Network Working Group J. Macker, editor
Internet-Draft NRL
Intended status: Standards Track SMF Design Team
Expires: April 8, 2007 IETF MANET WG
October 5, 2006
Simplified Multicast Forwarding for MANET
draft-ietf-manet-smf-03
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Abstract
This document describes the Simplified Multicast Forwarding (SMF)
protocol that provides a basic IP multicast forwarding capability
suitable for mobile ad-hoc networks (MANET). SMF is designed to have
limited applicability as a forwarding mechanism for multicast packets
within MANET routing areas. In addition, it provides mechanisms to
support interoperability with a connected fixed-infrastructure
networks. SMF uses a simplified forwarding mechanism that delivers
multicast packets to all MANET multicast receivers within a MANET
routing area. The core design does not use receiver specific group
information in favor of reduced complexity and state maintenance
within the mobile topology. Group-specific extensions may follow in
later specifications. The design accounts for the unique nature and
behavior of MANET interfaces and takes advantage of efficient relay
set algorithms previously designed and applied in the MANET routing
control plane. This document describes the SMF forwarding mechanisms
in detail, its use with the MANET Neighborhood Discovery Protocol
(NHDP), and several efficient relay set algorithms specified for use
in conjunction with SMF.
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Table of Contents
1. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4
2. Introduction and Scope . . . . . . . . . . . . . . . . . . . . 5
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Applicability and Scope . . . . . . . . . . . . . . . . . 7
3. SMF Core Design Issues . . . . . . . . . . . . . . . . . . . . 9
3.1. Previous Related Work . . . . . . . . . . . . . . . . . . 10
4. SMF Packet Processing and Forwarding . . . . . . . . . . . . . 11
5. SMF Duplicate Packet Detection . . . . . . . . . . . . . . . . 14
5.1. SMF IPv4 Packet Identification . . . . . . . . . . . . . . 15
5.2. SMF IPv6 Packet Identification . . . . . . . . . . . . . . 16
5.2.1. IPv6 SMF-DPD Header Option Format . . . . . . . . . . 17
6. Relay Set Selection . . . . . . . . . . . . . . . . . . . . . 18
7. SMF Neighborhood Discovery Requirements . . . . . . . . . . . 19
7.1. NHDP Description and SMF Requirements . . . . . . . . . . 19
8. SMF Multicast Border Gateway Considerations . . . . . . . . . 21
8.1. Forwarded Multicast Groups . . . . . . . . . . . . . . . . 21
8.2. Multicast Group Scoping . . . . . . . . . . . . . . . . . 22
8.3. Duplicate Packet Detection Marking . . . . . . . . . . . . 23
8.4. Interface with Exterior Multicast Routing Protocols . . . 23
8.5. Multiple Gateways . . . . . . . . . . . . . . . . . . . . 24
8.6. Non-SMF MANET Nodes . . . . . . . . . . . . . . . . . . . 25
9. Security Considerations . . . . . . . . . . . . . . . . . . . 26
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
12.1. Normative References . . . . . . . . . . . . . . . . . . . 29
12.2. Informative References . . . . . . . . . . . . . . . . . . 29
Appendix A. Source-based Multipoint Relay (S-MPR) . . . . . . . . 31
A.1. S-MPR Relay Set Selection . . . . . . . . . . . . . . . . 32
A.2. Neighborhood Discovery Requirements . . . . . . . . . . . 32
Appendix B. Essential Connecting Dominating Set (E-CDS)
Algorithm . . . . . . . . . . . . . . . . . . . . . . 33
B.1. E-CDS Relay Set Selection . . . . . . . . . . . . . . . . 33
B.2. E-CDS Forwarding Rules . . . . . . . . . . . . . . . . . . 33
B.3. Neighborhood Discovery Requirements . . . . . . . . . . . 34
Appendix C. Multipoint Relay Connected Dominating Set
(MPR-CDS) Algorithm . . . . . . . . . . . . . . . . . 35
C.1. MPR-CDS Relay Set Selection . . . . . . . . . . . . . . . 35
C.2. MPR-CDS Forwarding Rules . . . . . . . . . . . . . . . . . 35
C.3. Neighborhood Discovery Requirements . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36
Intellectual Property and Copyright Statements . . . . . . . . . . 37
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1. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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2. Introduction and Scope
Design and implementation progress has been made in demonstrating
effective ways to flood control packets within dynamic wireless
routing protocols. For example, algorithms within MANET RFC 3626
[RFC3626]and RFC 3684 [RFC3684] specify distributed methods of
dynamically electing reduced relay sets that efficiently optimize the
flooding of routing control packets amongst MANET routing nodes. In
this document, we specify the Simplified Multicast Forwarding (SMF)
framework. The main purpose of SMF is to adapt known efficient
flooding designs in MANET environments and apply these mechanisms to
IP multicast packet forwarding. When localized efficient flooding is
a sufficient technique, SMF can provide simplified multicast
forwarding to data flows within a MANET routing area. The SMF
baseline design limits the scope to basic, best effort multicast
forwarding and its applicability is intended to be constrained within
a MANET routing area. Figure 1 provides an overview of the logical
SMF node architecture, consisting of "Neighborhood Discovery", "Relay
Set Selection" and "Forwarding Process" components. Typically, relay
set selection (or even self-election) will occur based on input from
a neighborhood discovery process, and the forwarding process will be
controlled by status based upon relay set selection. In some cases,
the forwarding decision for a packet may also depend on previous hop
or incoming interface information. The asterisks (*) in Figure 1
mark the primitives and relationships needed by relay set algorithms
requiring previous-hop packet forwarding knowledge.
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______________ _____________
| | | |
| Neighborhood | | Relay Set |
| Discovery |------------->| Selection |
| Protocol | neighbor | Algorithm |
|______________| info |_____________|
\ /
\ /
neighbor\ /fowarding
info* \ ____________ / status
\ | | /
`-->| Forwarding |<--'
| Process |
~~~~~~~~~~~~~~~~~>|____________|~~~~~~~~~~~~~~~~~>
incoming packet, forwarded packets
interface id, and
previous hop*
Fig. 1 - SMF Node Architecture
SMF is a network layer multicast forwarding process compatible with
different neighborhood discovery protocols and relay set selection
algorithms. Different discovery mechanisms or relay set algorithms
may be applicable for different MANET routing protocols and
deployments. In the simplest case, Classical Flooding (CF) is
supported, eliminating the need for any relay set algorithm or
neighborhood topology information. However, more efficient flooding
techniques will typically be preferred due to expected gains in
network efficiency and reductions in wireless congestion and
contention. Efficient flooding is realized by selecting a _subset_
of all possible nodes in a MANET area as the forwarding relay set.
