Network Working Group F. Templin, Ed.
Internet-Draft S. Russert
Intended status: Informational S. Yi
Expires: February 21, 2009 Boeing Phantom Works
August 20, 2008
MANET Autoconfiguration using Virtual Enterprise Traversal (VET)
draft-templin-autoconf-dhcp-16.txt
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Abstract
Mobile Ad-hoc Networks (MANETs) connect routers on links with
asymmetric reachability characteristics, and may also connect to
other networks including the Internet. Routers in MANETs must have a
way to automatically provision IP addresses/prefixes and other
information. This document specifies a Virtual Enterprise Traversal
(VET) abstraction for autoconfiguration and operation of routers in
MANETs.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. MANET Characteristics . . . . . . . . . . . . . . . . . . . . 6
4. MANET Router Autoconfiguration . . . . . . . . . . . . . . . . 7
4.1. MANET Interface Autoconfiguration . . . . . . . . . . . . 8
4.2. VET Interface Autoconfiguration . . . . . . . . . . . . . 9
4.3. MANET Gateway List Discovery and MANET Identification . . 10
4.4. Site-interior Interface Autoconfiguration . . . . . . . . 10
4.4.1. Autoconfiguration of IPv4 Addresses/Prefixes . . . . . 10
4.4.2. Autoconfiguration of IPv6 Addresses/Prefixes . . . . . 11
4.4.3. Prefix and Route Maintenance . . . . . . . . . . . . . 12
4.5. Portable and Self-Configured IP Prefixes . . . . . . . . . 12
4.6. Separation of IP Addressing Domains . . . . . . . . . . . 13
5. Post-Autoconfiguration Operation . . . . . . . . . . . . . . . 13
5.1. Forwarding Packets to Off-MANET Destinations . . . . . . . 13
5.2. MANET-Local Communications . . . . . . . . . . . . . . . . 14
5.3. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 14
5.4. Service Discovery . . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
8. Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 15
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 15
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
11.1. Normative References . . . . . . . . . . . . . . . . . . . 16
11.2. Informative References . . . . . . . . . . . . . . . . . . 16
Appendix A. Duplicate Address Detection (DAD) Considerations . . 18
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
Intellectual Property and Copyright Statements . . . . . . . . . . 23
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1. Introduction
Mobile Ad-hoc Networks (MANETs) connect MANET Routers (MNRs) on links
with asymmetric reachability characteristics (see: [RFC4861], Section
2.2). From the standpoint of IP autoconfiguration, MANETs share
properties with enterprise networks [RFC4852] except that their
topologies may change dynamically over time and there may be
little/no active management by (centralized) network operation
authorities. These specialized characteristics require careful
considerations for MANET router autoconfiguration and operation,
however the same principles apply equally to enterprise network
scenarios that may be neither mobile nor ad-hoc.
MANET autoconfiguration entails the configuration of addresses/
prefixes and other information on routers in MANETs, where addresses
of different scopes may be assigned on various types of interfaces
with diverse properties. The different types of interfaces that may
occur on a MANET router are defined, and the autoconfiguration
mechanisms used for each type are specified. (Out of scope for this
document is the autoconfiguration of Internet-facing interfaces,
which must be coordinated in a manner specific to the service
provider's network.) Figure 1 below depicts the conceptual model for
a MANET Router:
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Internet-facing Interfaces
x x x
| | |
+----------------------+---+--------+----------+
| | | | | M
| | | .... | | A
| +---+---+--------+---+ | N
| | +--------+ /| | E
| I V I x----+ | Host | I /*+------+--< T
| n i n | |Function| n|**| |
| t r t | +--------+ t|**| | I
| e t e x----+ V e|**+------+--< n
| r u r . | E r|**| . | t
| n a f . | T f|**| . | e
| a l a . | +--------+ a|**| . | r
| l c . | | Router | c|**| . | f
| e x----+ |Function| e \*+------+--< a
| s | +--------+ \| | c
| +---+---+--------+---+ | e
| | | .... | | s
| | | | |
+----------------------+---+--------+----------+
| | |
x x x
Site-Interior Interfaces
Figure 1: MANET Router
This document specifies a Virtual Enterprise Traversal (VET)
abstraction for MANET autoconfiguration and operation with multilink
subnet avoidance; both IPv4 [RFC0791] and IPv6 [RFC2460] are
discussed within this context. The use of standard DHCP
[RFC2131][RFC3315] and neighbor discovery [RFC0826][RFC4861]
mechanisms is assumed unless otherwise specified.
