One document matched: draft-ietf-manet-smf-08.xml
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<rfc category="exp" docName="draft-ietf-manet-smf-08" ipr="full3978">
<front>
<title abbrev="SMF for MANET">Simplified Multicast Forwarding for
MANET</title>
<author fullname="Joseph Macker" initials="J" surname="Macker, editor">
<organization>NRL</organization>
<address>
<postal>
<street></street>
<city>Washington</city>
<region>DC</region>
<country>USA</country>
<code>20375</code>
</postal>
<email>macker@itd.nrl.navy.mil</email>
</address>
</author>
<author fullname="SMF Design Team" initials="" surname="SMF Design Team">
<organization>IETF MANET WG</organization>
<address>
<email>manet@ietf.org</email>
</address>
</author>
<date day="3" month="November" year="2008" />
<abstract>
<t>This document describes a Simplified Multicast Forwarding (SMF)
mechanism that provides basic IP multicast forwarding suitable for
wireless mesh and mobile ad hoc network (MANET) use. SMF specifies
techniques for multicast duplicate packet detection (DPD) to assist the
forwarding process. SMF also specifies DPD maintenance and checking
operations for with both IPv4 and IPv6. SMF also specifies the optional
use of reduced relay sets for efficient MANET multicast data
distribution within a mesh topology. The document describes interactions
with other protocols and multiple deployment approaches. Distributed
algorithms for selecting reduced relay sets and related discussion are
provided in the Appendices. Basic issues relating to the operation of
multicast MANET border routers are discussed but ongoing work remains in
this area beyond the scope of this document.</t>
</abstract>
</front>
<middle>
<section title="Requirements Notation">
<t>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 <xref
target="RFC2119"></xref>.</t>
</section>
<section title="Introduction and Scope">
<t>MANET unicast routing protocol designs have demonstrated effective
and efficient mechanisms to flood routing control plane messages
throughout a wireless routing area. For example, algorithms specified
within <xref target="RFC3626"></xref> and <xref target="RFC3684"></xref>
provide distributed methods of dynamically electing reduced relay sets
that attempt to optimize flooding of routing control messages amongst
MANET routing peers. Simplified Multicast Forwarding (SMF) extends
efficient flooding concept to the data forwarding plane. In use cases
where localized, efficient flooding is deemed an effective technique,
SMF provides an appropriate multicast forwarding capability. The SMF
baseline design is intended to provide a basic, best effort multicast
forwarding capability that is constrained to operate within a MANET or
wireless mesh routing region. The main design goals of this SMF
specification are to adapt efficient relay sets in MANET environments
<xref target="RFC2901"></xref> and to define the needed IPv4 and IPv6
multicast duplicate packet detection (DPD) mechanisms to support
multi-hop, packet forwarding. 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 self-election) will occur based on input from a
neighborhood discovery process, and the forwarding process will often be
determined by dynamic relay set selection. Note the neighborhood
discovery and/or relay set selection information MAY be obtained from a
coexistent process (e.g., MANET unicast routing protocol using relay
sets). In some cases, the forwarding decision for a packet can also
depend on previous hop or incoming interface information. The asterisks
(*) in <xref target="smfNodeArchitecture"></xref> mark the primitives
and relationships needed by relay set algorithms requiring previous-hop
packet forwarding knowledge.</t>
<figure align="center" anchor="smfNodeArchitecture"
title="SMF Node Architecture">
<artwork><![CDATA[ ______________ _____________
| | | |
| Neighborhood | | Relay Set |
| Discovery |------------->| Selection |
| Protocol | neighbor | Algorithm |
|______________| info |_____________|
\ /
\ /
neighbor\ /forwarding
info* \ ____________ / status
\ | | /
`-->| Forwarding |<--'
| Process |
~~~~~~~~~~~~~~~~~>|____________|~~~~~~~~~~~~~~~~~>
incoming packet, forwarded packets
interface id*, and
previous hop*]]></artwork>
</figure>
<t></t>
<t>Interoperable SMF implementations MUST use a common DPD approach and
be able to process the header options defined in this document for IPv6
operation. We define Classical Flooding (CF), as the simplest case of
SMF multicast forwarding. With CF, each SMF router forwards each
received forwardable multicast packet once. In this case, the need for
any relay set selection or neighborhood topology information is
eliminated but DPD functionality is still required. While SMF supports a
CF mode the use of more efficient relay set modes is RECOMMENDED to
reduce contention and congestion caused by unnecessary packet
retransmissions <xref target="NTSC99"></xref>. An efficient, reduced
relay set is realized by selecting and maintaining a
<spanx>subset</spanx> of all possible SMF routers in a MANET routing
region. Known relay set selection algorithms have demonstrated the
ability to provide and maintain a dynamic distribution mesh for
forwarding user multicast data <xref target="MDC04"></xref>. A few such
relay set selection algorithms are described in the Appendices of this
document and the basic designs borrow directly from previously
documented IETF work. SMF relay set configuration is extensible and an
additional relay set algorithms or extensions can be accommodated for
future use.</t>
<t>Determining and maintaining an optimized set of relay (forwarding)
nodes generally requires dynamic neighborhood topology information.
Neighborhood topology discovery functions MAY be externally provided by
a MANET unicast routing protocol or by using the MANET NeighborHood
Discovery Protocol (NHDP) <xref target="NHDP"></xref> running in
concurrence with SMF. Additionally, this specification allows
alternative processes that may be deemed more effective (e.g., lower
layer wireless interface) to provide the necessary neighborhood
information to support relay set election. Fundamentally, an SMF
implementation SHOULD provide the ability for multicast forwarding state
to be dynamically managed per operating network interface. Some of the
relay state maintenance options and interactions are outlined later in
<xref target="Relays"></xref>. This document states specific
requirements for neighborhood discovery with respect to the forwarding
process and the relay set selection algorithms described herein. In the
absence of a MANET unicast protocol or lower layer information
interface, SMF relies on the MANET NHDP specification to assist in IP
layer 2-hop neighborhood state discovery and maintenance for relay set
election except in the case of CF operation. A "SMF_RELAY_ALG" Message
TLV type (per <xref target="PacketBB"></xref>) is defined for use with
the NHDP protocol. It is RECOMMENDED that all nodes performing SMF
operation include this TLV type in their NHDP_HELLO messages when
operating with NHDP. This capability allows for nodes participating in
SMF to be explicitly identified along with their respective dynamic
relay set algorithm.</t>
<section title="Abbreviations">
<t>The following abbreviations are used throughout this document:</t>
<texttable>
<ttcol>Abbreviation</ttcol>
<ttcol align="left">Definition</ttcol>
<c>MANET</c>
<c>Mobile Ad hoc Network</c>
<c>SMF</c>
<c>Simplified Multicast Forwarding</c>
<c>CF</c>
<c>Classical Flooding</c>
<c>CDS</c>
<c>Connected Dominating Set</c>
<c>MPR</c>
<c>Multi-Point Relay</c>
<c>S-MPR</c>
<c>Source-based MPR</c>
<c>MPR-CDS</c>
<c>MPR-based CDS</c>
<c>E-CDS</c>
<c>Essential CDS</c>
<c>NHDP</c>
<c>Neighborhood Discovery Protocol</c>
<c>DPD</c>
<c>Duplicate Packet Detection</c>
<c>I-DPD</c>
<c>Identification-based DPD</c>
<c>H-DPD</c>
<c>Hash-based DPD</c>
<c>HAV</c>
<c>Hash-assist Value</c>
<c>FIB</c>
<c>Forwarding Information Base</c>
<c>TLV</c>
<c>type-length-value encoding</c>
</texttable>
</section>
</section>
<section title="SMF Applicability">
<t>Within dynamic, wireless routing topologies, maintaining traditional
forwarding trees to support a multicast routing protocol is often not as
effective as in wired networks due the reduced reliability and increased
dynamics of mesh topologies <xref target="MGL04"></xref> <xref
target="GM99"></xref>.<spanx style="emph"></spanx>A basic packet
forwarding service reaching all connected MANET SMF routers
participating within a localized routing region may provide a useful
group communication paradigm for various classes of applications.
Applications that could take advantage of a simple multicast forwarding
service within a MANET routing region include multimedia streaming,
interactive group-based messaging and applications, peer-to-peer
middleware multicasting, and multi-hop mobile discovery or registration
services.</t>
<t>Note again that Figure 1 provides a notional architecture for
<spanx>typical</spanx> MANET SMF-capable nodes. However, a goal is that
simple end-system (non-forwarding) wireless nodes may also participate
in multicast traffic transmission and reception with standard IP network
layer semantics (e.g., special or unnecessary encapsulation of IP
packets should be avoided in this case). It is important that SMF
deployed in a localized edge network setting be able to connect and
interoperate with existing standard multicast protocols operating within
more conventional Internet infrastructures. A multicast border router or
proxy mechanism MUST be used when deployed alongside more
fixed-infrastructure IP multicast routing such Protocol Independent
Multicast (PIM) variants <xref target="RFC3973"></xref> and <xref
target="RFC4601"></xref>. With present experimental implementations,
proxy methods have demonstrated gateway functionality at MANET border
routers operating with existing external IP multicast routing protocols.
SMF may be extended or combined with other mechanisms to provide
increased reliability and group specific filtering, but the details for
this are not discussed here.</t>
</section>
<section anchor="Forwarding" title="SMF Packet Processing and Forwarding">
<t>The SMF Packet Processing and Forwarding actions are conducted with
the following packet handling activities: <list style="numbers">
<t>Processing of outbound, locally-generated multicast packets.</t>
<t>Reception and processing of inbound packets on a specific network
interface(s).</t>
</list></t>
<t>The purpose of intercepting outbound, locally-generated multicast
packets is to apply any added packet marking needed to satisfy the DPD
requirements described later so that proper forwarding may be conducted.
Note that for some system configurations interception of outbound
packets for this purpose is not necessary.</t>
<t>Inbound multicast packets are received by the SMF implementation and
processed for possible forwarding. This document does not presently
support forwarding of directed broadcast addresses <xref
target="RFC2644"></xref>. SMF implementations MUST be capable of
forwarding "global scope" multicast packets to support generic multicast
application needs or to distribute designated multicast traffic
ingressing the MANET routing region via border routers. The multicast
addresses to be forwarded will be maintained by an <spanx style="emph">a
priori</spanx> list or a dynamic forwarding information base (FIB) that
MAY interact with future MANET dynamic group membership extensions or
management functions. There will also be a well-known multicast group
for flooding to all SMF forwarders. This multicast group is specified to
contain all MANET SMF routers of a connected MANET routing region, so
that packets transmitted to the multicast address associated with the
group will be delivered to all connected SMF routers. For IPv6, the
multicast address is specified to be "site-local". The name of the
multicast group is "SL-MANET-ROUTERS". Minimally SMF SHALL forward, as
instructed by the relay set selection algorithm, unique (non-duplicate)
packets received for this well-known group address when the TTL or hop
count value in the IP header is greater than 1. SMF SHALL forward all
additional global scope addresses specified within the dynamic FIB or
configured list as well. In all cases, the following rules SHALL be
observed for SMF multicast forwarding:</t>
<t><list style="numbers">
<t>Multicast packets with TTL <= 1 MUST NOT be forwarded.</t>
<t>Link local multicast packets MUST NOT be forwarded.</t>
<t>Incoming multicast packets with an IP source address matching one
of those of the local SMF router interface(s) MUST NOT be
forwarded.</t>
<t>Received packet frames with the MAC source address matching the
local SMF router interface(s) MUST NOT be forwarded.</t>
<t>Received packets for which SMF cannot reasonably ensure temporal
DPD uniqueness MUST NOT be forwarded.</t>
<t>When packets are forwarded, TTL or hop limit SHALL be decremented
by one.</t>
</list></t>
<t>Note that rule #3 is important because in wireless networks, the
local SMF router 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.</t>
<t>An additional processing rule also needs to be considered based upon
a potential security threat. As discussed further in <xref
target="Security"></xref>, there may be concern in some SMF deployments
that malicious nodes may conduct a denial-of-service attack by remotely
"previewing" (e.g., via a directional receive antenna) packets that an
SMF node would be forwarding and conduct a "pre-play" attack by
transmitting the packet before the SMF node would otherwise receive it
but with a reduced TTL (or Hop Limit) field value. This form of attack
could cause an SMF node to create a DPD entry that would block the
proper forwarding of the valid packet (with correct TTL) through the SMF
area. A RECOMMENDED approach to prevent this attack, when it is a
concern, would be to cache temporal packet TTL values along with the DPD
state (hash value(s) and/or identifier). Then, if a subsequent matching
(with respect to DPD) packet arrives with a <spanx
style="emph">larger</spanx> TTL value than the packet that was
previously forwarded, then SMF should forward the new packet <spanx
style="emph">and</spanx> update the TTL cached with corresponding DPD
state to the new, larger TTL value. There may be temporal cases where
SMF may unnecessarily forward some duplicate packets using this
approach, but those cases are expected to be minimal and acceptable when
compared with the potential threat outcome of denied service.</t>
<t>Once these criteria have been met, an SMF implementation MUST make a
forwarding decision dependent upon the relay set selection algorithm in
use. If the SMF implementation is using Classical Flooding (CF), the
forwarding decision is implicit once DPD uniqueness is determined.