Algorithms and running code exist that makes use of local network
neighborhood topology information to determine an appropriate relay
set in a distributed, dynamic fashion. These relay set selection
algorithms can be used to provide a distribution tree for user
multicast data[MDC04]. A few such relay set selection algorithms are
described in Appendices of this document, but additional relay set
algorithms or extensions may be specified in the future for use with
SMF.
Dynamic neighborhood topology information is often needed by
distributed relay set algorithms to determine and maintain an
optimized set of forwarding nodes. It is generally expected that
neighborhood topology discovery functions will be provided by a MANET
unicast routing protocol or a MANET NeighborHood Discovery Protocol
(NHDP) implementation running in concurrence with SMF. This
specification does not preclude a lower link layer from providing the
necessary neighborhood information through an enhanced interface.
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Different distributed relay set algorithms and associated forwarding
decision logic can have differing neighborhood discovery and
signaling demands. This document states specific requirements for
neighborhood discovery with respect to the forwarding process and
relay set selection algorithms described herein and relies on the
MANET NHDP specification to support operation independent of any
MANET unicast protocol and any lower layer information. As
mentioned, the CF mode can be supported with or without neighborhood
information or related discovery.
2.1. Terminology
MANET : Mobile Ad hoc Network
SMF : Simplified Multicast Forwarding
CF : Classical Flooding
CDS : Connected Dominating Set
MCDS : Minimum Connected Domination Set
MPR : Multi-point Relay
DPD: Duplicate Packet Detection
NHDP: Neighborhood Discovery Protocol
2.2. Applicability and Scope
A basic packet forwarding service that reaches all destinations
participating within a MANET area can provide a useful group
communication mechanism for an application layer. While the design
requirements for this are similar to those needed by the control
plane of many MANET unicast routing protocol layers, it is desirable
to provide a more general IP multicast forwarding function for use by
a variety of applications. This can be useful for some multicast
application flows that are global in scope but also is useful for
site-scoped multicast applications and data flows within a MANET
routing area. There are a number of application areas that could
take advantage of a simple site-scoped multicast forwarding service
within a MANET routing region (e.g., multimedia streaming, peer-to-
peer middleware multicasting, auto-configuration, and multi-hop
discovery services).
Note that Figure 1 provides a notional architecture for _typical_
MANET SMF-capable nodes. However, a goal is that simple end-system
(non-forwarding) wireless nodes may also participate in multicast
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traffic transmission and reception with standard network layer
semantics. Also, a multicast border gateway or proxying mechanism
MUST be used when interoperating with other IP multicast routing such
as that for fixed-infrastructure networks (e.g., PIM). In present
experiments, proxying methods have been used to enable some gateway
functionality at MANET border gateways operating with external IP
multicast routing protocol interfaces. Although SMF may be extended
or combined with other protocols to provide increased reliability and
group specific forwarding state, the details of those methods will be
discussed in other documents.
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3. SMF Core Design Issues
In CF, each participating forwarder node is required to rebroadcast
packets intended for dissemination once and only once. This approach
is extremely simple and only requires a means of duplicate packet
detection (DPD) and a basic forwarding mechanism. However, it is
well known that using CF, especially within dense networks, results
in a significant number of redundant transmissions often referred to
as the broadcast storm problem [NTSC99]. Within wireless multi-hop
networks, direct contention and interference is often correlated
beyond a one-hop neighbor link interface. Reducing unnecessary
channel contention within a MANET can significantly improve network
performance. Therefore, minimizing the number of required relay
nodes is a heightened design goal in this environment.
Unfortunately, reducing the number of relay nodes in a MANET
environment can also results in decreased robustness of packet
delivery within a mobile topology. The scenario and system dependent
design tradeoff between relay efficiency and delivery robustness
should be considered carefully. If needed, additional reliability
mechanisms MAY be considered for use with reduced relay sets (e.g.,
backup and redundant relay set) but the specification of limited hop-
by-hop retransmission schemes at the network layer are considered out
of scope for this document. If needed by an application, the use of
IETF reliable multicast transport layer protocols should be
transparently supported by SMF's best effort delivery mechanism. The
core design scope of SMF is to define a DPD mechanism, support simple
CF-based forwarding, and define the use of reduced relay set
algorithms for increased efficiency.
At a theoretic level, work in the area of minimizing packet
forwarders, or relay node sets, is sometimes related to basic graph
theory problems. In graph theory, a Dominating Set (DS) for a graph
is a set of vertices that, along with their neighbors, constitute all
the vertices in the graph. A Connected DS (CDS) is a DS where the
subgraph induced is connected. A Minimum CDS (MCDS) is a set such
that the number of vertices is the minimum required to form a CDS.
Finding a small dominating set is one of the most fundamental
problems of traditional graph theory and is often related to the
problem of optimizing flooding algorithms in MANET routing protocols.
Finding an MCDS in a given graph is known to be NP-hard [GJ79].
These basic static graph theoretic issues are important to apply in
developing efficient relay sets, but MANET relay set selection must
also consider distributed and dynamic operation. To better explain
the design requirements, we formulated the following characteristics
desired of an effective MANET flooding algorithm for use in SMF:
1. A resultant cover set that is small compared to the total number
of nodes as the network scales in size and density.
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2. A robust approach somewhat resilient to network mobility and link
dynamics.
3. A cover set election/maintenance mechanism that is lightweight,
distributed, and adaptive in nature.