This work is related to activites of the IETF autoconf, dhc, ipv6,
manet and v6ops working groups.
2. Terminology
The terms "inner" and "outer" are used throughout this document to
respectively refer to the innermost IP {address, protocol, header,
packet, etc.} *before* encapsulation, and the outermost IP {address,
protocol, header, packet, etc.} *after* encapsulation. (There may
also be "mid-layer" encapsulations between the inner and outer
layers, including IPSec [RFC4301], the Subnetwork Encapsulation and
Adaptation Layer (SEAL) [I-D.templin-seal], etc.)
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The terminology in [I-D.ietf-autoconf-manetarch] and the normative
references apply. The following terms are defined within the scope
of this document:
subnetwork
the same as defined in [RFC3819].
Mobile Ad-hoc Network (MANET)
a connected network region of MANET routers that maintain a
routing structure among themselves over asymmetric reachability
links (see: [RFC4861], Section 2.2). Further information on
MANETs can be found in [RFC2501] and
[I-D.ietf-autoconf-manetarch].
MANET Router (MNR)
a mobile router that forwards packets over MANET interfaces. For
the purpose of this specification, an MNR comprises a router
function, a host function, one or more MANET interfaces and zero
or more internal virtual, site-interior, Internet-facing and VET
interfaces.
MANET Border Router (MNBR)
an MNR that connects other networks to the MANET and/or connects
the MANET to other networks, including the Internet. MNBRs also
configure a seperate VET interface (used for automatic tunneling)
for each distinct MANET they connect to. All MNBRs are also MNRs.
MANET Gateway (MNGW)
a MNBR that connects the MANET to the Internet via Internet-facing
interfaces and can delegate addresses/prefixes to other MNBRs.
All MNGWs are also MNBRs.
Internal Virtual Interface
a MNBR's attachment to an internal virual link (e.g., a loopback
). Internal virtual interfaces are also considered as site-
interior interfaces.
Site-interior Interface
a MNBR's attachment to a link (e.g., an ethernet, a wireless
personal area network, etc.) that it connects to the MANET and/or
the Internet.
Internet-facing Interface
a MNBR's attachment to the Internet, or to a provider network
outside of the MANET via which the Internet can be reached.
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MANET Interface
a MNR's attachment to a link in a MANET. A MANET interface is
"neutral" in its orientation, i.e., it is inherently neither site-
interior nor Internet-facing. In particular, a packet may need to
be forwarded over several MANET interfaces before it is forwarded
via either a site-interior or Internet-facing interface.
MANET Local Address (MLA)
a MANET-scoped IP address (e.g., an IPv6 Unique Local Address
[RFC4193], an IPv4 privacy address [RFC1918], etc.) that is
assigned to a MANET interface and unique within the MANET. MLAs
are used as identifiers for operating the routing protocol and/or
locators for packet forwarding within the scope of the MANET; MLAs
are also used as *outer* IP addresses during encapsulation.
Virtual Enterprise Traversal (VET)
an abstraction that uses IP-in-IP encapsulation to span a multi-
link network (e.g., a MANET) in a single (inner) IP hop.
VET interface
a MNBR's interface used for virtual enterprise traversal. The
MNBR configures a VET interface over a set of underlying MANET
interface(s) belonging to the same MANET. The VET interface
encapsulates each inner IP packet in any mid-layer headers plus an
outer IP header then forwards it on an underlying MANET interface
such that the TTL/Hop Limit in the inner header is not decremented
as the packet traverses the MANET. The VET interface presents an
automatic tunneling abstraction that represents the MANET as a
single IP hop.