Otherwise, a forwarding decision depends upon the current
interface-specific relay set state. The descriptions of the relay set
selection algorithms in the Appendices to this document specify the
respective heuristics for multicast packet forwarding and specific DPD
or other processing required to achieve correct SMF behavior. For
example, one class of forwarding is based upon relay set election status
<spanx style="emph">and</spanx> the packet's previous hop (e.g. S-MPR
forwarding), while other classes designate the local SMF router as a
forwarder of all neighbor packets (e.g. E-CDS and MPR-CDS).</t>
</section>
<!-- Beginning of Duplicate Packet Detection Section -->
<section anchor="DPD" title="SMF Duplicate Packet Detection">
<t>Duplicate packet detection (DPD) is a common requirement in MANET
packet forwarding because packets may be transmitted out the same
physical interface upon which they arrived and nodes may also receive
copies of previously-transmitted packets from other forwarding
neighbors. SMF implementations MUST detect and avoid forwarding
duplicate multicast packets using temporal packet identification. It is
RECOMMENDED this be implemented by keeping a history of
recently-processed multicast packets for comparison to incoming packets.
For both IPv4 and IPv6, this document describes two basic approaches to
multicast duplicate packet detection: header content
identification-based (I-DPD) and hash-based (H-DPD) duplicate detection.
The two approaches are described for experimental purposes. Trade-offs
of the two approaches to DPD merit different consideration dependent
upon the specific SMF deployment scenario. Because of the potential
addition of a hop-by-hop option header with IPv6, SMF deployments MUST
be configured to use a common mechanism and DPD algorithm. The main
difference between IPv4 and IPv6 SMF DPD specification is the avoidance
of any additional header options in the IPv4 case.</t>
<t>For each network interface, SMF implementations MUST maintain DPD
packet state as needed to support the forwarding heuristics of the relay
set algorithm used. The specific requirements of several relay set
selection algorithms and their forwarding rules are described in the
Appendices of this document. In general this involves keeping track of
previously forwarded packets so that duplicates are not forwarded, but
some relay techniques (e.g., S-MPR) have additional considerations.</t>
<t>For I-DPD, packets are identified using explicit identifiers from the
IP header. The specific identifier to use depends upon the IP protocol
version and the type of packet. For example, IPv4 <xref
target="RFC0791"></xref> provides an "Identification" field that may
assist a DPD mechanism, and packets that contain IPSec protocol headers
also provide suitable packet identifiers. Fragmented packets also
provide additional identifiers that need to be considered. These
identifier fields are unique within the context of source address,
destination address, protocol type, and/or other header fields depending
upon the type of identifier used for DPD. Similarly, for H-DPD, it is
expected that packet hash values will be kept with respect to at least
the source address to help ensure hash collision avoidance. SMF
implementations MUST maintain DPD history per the applicable packet flow
context (e.g., <protocol:srcAddr:dstAddr> for DPD based upon IPv4
ID). The details for I-DPD and H-DPD for different types of packets are
described in the sections below. In either case, this history SHOULD be
kept long enough to span the maximum network traversal lifetime,
MAX_PACKET_LIFETIME, of multicast packets being forwarded within an SMF
operating area. The required size of the DPD cache is governed by this
timeout value and is also a function of the packet forwarding rates. The
DPD 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.</t>
<section anchor="DPDv6" title="IPv6 Duplicate Packet Detection">
<t>This section describes the mechanisms and options for SMF IPv6 DPD.
The core IPv6 packet header does not provide any explicit
identification header field that can be exploited for I-DPD. The
following areas are described to support IPv6 DPD:<list
style="numbers">
<t>a hop-by-hop SMF-DPD option header (with supporting identifier
or hash assistance value),</t>
<t>the use of IPv6 fragment header fields for I-DPD when they
exist,</t>
<t>the use of IPSec sequencing for I-DPD when a non-fragmented,
IPSec header is detected, and</t>
<t>an H-DPD approach assisted, as needed, by the SMF-DPD option
header.</t>
</list>SMF MUST provide a DPD marking module that can insert the
hop-by-hop IPv6 header option defined in this section. This process
MUST come after any source-based fragmentation that may occur with
IPv6. As with IPv4, SMF IPv6 DPD is presently specified to allow
either a packet hash or header identification method for DPD. An SMF
implementation MUST be configured to operate either in H-DPD or I-DPD
mode and perform the appropriate routines outlined in the following
sections.</t>
<section anchor="Opt-DPD" title="IPv6 SMF-DPD Header Option">
<t>As previously mentioned, the base IPv6 packet header does not
contain a unique identifier suitable for DPD. This section defines
an IPv6 Hop-by-Hop Option to serve this purpose for IPv6 I-DPD.
Additionally, the Option defined provides for a mechanism to
guarantee non-collision of hash values for different packets when
H-DPD is used. The value of the IPv6 SMF_DPD Hop-by-Hop Option Type
is TBD.</t>
<t>The first bit of the data field of the SMF-DPD option is the
"H-bit" that determines the format of the Option Data content. Two
different formats are supported. When the "H-bit" is cleared (zero
value), the SMF-DPD format to support I-DPD operation is specified
as shown in <xref target="idpdHeaderOption"></xref> and defines the
extension header in accordance with <xref
target="RFC2460"></xref>.</t>
<figure align="center" anchor="idpdHeaderOption"
title="IPv6 SMF-DPD Header Option in I-DPD mode">
<artwork><![CDATA[ 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... |0|0|0| OptType | Opt. Data Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|TidTyp|TidLen| TaggerId (optional) ... |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Identifier ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
</figure>
<t>The "TidType" is a 3-bit field indicating the presence and type
of the optional "TaggerId" field. The optional "TaggerId" is used to
differentiate multiple ingressing border gateways that may commonly
apply the SMF-DPD option header to packets from a particular source.
This is provided for experimental purposes. The following table
lists the valid TaggerId types:</t>
<texttable anchor="taggerId" title="TaggerId Types">
<preamble></preamble>
<ttcol>Name</ttcol>
<ttcol>Value</ttcol>
<ttcol>Purpose</ttcol>
<c>NULL</c>
<c>0</c>
<c>Indicates no "taggerId" field is present. "TidLen" MUST also be
set to ZERO.</c>
<c>DEFAULT</c>
<c>1</c>
<c>A "TaggerId" of non-specific context is present. "TidLen + 1"
defines the length of the TaggerId field in bytes.</c>
<c>IPv4</c>
<c>2</c>
<c>A "TaggerId" representing an IPv4 address is present. The
"TidLen" MUST be set to 3.</c>
<c>IPv6</c>
<c>3</c>
<c>A "TaggerId" representing an IPv6 address is present. The
"TidLen" MUST be set to 15.</c>
<c>ExtId</c>
<c>7</c>
<c>RESERVED FOR FUTURE USE (possible extended ID)</c>
</texttable>
<t>This format allows a quick check of the "TidType" field to
determine if a "TaggerId" field is present. If the <TidType>
is NULL, then the length of the DPD packet <Identifier> field
corresponds to the (<Opt. Data Len> - 1). If the
<TidType> is non-NULL, then the length of the "TaggerId" field
is equal to (<TidLen> - 1) and the remainder of the option
data comprises the DPD packet <Identifier> field. When the
"TaggerId" field is present, the <Identifier> field can be
considered a unique packet identifier in the context of the
<taggerId:srcAddr:dstAddr> tuple. When the "TaggerId" field is
not present, then it is assumed the source host applied the SMF-DPD
option and the <Identifier> can be considered unique in the
context of the IPv6 packet header <srcAddr:dstAddr> tuple.
IPV6 I-DPD operation details are described in <xref
target="I-DPDv6"></xref>.</t>
<t>When the "H-bit" in the SMF-DPD option data is set, the data
content value is interpreted as a Hash-Assist Value (HAV) used to
facilitate H-DPD operation. In this case, source hosts or ingressing
gateways apply the SMF-DPD with a HAV only when required to
differentiate the hash value of a new packet with respect to older
packets in the current DPD history cache. This helps to guarantee
the uniqueness of generated hash values when H-DPD is used.
Additionally, this also avoids the added overhead of applying the
SMF-DPD option header to every packet. For many hash algorithms, it
is expected that only sparse use of the SMF-DPD option may be
required. The format of the SMF-DPD header option for H-DPD
operation is given in <xref target="hdpdHeader"></xref>.</t>
<figure anchor="hdpdHeader"
title="IPv6 SMF_DPD Header Option in H-DPD Mode">
<artwork><![CDATA[ 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... |0|0|0| OptType | Opt. Data Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Hash Assist Value (HAV) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
</figure>
<t>The SMF-DPD option should be applied with a HAV to produce a
unique hash digest for packets within the context of the IPv6 packet
header <srcAddr>. The size of the HAV field is implied by the
"Opt. Data Len". The appropriate size of the field depends upon the
collision properties of the specific hash algorithm used. More
details on IPv6 H-DPD operation are provided in <xref
target="H-DPDv6"></xref>.</t>
</section>
<section anchor="I-DPDv6" title="IPv6 Identification-based DPD">
<t>The following table summarizes the IPv6 I-DPD processing
approach. Within the table '*' indicates a don't care condition.</t>
<texttable anchor="IPv6IDPDProcess"
title="IPv6 I-DPD Processing Rules">
<preamble></preamble>
<ttcol>IPv6 Fragment Header</ttcol>
<ttcol>IPv6 IPSec Header</ttcol>
<ttcol>IPv6 I-DPD Header</ttcol>
<ttcol>SMF IPv6 I-DPD Mode Action</ttcol>
<c>Present</c>
<c>*</c>
<c>*</c>
<c>Use Fragment Header I-DPD Check and Process for Forwarding</c>
<c>Not Present</c>
<c>Present</c>
<c>*</c>
<c>Use IPSec Header I-DPD Check and Process for Forwarding</c>
<c>Present</c>
<c>*</c>
<c>Present</c>
<c>Invalid, do not Forward</c>
<c>Not Present</c>
<c>Present</c>
<c>Present</c>
<c>Invalid, do not Forward</c>
<c>Not Present</c>
<c>Not Present</c>
<c>Not Present</c>
<c>Add I-DPD Header,and Process for Forwarding</c>
<c>Not Present</c>
<c>Not Present</c>
<c>Present</c>
<c>Use I-DPD Header Check and Process for Forwarding</c>
</texttable>
<t>If the IPv6 multicast packet is an IPv6 fragment, SMF MUST use
the fragment extension header fields for packet identification. This
identifier can be considered unique in the context of the
<srcAddr:dstAddr> of the IP packet. If the packet is an
unfragmented IPv6 IPSec packet, SMF MUST use IPSec fields for packet
identification. The IPSec header <sequence> field can be
considered a unique identifier in the context of the
<IPSecType:srcAddr:dstAddr:SPI> where the "IPSecType" is
either AH or ESP. For unfragmented, non-IPSec, IPv6 packets, the use
of the SMF DPD header option is necessary to support I-DPD
operation. The SMF DPD header option is applied in the context of
the <srcAddr> of the IP packet. End systems or ingressing SMF
gateways are responsible for applying this option to support DPD.