3.1. Previous Related Work
Previous work on MANET flooding and reduced relay set mechanisms has
been done and this document borrows from and builds off previous work
accomplished. In [WC02], a taxonomy of flooding algorithms for use
in MANET environments was presented and the work examined performance
issues related to various approaches. Other important work has
developed distributed mechanisms that select and maintain reduced
relay node sets. The design tradeoffs are further complicated by
wireless contention, topological classes, and the robustness of
packet delivery and set election under mobility scenarios. In
addition, the actual protocol implementation for IP multicast
forwarding based upon these flooding algorithms raises additional
design tradeoffs and issues. This includes:
1. protocol state maintenance
2. duplicate packet detection mechanisms
3. packet processing requirements and overhead
4. expected traffic distribution patterns
5. protocol signaling requirements
6. delivery robustness requirements
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4. SMF Packet Processing and Forwarding
The SMF Packet Processing and Forwarding actions are conducted with
the following packet handling activities:
1. Processing of outbound, locally-generated multicast packets.
2. Reception and processing of inbound packets on a specific network
interface(s).
In the case that sequence-based DPD as described in Section 5 is
used, the purpose of intercepting outbound, locally-generated
multicast packets is to apply resequencing of the IPv4 ID header
field or add options headers as needed (e.g. IPv6). In the case
that resequencing is deemed necessary, it is RECOMMENDED that
sequence numbering be applied such that a different sequence number
space per <sourceAddress::destinationAddress> duple be used. For
initial SMF purposes where no distinct routing path decisions for
different IP Multicast address destinations occur, it might appear to
be sufficient to use sequence number spaces aggregated across all IP
Multicast destinations (or across all IP destinations for a source as
is the default implementation of the IPv4 ID field in many operating
systems). However, future SMF extensions, beyond the present
discussion, may contain dynamic forwarding state dependent on the
multicast destination address. The future possibility that different
destinations may be routed differently suggests that "per source/
destination" identification be used. It should be noted that the
default global IPv4 ID sequence space may be sufficient for some SMF
deployments and interception of outbound packets may not be required
if end systems have numbered the IPv4 ID field in an acceptable
manner. In other cases, such as when IPSec headers have been applied
to packets, other sequence information may be available for the SMF
process to make use of in its duplicate table management.
Inbound multicast packets will be received by the SMF implementation
and processed for possible forwarding. Well-known multicast groups
for flooding to all routers of an ad hoc network are specified for
use with the network-layer flooding provided by SMF. These multicast
groups are specified to contain all MANET routers of a contiguous
MANET area, so that packets transmitted to the multicast address
associated with the group will be delivered to all nodes as desired.
For IPv6, the multicast address is specified to be "site-local". The
names of the multicast groups are given as "ALL_IPv4_MANET_ROUTERS"
(TBD) and "ALL_IPv6_MANET_ROUTERS" (TBD). This document does not
support transmissions to any directed broadcast address ranges.
Minimally SMF SHALL forward, as instructed by the the relay set
selection algorithm, unique (non-duplicate) packets received for
these well-known group addresses when the TTL or hop count value in
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the IP header is greater than 1. Optionally, SMF deployments may
choose to forward packets for additional "global scope" multicast
groups to support application needs or to distribute multicast
packets that have ingressed the MANET area via border gateways.
Additional addresses will be specified by an _a priori_ list or
possibly through a implementation of a dynamic address management
interface. In all cases, the following rules SHALL be observed for
SMF multicast forwarding:
1. Multicast packets with TTL <= 1 MUST NOT be forwarded*.
2. Link Local multicast packets MUST NOT be forwarded
3. Incoming multicast packets with an IP source address matching one
of those of the local host interface(s) MUST NOT be forwarded.
4. Received packet frames with the MAC source address matching the
local host interface(s) MUST NOT be forwarded.
Note that rule #3 is important because in wireless networks, the
local host may receive re-transmissions of its own packets when they
are forwarded by neighboring nodes. This rule avoids unnecessary
retransmission of locally-generated packets even when other
forwarding decision rules would apply.
Once these criteria have been met, the implementation should
reference a forwarding decision algorithm, possibly in concert with
duplicate packet detection, to determine the next step in packet
processing. The forwarding decision may be implicit, dependent upon
DPD results, only if the SMF implementation is configured to perform
classical flooding (CF) of IP multicast packets. Otherwise, the
forwarding decision may be controlled using additional information.
Neighborhood discovery protocols coupled with the Source-based Multi-
Point Relay (S-MPR) or other CDS selection algorithms described later
MAY be used to determine the local host's status with respect to
forwarding. For example, algorithms may control forwarding based on
a relay set election and previous hop indentifier (e.g. S-MPR
forwarding), while others may designate the local host as a forwarder
of all neighbor packets based on the neighborhood broadcast topology
(e.g. Essential CDS (E-CDS)).
DPD is a fundamental and critical portion of the SMF forwarding
process. In general, detection of received duplicate packets is
necessary to avoid forwarding the same packet multiple times.
However, in some cases (e.g., S-MPR), duplicate detection of some
non-forwarded packets is also needed to maintain efficient
forwarding. Details on different duplicate packet detection and
forwarding rules for the S-MPR, and E-CDS algorithms are given in
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Appendices of his document. The details for these classes of
algorithms may also apply to other similar algorithms.
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5. SMF Duplicate Packet Detection
One important design difference between routing for MANET interfaces
and classical infrastructure network interfaces is that forwarding a
packet via the same physical interface that it arrived upon is a
normal operation. This operation is often disallowed or discouraged
in many multicast routing designs to avoid possible looping.
Similarly, any Reverse Path Forwarding (RPF) logic used may need to
be softened when operating over a single MANET interface. This MANET
interface characteristic leads to DPD as a common requirement in
MANET packet flooding. While this requires increased per-packet
processing, it is necessary in MANET-specific multicasting because
packets may be forwarded out the same physical interface upon which
they arrived and nodes can receive copies of previously-transmitted
packets from other forwarding neighbors. This section describes a
basic SMF DPD mechanism and some alternative operational options as
considerations.
SMF SHOULD implement explicit detection of duplicate multicast
packets by a temporal packet identification scheme. This is
typically implemented by keeping a history of previous received and
forwarded packet identifiers for comparison against recently
forwarded multicast packets. There are different possible approaches
to packet identification that have been considered. Possibilities
include unique markings within packet header fields, such as packet
sequence numbering, or application of hash algorithms or similar
techniques to compactly and uniquely describe the history of recently
received packets. This document RECOMMENDS simple, sequence-based
schemes that can be accomplished without additional (non-IP)
encapsulation of packets and/or their content. Encapsulation
approaches are considered out-of-scope so that non-forwarding edge
nodes within a MANET area may easily receive flooded content without
any additional software beyond that of a typical IP stack. Packet
hashing approaches for DPD may be applicable in some cases, yet early
examination of these approaches indicated the computational
complexity may be prohibitive for per-packet processing on many
candidate MANET platforms (e.g., PDAs). Additionally, the
unavoidable "cache-miss" rates, while possibly low for some
algorithms, result in the severe penalty of false DPD (and thus
packet loss) rather than the more benign penalty of additional
computation cycles as associated with most applications of hashing.