The following additional abbreviations are used throughout the
document:
CGA - Cryptographically Generated Address
DHCP[v4,v6] - the Dynamic Host Configuration Protocol
IP[v4,v6] - the Internet Protocol
ISATAP - Intra-Site Automatic Tunnel Addressing Protocol
ND - Neighbor Discovery
PIO - Prefix Information Option
RIO - Route Information Option
RS/RA - IPv6 Neighbor Discovery Router Solicitation/Advertisement
SEAL - Subnetwork Encapsulation and Adaptation Layer
SLAAC - IPv6 StateLess Address AutoConfiguation
3. MANET Characteristics
MNRs typically participate in a routing protocol over MANET
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interfaces to discover routes across the MANET using multiple Layer-2
or Layer-3 forwarding hops if necessary. MANETs may also connect to
other networks via MANET Border Routers (MNBRs) and connect to the
Internet via MANET Gateways (MNGWs). A MANET may be as simple as a
small collection of MNRs (and their attached networks); a MANET may
also contain other MANETs and/or be a subnetwork of a larger MANET.
MANETs that comprise homogeneous link types within a single IP subnet
can configure the routing protocol to operate as a sub-IP layer
mechanism such that IP 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 without IP layer encapsulation.
MANETs that comprise heterogeneous link types and/or multiple IP
subnets must also provide a routing service that operates as an IP
layer mechanism, e.g., to accommodate 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
such that specific autoconfiguration procedures are necessary to
avoid multilink subnet issues [RFC4903]. In particular, we describe
herein the use of IP-in-IP encapsulation to span the MANET in a
single (inner) IP hop in order to avoid the multilink subnet issues
that arise when MANET interfaces are used directly by applications.
Conceptually, a MNR embodies both a host function and router
function. The host function enables the MNR to generate and receive
packets over any of its non-MANET interfaces according to the weak
end system model [RFC1122]. The router function connects the MNR's
attached networks to MANETs via MANET interfaces and/or connects the
MANET to other networks including the Internet (see: Figure 1).
MNBRs also configure a VET interface that views all routers in the
MANET as single-hop neighbors, where the MANET can also appear as a
single IP hop within another MANET. MNBRs configure a seperate VET
interface for each distinct MANET to which they connect, and discover
a list of MNBRs for each VET interface that can be used for
forwarding packets to off-MANET destinations. The following sections
present the Virtual Enterprise Traversal approach for MANET
Autoconfiguration.
4. MANET Router Autoconfiguration
MNRs configure one or more MANET interfaces and engage in any MANET
routing protocols over those interfaces. They also configure zero or
more Internet-facing interfaces that connect the MANET to the
Internet, and zero or more site-interior interfaces (including
internal virtual interfaces such as a loopback interface) that attach
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other networks to the MANET.
MNRs that configure site-interior/Internet-facing interfaces also act
as MNBRs, and configure a VET interface over a set of underlying
MANET interfaces belonging to the same MANET. (Note that a MNBR may
connect to multiple distinct MANETs, in which case it would configure
multiple VET interfaces.) MNRs obtain addresses/prefixes and other
autoconfiguration information using the mechanisms specified in the
following sections.
4.1. MANET Interface Autoconfiguration
When a MNR joins a MANET, it first configures a unique IPv6 link-
local address on each MANET interface that requires an IPv6 link-
local capability and an IPv4 link-local address on each MANET
interface that requires an IPv4 link-local capability. IPv6 link-
local address generation mechanisms that provide sufficient
uniqueness include Cryptographically Generated Addresses (CGAs)
[RFC3972], StateLess Address AutoConfiguration (SLAAC) using EUI-64
interface identifiers [RFC4862], etc. The mechanisms specified in
[RFC3927] provide an IPv4 link-local address generation capability.
Next, the MNR configures a MANET Local Address (MLA) of the outer IP
protocol version on each of its MANET interfaces and engages in any
MANET routing protocols on those interfaces. The MNR can configure
an MLA via explicit management, DHCP autoconfiguration, pseudo-random
self-generation from a suitably large address pool, or through an
alternate autoconfiguration mechanism.
DHCP configuration of MLAs may require support from relays within the
MANET that have already autoconfigured an MLA as well as a MANET-wide
multicast forwarding capability. For DHCPv6, relays that do not
already know the MLA of a server relay requests to the
'All_DHCP_Servers' site-scoped IPv6 multicast group. For DHCPv4,
relays that do not already know the MLA of a server relay requests to
the site-scoped IPv4 multicast group address TBD (see: Section 6).
DHCPv4 servers that delegate MLAs join the TBD multicast group and
service any DHCPv4 messages received for that group.