The following table summarizes these packet identification
types:</t>
<texttable anchor="IPv6IDPDId"
title="IPv6 I-DPD Packet Identification Types">
<preamble></preamble>
<ttcol>IPv6 Packet Type</ttcol>
<ttcol>Packet DPD ID Context</ttcol>
<ttcol>Packet DPD ID</ttcol>
<c>Fragment</c>
<c><srcAddr:dstAddr></c>
<c><fragmentOffset:id></c>
<c>IPSec Packet</c>
<c><IPSecType:srcAddr:dstAddr:SPI></c>
<c><sequence></c>
<c>Regular Packet</c>
<c><[taggerId:]srcAddr:dstAddr></c>
<c><SMF-DPD option header id></c>
</texttable>
<t>"IPSecType" is either Authentication Header (AH) or Encapsulating
Security Payload (ESP).</t>
<t>The "taggerId" is an optional feature of the IPv6 SMF-DPD header
option.</t>
</section>
<section anchor="H-DPDv6" title="IPv6 Hash-based DPD">
<t>A default hash-based DPD approach (H-DPD) for use by SMF is
specified as follows. An MD5 <xref target="RFC1321"></xref> hash of
the non-mutable header fields, options fields, and data content of
the IPv6 multicast packet is used to produce a 128-bit digest. The
lower 64 bits of this digest (MD5_64) is used for SMF packet
identification. The approach for calculating this hash value SHOULD
follow the same guidelines described for calculating the Integrity
Check Value (ICV) described in <xref target="RFC4302"></xref> with
respect to non-mutable fields. This approach should have a
reasonably low probability of digest collision when packet headers
and content are varying. MD5 is being applied in SMF only to provide
a low probability of collision and is not being used for
cryptographic or authentication purposes. A history of the packet
hash values SHOULD be maintained within the context of the IPv6
packet header <srcAddr>. This history is used by forwarding
SMF nodes (non-ingress points) to avoid forwarding duplicates. SMF
ingress points (i.e., source hosts or gateways) use this history to
confirm that new packets are unique with respect to their hash
value. The Hash-assist Value (HAV) field described in <xref
target="Opt-DPD"></xref> is provided as a differentiating field when
a digest collision would otherwise occur. Note that the HAV is an
immutable option field and SMF MUST use any included H-DPD hash
assist value (HAV) option header (see <xref
target="Opt-DPD"></xref>) in its hash calculation.</t>
<t>If a packet results in a digest collision (i.e., by checking the
H-DPD digest history) within the limited history kept by SMF
forwarders, the packet should be silently dropped. If a digest
collision is detected at an SMF ingress point (i.e., including
SMF-aware sources), the H-DPD option header is applied with a HAV.
The packet is retested for collision and the HAV is re-applied as
needed to produce a non-colliding hash value. The multicast packet
is then forwarded with the added IPv6 SMF-DPD header option.</t>
<t>The MD5 indexing and IPv6 HAV approaches are specified at present
for consistency and robustness to suit experimental uses. Future
approaches and experimentation may discover designs tradeoffs in
hash robustness and efficiency worth considering. This MAY include
reducing the maximum payload length that is processed, determining
shorter indexes, or applying more efficient hashing algorithms. Use
of the HAV functionality may allow for application of
"lighter-weight" hashing techniques that might not have been
initially considered due to poor collision properties otherwise.
Such techniques could reduce packet processing overhead and memory
requirements.</t>
</section>
</section>
<section anchor="DPDv4" title="IPv4 Duplicate Packet Detection">
<t>This section describes the mechanisms and options for IPv4 DPD. The
IPv4 packet header 16-bit "Identification" field MAY be used for DPD
assistance, but practical limitations may require alternative
approaches in some situations. The following areas are described to
support IPv4 DPD::<list style="numbers">
<t>the use of IPv4 fragment header fields for I-DPD when they
exist,</t>
<t>the use of IPSec sequencing for I-DPD when a non-fragmented
IPv4 IPSec packet is detected, and</t>
<t>a H-DPD approach.</t>
</list>A specific SMF-DPD marking option is not specified for IPv4
since header options are not as tractable for end systems as for IPv6.
IPv4 packets from a particular source are assumed to be marked with a
temporally unique value in the "Identification" field of the packet
header <xref format="title" target="RFC0791"></xref> that can serve
for SMF DPD purposes. However, in present operating system networking
kernels, the IPv4 header "Identification" value is not always
generated properly, especially when the "don't fragment" (DF) bit is
set. The IPv4 I-DPD mode of this specification requires that IPv4
"Identification" fields are managed reasonably by source hosts and
that temporally unique values are set within the context of the packet
header <protocol:srcAddr:dstAddr> tuple. If this is not expected
during an SMF deployment, then it is RECOMMENDED that the H-DPD method
be used as a more reliable approach.</t>
<t>Since IPv4 SMF does not specify an options header, the
interoperability constraints are looser than the IPv6 version and
forwarders may be operate with mixed H-DPD and I-DPD modes as long as
they consistently perform the appropriate DPD routines outlined in the
following sections. However, it is RECOMMENDED that a deployment be
configured with a common mode for operational consistency.</t>
<section title="IPv4 Identification-based DPD">
<t>The following table summarizes the IPv4 I-DPD processing approach
once a packet has passed the basic forwardable criteria described in
earlier SMF sections. Within the table '*' indicates a don't care
condition.</t>
<texttable anchor="IPv4IDPDProcess"
title="IPv4 I-DPD Processing Rules">
<ttcol>df</ttcol>
<ttcol>mf</ttcol>
<ttcol>fragment offset</ttcol>
<ttcol>IPSec</ttcol>
<ttcol>IPv4 I-DPD Action</ttcol>
<c>1</c>
<c>1</c>
<c>*</c>
<c>*</c>
<c>Invalid, Do Not Forward</c>
<c>1</c>
<c>0</c>
<c>nonzero</c>
<c>*</c>
<c>Invalid, Do Not Forward</c>
<c>*</c>
<c>0</c>
<c>zero</c>
<c>not Present</c>
<c>Tuple I-DPD Check and Process for Forwarding</c>
<c>*</c>
<c>0</c>
<c>zero</c>
<c>Present</c>
<c>IPSec enhanced Tuple I-DPD Check and Process for Forwarding</c>
<c>0</c>
<c>0</c>
<c>nonzero</c>
<c>*</c>
<c>Extended Fragment Offset Tuple I-DPD Check and Process for
Forwarding</c>
<c>0</c>
<c>1</c>
<c>zero or nonzero</c>
<c>*</c>
<c>Extended Fragment Offset Tuple I-DPD Check and Process for
Forwarding</c>
</texttable>
<t>For performance reasons, IPv4 network fragmentation and
reassembly of multicast packets within wireless MANET networks
should be minimized, yet SMF provides the forwarding of fragments
when they occur. If the IPv4 multicast packet is a fragment, SMF
MUST use the fragmentation header fields for packet identification.
This identification can be considered temporally unique in the
context of the <protocol:srcAddr:dstAddr> of the IPv4 packet.
If the packet is an unfragmented IPv4 IPSec packet, SMF MUST use
IPSec fields for packet identification. The IPSec header
<sequence> field can be considered a unique identifier in the
context of the <IPSecType:srcAddr:dstAddr:SPI> where the
"IPSecType" is either AH or ESP. Finally, for unfragmented,
non-IPSec, IPv4 packets, the "Identification" field can be used for
I-DPD purposes. The "Identification" field can be considered unique
in the context of the IPv4 <protocol:scrAddr:dstAddr> tuple.
The following table summarizes these packet identification
types:</t>
<texttable anchor="IPv4IDPDId"
title="IPv4 I-DPD Packet Identification Types">
<ttcol>IPv4 Packet Type</ttcol>
<ttcol>Packet Identification Context</ttcol>
<ttcol>Packet Identifier</ttcol>
<c>Fragment</c>
<c><protocol:srcAddr:dstAddr></c>
<c><fragmentOffset:id></c>
<c>IPSec Packet</c>
<c><IPSecType:srcAddr:dstAddr:SPI></c>
<c><sequence></c>
<c>Regular Packet</c>
<c><protocol:srcAddr:dstAddr></c>
<c><id></c>
</texttable>
<t>"IPSecType" is either Authentication Header (AH) or Encapsulating
Security Payload (ESP).</t>
<t>The limited size (16 bits) of the IPv4 header "Identification"
field may result in more frequent value field wrapping, particularly
if a common sequence space is used by a source for multiple
destinations. If I-DPD operation is required, the use of the
"internal hashing" technique described in <xref
target="I-HASH"></xref> may mitigate this limitation of the IPv4
"Identification" field for SMF DPD. In this case the "internal hash"
value would be concatenated with the "Identification" value for
I-DPD operation.</t>
</section>
<section title="IPv4 Hash-based DPD">
<t>To ensure consistent IPv4 H-DPD operation among SMF nodes, a
default hashing approach is specified. This is similar to that
specified for IPv6, but the H-DPD header option with HAV is not
considered. SMF MUST perform an MD5 <xref target="RFC1321"></xref>
hash of the immutable header fields, option fields and data content
of the IPv4 multicast packet resulting in a 128-bit digest. The
lower 64 bits of this digest (MD5_64) is used for SMF packet
identification. The approach for calculating the hash value SHOULD
follow the same guidelines described for calculating the Integrity
Check Value (ICV) described in <xref target="RFC4302"></xref> with
respect to non-mutable fields. A history of the packet hash values
SHOULD be maintained in the context of
<protocol:srcAddr:dstAddr>. The context for IPv4 is more
specific than that of IPv6 since the SMF-DPD HAV cannot be employed
to mitigate hash collisions.</t>
<t>The MD5 hash is specified at present for consistency and
robustness. Future approaches and experimentation may discover
designs tradeoffs in hash robustness and efficiency worth
considering for future versions of SMF. This MAY include reducing
the packet payload length that is processed, determining shorter
indexes, or applying a more efficient hashing algorithm.</t>
</section>
</section>
<section anchor="I-HASH"
title="Internal Hash Computation Considerations">
<t>Forwarding protocols that use DPD techniques, such as SMF, may be
vulnerable to denial-of-service (DoS) attacks based on spoofing
packets with apparently valid packet identifier fields. Such a
consideration is pointed out in <xref target="Security"></xref>. In
wireless environments, where SMF will most likely be used, the
opportunity for such attacks is more prevalent than in wired networks.
In the case of IPv4 packets, fragmented IP packets or packets with
IPSec headers applied, the DPD "identifier" of potential future
packets that might be forwarded is highly predictable and easily
subject to denial-of-service attacks against forwarding. A RECOMMENDED
technique to counter this concern is for SMF implementations to
generate an "internal" hash value that is concatenated with the
explicit I-DPD packet identifier to form a unique identifier that is a
function of the packet content as well as the visible identifier. SMF
implementations could seed their hash generation with a random value
to make it unlikely that an external observer could guess how to spoof
packets used in a denial-of-service attack against forwarding. Since
the hash computation and state is kept completely internal to SMF
nodes, the cryptographic properties of this hashing would not need to
be extensive and thus possibly of low complexity. Experimental
implementations may determine that a lightweight hash of even only
portions of packets may suffice to serve this purpose.</t>
<t>For IPv4 I-DPD based on the limited 16-bit IP header
"Identification" field, it is possible that use of this "internal
hash" technique may also enhance I-DPD performance in cases where the
IPv4 "Identification" field may frequently wrap due to sources
supporting high data rate flows.</t>
<t>While H-DPD is not as readily susceptible to this form of DoS
attack, it is possible that a sophisticated adversary could use side
information to construct spoofing packets to mislead forwarders using
a well-known hash algorithm. Thus, similarly, a separate "internal"
hash value could be concatenated with the well-known hash value to
alleviate this security concern.</t>
</section>
</section>
<!-- End of Duplicate Packet Detection Section -->
<!-- Beginning of Relay Set Section -->
<section anchor="Relays"
title="Reduced Relay Set Forwarding and Relay Selection Capability">
<t>SMF implementations MUST support CF as a basic forwarding mechanism
when reduced relay set information is not available or not selected for
operation. In CF mode, each node transmits a locally generated or newly
received forwardable packet exactly once. The DPD techniques described
in <xref target="DPD"></xref> are critical to proper operation and
prevent duplicate packet retransmissions by the same forwarding
node.</t>
<t>A goal of SMF is to apply reduced relay sets for more efficient
multicast dissemination within dynamic topologies. To accomplish this
SMF MUST support the ability to modify its multicast packet forwarding
rules based upon relay set state received dynamically during operation.