Implementations will need to age and/or timeout duplicate packet
state as new packets are received and forwarded. In the case that
sequence-based packet identification is used, implementations SHOULD
timeout stale histories for <sourceAddress::destinationAddress>
entries where new, _non-duplicate_ packets have not been recently
received. The proper minimum duration of any timeout delay is a
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function of expected possible network traversal time, roughly
NET_DIAMETER (in hops) times NODE_TRAVERSAL_TIME. NET_DIAMETER
measures the maximum possible number of hops given any two nodes in
the network. NODE_TRAVERSAL_TIME is a conservative estimate of the
average one hop traversal time for packets and should include
queueing delays, interrupt processing times, medium access delays,
and propagation delays. If the timeout is reset only upon reception
of non-duplicate packets, it also limits the time that packets might
be incorrectly dropped if a source node is stopped and restarted in
the case of sequence-based packet identification. The required size
of the DPD cache is similarly governed and is also a function of the
maximum expected packet rate. It should be noted that less stateful
bitmask approaches to marking packet status can be used by using a
contiguous space of sequence numbers rather than explicit lists of
arbitrary packet identifiers.
Of course, the duplicate packet detection mechanism SHOULD avoid
keeping unnecessary state for packet flows such as those that are
locally generated or link local destinations that would not be
considered for forwarding.
5.1. SMF IPv4 Packet Identification
IPv4 multicast packets from a particular source are assumed to be
marked with a temporally unique identification number in the ID field
of the IPv4 packet header that can serve as a "packetIdentifier" for
SMF purposes. Unfortunately, in present operating system networking
kernels, the IP ID header field value is not always generated or
applied in a consistent manner with respect to SMF needs. In order
to build a working implementation without encapsulating packets, an
SMF implementation SHOULD provide a sequence generation and marking
module that can maintain and set a monotonically increasing IP ID
field for locally-generated multicast packets with independent
sequence number spaces applied on a <sourceAddress::
destinationAddress> basis. This process will also need to
recalculate and replace a proper IP header checksum for the modified
header. For gateways injecting external IPv4 traffic into an SMF
MANET area, the gateways SHOULD perform this same IP ID field re-
sequencing. Note the presence of IPSec may prevent such
resequencing, but fortunately, IPSec does provide its own organic
means for duplicate packet detection.
The use of IPSec for candidate packet flows presents the opportunity
to make use of the additional, perhaps more reliable, sequencing
information of the IPSec header for unique packet identification.
The IPSec header provides a packet identifier field that can be used
on a "per-security assocation" basis. The IP addressing and IPSec
Security Parameters Index (SPI) fields are used to identify security
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associations and, hence, packet flows. So, if the packet is IPSec
encapsulated, SMF will check the <sourceAddress::destinationAddress::
SPI::packetIdentifier> where the <ESP_seq_number> or <AH_seq_number>
from the IPSec header serves as the "packetIdentifier" value.
Although it would be possible to support IP layer fragmentation , SMF
traffic sources or gateways SHOULD set the don't fragment bit for
traffic intended to be carried by SMF. This is recommended to avoid
the additional complexity and inefficiencies arising from supporting
IP layer fragmentation.
To perform duplicate detection, SMF will check the <sourceAddress::
destinationAddress::[SPI::]packetIdentifier> combination against a
history of received packet identifiers. Note some forwarding
algorithms may require that unique packets are noted when received
from certain neighbor nodes regardless of whether the packets are
forwarded. Multiple interface semantics may also add some additional
considerations to the forwarding process depending upon the specific
relay set selection forwarding rules.
Although its use has been demonstrated in running prototype code, the
adoption of the IPv4 ID field for widespread packet duplication
detection has some disadvantages that should be discussed. The main
disadvantage is the use and interpretation of the field is known to
be inconsistent across operating systems. The IPv4 ID field is also
limited and may provide less robust detection for high bandwidth
applications since sequence wrap-around may occur relatively
frequently if it is not possible to achieve "per source/destination"
sequencing. As an alternative, the use of a header option or
encapsulation header in future implementations may provide more
flexibility and consistency (see IPv6 DPD). Another advantage of
using a header option (or other encapsulation, if determined
absolutely necessary) is that it would be possible for MANET gateway
nodes to assess whether packets ingressing a MANET area have already
been properly sequenced to avoid unnecessary re-injection of packets.
We leave these design alternatives to be further defined and
discussed in future work. A basic sequencing and marking design
similar to the one we formulate here can be easily adapted to work
with future approaches or can be bypassed when not needed.
5.2. SMF IPv6 Packet Identification
The following section describes the mechanism and options for SMF
IPv6 DPD. The core IPv6 header does not provide an explicit
identification header field that can be exploited for DPD. SMF
defines two methods for IPv6 use:
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1. a hop-by-hop DPD options header, and
2. the use of IPSec sequencing when an IPSec header is detected.
SMF MUST provide a DPD marking module that can insert the hop-by-hop
IPv6 header option defined for locally generated multicast packets.
If the packet is _not_ IPSec encapsulated, SMF will use the IPv6
packet header and IPv6 DPD option to form the <sourceAddress::
destinationAddress::packetIdentifier> that is checked against a cache
history of received IPv6 packet identifiers. Similarly to the case
for IPv4, the presence of IPSec may prevent the intermediate addition
of a hop-by-hop options header. Again, the IPSec header provides a
packet identifier field that can be used on a "per-security
assocation" basis. The IP addressing fields and IPSec Security
Parameters Index (SPI) fields are used to identify security
associations and, hence, packet flows. So, if the packet is IPSec
encapsulated, SMF will check the <sourceAddress::destinationAddress::
SPI::packetIdentifier> where the <ESP_seq_number> or <AH_seq_number>
from the IPv6 IPSec header serves as a "packetIdentifier" value.