Self-generation of MLAs for IPv6 can be from a large IPv6 local-use
address range, e.g., IPv6 Unique Local Addresses [RFC4193]. Self-
generation of MLAs for IPv4 can be from a large IPv4 private address
range, e.g., 240/4 [I-D.fuller-240space]. When self-generation is
used alone, the MNR must continuously monitor the MLAs for
uniqueness, e.g., by monitoring the routing protocol, sending
beacons, etc. (This continuous monitoring process is sometimes known
as "in-service duplicate address detection").
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A combined approach using both DHCP and self-generation is also
possible. In this combined approach, the MNR first self-generates a
temporary MLA which it will use only for the purpose of procuring an
actual MLA from a DHCP server. Acting as a combined client/relay,
the MNR then uses the temporary MLA to engage in the routing protocol
and performs a relay-server exchange using the temporary MLA as an
address for the relay. When the DHCP server delegates an actual MLA,
the MNR abandons the temporary MLA, assigns the actual MLA to the
MANET interface and re-engages in the routing protocol. Note that
the range of MLAs delegated by a DHCP server must be disjoint from
the range of MLAs used by the MNR for self-generation.
4.2. VET Interface Autoconfiguration
MNBRs configure a VET interface over a set of underlying MANET
interfaces belonging to the same MANET, where the VET interface sees
all MNBRs in the MANET as single hop neighbors. Inner IP packets
forwarded over the VET interface are encapsulated in any mid-layer
headers (e.g., IPsec, the SEAL header, etc.) followed by an outer IP
header, then submitted to the outer IP forwarding engine for
transmission on an underlying MANET interface (further encapsulation
details are specified in Section 5.)
When IPv6 and IPv4 are used as the inner/outer protocols
(respectively), the MNBR autoconfigures an ISATAP link-local address
([RFC5214], Section 6.2) on the VET interface to support packet
forwarding and operation of the IPv6 neighbor discovery protocol.
The ISATAP address embeds an IPv4 MLA assigned to an underlying MANET
interface, and need not be checked for uniqueness since the IPv4 MLA
itself was already determined to be unique. Link-local address
configuration for other inner/outer IP protocol combinations is
through administrative configuration or through an unspecified
alternate method.
After the MNBR configures a VET interface, it can communicate with
other MNBRs as single-hop neighbors, i.e., it can confirm
reachability of other MNBRs through Neighbor Discovery (ND) and/or
DHCP exchanges over the VET interface. (The MNBR can also confirm
reachability through information conveyed in the MANET routing
protocol or through some other means associated with the specific
MANET subnetwork technology.)
The MNBR must be able to detect and recover from the loss of VET
interface neighbors due to e.g., MANET partitions, node failures,
etc. Mechanisms specified outside of this document such as
monitoring the routing protocol, ND beaconing/polling, DHCP renewals/
leasequeries, upper layer protocol hints of forward progress,
bidirectional forward detection, detection of network attachment,
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etc. can be used according to the particular deployment scenario.
4.3. MANET Gateway List Discovery and MANET Identification
After the MNBR configures its VET interfaces, it next discovers a
list of MNGWs for each distinct MANET to which it connects. The list
can be discovered through information conveyed in the routing
protocol or through the discovery mechanisms outlined in [RFC5214],
Section 8.3.2.
In particular, whether or not routing information is available the
MNBR can discover the list of MNGWs by resolving an identifying name
for the MANET using a MANET-local name resolution service (such as
LLMNR [RFC4759] over the VET interface). In the absence of other
identifying names, the MNBR can resolve either the hostname "6over4"
or the FQDN "6over4.example.com" (i.e., if a MANET-specific suffix
"example.com" is known) for multicast-capable MANETs. For non-
multicast MANETs, the MNBR can instead resolve the hostname "isatap"
or the FQDN "isatap.example.com".
Identifying names along with addresses of MNGWs and/or the prefixes
they aggregate serve as an identifier for the MANET.
4.4. Site-interior Interface Autoconfiguration
MNBRs can acquire addresses and/or prefix delegations for assignment
on site-interior interfaces through autoconfiguration exchanges with
MNGWs over the VET interface. Site-interior interface
autoconfiguration considerations are discussed in the following
sections:
4.4.1. Autoconfiguration of IPv4 Addresses/Prefixes
When IPv4 is used as the inner protocol, the MNBR discovers the
addresses of one or more MNGWs that delegate IPv4 prefixes then
performs a DHCPv4 prefix delegation exchange
[I-D.ietf-dhc-subnet-alloc] over the VET interface to obtain IPv4
prefixes for assignment and/or sub-delegation on its site-interior
interfaces.