In this way, SMF forwarding operates effectively as neighbor adjacencies
or multicast forwarding policies within the topology change.</t>
<t>In early SMF experimental deployments, the relay set information has
been derived from coexistent unicast MANET protocol coexistent control
plane traffic flooding processes. From this experience, extra pruning
considerations were sometimes required when utilizing a relay set from a
separate routing protocol process. As an example, relay sets formed for
the unicast control plane flooding MAY include additional redundancy
that may not be desired for multicast forwarding use (e.g., biconnected
CDS mesh for control plane purposes).</t>
<t>Here is a recommended criteria list for SMF relay set selection
algorithm candidates:</t>
<t><list style="numbers">
<t>Robustness to topological dynamics and mobility</t>
<t>Localized election or coordination of any relay sets</t>
<t>Reasonable minimization of relay set size to achieve CDS given
above constraints</t>
<t>Heuristic support for preference or election metrics (Better
enables scenario-specific management of relay set)</t>
</list></t>
<t>Some relay set algorithms meeting these 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 specifications in the
future. The Appendices in this document can serve as a template for the
content of such potential future specifications.</t>
<t><xref target="smfControlOptions"></xref> depicts a state information
diagram of possible relay set control options.</t>
<figure align="center" anchor="smfControlOptions"
title="SMF Relay Set Control Options">
<artwork><![CDATA[
Possible L2 Trigger/Information
|
|
______________ ______v_____ __________________
| MANET | | | | |
| Neighborhood | | Relay Set | | Other Heuristics |
| Discovery |----------->| Selection |<------| (Preference,etc) |
| Protocol | neighbor | Algorithm | | |
|______________| info |____________| |__________________|
\ /
\ /
neighbor\ / Dynamic Relay
info* \ ____________ / Set Status
\ | SMF | / (State, {neighbor info})
`-->| Relay Set |<--'
| State |
-->|____________|
/
/
______________
| Coexistent |
| MANET |
| Unicast |
| Process |
|______________|
]]></artwork>
</figure>
<t>There are basically three styles of SMF operation with reduced relay
sets:</t>
<t><list style="numbers">
<t>Independent operation: SMF performs its own relay set selection
using information from an associated MANET NHDP process. In this
case, NHDP messaging SHOULD be appended with additional <xref
target="PacketBB"></xref> type-length-value (TLV) content to support
SMF-specific requirements as discussed in <xref
target="Neighborhood"></xref> and for the applicable relay set
algorithm described in the Appendices of this document or future
specifications.</t>
<t>Operation with CDS-aware unicast routing protocol: Coexistent
unicast routing protocol provides dynamic relay set state based upon
its own control plane CDS or neighborhood discovery information. If
it is desired that the SMF data plane forwarding use a different
relay set selection algorithm than used for the routing protocol
control plane, then the routing protocol NHDP instance (if
applicable) SHOULD append its messages with the appropriate
SMF-specific TLV content (see <xref target="Neighborhood"></xref>
and the relay set algorithm Appendices).</t>
<t>Cross-layer Operation: SMF operates using neighborhood status and
triggers from a cross-layer information base for dynamic relay set
selection and maintenance (e.g., lower link layer) .</t>
</list></t>
</section>
<!-- End of Relay Set Section -->
<!-- Begin Neighborhood Discovery Section -->
<section anchor="Neighborhood"
title="SMF Neighborhood Discovery Requirements">
<t>This section defines the requirements for use of the <xref
target="NHDP">MANET Neighborhood Discovery Protocol (NHDP)</xref> to
support SMF operation. Note that basic CF forwarding requires no
neighborhood topology knowledge since every SMF node relays all traffic
while supporting more efficient SMF relay set operation requires the
discovery and maintenance of dynamic neighborhood topology information.
The MANET NHDP protocol can provide this necessary information, but in
some circumstances there are SMF-specific requirements for related NHDP
use. This can be the case for both "independent" SMF operation where
NHDP is being used specifically to support SMF or when one NHDP instance
is used for both for SMF and a coexistent MANET unicast routing
protocol.</t>
<t>Core NHDP messages and the resultant neighborhood information base
are described separately within the NHDP specification. To summarize,
the NHDP protocol provides the following basic functions: <list
style="numbers">
<t>1-hop neighbor link sensing and bidirectionality checks of
neighbor links,</t>
<t>2-hop neighborhood discovery including collection of 2-hop
neighbors and connectivity information,</t>
<t>Collection and maintenance of the above information across
multiple interfaces, and</t>
<t>A method for signaling SMF information throughout the 2-hop
neighborhood such as the existence of an SMF instance and any
related relay set selection information.</t>
</list></t>
<t>The Appendices of this document describe a set of CDS-based relay set
selection algorithms that can be used to achieve efficient SMF
operation, even in dynamic, mobile networks<xref target="MDDA07">
</xref>. For some of these algorithms, the core NHDP specification can
provide all the necessary information to conduct relay set selection.
For others, NHDP messaging needs to be extended to support SMF
discovery, relay set selection, and maintenance. For example, the <xref
target="OLSRv2"></xref> specification specifies TLV constructs for NHDP
messages to support its use of the S-MPR algorithm.</t>
<t>The following sub-sections specify some SMF-specific TLV types to
support general SMF operation or to support the algorithms described in
the Appendices to this document. The Appendices describing each of the
relay set algorithms also specify any additional requirements for NHDP
to support their operation and reference the applicable TLV types as
needed.</t>
<section anchor="SMFTLVs" title="SMF Relay Algorithm TLV Types">
<t>This section specifies TLV types to be used within NHDP messages to
identify the CDS relay set selection algorithm(s) in use. Two TLV
types are defined, one message TLV type and one address TLV type.</t>
<section title="SMF Message TLV Type">
<t>The SMF message TLV type denoted SMF_TYPE is used to identify the
existence of an SMF instance operating in conjunction with NHDP.
This message type makes use of the extended type field as defined by
<xref target="PacketBB"></xref> to convey the CDS relay set
selection algorithm currently in use by the SMF message originator.
When NHDP is used to support SMF operation, the SMF_TYPE TLV,
containing the extended type field with the appropriate value,
SHOULD be included in NHDP_HELLO messages generated. This allows SMF
nodes to learn when neighbors are configured to use NHDP for
information exchange including algorithm type and related algorithm
information. This information can be used to take action, such as
ignoring neighbor information using incompatible algorithms. It is
possible that SMF neighbors MAY be configured differently and still
operate cooperatively, but these cases will vary dependent upon the
algorithm types designated.</t>
<t>This document defines the following Message TLV type<xref
target="smfType_Message"></xref> conforming to <xref
target="PacketBB"></xref>. Extended type field values communicate
"Relay Algorithm Type" to other 1-hop SMF neighbors and value fields
may contain algorithm specific information.</t>
<texttable anchor="smfType_Message" title="SMF Type Message TLV">
<preamble></preamble>
<ttcol></ttcol>
<ttcol>packetBB TLV syntax</ttcol>
<ttcol>Field Values</ttcol>
<c>type</c>
<c><tlv-type></c>
<c>SMF_TYPE</c>
<c>extended type</c>
<c><tlv-type-ext></c>
<c><relayAlgorithmid></c>
<c>length</c>
<c><length></c>
<c>variable</c>
<c>value</c>
<c><value></c>
<c>variable</c>
</texttable>
<t>In <xref target="smfType_Message"></xref>
<relayAlgorithmId> is an 8-bit field containing a number 0-255
representing the "Relay Algorithm Type" of the originator address of
the corresponding NHDP message.</t>
<t>Possible values for the <relayAlgorithmId> are defined in
<xref target="IdTLVValues"></xref>. The table provides value
assignments, future IANA assignment spaces, and an experimental
space. The experimental space use MUST NOT assume uniqueness and
thus should not be used for general interoperable deployment prior
to official IANA assignment.</t>
<texttable anchor="IdTLVValues"
title="SMF Relay Algorithm Type Values">
<ttcol align="center" width="30%">Extended Type Value</ttcol>
<ttcol align="center" width="60%">Algorithm</ttcol>
<c>0</c>
<c>CF</c>
<c>1</c>
<c>S-MPR</c>
<c>2</c>
<c>E-CDS</c>
<c>3</c>
<c>MPR-CDS</c>
<c>4-127</c>
<c>Future Assignment with STD action</c>
<c>128-239</c>
<c>No STD action required</c>
<c>240-255</c>
<c>Experimental Space</c>
</texttable>
<t>Acceptable <length> and <value> fields of an SMF_TYPE
TLV are extended type dependent. The appropriate algorithm type, as
conveyed in the <tlv-type-ext> field, defines the meaning and
format of its TLV <value> field. For algorithms defined by
this document see the appropriate appendix for the <value>
field format.</t>
</section>
<section title="SMF Address Block TLV Type">
<t>An address block TLV type, denoted SMF_NBR_TYPE (i.e., SMF
neighbor relay algorithm) <xref target="smfType_Addr"></xref>, is
specified so that CDS relay algorithm operation and configuration
can be shared among 2-hop neighborhoods This is useful for the case
when mixed relay algorithm operation is possible.</t>
<t>The message SMF_TYPE TLV and address block SMF_NBR_TYPE TLV types
share a common format.</t>
<texttable anchor="smfType_Addr" title="SMF Type Address Block TLV">
<preamble></preamble>
<ttcol></ttcol>
<ttcol>packetBB TLV syntax</ttcol>
<ttcol>Field Values</ttcol>
<c>type</c>
<c><tlv-type></c>
<c>SMF_NBR_RELAY_ALG</c>
<c>extended type</c>
<c><tlv-type-ext></c>
<c><relayAlgorithmid></c>
<c>length</c>
<c><length></c>
<c>variable</c>
<c>value</c>
<c><value></c>
<c>variable</c>
</texttable>
<t><relayAlgorithmId> in <xref target="IdTLVValues"></xref> is
an 8-bit field containing a number 0-255 representing the "Relay
Algorithm Type" value that corresponds to any indicated address in
the address block. Note that "Relay Algorithm Type" values for 2-hop
neighbors can be conveyed in a single TLV or multiple value TLVs as
described in <xref target="PacketBB"></xref>. It is expected that
SMF nodes using NHDP construct address blocks with SMF_NBR_TYPE TLVs
to advertise "Relay Algorithm Type" and to advertise neighbor
algorithm values received in SMF_TYPE TLVs from those neighbors.</t>
<t>Again values for the <relayAlgorithmId> are defined in
<xref target="IdTLVValues"></xref>.</t>
<t>Value length and value content of an SMF_NBR_TYPE TLV is defined
by the appropriate algorithm type contained in the extended type
field. See appropriate the appendix for definitions of value fields
for algorithms defined by this document.</t>
</section>
</section>
</section>
<!-- End of Neighborhood Discovery Requirements Section -->
<section anchor="Gateways" title="SMF Border Gateway Considerations">
<t>It is expected that SMF will be used to provide simple forwarding of
multicast trafficwithin a MANET mesh routing topology. A border router
approach should be used to allow interconnection of SMF areas with
networks using other multicast routing protocols (e.g., PIM). It is
important to note that there are many scenario-specific issues that
should be addressed when discussing border routers. At the present time,
experimental deployments of SMF and PIM border router approaches have
been demonstrated. Some of the functionality border routers may need to
address include the following:</t>
<t><list style="numbers">
<t>Determining which multicast groups should transit the border
router whether entering or exiting the attached MANET routing
region(s).</t>
<t>Enforcement of TTL threshold or other scoping policies.</t>
<t>Any marking or labeling to enable DPD on ingressing packets.</t>
<t>Interface with exterior multicast routing protocols.</t>
<t>Possible operation with multiple border routers (presently beyond
scope of this document).</t>
<t>Provisions for participating non-SMF nodes.</t>
</list></t>
<t>Note the behavior of border router SMF nodes is the same as that of
non-border SMF nodes when forwarding packets on interfaces within the
MANET routing region. Packets that are passed outbound to interfaces
operating fixed-infrastructure multicast routing protocols SHOULD be
evaluated for duplicate packet status since present standard multicast
forwarding mechanisms do not usually perform this function.</t>
<section anchor="ForwardedGroups" title="Forwarded Multicast Groups">
<t>Mechanisms for dynamically determining groups for forwarding into a
MANET SMF routing region is an evolving technology area. Ideally, only
groups for which there is active group membership should be injected
into the SMF domain. This can 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 border routers (and hence multicast networks) of their
current group membership status. For specific systems and services it
may be possible to statically configure group membership joins in
border routers, 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.</t>
<t>Outbound traffic is less problematic. SMF border routers can
perform duplicate packet detection and forward non-duplicate traffic
that meets TTL/hop limit and scoping criteria to other interfaces.