5.2.1. IPv6 SMF-DPD Header Option Format
Figure 2 illustrates the format of the IPv6 SMF Duplication Packet
Detection (SMF-DPD) hop-by-hop header option. If this is the only
hop-by-hop option present, this will result in the addition of 8
bytes to the IPv6 packet header including the "Next Header", "Header
Extension Length", SMF-DPD option fields, and padding.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... | Option Type | Opt. Data Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DPD packet identifier | ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fig. 2 - IPv6 SMF-DPD Hop-by-hop Header Option
Option Type = (TBD)
Opt. Data Len = 2
DPD packet identifier = monotonically increasing 16-bit sequence
number assigned on a per <sourceAddress::destinationAddress> basis.
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6. Relay Set Selection
As mentioned SMF MUST support CF-based forwarding as a basic
forwarding mechanism when optimized relay set information is not
available or not selected. In CF mode, each node transmits a locally
generated or newly received packet exactly once. The DPD technique
mentioned in the previous section is critical to proper operation and
avoids any duplicate packet retransmissions by the same forwarding
node.
In the requirements sections, it was stated that SMF MUST support the
ability to modify forwarding rules based upon relay set information
received dynamically during operation. In this way, SMF can operate
more efficiently within the MANET multicast area as neighborhoods
change. In the section we define the interface and processing
semantics to allow SMF to support a variety of different relay set
algorithms and approaches.
Here is a recommended criteria list for relay set selection algorithm
candidates:
1. Robust with respect to mobility or other network dynamics
2. Minimal signaling requirements for neighborhood discovery and/or
control
3. Support for preference levels for/against selection as relay
Some relay set algorithms that meet this criteria are described in
the Appendices of this document. Different algorithms may be more
suitable for different MANET routing types or deployments.
Additional relay set selection algorithms may be specified in
separate documents in the future. The Appendices in this document
can serve as a template for the content of such potential future
specifications.
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7. SMF Neighborhood Discovery Requirements
In absence of a compatible, coexisting unicast routing protocol or
MAC layer protocol that provides neighborhood toplogy information
sufficient for relay set selection, this section defines the issues
and additional requirements for a MANET Neighborhood Discovery
Protocol (NHDP) that MAY be operational between SMF nodes.
With respect to neighborhood topology knowledge and/or discovery,
there are three basic modes of SMF operation:
1. Classical Flooding (CF) mode: with no requirements for discovery
or knowledge of neighborhood topology,
2. External CDS control mode: an external process dynamically
determines the local SMF relay status (e.g., SMF prototypes have
leveraged neighborhood toplogy information collected by MANET
unicast routing protocols such as OLSRv2 or Manet-OSPF ), and
3. Independent CDS control mode: SMF uses the MANET Neighborhood
Discovery Protocol (NHDP) [NHDP] to collect localized link
information required for the various CDS algorithm modes
discussed in the Appendices.
We have previously discussed modes 1 and 2. This section will
describe mode 3, using NHDP to support CDS relay set capability
independent of any MANET unicast routing protocol process. This
design uses and is consistent with the Generalized MANET Packet/
Message Format [PacketBB] and NHDP protocol work in progress within
the MANET WG.
7.1. NHDP Description and SMF Requirements
Core NHDP messages and the neighborhood information base are
described separately within the NHDP specification (ref). In this
mode, SMF uses and relies upon an implementation of NHDP. The NHDP
protocol provides the following basic functions:
1. 1-hop neighbor link sensing: maintaining neighbor lists and
performing a basic bidirectionality check of neighbor links
2. 2-hop Neighborhood Discovery: collecting 2-hop bidirectional
neighborhood information and any information relevant to relay
set election
3. The collection and maintenance of the above information across
multiple interfaces.
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4. Relay Set Signaling: signal relay set selection to neighbor nodes
if the relay set algorithm requires such information
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8. SMF Multicast Border Gateway Considerations
Typically, it is expected that SMF will be used to distribute
multicast traffic within a MANET area. However, it is also
envisioned to allow interconnection of SMF operation with networks
using other multicast routing protocols if appropriate conditions are
met. It is important to note that there are many issues that need to
be resolved for this type of interconnection to successfully occur:
1. Determining which multicast groups should transit the gateway
whether entering or exiting the attached MANET area(s).
2. TTL threshold or other scoping policies.
3. Any marking or labeling to enable DPD on ingressing packets.
4. Interface with exterior multicast routing protocols.
5. Possible operation with multiple gateways (presently beyond scope
of this document).
6. Provision for participating non-SMF nodes.
Note the behavior of gateway nodes is the same as that of non-gateway
nodes when forwarding packets on interfaces within the MANET area.
And packets that are passed outbound to interfaces operating typical
multicast routing protocols SHOULD be evaluated for duplicate packet
status since present standard multicast forwarding mechanisms do not
usually perform this function.
8.1. Forwarded Multicast Groups
Determining which groups should be forwarded into a MANET SMF area is
problematic. Ideally, only groups for which there is active group
membership should be injected into the SMF domain. This might be
accomplished by providing an IPv4 Internet Group Membership Protocol
(IGMP) or IPV6 Multicast Listener Discovery (MLD) proxy protocol so
that MANET SMF nodes can inform attached gateways (and hence
multicast networks) of their current group membership status. For
specific systems and services it may be possible to statically
configure group membership in border gateways, but it is RECOMMENDED
that some form of IGMP/MLD proxy or other explicit, dynamic control
of membership be provided. Specification of such an IGMP/MLD proxy
protocol is beyond the scope of this document.
Outbound traffic is less problematic. SMF gateways can perform
duplicate packet detection and forward non-duplicate traffic that
meets TTL/hop limit and scoping criteria to other interfaces.
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Appropriate IP multicast routing (PIM, etc) on those interfaces can
then make further forwarding decisions with respect to the given
traffic and its MANET source address. Note that the presence of
multiple gateways associated with a MANET area may create some
additional issues. This is further discussed in Section 8.5.
