MRs) that
have zero or more attached devices and participate in a routing
protocol over limited-range (typically wireless) interfaces such that
packets exchanged between MRs may need to be forwarded across
multiple hops. MANETs attach to provider networks (and/or the global
Internet) via zero or more MANET Gateways (MGs), and MRs may be
multiple hops away from their nearest MG in some scenarios. MRs that
require global Internet access must have a means to autoconfigure
global IP addresses/prefixes and/or other configuration information.
MANETs that comprise MRs with homogeneous MANET interfaces can
configure the routing protocol to operate as a Layer-2 mechanism
(e.g., IEEE 802) for route calculations and packet forwarding such
that the Layer-3 protocol (e.g., IP) sees the MANET as a non-
broadcast, multiple access (NBMA) link. When a Layer-2 flooding
mechanism is also used, the Layer-3 protocol sees the MANET as a
unified broadcast/multicast capable link, i.e., the same as for a
(bridged) campus LAN. In such Layer-2 MANETs, MRs and MGs can
autoconfigure global IP addresses/prefixes using standard BOOTP/DHCP
[RFC0951][RFC2131][RFC3315][RFC3633] and neighbor discovery
[RFC0826][RFC1256][RFC2461][RFC2462] mechanisms.
MANETs that comprise MRs with heterogeneous MANET interfaces must
configure the routing protocol to operate as a Layer-3 mechanism such
that route calculations and packet forwarding are based on Layer-3
MANET-local addresses/prefixes (MLAs) to avoid issues associated with
bridging media types with dissimilar Layer-2 address formats and
maximum transmission units (MTUs). In such Layer-3 MANETs, standard
DHCP and neighbor discovery mechanisms are not sufficient to support
global IP address/prefix autoconfiguration since the MANET may appear
as multiple links.
This document specifies DHCP and neighbor discovery extensions for MR
autoconfiguration in Layer-3 MANETs as well as details of operation
for multiple MGs that apply to both Layer-2 and Layer-3 MANETs.
Solutions for both IPv4 [RFC0791] and IPv6 [RFC2460] are given.
2. Terminology
The terminology in the normative references apply; the following
terms are defined within the scope of this document:
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Mobile Ad-hoc Network (MANET)
a connected network region (i.e., a "site") that comprises MANET
routers that maintain a routing structure among themselves in a
relatively arbitrary fashion over dynamic (wireless) MANET
interfaces. Further information on the characteristics of MANETs
can be found in [RFC2501].
MANET Interface
a node's attachment to a MANET.
MANET Router (MR)
a node with zero or more attached devices that participates in the
MANET routing protocol on one or more limited-range (typically
wireless) MANET interface(s). For the purpose of this
specification, MANET routers configure both a DHCP client and
relay that are tightly-coupled.
MANET Gateway (MG)
an MR that also provides gateway service to a provider network
and/or the global Internet.
MANET Local Address (MLA)
a Layer-3 unicast address/prefix configured by an MR that is used
only within the scope of the connected MANET. MRs can use MLAs
for intra-MANET data communications. (For IPv6, Unique Local
Addresses (ULAs) provide a natural MLA mechanism - see: [RFC4193]
and [I-D.jelger-autoconf-mla]).
Extended Router Advertisement/Solicitation (ERA/ERS)
an IP Router Advertisement/Solicitation (RA/RS) message [RFC1256]
[RFC2461] encapsulated in an outer header for transmission over a
Layer-3 MANET with destination address set to an MLA or a site-
scoped multicast address (see: Section 3.5).
3. Autoconfiguration Extensions for Layer-3 MANETs
The following sections specify extensions necessary to support DHCP-
based autoconfiguration for Layer-3 MANETs:
3.1. MANET Router (MR) Extensions
When an MR first powers on, activates a MANET interface, or when it
receives an indication of movement to a new MANET, it configures one
or more MLAs (through a means outside the scope of this
specification) and engages in the MANET routing protocol. Next, if
the MR requires global IP address/prefix delegations, it listens for
either ERAs from nearby MGs or a MG indication carried via the MANET
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routing protocol through a means outside the scope of this
specification. If ERAs or MG indications are heard, it sends a small
number of ERSs to elicit immediate ERAs. When it needs to send ERSs,
the MR should set a small value (e.g., 2, 5, 10, etc.) in the TTL
(IPv4), Hop Limit (IPv6), or other Layer-3 protocol field of the
encapsulating header to limit the scope.
After the MR discovers MGs, it selects one or more MGs as default MGs
and selects one MG as its primary MG. The MR's DHCP client function
then forwards a DHCP DISCOVER (DHCPv4) or Solicit (DHCPv6) via its
relay function to an MLA for its primary MG. The DHCP request must
include an MLA for the MR in a DHCPv4 MLA option or the DHCPv6 "peer-
address" field (see: Section 3.4) and will elicit a DHCP reply from
the server with IP address/prefix delegations.