Appropriate IP multicast routing (PIM, etc) on those interfaces can
then make further forwarding decisions with respect to the given
traffic destination and potentially its source addresses. Note that
the presence of multiple border routers associated with a MANET
routing region raises additional issues. This is further discussed in
<xref target="MultipleGateways"></xref> but further work is expected
to be needed here.</t>
</section>
<section title="Multicast Group Scoping">
<t>Multicast scoping is used by network administrators to control the
network routing regions reachable by multicast packets. This is
usually done by configuring external interfaces of border routers in
the border of an routing region to not forward multicast packets which
must be kept within the routing region. This is commonly done based on
TTL of messages or the basis of group addresses. These schemes are
known respectively as:</t>
<t><list style="numbers">
<t>TTL scoping.</t>
<t>Administrative scoping.</t>
</list></t>
<t>For IPv4, network administrators can configure border routers 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 SHOULD be taken into
account that the packet could traverse multiple hops within the MANET
SMF routing region before reaching the border router. Thus, TTL
thresholds SHOULD be selected carefully.</t>
<t>For IPv6, multicast address spaces include information about the
scope of the group. Thus, border routers of an SMF routing region know
if they must forward a packet based on the IPv6 multicast group
address. For the case of IPv6, it is RECOMMENDED that a MANET SMF
routing region be designated a site. Thus, all IPv6 multicast packets
in the range FF05::/16 SHOULD be kept within the MANET SMF routing
region by border routers. IPv6 packets in any other wider range scopes
(i.e. FF08::/16, FF0B::/16 and FF0E::16) MAY traverse border routers
unless other restrictions different from the scope applies.</t>
<t>Given that scoping of multicast packets is performed at the border
routers, and given that existing scoping mechanisms are not designed
to work with mobile routers, it is assumed that non-border SMF routers
will not stop forwarding multicast data packets of the appropriate
site scoping. That is, it is assumed that the entire MANET SMF routing
region is a site scoped area.</t>
</section>
<section title="Interface with Exterior Multicast Routing Protocols">
<t>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, border
routers can be considered leaf routers. Mechanisms for multicast
sources and receivers to interoperate with border routers over the
multihop MANET SMF routing region as if they were directly connected
to the router need to be defined. The following issues need to be
addressed:</t>
<t><list style="numbers">
<t>Mechanism by which border routers gather membership
information.</t>
<t>Mechanism by which multicast sources are known by the border
router.</t>
<t>Exchange of exterior routing protocol messages across the MANET
routing region if the MANET routing region is to provide transit
connectivity for multicast traffic.</t>
</list></t>
<t>It is beyond the scope of this document to address implementation
solutions to these issues. As described in <xref
target="ForwardedGroups"></xref>, 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
routing region. But, because MANET routing regions 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.</t>
<t>The need for the border router to receive traffic from recognized
multicast sources within the MANET SMF routing region is important to
achieve a smooth interworking with existing routing protocols. For
instance, PIM-S requires routers with locally attached multicast
sources to register them to the Rendezvous Point (RP) so that nodes
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.</t>
</section>
<section anchor="MultipleGateways" title="Multiple Border Routers">
<t>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 routing region can be beneficial since it can increase
reliability, and provide better service. For example, if the MANET
routing region were to fragment with different MANET nodes maintaining
connectivity to different border routers, multicast service could
still continue successfully. But, the case of multiple border routers
connecting a MANET routing region to external networks presents
several challenges for SMF:</t>
<t><list style="numbers">
<t>Detection/hash collision/sequencing of duplicate unmarked IPv4
or IPv6 (without IPSec encapsulation or DPD option) packets
possibly injected by multiple border routers.</t>
<t>Source-based relay algorithms handling of duplicate traffic
injected by multiple border routers.</t>
<t>Determination of which border router(s) will forward outbound
multicast traffic.</t>
<t>Additional challenges with interfaces to exterior multicast
routing protocols.</t>
</list>One of the most obvious issues is when multiple border
routers are present and may be alternatively (due to route changes) or
simultaneously injecting common traffic into the MANET routing region
that has not been previously marked for SMF DPD. Different border
routers would not be able to implicitly synchronize sequencing of
injected traffic since they may not receive exactly the same messages
due to packet losses. For IPv6 I-DPD operation, the optional
"TaggerId" field described for the SMF-DPD header option can be used
to mitigate this issue. When multiple border routers are injecting a
flow into a MANET routing region, there are two forwarding policies
that SMF I-DPD nodes may implement:</t>
<t><list style="numbers">
<t>Redundantly forward the multicast flows (identified by
<sourceAddress:destinationAddress>) from each border router,
performing DPD processing on a <taggerID:destinationAddress>
or <taggerID:sourceAddress:destinationAddress> basis, or</t>
<t>Use some basis to select the flow of one tagger (border router)
over the others and forward packets for applicable flows
(identified by <sourceAddress:destinationAddress>) only for
that "Tagger ID" until timeout or some other criteria to favor
another tagger occurs.</t>
</list>It is RECOMMENDED that the first approach be used in the case
of I-DPD operation unless the SMF system is specifically designed to
implement the second option. Additional specification may be required
to describe an interoperable forwarding policy based on this second
option. Note that the implementation of the second option requires
that per-flow (i.e., <sourceAddress::destinationAddress>) state
be maintained for the selected "Tagger ID".</t>
<t>The deployment of a H-DPD operational mode may alleviate DPD
resolution when ingressing traffic comes from multiple border routers.
Non-colliding hash indexes (those not requiring the H-DPD options
header in IPv6) should be resolved effectively.</t>
</section>
</section>
<section title="Non-SMF MANET Node Interaction">
<t>There may be scenarios in which some neighboring wireless MANET node
are not running SMF and/or not forwarding, but 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, NHDP, and/or SMF forwarding operation. These devices
include:</t>
<t><list style="numbers">
<t>Devices that opportunistically receive multicast traffic due to
proximity with SMF relays (possibly with asymmetric IP connectivity
e.g., sensor network device).</t>
<t>Devices that participate in NHDP (directly or via routing
protocol signaling) but do not forward traffic.</t>
</list>Note there is no guarantee of traffic delivery with category 1
above, but the election heuristics shown in <xref
target="smfControlOptions"></xref> MAY be adjusted via management to
better support such devices. However, 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 routing regions
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 routers or
intermediate systems providing IP Multicast routing functions.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>Gratuitous use of option headers can cause problems in routers.
Routers outside of MANET routing regions should ignore SMF-specific
header options if encountered. The header options types are encoded
appropriately for this behavior.</t>
<t>Sequence-based packet identifiers are predictable and thus provide an
opportunity for a denial-of-service attack against forwarding. The use
of the "internal hashing" as described in <xref target="I-HASH"></xref>
for the I-DPD operation helps to mitigate denial-of-service attacks on
predictable packet identifiers. In this case, spoofed packets MAY be
forwarded but the additional internal history identifier will protect
against false collision events that may result from a predictive
denial-of-service attack.</t>
<t>Another potential denial-of-service attack against SMF forwarding is
possible when a bad-behaving node has a form of "wormhole" access (via a
directional antenna, etc) to preview packets before a particular SMF
node would receive them. The bad-behaving node could reduce the TTL or
Hop Limit of the packet and transmit it to the SMF node causing it to
forward the packet with a limited TTL (or even drop it) and make a DPD
entry that would block forwarding of the subsequently-arriving valid
packet with appropriate TTL value. This would be a relatively low-cost,
high-payoff attack that would be hard to detect and thus attractive to
potential attackers. An approach of caching TTL information with DPD
state and taking appropriate forwarding actions is identified in <xref
target="Forwarding"></xref> to mitigate this form of attack.</t>
<t>The support of forwarding IPSec datagrams without further
modification for both IPv4 and IPv6 is supported by this
specification.</t>
<t>Authentication mechanisms to identify the source of IPv6 option
headers should be considered to reduce vulnerability to a variety of
attacks.</t>
</section>
<section title="IANA Considerations">
<t>This document raises multiple IANA Considerations. These include the
IPv6 SMF_DPD hop-by-hop Header Extension defined and multiple
Type-Length-Value (TLV) constructs (see <xref target="PacketBB"></xref>)
used to extend NHDP operation as needed to support different forms of
SMF operation.</t>
<section title="IPv6 SMF_DPD Header Extension">
<t>This document requests IANA assignment of the "SMF_DPD" hop-by-hop
option type from the IANA "IPv6 Hop-by-Hop Options Option Type"
registry (see Section 5.5 of <xref target="RFC2780"></xref>).</t>
<t>The format of this new option type is described in <xref
target="Opt-DPD"></xref>. A portion of the option data content is the
"taggerIdType" that provides a context for the "taggerId" that is
optionally included to identify the intermediate system that added the
SMF_DPD option to the packet. This document defines a name-space for
IPv6 SMF_DPD Tagger Identifier Types:</t>
<figure>
<artwork align="center"><![CDATA[ietf:manet:smf:taggerIdTypes]]></artwork>
</figure>
<t>The values that can be assigned within the
"ietf:manet:smf:taggerIdTypes" name-space are numeric indexes in the
range [0, 7], boundaries included. All assignment requests are granted
on a "IETF Consensus" basis as defined in <xref
target="RFC2434"></xref>.</t>
<t>This specification registers Tagger Identification Type values from
<xref target="taggerIdTypes"></xref> in the registry
"ietf:manet:smf:taggerIdTypes":</t>
<texttable anchor="taggerIdTypes" title="TaggerId Types">
<ttcol align="center">Mnemonic</ttcol>
<ttcol align="center">Value</ttcol>
<ttcol>Reference</ttcol>
<c>NULL</c>
<c>0</c>
<c>This document</c>
<c>DEFAULT</c>
<c>1</c>
<c>This document</c>
<c>IPv4</c>
<c>2</c>
<c>This document</c>
<c>IPv6</c>
<c>3</c>
<c>This document</c>
<c>ExtId</c>
<c>7</c>
<c>This document</c>
</texttable>
</section>
<section title="SMF Type-Length-Value">
<t>This document requests an IANA assignment one message "SMF_TYPE"
TLV value and one address block "SMF_NBR_TYPE" TLV value from the
<xref target="NHDP"></xref> specific registry space.</t>
<t>The format of this new TLV type is described in <xref
target="smfType_Message"></xref> and <xref
target="smfType_Addr"></xref>. Furthermore this document defines a
namespace for algorithm ID types using the extended type TLV value
field defined by <xref target="PacketBB"></xref>. Both SMF_TYPE and
SMF_NBR_TYPE TLVs use this namespace.</t>
<figure>
<artwork align="center"><![CDATA[ietf:manet:packetbb:nhdp:smf:relayAlgorithmID]]></artwork>
</figure>
<t>The values that can be assigned within the
"ietf:manet:packetbb:nhdp:smf:relayAlgorithmID" name-space are numeric
indexes in the range [0, 239], boundaries included. Assignment
requests for the [0-127] are granted on a "IETF Consensus" basis as
defined in <xref target="RFC2434"></xref>. Standards action is not
required for assignment requests of the range [128-239]. Documents
requesting relayAlgorithmId values SHOULD define value field uses
contained by the SMF_TYPE:<relayAlgorithmID> and
SMF_NBR_TYPE:<relayAlgorithmID> full type TLVs.</t>
<t>This specification registers the following Relay Algorithm ID Type
values shown in <xref target="RelaySetTypes"></xref> in the registry
"ietf:manet:packetbb:nhdp:smf:relayAlgorithmID</t>
<texttable anchor="RelaySetTypes"
title="Relay Set Algorithm Type Values">
<ttcol>Mnemonic</ttcol>
<ttcol>Value</ttcol>
<ttcol>Reference</ttcol>
<c>CF</c>
<c>0</c>
<c>This document</c>
<c>S-MPR</c>
<c>1</c>
<c><xref target="smprAppendix"></xref></c>
<c>E-CDS</c>
<c>2</c>
<c><xref target="ecdsAppendix"></xref></c>
<c>MPR-CDS</c>
<c>3</c>
<c><xref target="mprcdsAppendix"></xref></c>
</texttable>
</section>
</section>
<section title="Acknowledgments">
<t>Many of the concepts and mechanisms used and adopted by SMF resulted
from many years of discussion and related work within the MANET WG since
the late 1990s. There are obviously many contributors 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 earlier
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 design, content editing,
prototype implementation, and core discussions are listed below in
alphabetical order. We appreciate input from many others we may have
missed in this list as well.<list style="empty">
<t>Design contributors in alphabetical order:</t>
<t>Brian Adamson</t>
<t>Teco Boot</t>
<t>Ian Chakeres</t>
<t>Thomas Clausen</t>
<t>Justin Dean</t>
<t>Brian Haberman</t>
<t>Charles Perkins</t>
<t>Pedro Ruiz</t>
<t>Fred Templin</t>
<t>Maoyu Wang</t>
</list></t>
<t>The RFC text was produced using Marshall Rose's xml2rfc tool and Bill
Fenner's XMLmind add-ons.</t>
</section>
</middle>
<back>
<references title="Normative References">
<reference anchor="RFC2460">
<front>
<title abbrev="IPv6 Specification">Internet Protocol, Version 6
(IPv6) Specification</title>
<author fullname="Stephen E. Deering" initials="S.E."