8.2. Multicast Group Scoping
Multicast scoping is used by network administrators to control the
network areas which are reached by multicast packets. This is
usually done by configuring external interfaces of gateways in the
border of an area to not forward multicast packets which must be kept
within the area. This is commonly done based on TTL of messages or
group addresses. These schemes are known respectively as:
1. TTL scoping.
2. Administrative scoping.
For IPv4, network adminstrators can configure gateways with the
appropriate TTL thresholds or administratively scoped multicast
groups in the router's interfaces as with any traditional multicast
router. However, for the case of TTL scoping it must be taken into
account that the packet could traverse multiple hops within the MANET
SMF area before reaching the gateway. Thus, TTL thresholds must be
selected carefully.
For IPv6, multicast addresses themselves include information about
the scope of the group. Thus, gateways in the border of an area know
if they must forward a packet based on the IPv6 multicast group
address. For the case of IPv6, we recommend a MANET SMF routing area
be designated a site. Thus, all multicast packets in the range
FF05::/16 will be kept within the MANET SMF area by gateways.
Packets in any other wider range (i.e. FF08::/16, FF0B::/16 and
FF0E::16) will traverse gateways unless any other restrictions
different from the scope applies.
Given that scoping of multicast packets is performed at the area
gateways, and given that existing scoping mechanisms are not designed
to work with mobile routers, we assume that non-gateway SMF nodes,
will not stop forwarding multicast data packets because of their
scope. That is, we assume that the whole MANET SMF area is an non-
divisible scoping area except in the case of link-local addresses
that are not forwarded by SMF.
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8.3. Duplicate Packet Detection Marking
Packets sourced external to an SMF area may not have duplicate packet
sequencing properly applied and the gateway may need to provide that
sequencing information upon entry into the MANET area. In the case
of IPv6, the gateway can apply the SMF DPD Hop-by-Hop options header
to packets forwarded into the MANET area for those packets that do
not already have the option applied. If this option has been
applied, this indicates the packet has already been marked for
potential handling by SMF relays. Similarly, IP packets that have
been encapsulated with IPSec may also be treated as appropriately
marked for DPD and may be forwarded without modification. Both of
these indicators (the IPv6 SMF DPD option and IPSec encapsulation)
provide the side benefit for the gateway to explicitly determine if
the packet has already been marked. In this case, the gateway can
use the packet identification field to ensure it is not re-injecting
a duplicate packet into the MANET area. For IPv4 packets that are
not IPSec encapsulated, it is RECOMMENDED that gateway nodes re-
sequence the ID field of packets injected into the area. However,
the IPv4 ID field does not provide the gateway with explicit
information on whether the field has been previously set for SMF
purposes. Thus, the potential exists that duplicate IPv4 packets may
be re-injected by a gateway into an SMF area if a multicast routing
loop has occurred. If multiple multicast gateways are envisioned,
additional considerations must be taken into account and solutions
are considered out of scope for this document. See Section 8.5 for
more discussion of related issues.
8.4. Interface with Exterior Multicast Routing Protocols
The traditional operation of multicast routing protocols is tightly
integrated with the group membership function. Leaf routers are
configured to periodically gather group membership information, while
intermediate routers conspire to create multicast trees connecting
routers with directly-connected multicast sources and routers with
active multicast receivers. In the concrete case of SMF, we can
consider gateways as leaf routers. Mechanisms for multicast sources
and receivers to interoperate with gateways over the multihop MANET
SMF area as if they were directly connected to the router need to be
defined. The following issues need to be addressed:
1. Mechanism by which gateways gather membership information.
2. Mechanism by which multicast sources are known by the gateway.
3. Exchange of exterior routing protocol messages across the MANET
area if the MANET area is to provide transit connectivity for
multicast traffic.
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It is beyond the scope of this document to address implementation
solutions to these issues. As described in Section 8.1, IGMP/MLD
proxy mechanisms can be deployed to address some of these issues.
Similarly, exterior routing protocol messages could be tunneled or
conveyed across the MANET area. But, because MANET areas are multi-
hop and potentially unreliable, as opposed to the single-hop LAN
interconnection that neighboring IP Multicast routers might typically
enjoy, additional provisions may be required to achieve successful
operation.
The need for the gateway to receive traffic from recognized multicast
sources within the MANET SMF area is important to achieve a smooth
interworking with existing routing protocols. For instance,
protocols like PIM-SM, a commonly used multicast protocol, require
routers with locally attached multicast sources to register them to
the Rendezvous Point (RP) so that other people can join the multicast
tree. In addition, if those sources are not advertised to other
autonomous systems (AS) using MSDP, receivers in those external
networks are not able to join the multicast tree for that source.
8.5. Multiple Gateways
A MANET might be deployed with multiple participating nodes having
connectivity to external (to the MANET), fixed-infrastructure
networks. Allowing multiple nodes to forward multicast traffic to/
from the MANET area can be benefitial since it can increase
reliability, and provide better service. For example, if the MANET
area were to fragment with different MANET nodes maintaining
connectivity to different gateways, multicast service could still
continue successfully. But, the case of multiple gateways connecting
a MANET area to external networks presents several challenges for
SMF:
1. Detection/sequencing of duplicate unmarked IPv4 or IPv6 (without
IPSec encapsulation or DPD option) packets possibly injected by
multiple gateways.
2. Source-based relay algorithms handling of duplicate traffic
injected by multiple gateways.
3. Determination of which gateway(s) will forward outbound multicast
traffic.
4. Additional challenges with interfaces to exterior multicast
routing protocols.
One of the most obvious issues is when multiple gateways are present
and may be alternatively (due to route changes) or simultaneously
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injecting traffic into the MANET area that has not been previously
marked for SMF DPD. Different gateways would not be able to
implicitly synchronize sequencing of injected traffic since they may
not receive exactly the same messages due to packet losses. While
not covered in this document, an approach needs to be identified to
allow multiple gateways to properly mark traffic that is being
injected or carefully control that only one gateway is exclusively
injecting a given "flow" of multicast traffic into the MANET area.
Related to this, when source-based relay algorithms such as S-MPR are
used, the efficiency or correctness of the algorithm may be
compromised when multiple sources inject the same traffic into a
MANET area. Multiple solutions to these gateway issues are possible
and detailed solution proposals are considered out of scope of the
present document.