To perform the DHCPv4 prefix delegation exchange, a DHCPv4 client
associated with the MNBR's host function forwards a DHCPDISCOVER
message with a Subnet Allocation option to a DHCPv4 relay associated
with its router function, i.e., the MNBR acts as both client and
relay. The relay then forwards the message over the VET interface to
the DHCPv4 server on a MNGW. The forwarded DHCPDISCOVER will elicit
a DHCPOFFER from the server containing IPv4 prefix delegations, and
the MNBR completes the delegation through a DHCPREQUEST/DHCPACK
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exchange (again using the combined client/relay approach).
When the MNBR receives IPv4 prefix delegations, it assigns the
prefixes on site-interior interfaces; it does not assign them on the
VET interface or on MANET interfaces. The MNBR can also obtain /32
prefixes using DHCPv4 prefix delegation the same as for any IPv4
prefix, and can assign them as IPv4 addresses with /32 netmasks on
site-interior interfaces.
4.4.2. Autoconfiguration of IPv6 Addresses/Prefixes
When IPv6 is used as the inner protocol, the MNBR sends unicast IPv6
Router Solicitation (RS) messages to MNGWs over the VET interface to
receive Router Advertisements (RAs) with Prefix Information Options
(PIOs) and/or with the 'M' flag set to signify whether DHCPv6
autoconfiguration is available. When the MNBR receives an RA
containing PIOs with the 'A' and 'L' bits set to 1, it autoconfigures
IPv6 addresses from the prefixes using SLAAC and assigns them to the
VET interface. (When IPv4 is used as the outer IP protocol, the
addresses are autoconfigured and assigned as ISATAP addresses the
same as specified in [RFC5214].)
When the MNBR receives an RA with the 'M' flag set to 1, the MNGW
that sent the RA also hosts a DHCPv6 server capable of delegating
IPv6 prefixes (support for the MNGW acting as a DHCPv6 relay may be
considered in the future). If the RA also contains PIOs with the 'L'
bit set to 0, the MNBR can use them as hints of prefixes the server
is willing to delegate. For example, a MNGW can include a PIO with a
prefix such as 2001::DB8::/48 as a hint of an aggregated prefix from
which it is willing to delegate longer prefixes. Whether or not such
hints are available, the MNBR (acting as a requesting router) can use
DHCPv6 prefix delegation [RFC3633] over the VET interface to obtain
IPv6 prefixes from the MNGW (acting as a delegating router). The
MNBR can then use the delegated prefixes for assignment and/or sub-
delegation on its site-interior interfaces.
The MNBR obtains prefixes using either a 2-message or 4-message
DHCPv6 exchange [RFC3315]. For example, to perform the 2-message
exchange a DHCPv6 client associated with the MNBR's host function
forwards a Solicit message with an IA_PD option to a DHCPv6 relay
associated with its router function, i.e., the MNBR acts as both
client and relay. The relay then forwards the message over the VET
interface to the DHCPv6 server. The forwarded Solicit message will
elicit a Reply from the server containing IPv6 prefix delegations.
When the MNBR receives IPv6 prefix delegations, it assigns the
prefixes on site-interior interfaces only; it does not assign them on
Internet-facing, VET, or MANET interfaces (see: [RFC3633], Section
12.1).
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The MNBR can also propose a specific prefix to the DHCPv6 server per
Section 7 of [RFC3633], e.g., if a prefix delegation hint is
available. The server will check the proposed prefix for consistency
and uniqueness, then return it in the reply to the MNBR if it was
able to perform the delegation. The MNBR can use mechanisms such as
CGAs [RFC3972], IPv6 privacy address [RFC4941], etc. to self-generate
addresses in conjunction with prefix delegation.
4.4.3. Prefix and Route Maintenance
When DHCP prefix delegation is used, the MNGW's DHCP server ensures
that the delegations are unique within the MANET and that its router
function will forward IP packets over the VET interface to the MNBR
to which the prefix was delegated. The prefix delegation remains
active as long as the MNBR continues to issue renewals over the VET
interface before the lease lifetime expires. The lease lifetime also
keeps the delegation state active even if communications between the
MNBR and MNGW is disrupted for a period of time (e.g., due to a MANET
partition) before being reestablished (e.g., due to a MANET merge).