surname="Deering">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>170 West Tasman Drive</street>
<street>San Jose</street>
<region>CA</region>
<code>95134-1706</code>
<country>USA</country>
</postal>
<phone>+1 408 527 8213</phone>
<facsimile>+1 408 527 8254</facsimile>
<email>deering@cisco.com</email>
</address>
</author>
<author fullname="Robert M. Hinden" initials="R.M." surname="Hinden">
<organization>Nokia</organization>
<address>
<postal>
<street>232 Java Drive</street>
<street>Sunnyvale</street>
<region>CA</region>
<code>94089</code>
<country>USA</country>
</postal>
<phone>+1 408 990 2004</phone>
<facsimile>+1 408 743 5677</facsimile>
<email>hinden@iprg.nokia.com</email>
</address>
</author>
<date month="December" year="1998" />
<area>Internet</area>
<keyword>internet protocol version 6</keyword>
<keyword>IPv6</keyword>
<abstract>
<t>This document specifies version 6 of the Internet Protocol
(IPv6), also sometimes referred to as IP Next Generation or
IPng.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="2460" />
<format octets="85490" target="ftp://ftp.isi.edu/in-notes/rfc2460.txt"
type="TXT" />
<format octets="99496"
target="http://xml.resource.org/public/rfc/html/rfc2460.html"
type="HTML" />
<format octets="93343"
target="http://xml.resource.org/public/rfc/xml/rfc2460.xml"
type="XML" />
</reference>
<reference anchor="RFC2119">
<front>
<title abbrev="RFC Key Words">Key words for use in RFCs to Indicate
Requirement Levels</title>
<author fullname="Scott Bradner" initials="S." surname="Bradner">
<organization>Harvard University</organization>
<address>
<postal>
<street>1350 Mass. Ave.</street>
<street>Cambridge</street>
<street>MA 02138</street>
</postal>
<phone>- +1 617 495 3864</phone>
<email>sob@harvard.edu</email>
</address>
</author>
<date month="March" year="1997" />
<area>General</area>
<keyword>keyword</keyword>
<abstract>
<t>In many standards track documents several words are used to
signify the requirements in the specification. These words are
often capitalized. This document defines these words as they
should be interpreted in IETF documents. Authors who follow these
guidelines should incorporate this phrase near the beginning of
their document: <list style="empty">
<t>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 RFC 2119.</t>
</list></t>
<t>Note that the force of these words is modified by the
requirement level of the document in which they are used.</t>
</abstract>
</front>
<seriesInfo name="BCP" value="14" />
<seriesInfo name="RFC" value="2119" />
<format octets="4723" target="ftp://ftp.isi.edu/in-notes/rfc2119.txt"
type="TXT" />
<format octets="14486"
target="http://xml.resource.org/public/rfc/html/rfc2119.html"
type="HTML" />
<format octets="5661"
target="http://xml.resource.org/public/rfc/xml/rfc2119.xml"
type="XML" />
</reference>
<reference anchor="RFC2644">
<front>
<title abbrev="Default Change for Directed Broadcast">Changing the
Default for Directed Broadcasts in Routers</title>
<author fullname="Daniel Senie" initials="D." surname="Senie">
<organization>Amaranth Networks Inc.</organization>
<address>
<postal>
<street>324 Still River Road</street>
<city>Bolton</city>
<region>MA</region>
<code>01740</code>
<country>US</country>
</postal>
<phone>+1 978 779 6813</phone>
<email>dts@senie.com</email>
</address>
</author>
<date month="August" year="1999" />
</front>
<seriesInfo name="BCP" value="34" />
<seriesInfo name="RFC" value="2644" />
<format octets="6820" target="ftp://ftp.isi.edu/in-notes/rfc2644.txt"
type="TXT" />
</reference>
<reference anchor="RFC1321">
<front>
<title abbrev="MD5 Message-Digest Algorithm">The MD5 Message-Digest
Algorithm</title>
<author fullname="Ronald L. Rivest" initials="R." surname="Rivest">
<organization>Massachusetts Institute of Technology, (MIT)
Laboratory for Computer Science</organization>
<address>
<postal>
<street>545 Technology Square</street>
<street>NE43-324</street>
<city>Cambridge</city>
<region>MA</region>
<code>02139-1986</code>
<country>US</country>
</postal>
<phone>+1 617 253 5880</phone>
<email>rivest@theory.lcs.mit.edu</email>
</address>
</author>
<date month="April" year="1992" />
</front>
<seriesInfo name="RFC" value="1321" />
<format octets="35222" target="ftp://ftp.isi.edu/in-notes/rfc1321.txt"
type="TXT" />
</reference>
<reference anchor="RFC0791">
<front>
<title abbrev="Internet Protocol">Internet Protocol</title>
<author fullname="Jon Postel" initials="J." surname="Postel">
<organization>University of Southern California (USC)/Information
Sciences Institute</organization>
<address>
<postal>
<street>4676 Admiralty Way</street>
<city>Marina del Rey</city>
<region>CA</region>
<code>90291</code>
<country>US</country>
</postal>
</address>
</author>
<date day="1" month="September" year="1981" />
</front>
<seriesInfo name="STD" value="5" />
<seriesInfo name="RFC" value="791" />
<format octets="97779" target="ftp://ftp.isi.edu/in-notes/rfc791.txt"
type="TXT" />
</reference>
<reference anchor="RFC3626">
<front>
<title>Optimized Link State Routing Protocol</title>
<author fullname="Thomas Clausen" initials="T" surname="Clausen">
<organization>INRIA</organization>
</author>
<author fullname="Phillipe Jacquet" initials="P" surname="Jacquet">
<organization>INRIA</organization>
</author>
<date year="2003" />
</front>
</reference>
<reference anchor="E-CDS">
<front>
<title>MANET Extension of OSPF Using CDS Flooding</title>
<author fullname="Richard Ogier" initials="R" surname="Ogier">
<organization></organization>
</author>
<date month="March" year="2005" />
</front>
<seriesInfo name="Proceedings of the 62nd IETF" value="" />
</reference>
<reference anchor="PacketBB">
<front>
<title>Generalized MANET Packet/Message Format</title>
<author fullname="Thomas Clausen" initials="T" surname="Clausen">
<organization></organization>
</author>
<author fullname="" initials="" surname="et al">
<organization></organization>
</author>
<date day="14" month="November" year="2007" />
</front>
<seriesInfo name="draft-ietf-manet-packetbb-11, Work in progress"
value="" />
</reference>
<reference anchor="NHDP">
<front>
<title>Neighborhood Discovery Protocol</title>
<author fullname="Thomas Clausen" initials="T" surname="Clausen">
<organization></organization>
</author>
<author fullname="" initials="" surname="et al">
<organization></organization>
</author>
<date day="6" month="December" year="2007" />
</front>
<seriesInfo name="draft-ietf-manet-nhdp-05, Work in progress" value="" />
</reference>
<reference anchor="OLSRv2">
<front>
<title>Optimized Link State Routing Protocol version 2</title>
<author fullname="Thomas Clausen" initials="T" surname="Clausen">
<organization></organization>
</author>
<author fullname="" initials="" surname="et al">
<organization></organization>
</author>
<date month="July" year="2007" />
</front>
<seriesInfo name="draft-ietf-manet-olsrv2-04, Work in progress"
value="" />
</reference>
<reference anchor="MPR-CDS">
<front>
<title>Computing Connected Dominating Sets with Multipoint
Relays</title>
<author fullname="Cedrid Adjih" initials="C" surname="Adjih">
<organization>INRIA</organization>
</author>
<author fullname="Phillipe Jacquet" initials="P" surname="Jacquet">
<organization>INRIA</organization>
</author>
<author fullname="Laurent Viennot" initials="L" surname="Viennot">
<organization>INRIA</organization>
</author>
<date month="January" year="2005" />
</front>
<seriesInfo name="Ad Hoc and Sensor Wireless Networks" value="" />
</reference>
<reference anchor="RFC4302">
<front>
<title>IP Authentication Header</title>
<author fullname="Stephen Kent" initials="S" surname="Kent">
<organization>BBN Technologies</organization>
</author>
<date month="December" year="2005" />
</front>
</reference>
<reference anchor="RFC2780">
<front>
<title>IANA Allocation Guidelines For Values In the Internet
Protocol and Related Headers</title>
<author fullname="Scott Bradner" initials="S" surname="Bradner">
<organization>S</organization>
</author>
<date month="March" year="2000" />
</front>
</reference>
<reference anchor="RFC2434">
<front>
<title abbrev="Guidelines for IANA Considerations">Guidelines for
Writing an IANA Considerations Section in RFCs</title>
<author fullname="Thomas Narten" initials="T." surname="Narten">
<organization>IBM Corporation</organization>
<address>
<postal>
<street>3039 Cornwallis Ave.</street>
<street>PO Box 12195 - BRQA/502</street>
<street>Research Triangle Park</street>
<street>NC 27709-2195</street>
</postal>
<phone>919-254-7798</phone>
<email>narten@raleigh.ibm.com</email>
</address>
</author>
<author fullname="Harald Tveit Alvestrand" initials="H.T."