8.6. Non-SMF MANET Nodes
There may be scenarios in which some MANET nodes may not wish to run
the SMF protocol and/or conduct forwarding, but they are interested
in receiving multicast data. For example, a MANET service might be
deployed that is accessible to wireless edge devices that do not
participate in MANET routing and/or SMF forwarding operation. These
devices include:
1. Devices that opportunistically receive multicast traffic due to
proximity with SMF relays.
2. Devices that participate in NHDP (directly or via routing
protocol signaling) but do not forward traffic.
Note there is no guarantee of traffic delivery with category 1 above,
so it is RECOMMENDED that nodes participate in NHDP when possible.
Such devices may also transmit multicast traffic, but it is important
to note that SMF areas using source-specific relay set algorithms
such as (S-MPR) may not forward such traffic. These devices SHOULD
also listen for any IGMP/MLD Queries that are provided and transmit
IGMP/MLD Reports for groups they have joined per usual IP Multicast
operation. While it is not in the scope of this document, IGMP/MLD
proxy mechanisms may be in place to convey group membership
information to any border gateways or intermediate systems providing
IP Multicast routing functions.
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9. Security Considerations
Gratuitous use of option headers can cause problems in routers.
Routers outside of MANET routing areas should ignore SMF header
options if encountered.
Authentication mechanisms to identify the source of an option header
should be considered to reduce vulnerability to a variety of attacks.
Additional security consideration TBD.
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10. IANA Considerations
There are number of discussions within this SMF specification that
will be subject to IANA registration. The IP Header Extensions being
defined within this document MUST have an IANA registry established
for them upon publication of the first RFC. Additionally, the well-
known multicast addresses intended for default use by the SMF
forwarding process should be registered and defined by the first RFC
published. These IANA considerations may in common or may be handed
in comjunction with other MANET protocol efforts including the
General Message Format specification and potentially common
neighborhood discovery protocol considerations.
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11. Acknowledgments
Many of the concepts and mechanisms used and adopted by SMF resulted
from many years of discussion of related work within the MANET WG.
There are obviously many people that have contributed to past
discussions and related draft documents within the WG that have
influenced the development of SMF concepts that deserve
acknowledgment. In particular, the document is largely a direct
product of the SMF design team within the IETF MANET WG and borrows
text and implementation ideas from the related individuals. Some of
the contributors who have been involved in document content editing
or discussions are listed below. We appreciate input from others we
may have missed in this list as well.
SMF Design Team Contributors:
Brian Adamson
Ian Chakeres
Thomas Clausen
Justin Dean
Brian Haberman
Charles Perkins
Pedro Ruiz
Maoyu Wang
Et al
The RFC text was produced using Marshall Rose's xml2rfc tool.
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12. References
12.1. Normative References
[E-CDS] Ogier, R., "MANET Extension of OSPF Using CDS Flooding",
Proceedings of the 62nd IETF , March 2005.
[MPR-CDS] Adjih, C., Jacquet, P., and L. Viennot, "Computing
Connected Dominating Sets with Multipoint Relays", Ad Hoc
and Sensor Wireless Networks , January 2005.
[NHDP] Clausen, T. and et al, "Neighborhood Discovery Protocol",
draft-ietf-manet-ndp-00, Work in progress , July 2006.
[OLSRv2] Clausen, T. and et al, "Optimized Link State Routing
Protocol version 2", draft-ietf-manet-olsrv2-00, Work in
progress , March 2006.
[PacketBB]
Clausen, T. and et al, "Generalized MANET Packet/Message
Format", draft-ietf-manet-packetbb-00, Work in progress ,
March 2006.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3626] Clausen, T. and P. Jacquet, "Optimized Link State Routing
Protocol", 2003.
12.2. Informative References
[GJ79] Garey, M. and D. Johnson, "Computers and Intractability: A
Guide to the Theory of NP-Completeness.", Freeman and
Company , 1979.
[JLMV02] Jacquet, P., Laouiti, V., Minet, P., and L. Viennot,
"Performance of multipoint relaying in ad hoc mobile
routing protocols", Networking , 2002.
[MDC04] Macker, J., Dean, J., and W. Chao, "Simplified Multicast
Forwarding in Mobile Ad hoc Networks", IEEE MILCOM 2004
Proceedings , 2004.
[NTSC99] Ni, S., Tseng, Y., Chen, Y., and J. Sheu, "The Broadcast
Storm Problem in Mobile Ad hoc Networks", Proceedings Of
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ACM Mobicom 99 , 1999.
[RFC2901] Macker, JP. and MS. Corson, "Mobile Ad hoc Networking
(MANET): Routing Protocol Performance Issues and
Evaluation Considerations", 1999.
[RFC3684] Ogier, R., Templin, F., and M. Lewis, "Topology
Dissemination Based on Reverse-Path Forwarding", 2003.
[WC02] Williams, B. and T. Camp, "Comparison of Broadcasting
Techniques for Mobile Ad hoc Networks", Proceedings of ACM
Mobihoc 2002 , 2002.
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Appendix A. Source-based Multipoint Relay (S-MPR)
The source-based multipoint relay (S-MPR) set selection algorithm
enables individual nodes, using two-hop topology information to
select a minimum set of neighboring nodes that can provide relay to
all nodes within a two-hop radius. This distributed technique has
been shown to approximate selection of a MCDS in [JLMV02].
Individual nodes must collect two-hop neighborhood information from
neighbors, determine an appropriate current relay set, and then
inform the resultant selected neighbors of their relay status. The
Optimized Link State Routing (OLSR) protocol has used this algorithm
and protocol for relay of link state updates and other control
information[RFC3626] and has been shown to operate well even in
dynamic network environments.
Because a node's status as a relay is with respect to neighboring
nodes who have selected it (i.e., its "selectors"), the relaying node
must know the previous-hop transmitter of packets it receives in
order to make an appropriate forwarding decision. Additionally, it
is important that relay nodes forward packets only for those nodes
currently identified as symmetric, one-hop neighbors to maintain
correctness. Also, because the selection of relays does not result
in a common set among neighboring nodes, relays MUST mark in their
duplicate table any transmissions from non-selector, symmetric, one-
hop neighbors (for a given interface) and not forward subsequent
received copies of that packet even if received from a selector
neighbor. Deviation here may result in unecessary, even excessive,
repeat transmission of packets throughout the network. Or incorrect
duplicate table recording of packets received from non-symmetric
neighbors may result in incomplete flooding. In these respects,
flooding based on the S-MPR algorithm is more complex than that based
upon some other relay set selection algorithms.