Since the DHCP client and relay are co-resident on the same MNBR, no
special coordination is necessary for the MNGW to maintain routing
information. The MNGW simply retains forwarding information base
entries that identify the MNBR as the next-hop toward the prefix via
the VET interface, and issues ordinary redirects over the VET
interface when necessary .
4.5. Portable and Self-Configured IP Prefixes
Independent of any MNGW-aggregated addresses/prefixes (see:
Section 4.4), a MNBR can retain portable IP prefixes (e.g., prefixes
taken from a home network, IPv6 Unique Local Addresses (ULAs)
[RFC4193][I-D.ietf-ipv6-ula-central], etc.) as it travels between
visited networks as long it coordinates in some fashion, e.g., with a
mapping agent, prefix aggregation authority, etc. MNBRs can sub-
delegate portable (and other self-configured) prefixes on networks
connected on their site-interior interfaces.
Portable prefixes are not aggregated, redistributed or advertised by
MNGWs and can therefore travel with the MNBR as it moves to new
visited networks and/or configures peering arrangements with other
nodes. Generation and coordination of portable (and other self-
configured) prefixes can therefore occur independently of any other
autoconfiguration considerations.
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4.6. Separation of IP Addressing Domains
When the inner and outer IP protocols are different (i.e., IPv6-in-
IPv4 or IPv4-in-IPv6), the MNBR's dual-stack orientation provides a
natural separation between the inner and outer IP addressing domains,
and separate default routes can be configured for each domain.
When the inner and outer IP protocols are the same (i.e., IPv4-in-
IPv4 or IPv6-in-IPv6) separation between inner and outer IP
addressing domains can only be determined through the examination of
IP prefixes. In that case, special configurations/mechanisms may be
necessary to support unambiguous determination of when to encapsulate
using the VET interface vs when to forward using a MANET interface.
5. Post-Autoconfiguration Operation
After a MNR has been autoconfigured, it participates in any MANET
routing protocols over MANET interfaces and forwards outer IP packets
within the MANET as for any ordinary router. MNBRs can additionally
participate in any inner IP routing protocols over non-MANET
interfaces and forward inner IP packets to off-MANET destinations.
The following sections discuss post-autoconfiguration operations:
5.1. Forwarding Packets to Off-MANET Destinations
MNBRs consult the inner IP forwarding table to determine the next hop
address (e.g., the VET interface address of another MNBR) for
forwarding packets to off-MANET destinations. When there is no
forwarding information available, the MNBR can discover the next-hop
through FQDN or reverse lookup using the same name resolution
services as for MNGW discovery (see Section 4.3).
For forwarding to next-hop addresses over VET interfaces that use
IPv6-in-IPv4 encapsulation, MNBRs determine the outer destination
address through static extraction of the IPv4 address embedded in the
next-hop ISATAP address. For other IP-in-IP encapsulations,
determination of the outer destination address is through
administrative configuration or through an unspecified alternate
method.
MNBRs that use IPv6 as the inner protocol can discover default router
preferences and more-specific routes [RFC4191] by sending an RS over
the VET interface to elicit an RA from another MNBR. After default
and/or more-specific routes are discovered, the MNBR can forward IP
packets via a specific MNBR as the next-hop router on the VET
interface. When multiple default routers are available, the MNBR can
use default router preferences, routing protocol information, traffic
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engineering configurations, etc. to select the best exit router.
5.2. MANET-Local Communications
When permitted by policy, pairs of MNRs that configure the endpoints
of a communications session can avoid VET interface encapsulation by
directly invoking the outer IP protocol using MLAs assigned to their
MANET interfaces. For example, when the outer protocol is IPv4 a
pair of communicating MNRs can use IPv4 MLAs for direct
communications over their MANET interfaces without using the VET
interface.
5.3. Multicast
In multicast-capable deployments, MNRs provide a MANET-wide
multicasting service such as Simplified Multicast Forwarding (SMF)
[I-D.ietf-manet-smf] over their MANET interfaces such that outer IP
multicast messages of site- or greater scope will be propagated
across the MANET. For such deployments, MNBRs can also provide an
inner IP multicast/broadcast capability over their VET interfaces
through mapping of the inner IP multicast address space to the outer
IP multicast address space.