surname="Alvestrand">
<organization>Maxware</organization>
<address>
<postal>
<street>Pirsenteret</street>
<street>N-7005 Trondheim</street>
<country>Norway</country>
</postal>
<phone>+47 73 54 57 97</phone>
<email>Harald@Alvestrand.no</email>
</address>
</author>
<date month="October" year="1998" />
<area>General</area>
<keyword>Internet Assigned Numbers Authority</keyword>
<keyword>IANA</keyword>
<abstract>
<t>Many protocols make use of identifiers consisting of constants
and other well-known values. Even after a protocol has been
defined and deployment has begun, new values may need to be
assigned (e.g., for a new option type in DHCP, or a new encryption
or authentication algorithm for IPSec). To insure that such
quantities have consistent values and interpretations in different
implementations, their assignment must be administered by a
central authority. For IETF protocols, that role is provided by
the Internet Assigned Numbers Authority (IANA).</t>
<t>In order for the IANA to manage a given name space prudently,
it needs guidelines describing the conditions under which new
values can be assigned. If the IANA is expected to play a role in
the management of a name space, the IANA must be given clear and
concise instructions describing that role. This document discusses
issues that should be considered in formulating a policy for
assigning values to a name space and provides guidelines to
document authors on the specific text that must be included in
documents that place demands on the IANA.</t>
</abstract>
</front>
<seriesInfo name="BCP" value="26" />
<seriesInfo name="RFC" value="2434" />
<format octets="25092" target="ftp://ftp.isi.edu/in-notes/rfc2434.txt"
type="TXT" />
<format octets="37803"
target="http://xml.resource.org/public/rfc/html/rfc2434.html"
type="HTML" />
<format octets="26924"
target="http://xml.resource.org/public/rfc/xml/rfc2434.xml"
type="XML" />
</reference>
</references>
<references title="Informative References">
<reference anchor="RFC2901">
<front>
<title>Mobile Ad hoc Networking (MANET): Routing Protocol
Performance Issues and Evaluation Considerations</title>
<author fullname="Joseph Macker" initials="JP" surname="Macker">
<organization>NRL</organization>
</author>
<author fullname="Scot Corson" initials="MS" surname="Corson">
<organization>Univ of Md</organization>
</author>
<date year="1999" />
</front>
</reference>
<reference anchor="RFC3973">
<front>
<title>Protocol Independent Multicast - Dense Mode (PIM-DM):
Protocol Specification (Revised)</title>
<author fullname="A. Adams" initials="A." surname="Adams">
<organization></organization>
</author>
<author fullname="J. Nicholas" initials="J." surname="Nicholas">
<organization></organization>
</author>
<author fullname="W. Siadak" initials="W." surname="Siadak">
<organization></organization>
</author>
<date month="January" year="2005" />
<abstract>
<t>This document specifies Protocol Independent Multicast - Dense
Mode (PIM-DM). PIM-DM is a multicast routing protocol that uses
the underlying unicast routing information base to flood multicast
datagrams to all multicast routers. Prune messages are used to
prevent future messages from propagating to routers without group
membership information. This memo defines an Experimental Protocol
for the Internet community.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="3973" />
<format octets="136708"
target="ftp://ftp.isi.edu/in-notes/rfc3973.txt" type="TXT" />
</reference>
<reference anchor="RFC4601">
<front>
<title>Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)</title>
<author fullname="B. Fenner" initials="B." surname="Fenner">
<organization></organization>
</author>
<author fullname="M. Handley" initials="M." surname="Handley">
<organization></organization>
</author>
<author fullname="H. Holbrook" initials="H." surname="Holbrook">
<organization></organization>
</author>
<author fullname="I. Kouvelas" initials="I." surname="Kouvelas">
<organization></organization>
</author>
<date month="August" year="2006" />
<abstract>
<t>This document specifies Protocol Independent Multicast - Sparse
Mode (PIM-SM). PIM-SM is a multicast routing protocol that can use
the underlying unicast routing information base or a separate
multicast-capable routing information base. It builds
unidirectional shared trees rooted at a Rendezvous Point (RP) per
group, and optionally creates shortest-path trees per source.</t>
<t>This document obsoletes RFC 2362, an Experimental version of
PIM-SM. [STANDARDS TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="4601" />
<format octets="340632"
target="ftp://ftp.isi.edu/in-notes/rfc4601.txt" type="TXT" />
<format octets="304538"
target="ftp://ftp.isi.edu/in-notes/rfc4601.pdf" type="PDF" />
</reference>
<reference anchor="RFC3684">
<front>
<title>Topology Dissemination Based on Reverse-Path
Forwarding</title>
<author fullname="Richard Ogier" initials="R" surname="Ogier">
<organization>SRI</organization>
</author>
<author fullname="Fred Templin" initials="F" surname="Templin">
<organization>Nokia</organization>
</author>
<author fullname="Mark Lewis" initials="M" surname="Lewis">
<organization>S</organization>
</author>
<date year="2003" />
</front>
</reference>
<reference anchor="NTSC99">
<front>
<title>The Broadcast Storm Problem in Mobile Ad hoc Networks</title>
<author initials="S" surname="Ni">
<organization></organization>
</author>
<author initials="Y" surname="Tseng">
<organization></organization>
</author>
<author initials="Y" surname="Chen">
<organization></organization>
</author>
<author initials="J" surname="Sheu">
<organization></organization>
</author>
<date year="1999" />
</front>
<seriesInfo name="Proceedings Of ACM Mobicom 99" value="" />
</reference>
<reference anchor="MGL04">
<front>
<title>Group Communications in Mobile Ad hoc Networks</title>
<author fullname="Prasant Mohapatra" initials="P"
surname="Mohapatra">
<organization>University of California, Davis</organization>
</author>
<author fullname="Chao Gui" initials="C" surname="Gui">
<organization>University of California, Davis</organization>
</author>
<author fullname="Jian Li" initials="J" surname="Li">
<organization>University of California, Davis</organization>
</author>
<date month="February" year="2004" />
</front>
<seriesInfo name="IEEE Computer" value="Vol. 37, No. 2" />
</reference>
<reference anchor="GM99">
<front>
<title>The core-assisted mesh protocol</title>
<author fullname="J.J. Garcia-Luna-Aceves" initials="JJ"
surname="Garcia-Luna-Aceves">
<organization>University of California, Santa Cruz</organization>
</author>
<author fullname="E.L. Madruga" initials="E" surname="Madruga">
<organization>University of California, Santa Cruz</organization>
</author>
<date month="August" year="1999" />
</front>
<seriesInfo name="Selected Areas in Communications, IEEE Journal on "
value="Volume 17, Issue 8" />
</reference>
<reference anchor="MDDA07">
<front>
<title>Evaluation of distributed cover set algorithms in mobile ad
hoc network for simplified multicast forwarding</title>
<author initials="J" surname="Macker">
<organization></organization>
</author>
<author initials="I" surname="Downard">
<organization></organization>
</author>
<author initials="J" surname="Dean">
<organization></organization>
</author>
<author initials="R.B." surname="Adamson">
<organization></organization>
</author>
<date day="1" month="July" year="2007" />
</front>
<seriesInfo name="ACM SIGMOBILE Mobile Computing and Communications Review "
value="Volume 11 , Issue 3 (July 2007)" />
</reference>
<reference anchor="GJ79">
<front>
<title>Computers and Intractability: A Guide to the Theory of
NP-Completeness.</title>
<author initials="M.R." surname="Garey">
<organization></organization>
</author>
<author initials="D.S." surname="Johnson">
<organization></organization>
</author>
<date year="1979" />
</front>
<seriesInfo name="Freeman and Company" value="" />
</reference>
<reference anchor="WC02">
<front>
<title>Comparison of Broadcasting Techniques for Mobile Ad hoc
Networks</title>
<author initials="B." surname="Williams">
<organization></organization>
</author>
<author initials="T" surname="Camp">
<organization></organization>
</author>
<date year="2002" />
</front>
<seriesInfo name="Proceedings of ACM Mobihoc 2002" value="" />
</reference>
<reference anchor="JLMV02">
<front>
<title>Performance of multipoint relaying in ad hoc mobile routing
protocols</title>
<author initials="P" surname="Jacquet">
<organization></organization>
</author>
<author initials="V" surname="Laouiti">
<organization></organization>
</author>
<author initials="P" surname="Minet">
<organization></organization>
</author>
<author initials="L" surname="Viennot">
<organization></organization>
</author>
<date year="2002" />
</front>
<seriesInfo name="Networking" value="" />
</reference>
<reference anchor="MDC04">
<front>
<title>Simplified Multicast Forwarding in Mobile Ad hoc
Networks</title>
<author initials="J" surname="Macker">
<organization></organization>
</author>
<author initials="J" surname="Dean">
<organization></organization>
</author>
<author initials="W" surname="Chao">
<organization></organization>
</author>
<date year="2004" />
</front>
<seriesInfo name="IEEE MILCOM 2004 Proceedings" value="" />
</reference>
</references>
<section anchor="ecdsAppendix"
title="Essential Connecting Dominating Set (E-CDS) Algorithm">
<t>The "Essential Connected Dominating Set" (E-CDS) algorithm <xref
target="E-CDS"></xref> allows nodes to use 2-hop neighborhood topology
information to dynamically perform relay self election to form a CDS.
Its packet forwarding rules are not dependent upon previous hop
knowledge. Additionally, E-CDS SMF forwarders can be easily mixed
without problems with CF SMF forwarders, even those not participating in
NHDP. Another benefit is that packets opportunistically received from
non-symmetric neighbors may be forwarded without compromising flooding
efficiency or correctness. Furthermore, multicast sources not
participating in NHDP may freely inject their traffic and any
neighboring E-CDS relays will properly forward the traffic. The E-CDS
based relay set selection algorithm is based upon the summary within
<xref target="E-CDS"></xref>. E-CDS was originally discussed in the
context of forming partial adjacencies and efficient flooding for MANET
OSPF extensions work and the core algorithm is applied here for SMF.</t>
<t>It is RECOMMENDED that the SMF_TYPE:E-CDS message TLV be included in
NHDP_HELLO messages that are generated by nodes conducting E-CDS SMF
operation. It is also RECOMMENDED that the SMF_NBR_TYPE:E-CDS address
block TLV be used to advertise neighbor nodes that are also conducting
E-CDS SMF operation.</t>
<section title="E-CDS Relay Set Selection Overview">
<t>The E-CDS relay set selection requires 2-hop neighborhood
information collected through NHDP or another process. Relay nodes, in
E-CDS SMF selection, are "self-elected" using a router identifier
(Router ID) and an optional nodal metric, referred to here as "Router
Priority" for all 1-hop and 2-hop neighbors. To ensure proper relay
set self-election, the Router ID and Router Priority MUST be
consistent among nodes participating and it is RECOMMENDED that NHDP
be used to share this information. The Router ID is a logical
identification that MUST be consistent across interoperating SMF
neighborhoods and it is RECOMMENDED to be chosen as the largest
interface address advertised by NHDP. The E-CDS self-election process
can be summarized as follows:</t>
<t><list style="numbers">
<t>If an SMF node has a higher ordinal (Router Priority, Router
ID) than all of its symmetric neighbors, it elects itself to act
as a forwarder for all received multicast packets,</t>
<t>Else, if there does not exist a path from neighbor "j" with
largest (Router Priority, Router ID) to any other neighbor, <spanx
style="emph">via</spanx> neighbors with larger values of (Router
Priority, Router ID), then it elects itself to the relay set.</t>
</list></t>
<t>The basic form of E-CDS described and applied within this
specification does not provide for redundant relay set election (e.g.,
bi-connected) but such capability is supported by the basic E-CDS
design.</t>
</section>
<section title="E-CDS Forwarding Rules">
<t>With E-CDS, any SMF node that has selected itself as a relay
performs DPD and forwards all non-duplicative multicast traffic
allowed by the present forwarding policy. Packet previous hop
knowledge is not needed for forwarding decisions when using E-CDS.</t>
<t><list style="numbers">
<t>Upon packet reception, DPD is performed. Note E-CDS requires a
single duplicate table for the set of interfaces associated with
the relay set selection.</t>
<t>If the packet is a duplicate, no further action is taken.</t>
<t>If the packet is non-duplicative:<list style="letters">
<t>A DPD entry is made for the packet identifier</t>
<t>The packet is forwarded out all interfaces associated with
the relay set selection</t>
</list></t>
</list>As previously mentioned, even packets sourced (or relayed) by
nodes not participating in NHDP and/or the E-CDS relay set selection
may be forwarded by E-CDS forwarders without problem. A particular
deployment MAY choose to not forward packets from sources or relays
that have been not explicitly identified via NHDP or other means as
operating as part of a different relay set algorithm (e.g. S-MPR) to
allow coexistent deployments to operate correctly. Also, E-CDS relay
set selection may be configured to be influenced by
statically-configured CF relays that are identified via NHDP or other
means.</t>
</section>
<section title="E-CDS Neighborhood Discovery Requirements">
<t>It is possible to perform E-CDS relay set selection without
modification of NHDP, basing the self-election process exclusively on
the Router IDs (interface addresses) of participating SMF nodes.
However steps MUST be taken to insure that all NHDP instances not
using SMF_TYPE:E-CDS full type message TLVs are in fact running SMF
E-CDS, otherwise incorrect forwarding may occur. Furthermore, it has
been shown that use of a "Router Priority" metric as part of the
selection process can result in improved performance in certain cases.
Note that SMF nodes with higher "Router Priority" values will tend to
be favored as relays over other nodes. Thus, preferred relays MAY be
administratively configured to be selected when possible.