When multiple interfaces are present, the S-MPR SMF forwarded must
keep some independent state for each interface with regards to
duplicate packets. For example, when a packet is received from a
non-selector, one-hop symmetric neighbor, an SMF forwarder using the
S-MPR algorithm must update its duplicate packet state with respect
to the interface on which the packet was received. If the SMF
forwarder receives that same packet from a selector neighbor on a
different interface, it MUST still forward that packet on all
interfaces it has not received that packet from a one-hop symmetric
neighbor. Once a packet has been forwarded in this fashion,
subsequent duplicates received on any interface are ignored.
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A.1. S-MPR Relay Set Selection
If SMF is operating S-MPR relay set election independent of
coexistent OLSR operation, based upon NHDP mechanisms, the election
algorithm defined within RFC3626 [RFC3626] should be used.
A.2. Neighborhood Discovery Requirements
S-MPR election operation requires 2-hop neighbor knowledge as
provided by the NHDP protocol[NHDP] or as available from external
sources. MPRs are dynamically selected by each node and selections
MUST be advertised and dynamically updated within the SMF NDP or
equivalent protocol. In this mode, the MPR specific TLVs defined in
OLSRv2 [OLSRv2]are also required to be implemented by NHDP.
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Appendix B. Essential Connecting Dominating Set (E-CDS) Algorithm
The "Essential Connected Dominating Set" (E-CDS) algorithm [E-CDS]
allows nodes to use two-hop topology information to appropriately
elect _themselves_ as relay nodes to form an efficient (for flooding)
CDS. While this algorithm does not tend to produce as small a set of
relay nodes (per forwarded packet) as the previously-described S-MPR
algorithm, it is not dependent upon previous-hop information to make
a forwarding decision; it simply forwards any received non-duplicate
packets. This property also allows relay nodes using the E-CDS
algorithm to be intermixed with nodes performing only classical
flooding. Additionally, the semantics for multiple interface support
are simplified as compared to S-MPR and even packets that are
received from non-symmetric neighbors may be forwarded without
compromising flooding efficiency or correctness.
B.1. E-CDS Relay Set Selection
This section provides a short description of the E-CDS based relay
set selection algorithm and is based upon Richard Ogier's original
summary within [E-CDS]. This was originally discussed in the context
of forming partial adjacencies and efficient flooding for MANET-OSPF
work but its core algorithm is applied here.
E-CDS requires two-hop neighbor information collected through the
SMF-NDP or other process. Each router has a Router Identifier (may
be represented by an interface address) and Router Priority value.
The Router Priority value may be dynamic and represent such metrics
as node degree. The fundamental election steps are as follows:
1. If an SMF node has a higher (Router Priority, Router ID) than all
of its symmetric neighbors, it elects itself to the relay set.
2. Else, if there does not exist a path from neighbor j with largest
(Router Priority, Router ID) to some other neighbor, via
neighbors with larger values of (Router Priority, Router ID),
then it elects itself to the relay set.
The basic form of E-CDS described and applied within this
specification does not at present define redundant relay set election
but such capability is supported by the E-CDS design.
B.2. E-CDS Forwarding Rules
E-CDS forwarding is quite simple and straightforward. As mentioned,
there is no need to check previous hop information during forwarding.
Upon electing itself as an E-CDS relay set forwarder, SMF nodes
perform DPD functions and forward all ranges of non-duplicative
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multicast traffic allowed by the present forwarding policy.
B.3. Neighborhood Discovery Requirements
To support functions required by the core E_CDS relay set algorithm
the following TLV is required to be transmitted by each node within a
NHDP HELLO message:
*Router Priority*: type=SMF_ROUTER_PRIORITY, length=1, value =
priority*
For E-CDS operation, some value of SMF_ROUTER_PRIORITY must be given
or assumed for each address in the <address-block> portion of the
SMF_HELLO message. If a SMF_HELLO message originator does not
provide a SMF_ROUTER_PRIORITY value for given address(es), a default
value SMF_RPRI_DEFAULT=(TBD) should be assumed. Local determination
of a node SMF_ROUTER_PRIORITY value can be done in multiple ways as
described in the [E-CDS]. An early implementation of SMF and E-CDS
has used node degree computed during neighbor discovery, yet it is
still unclear if this is the best method. Unlike the MPR method, the
E-CDS is a self-electing algorithm. SMF_ROUTER_PRIORITY needs to be
shared with all immediate neighbor nodes and 2-hop neighbor knowledge
is needed during the self election process. Further algorithm
examples and details are covered in the Appendices.
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Appendix C. Multipoint Relay Connected Dominating Set (MPR-CDS)
Algorithm
The MPR-CDS algorithm is an extension to the basic MPR election
algorithm and results in a shared relay set that forms a CDS. Its
forwarding rules within SMF are non-dependent upon previous hop
information similar to E-CDS.
C.1. MPR-CDS Relay Set Selection
An overview of the the MPR-CDS selection algorithm is provided in
[MPR-CDS]. The basic requirements for election are similar to the
basic MPR algorithm with the addtion that some node ordering
knowledge is required. This is similar to the E-CDS requirement and
can be based upon node IP address or some other unique router
identifier. The rules for election are as follows:
A node decides it is in the relay set if:
1. the node is smaller than all its neighbors (Rule 1)
2. or the node is an MPR of its smallest neighbor (Rule 2)
C.2. MPR-CDS Forwarding Rules
MPR-CDS forwarding are quite simple and straightforward. As with
E-CDS, there is no need to check previous hop information during
forwarding. Upon electing itself as a MPR-CDS relay set forwarder,
SMF nodes perform DPD functions and forward all ranges of multicast
traffic allowed.
C.3. Neighborhood Discovery Requirements
No additional discovery requirements are needed beyond the basic MPR-
related TLVs already discussed.
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Authors' Addresses
Joseph Macker
NRL
Washington, DC 20375
USA
Email: macker@itd.nrl.navy.mil
SMF Design Team
IETF MANET WG
Email: manet@ietf.org
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Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
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Macker, editor & SMF Design Team Expires April 8, 2007 [Page 37]