For IPv6, the MR can use DHCP prefix delegation per [RFC3633] and
configure addresses for itself and/or its attached devices from the
delegated prefixes per [I-D.thaler-autoconf-multisubnet-manets]. If
the ERAs include prefix options, the MR can alternatively configure
addresses from the advertised prefixes per [RFC2462]. In the latter
case, MGs should not advertise the same prefixes to more than one MR
so that multilink subnet issues are avoided - see:
[I-D.thaler-intarea-multilink-subnet-issues].
After the MR configures global IP addresses/prefixes, it can send IP
packets to off-MANET destinations using any of the MGs in its default
MG list as egress gateways. For MANETs in which MGs can inject a
'default' route that propagates throughout the MANET, 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 MGs
cannot propagate a default route, the MR either: a) encapsulates IP
packets with an MLA for an MG as the destination address in the outer
header (i.e., tunnels the packets to the MG), or b) inserts an IPv4
source routing header (likewise IPv6 routing header) to ensure that
the packets will be forwarded through an MG.
The above MR specifications are analogous to the more detailed Mobile
Node (MN) specifications found in
([I-D.templin-autoconf-netlmm-dhcp], section 4.1).
3.2. MANET Gateway Extensions
MGs send periodic/solicited ERAs on their attached MANET interfaces
instead of sending periodic/solicited RAs. (In certain use case
scenarios, MGs can inject MG indications into the MANET routing
protocol instead of sending periodic ERAs.) The ERAs should set a
small value (e.g., 2, 5, 10, etc.) in the TTL (IPv4), Hop Limit
(IPv6), or other protocol field of the encapsulating header to limit
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the scope. MGs should not advertise the same prefixes to more than
one MR so that multilink subnet issues are avoided - see:
[I-D.thaler-intarea-multilink-subnet-issues].
MGs act as BOOTP/DHCP relays for the DHCP requests/replies exchanged
between MRs and DHCP servers. (When the DHCP server function resides
on the MG itself, the MG acts as a DHCP server.) For DHCPv4, when a
MG acting as a relay forwards a MR's 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 each DHCP reply message it processes pertaining to address/prefix
delegation, the MG creates a tunnel (if necessary) 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 MG 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.
When MGs forward IP packets to an MR, they either: a) encapsulate the
packets with the MLA for the MR as the destination address in the
outer header (i.e., tunnel the packets to the MR), or b) insert an
IPv4 source routing header (likewise IPv6 routing header) to ensure
that the packets will be forwarded to the correct MR.
The above MG specifications are analogous to the more detailed Access
Router (AR) specifications found in
([I-D.templin-autoconf-netlmm-dhcp], Section 4.2).
3.3. DHCP Server Extensions
DHCP servers can reside on provider networks, the Internet or on the
MGs themselves.
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).
No MANET-specific extensions are required for DHCPv6 servers.
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 so that the MG can direct DHCPv4 replies to
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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 | ...
+-----+-----+-----+-----+-----+-----+---
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
MRs and MGs in Layer-3 MANETs that implement this specification
require a MANET flooding mechanism (e.g., Simplified Multicast
Forwarding (SMF) [I-D.ietf-manet-smf]) so that site-scoped multicast
ERA/ERS messages can be propagated across multiple Layer-3 hops.
4. Operation with Multiple MGs
When the Layer-2 or Layer-3 MANET connects to provider networks or
the global Internet via multiple MGs, MR operation and localized
mobility management is based on the nature of MG deployment.
For a set of MGs that attach to the same provider network, MRs can
retain their global IP address/prefix delegations as they move
between different MGs if the network configures a mobility anchor
point that participates with the MGs and MRs in a localized mobility
management scheme, e.g., see: [I-D.templin-autoconf-netlmm-dhcp].
For a set of MGs that attach to different provider networks and/or
serve different global IP prefixes from within the same provider
network, MRs must configure new global IP addresses/prefixes as they
change between different MGs unless inter-MG tunnels and routing
protocol exchanges are supported, e.g., see:
[I-D.templin-autoconf-netlmm-dhcp], Appendix A.
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Global mobility management mechanisms for MRs that configure new
global IP addresses/prefixes as they move between different MGs 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
Security considerations for this document are the same as for
[I-D.templin-autoconf-netlmm-dhcp].
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 proposals targeted for the IETF AUTOCONF working
group have suggested stateless mechanisms for address configuration.
8. Acknowledgements
The Naval Research Lab (NRL) Information Technology Division uses
DHCP in their MANET research testbeds.
The following individuals (in chronological order) have provided
valuable input: Thomas Henderson.
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.
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[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.
9.2. Informative References
[I-D.ietf-manet-smf]
Macker, J., "Simplified Multicast Forwarding for MANET",
draft-ietf-manet-smf-02 (work in progress), March 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-03 (work in
progress), September 2006.
[I-D.thaler-autoconf-multisubnet-manets]
Thaler, D., "Multi-Subnet MANETs",
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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.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
Appendix A. Change Log
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
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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
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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