Network Working Group F. Templin
Internet-Draft S. Russert
Intended status: Informational I. Chakeres
Expires: June 18, 2007 S. Yi
Boeing Phantom Works
December 15, 2006
MANET Autoconfiguration
draft-templin-autoconf-dhcp-03.txt
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Copyright (C) The Internet Society (2006).
Abstract
Mobile Ad-hoc Networks (MANETs) comprise asymmetric reachability link
types that connect MANET routers, and connect to the global Internet
via zero or more MANET gateways. MANET routers with nodes on
downstream-attached links that require global Internet access must
have a way to automatically provision globally routable and unique IP
addresses/prefixes. This document specifies mechanisms for MANET
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autoconfiguration (AUTOCONF). Solutions for both IPv4 and IPv6 are
given.
1. Introduction
Mobile Ad-hoc Networks (MANETs) comprise asymmetric reachability link
types ([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 attach to
provider networks (and/or the global Internet) via zero or more MANET
Gateways (MGs), and MRs may be multiple IP hops away from their
nearest MG in some scenarios. MRs with nodes on downstream-attached
links that require global Internet access must have a means to
delegate global IP addresses/prefixes and/or other configuration
information.
MRs comprise a router entity and a host entity that are connected via
a virtual point-to-point VLAN configured over an imaginary shared
link for the MANET (e.g., via a loopback interface). The imaginary
shared link provides the appearance of a fully-connected link to
which all MRs attach, and has an associated "landmark" prefix that
MRs can use to identify the MANET(s) to which they attach. 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 Layer-2 mechanism such that Layer-3 (i.e.,
IP) sees the MANET as a non-broadcast, multiple access (NBMA) link.
When a Layer-2 broadcast/multicast flooding mechanism is also used,
IP sees the MANET as an ordinary shared link, i.e., 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 and packet forwarding are based on Layer-3 MANET-
Local Addresses (MLAs) 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 DHCP and neighbor discovery operation for
MANET autoconfiguration as well as details of operation for multiple
MGs. Operation using standard BOOTP/DHCP
[RFC0951][RFC2131][RFC3315][RFC3633] and neighbor discovery
[RFC0826][RFC1256][RFC2461][RFC2462] mechanisms is assumed unless
otherwise specified. Solutions for both IPv4 [RFC0791] and IPv6
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[RFC2460] are given.
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 asymmetric reachability link types
([RFC2461], Section 2.2). 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), connects its downstream-attached links to the MANET
and forwards packets on behalf of other MRs. An MR comprises a
router entity and a host entity that communicate via a virtual
point-to-point VLAN configured over an imaginary shared link for
the MANET (e.g., via a loopback interface). 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.
landmark prefix
an IP prefix associated with the imaginary shared link that
connects MRs in a MANET; used by MRs to identify their current
MANET point(s) of attachment and as an identifier for the virtual
interface(s) configured over the imaginary link.
MANET Gateway (MG)
an MR that also provides gateway service to a provider network
and/or the global Internet. For the purpose of this
specification, MGs 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.
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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
may travel multiple IP hops.
3. MANET Autoconfiguration
The following sections specify autoconfiguration operation for
MANETs. In-scope for this specification are "stub" MANETs with zero
or more gateways that connect either to the same provider network or
to the public Internet using provider-independent addressing. The
mechanisms in this specification are also necessary (but may not be
sufficient) for supporting multihomed MANETs, MANETs configured as
transit networks, default MG selection, etc.
3.1. MANET Router (MR) Operation
Each MR configures one or more MLAs on each of its MANET interfaces.
For IPv6, MLAs are generated using [RFC4193][I-D.jelger-autoconf-mla]
with interface identifiers that are either managed for uniqueness
([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 then discovers the MLAs
of MGs and a landmark prefix for the MANET's imaginary shared link by
either receiving ERAs or through a means outside the scope of this
specification, e.g., via an out-of-band service discovery protocol,
via information conveyed in the routing protocol itself, etc. MRs
can also send a small number of ERSs to elicit immediate ERAs if no
unsolicited ERAs are received.
After a MR discovers the MLAs of MGs, it selects one or more MGs as
default MGs. The MR's DHCP client function then sends a DHCP
DISCOVER (DHCPv4) or Solicit (DHCPv6) request to its DHCP relay
function across the virtual interface that connects its host and
router functions. The relay function then forwards the request to
the MLA(s) for one or more MG, to the MLAs of other known DHCP
servers within the MANET, or to a site-scoped "All-DHCP-Servers"
multicast address.
For DHCPv4, the relay writes an MLA from the outgoing MANET interface
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(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 landmark prefix for the MANET's imaginary shared
link.
For DHCPv6, the relay writes an MLA from the outgoing MANET interface
in the "peer-address" field and also writes an address from the
landmark prefix for the MANET's imaginary shared link in the "link-
address" field. 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 a MANET interface. When prefixes are delegated, the MR
can further sub-delegate the prefixes to its downstream-attached
links, including physical links and virtual links of the MR itself.
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 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.
3.2. MANET Gateway Operation
MGs send periodic and/or solicited ERAs on their attached MANET
links. For IPv6, MGs advertise prefixes in ERAs that are to be used
as landmark prefixes for the MANET (e.g., by setting the 'A', 'L'
bits in Prefix Information Options to 0).
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
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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. For MANETs in which MRs will inject delegated
addresses/prefixes into the routing protocol, tunneling from the MG
is not necessary since standard IP routing within the MANET will
direct packets to the correct MR.
3.3. DHCP Server Deployments and Extensions
DHCP servers can reside on provider networks, the Internet or on the
MGs themselves; they can also reside on some non-MG node within the
MANET.
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 for DHCP transactions that will traverse a
MG, i.e., so that the MG 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 | ...
+-----+-----+-----+-----+-----+-----+---
Code
a one-octet field that identifies the option type (see:
Section 5).
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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
messages can be propagated across multiple Layer-3 hops.
4. Operation with Multiple MGs
MGs are associated with landmark prefixes that identify the MANET's
point of attachment to a provider network. 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
landmark prefix stays the same and if the network 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.
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
Threats relating to MANET routing protocols also apply to this
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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. Many of the ideas on this
document originated from IETF Autoconf working group discussions on
various aspects of autoconfiguration for MANETs.
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.
[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.
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[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.
[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.
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[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, but the primary use for link-locals seems to
be for the purpose of uniquely identifying routers on the link.
Also, it is an open question 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, in-service DAD upon link change is problematic,
since MANET links are constantly changing due to node mobility.
Also, pre-service DAD on a MANET link 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. In both
instances, the overhead for performing DAD is substantial and prone
to false-negatives due to packet loss. Note also that link-local
addresses 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 and in-
service DAD based on link change can be avoided and a passive DAD,
e.g., one that monitors routing protocol messages, can be used
instead.
Note also that no DAD is required for the global addresses/prefixes
delegated to MRs as long as the addresses are configured on the MR's
downstream-attached links (and not the MANET link) and as long as
standard DAD procedures are observed on the downstream-attached links
themselves.
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Appendix B. Change Log
Changes from -02 to -03:
o updated terminology based on RFC2461 "asymmetric reachability"
link type; IETF67 MANET Autoconf wg discussions.
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
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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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