MNBRs encapsulate inner IP multicast messages sent over the VET
interface in any mid-layer headers (e.g., IPsec, SEAL, etc.) plus an
outer IP header with a site-scoped outer IP multicast address as the
destination. For the case of IPv6 and IPv4 as the inner/outer
protocols (respectively), [RFC2529] provides mappings from the IPv6
multicast address space to the IPv4 multicast address space. For
other IP-in-IP encapsulations, mappings are established through
administrative configuration or through an unspecified alternate
method.
For multicast-capable MANETs, use of the inner IP multicast service
for operating the ND protocol over the VET interface is available but
should be used sparingly to minimize MANET-wide flooding. Therefore,
MNBRs should use unicast ND services over the VET interface instead
of multicast whenever possible.
5.4. Service Discovery
MNRs can peform MANET-wide service discovery using a suitable name-
to-address resolution service. Examples of flooding-based services
include the use of LLMNR [RFC4759] over the VET interface or mDNS
[I-D.cheshire-dnsext-multicastdns] over an underlying MANET
interface. More scalable and efficient service discovery mechanisms
for MANETs are for further study.
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6. IANA Considerations
A site-scoped IPv4 multicast group (TBD) for DHCPv4 server discovery
is requested.
7. Security Considerations
Security considerations for MANETs are found in
[RFC2501][I-D.ietf-autoconf-manetarch] and apply also to the
mechanisms and procedures specified in this document.
Security considerations for MANET routing protocols that may be used
within this context are found in their respective specifications.
8. Related Work
The authors acknowledge the work done by Brian Carpenter and Cyndi
Jung in [RFC2529] that introduced the concept of intra-site automatic
tunneling. This concept was later called: "Virtual Ethernet" and
investigated by Quang Nguyen under the guidance of Dr. Lixia Zhang.
Telcordia has proposed DHCP-related solutions for the CECOM MOSAIC
program. The Naval Research Lab (NRL) Information Technology
Division uses DHCP in their MANET research testbeds. Various
proposals within the IETF have suggested similar mechanisms.
9. Acknowledgements
The following individuals gave direct and/or indirect input that was
essential to the work: Jari Arkko, Teco Boot, Emmanuel Bacelli, James
Bound, Thomas Clausen, Eric Fleischman, Bob Hinden, Joe Macker,
Thomas Narten, Alexandru Petrescu, John Spence, Jinmei Tatuya, Dave
Thaler, Michaela Vanderveen and others in the IETF AUTOCONF and MANET
working groups. Many others have provided guidance over the course
of many years.
10. Contributors
Thomas Henderson (thomas.r.henderson@boeing.com) contributed to this
document. Ian Chakeres (ian.chakeres@gmail.com) contributed to
earlier versions of the document.
11. References
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11.1. Normative References
[I-D.ietf-dhc-subnet-alloc]
Johnson, R., "Subnet Allocation Option",
draft-ietf-dhc-subnet-alloc-07 (work in progress),
July 2008.
[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.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, 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.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
11.2. Informative References
[I-D.cheshire-dnsext-multicastdns]
Cheshire, S. and M. Krochmal, "Multicast DNS",
draft-cheshire-dnsext-multicastdns-06 (work in progress),
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August 2006.
[I-D.fuller-240space]
Fuller, V., "Reclassifying 240/4 as usable unicast address
space", draft-fuller-240space-02 (work in progress),
March 2008.
[I-D.ietf-autoconf-manetarch]
Chakeres, I., Macker, J., and T. Clausen, "Mobile Ad hoc
Network Architecture", draft-ietf-autoconf-manetarch-07
(work in progress), November 2007.
[I-D.ietf-ipv6-ula-central]
Hinden, R., "Centrally Assigned Unique Local IPv6 Unicast
Addresses", draft-ietf-ipv6-ula-central-02 (work in
progress), June 2007.
[I-D.ietf-manet-smf]
Macker, J. and S. Team, "Simplified Multicast Forwarding
for MANET", draft-ietf-manet-smf-07 (work in progress),
February 2008.
[I-D.templin-seal]
Templin, F., "The Subnetwork Encapsulation and Adaptation
Layer (SEAL)", draft-templin-seal-23 (work in progress),
August 2008.
[RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2501] Corson, M. and J. Macker, "Mobile Ad hoc Networking
(MANET): Routing Protocol Performance Issues and
Evaluation Considerations", RFC 2501, January 1999.
[RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529, March 1999.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC3753] Manner, J. and M. Kojo, "Mobility Related Terminology",
RFC 3753, June 2004.
[RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,
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Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, July 2004.
[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.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4759] Stastny, R., Shockey, R., and L. Conroy, "The ENUM Dip
Indicator Parameter for the "tel" URI", RFC 4759,
December 2006.
[RFC4852] Bound, J., Pouffary, Y., Klynsma, S., Chown, T., and D.
Green, "IPv6 Enterprise Network Analysis - IP Layer 3
Focus", RFC 4852, April 2007.
[RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
June 2007.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
Appendix A. Duplicate Address Detection (DAD) Considerations
A-priori uniqueness determination (also known as "pre-service DAD")
for an MLA assigned on a MANET interface (such as specified in
[RFC4862]) 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 localized 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 intermittent connectivity. 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 IPv6 MLAs can be generated with mechanisms such as
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CGAs, IPv6 privacy addresses, etc. with very small probability of
collision. Pseudo-random IPv4 MLAs can be generated through random
assignment from a suitably large IPv4 prefix space, e.g., the soon-
to-be-reclassified 240/4 space [I-D.fuller-240space].
Consistent operational practices can assure uniqueness for MNGW-
aggregated addresses/prefixes, while statistical properties for
pseudo-random address self-generation can assure uniqueness for the
MLAs assigned on a MNR's MANET interfaces. Still, an MLA delegation
authority should be used when available, while a passive in-service
DAD mechanism should be used to detect MLA duplications when there is
no MLA delegation authority.
Appendix B. Change Log
(Note to RFC editor - this section to be removed before publication
as an RFC.)
Changes from -14 to 15:
o title change to "Virtual Enterprise Traversal (VET) for MANETs".
o Address review comments
Changes from -12 to 14:
o title change to "The MANET Virtual Ethernet Abstraction".
o Minor section rearrangement.
o Clartifications on portable and self-configured prefixes.
o Clarifications on DHCPv6 prefix delegation procedures.
Changes from -11 to 12:
o title change to "MANET Autoconfiguration using Virtual Ethernet".
o DHCP prefix delegation for both IPv4 and IPv6 as primary address
delegation mechanism.
o IPv6 SLAAC for address autoconfiguration on the VET interface.
o fixed editorials based on comments received.
Changes from -10 to 11:
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o removed the transparent/opaque VET portal abstractions.
o removed routing header as an option for MANET exit router
selection.
o included IPv6 SLAAC as an endorsed address configuration mechanism
for the VET interface.
Changes from -08 to -09:
o Introduced the term "VET".
o Changed address delegation language to speak of "MNBR-aggregated"
instead of global/local.
o Updated figures 1-3.
o Explained why a MANET interface is "neutral".
o Removed DHCPv4 "MLA Address option". Now, MNBRs can only be
DHCPv4 servers; not relays.
Changes from -07 to -08:
o changed terms "unenhanced" and "enhanced" to "transparent" and
"opaque".
o revised MANET Router diagram.
o introduced RFC3753 terminology for Mobile Router; ingress/egress
interface.
o changed abbreviations to "MNR" and "MNBR".
o added text on ULAs and ULA-Cs to "Self-Generated Addresses".
o rearranged Section 3.1.
o various minor text cleanups
Changes from -06 to -07:
o added MANET Router diagram.
o added new references
o various minor text cleanups
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Changed from -05 to -06:
o Changed terms "raw" and "cooked" to "unenhanced" and "enhanced".
o minor changes to preserve generality
Changed from -04 to -05:
o introduced conceptual "virtual ethernet" model.
o support "raw" and "cooked" modes as equivalent access methods on
the virutal ethernet.
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.
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
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Authors' Addresses
Fred L. Templin (editor)
Boeing Phantom Works
P.O. Box 3707 MC 7L-49
Seattle, WA 98124
USA
Email: fltemplin@acm.org
Steven W. Russert
Boeing Phantom Works
P.O. Box 3707 MC 7L-49
Seattle, WA 98124
USA
Email: steven.w.russert@boeing.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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