Additionally, other metrics (e.g. nodal degree, energy capacity, etc)
may also be taken into account in constructing a "Router Priority"
value. When using “Router Priority” with multiple
interfaces all interfaces on a node MUST use and advertise a common
"Router Priority" value.</t>
<t>To share a node's "Router Priority" with its 1-hop neighbors the
SMF_TYPE:E-CDS message TLV's <value> field is defined as shown
in <xref target="ecdsMsgTLVValueDef"></xref>.</t>
<texttable anchor="ecdsMsgTLVValueDef"
title="E-CDS Message TLV Values">
<ttcol>Length(bytes)</ttcol>
<ttcol>Value</ttcol>
<ttcol>Router Priority</ttcol>
<c>0</c>
<c>N/A</c>
<c>64</c>
<c>1</c>
<c><value></c>
<c>0-127</c>
</texttable>
<t>Where <value> is a one byte bit field which is defined
as:</t>
<t>bit 0: is reserved and SHOULD be set to 0.</t>
<t>bit 1-7: contain the priority value, 0-127, which is associated
with the originator address.</t>
<t>Combinations of value field lengths and values other than specified
here are NOT permitted and SHOULD be ignored. Below is an example
SMF_TYPE:E-CDS message TLV</t>
<t><figure anchor="ecdsMsgTLVExample"
title="E-CDS Message TLV Example">
<artwork><![CDATA[ 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... | SMF_TYPE |1|0|0|1|0|0| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| E-CDS |0|0|0|0|0|0|0|1|R| priority | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
</figure>To convey "Router Priority" values among 2-hop
neighborhoods the SMF_NBR_TYPE:E-CDS address block TLV's <value>
field is defined thus:</t>
<texttable anchor="ecdsAddrTLVValueDef"
title="E-CDS Address Block TLV Values">
<ttcol>Length(bytes)</ttcol>
<ttcol># Addr</ttcol>
<ttcol>Value</ttcol>
<ttcol>Router Priority</ttcol>
<c>0</c>
<c>Any</c>
<c>N/A</c>
<c>64</c>
<c>1</c>
<c>Any</c>
<c><value></c>
<c><value> is for all addresses</c>
<c>N</c>
<c>N</c>
<c><value>*</c>
<c>Each address gets its own <value></c>
</texttable>
<t>Where <value> is a one byte bit field which is defined
as:</t>
<t>bit 0: is reserved and SHOULD be set to 0.</t>
<t>bit 1-7: contain a priority value, 0-127, which is associated with
the appropriate address.</t>
<t>Combinations of value field lengths and # of addresses other than
specified here are NOT permitted and SHOULD be ignored. A default
technique of using nodal degree (i.e. count of 1-hop neighbors) is
RECOMMENDED for the value field of these TLV types. Below are two
example SMF_NBR_TYPE:E-CDS address block TLVs.</t>
<t><figure anchor="ecdsAddrTLVExample1"
title="E-CDS Address Block TLV Example 1">
<artwork><![CDATA[ 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... | SMF_NBR_TYPE |1|0|0|1|0|0| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| E-CDS |0|0|0|0|0|0|0|1|R| priority | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
</figure>This single value example TLV specifies that all
address(es) contained in the address block are running SMF using the
E-CDS algorithm and all address(es) share the value field and
therefore the same priority value.<figure anchor="ecdsAddrTLVExample2"
title="E-CDS Address Block TLV Example 2">
<artwork><![CDATA[ 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... | SMF_NBR_TYPE |1|0|1|1|0|1| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| E-CDS | index-start | index-end | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| priority0 |R| priority1 | ... |R| priorityn |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
</figure>This example multivalue TLV specifies that address(es)
contained in the address block from index-start to index-end inclusive
are running SMF using the E-CDS algorithm. Each address is associated
with its own value byte and therefore their own priority value.</t>
</section>
<section title="E-CDS Selection Algorithm">
<t>This section describes an algorithm for E-CDS relay selection
(self-election). The algorithm described uses 2-hop information. Note
it is possible to extend this algorithm to use k-hop information with
added computational complexity and mechanisms for sharing k-hop
topology information that are not described in this document or wihtin
the NHDP specification. It should also be noted that this algorithm
does not impose the "hop limit" bound described in <xref
target="E-CDS"></xref> when performing the path search that is used
for relay selection. However, the algorithm below could be easily
augmented to accommodate this additional criteria. In normal
operation, it is not expected that the "hop limit" bound will provide
significant benefit.</t>
<t>The tuple of "Router Priority" and "Router ID" is used in E-CDS
relay set selection. Precedence is given to the "Router Priority"
portion and the "Router ID" value is used as a tie-breaker. The
evaluation of this tuple is referred to as "RtrPri(n)" in the
description below where "n" references a specific node. Note it is
possible that the "Router Priority" portion may be optional and the
evaluation of "RtrPri()" be solely based upon the unique "Router ID".
Since there MUST NOT be any duplicate "Router ID" values among SMF
nodes, a comparison of RtrPri(n) between any two nodes will always be
an inequality. The use of nodal degree for calculating "Router
Priority" is RECOMMENDED as default and the largest IP address
associated across interfaces advertised by NHDP MUST be used as the
"Router ID". NHDP provides all interface address throughout the 2-hop
neighborhood so explicity conveying a "Router ID" is not necessary.
The following steps describe a basic algorithm for conducting E-CDS
relay selection for a node "n0": <list style="numbers">
<t>Initialize the set "N1" to include all 1-hop neighbors of
"n0".</t>
<t>If "N1" has less than 2 members, then "n0" does not elect
itself as a relay and no further steps are taken.</t>
<t>Initialize the set "N2" to include all 2-hop neighbors,
excluding "n0" and any nodes in "N1".</t>
<t>If "RtrPri(n0)" is greater than that of all nodes in the union
of "N1" and "N2", then "n0" selects itself as a relay and no
further steps are taken.</t>
<t>Initialize all nodes in the union of "N1" and "N2" as
"unvisited".</t>
<t>Find the node "n1_Max" that has the largest "RtrPri()" of all
nodes in "N1"</t>
<t>Initialize queue "Q" to contain "n1_Max", marking "n1_Max" as
"visited"</t>
<t>While node queue "Q" is not empty, remove node "x" from the
head of "Q", and for each 1-hop neighbor "n" of node "x"
(excluding "n0") that is not marked "visited"<list style="letters">
<t>Mark node "n" as "visited"</t>
<t>If "RtrPri(n)" is greater than "RtrPri(n0), append "n" to
"Q"</t>
</list></t>
<t>If any node in "N1" remains "unvisited", then "n0" selects
itself as a relay. Otherwise "n0" does not act as an relay.</t>
</list>Note these steps are re-evaluated upon neighborhood status
changes. Steps 5 through 8 of this procedure describe an approach to a
path search. The purpose of this path search is to determine if paths
exist from the 1-hop neighbor with maximum "RtrPri()" to all other
1-hop neighbors without traversing an intermediate node with a
""RtrPri()" value less than "RtrPri(n0)". These steps comprise a
breadth-first traversal that evaluates only paths that meet that
criteria. If all 1-hop neighbors of "n0" are "visited" during this
traversal, then the path search has succeeded and node "n0" does not
need to provide relay. It can be assumed that other nodes will provide
relay operation to ensure SMF connectivity.</t>
<t>It is possible to extend this algorithm to consider neighboring SMF
nodes that are known to be statically configured for CF (always
relaying). The modification to the above algorithm is to process such
nodes as having a maximum possible "Router Priority" value. It is
expected that nodes configured for CF and participating in NHDP would
indicate this with use of the SMF_TYPE:CF and SMF_NBR_TYPE:CF TLV
types in their NHDP_HELLO message and address blocks,
respectively.</t>
</section>
</section>
<section anchor="smprAppendix"
title="Source-based Multipoint Relay (S-MPR)">
<t>The source-based multipoint relay (S-MPR) set selection algorithm
enables individual nodes, using two-hop topology information, to select
relays from their set of neighboring nodes. Relays are selected so that
forwarding to the node's complete two-hop neighbor set is covered. This
distributed relay set selection technique has been shown to approximate
a minimal connected dominating set (MCDS) in <xref
target="JLMV02"></xref>. Individual nodes must collect two-hop
neighborhood information from neighbors, determine an appropriate
current relay set, and inform selected neighbors of their relay status.
Note that since each node picks its neighboring relays independently,
S-MPR forwarders depend upon previous hop information (e.g, source MAC
address) to operate correctly. The Optimized Link State Routing (OLSR)
protocol has used this algorithm and protocol for relay of link state
updates and other control information <xref target="RFC3626"></xref> and
it has been demonstrated operationally in dynamic network
environments.</t>
<t>It is RECOMMENDED that the SMF_TYPE:S-MPR message TLV be included in
NHDP_HELLO messages that are generated by nodes conducting S-MPR SMF
operation. It is also RECOMMENDED that the SMF_NBR_TYPE:S-MPR address
block TLV be used to specifiy which neighbor nodes are conducting S-MPR
SMF operation.</t>
<section title="S-MPR Relay Set Selection Overview">
<t>A RECOMMENDED algorithm for S-MPR set selection is described in the
<xref target="OLSRv2"></xref> specification. As this algorithm has had
considerable use to support the OLSR control plane, it is expected to
perform adequately to support data plane multicast traffic. To
summarize, the S-MPR algorithm uses bi-directional 1-hop and 2-hop
neighborhood information collected via NHDP to select, from a node's
1-hop neighbors, a set of relays that will cover the node's entire
2-hop neighbor set upon forwarding. The algorithm described uses a
"greedy" heuristic of first picking the 1-hop neighbor who will cover
the most 2-hop neighbors. Then, excluding those 2-hop neighbors that
have been covered, additional relays from its 1-hop neighbor set are
iteratively selected until the entire 2-hop neighborhood is covered.
Note that 1-hop neighbors also identified as 2-hop neighbors are
considered as 1-hop neighbors only. This is only a partial description
of the S-MPR algorithm. The <xref target="RFC3626"></xref>
specification provides a complete description including the use of a
"WILLINGNESS" metric, termed here "Router Priority", that can be used
to influence S-MPR forwarder selection.</t>
<t>NHDP_HELLO messages supporting S-MPR forwarding operation SHOULD
use the TLVs defined in <xref target="SMFTLVs"></xref> using the S-MPR
extended type. The value field of an address block TLV which has a
full type value of SMF_NBR_TYPE:S-MPR is defined in <xref
target="smprAddrTLVValueDef"></xref> such that signaling of multi
point relay (MPR) selections to 1-hop neighbors is possible. The value
field of a message block TLV which has a full type value of
SMF_TYPE:S-MPR is defined in <xref target="smprMsgTLVValueDef"></xref>
such that signaling of "Router Priority" (described as "WILLINGNESS"
in <xref target="OLSRv2"></xref>) to 1-hop neighbors is possible. In
some cases "MPR" address block TLV specified in <xref
target="RFC3626"></xref> MAY be used in place of the SMF_NBR_TYPE:SMPR
TLV to mark the addresses of selected neighbor relays in the
NHDP_HELLO message address block(s), however in this case steps must
be taken to insure SMF operation of neighbor nodes otherwise improper
forwarding selection can occur. It is important to note that S-MPR
forwarding is dependent upon the previous hop of an incoming packet. A
S-MPR node MUST forward packets only for neighbors which have
explicitly selected it as a relay (i.e., its "selectors"). There are
also some additional requirements for duplicate packet detection to
support S-MPR SMF operation that are described below.</t>
<t>For multiple interface operation, MPR selection SHOULD be conducted
on a per-interface basis. However, it is possible to economize MPR
selection among multiple interfaces by selecting common MPRs to the
extent possible. It is important to note that the S-MPR forwarding
rules described in <xref target="OLSRv2"></xref> assume per-interface
MPR selection (i.e. MPRs are <spanx style="emph">not</spanx> selected
in the context of all interfaces). This is consistent with the MPR
selection heuristics described in <xref target="RFC3626"></xref>.
Other source-based approaches may be possible, but would require
alternative selection and forwarding rules to be specified.</t>
</section>
<section anchor="smprForwarding" title="S-MPR Forwarding Rules">
<t>An S-MPR relay MUST only forward packets for neighbors that have
explicitly selected it as a forwarder. The source-based forwarding
technique also stipulates some additional duplicate packet detection
operations. For multiple network interfaces, independent DPD state
MUST be maintained for each separate interface. The following table
provides the procedure for S-MPR packet forwarding given the arrival
of a packet on a given interface, denoted <srcIface>. There are
three possible actions, depending upon the previous-hop
transmitter:<list style="numbers">
<t>If the previous-hop transmitter has selected the current node
as a relay,<list style="letters">
<t>The packet identifier is checked against the DPD state for
each possible outbound interface, including the
<srcIface>.</t>
<t>If the packet is not a duplicate for an outbound interface,
the packet is forwarded via that interface and a DPD entry is
made for the given packet identifier for the interface.</t>
<t>If the packet is a duplicate, no action is taken for that
interface.</t>
</list></t>
<t>Else, if the previous-hop transmitter is a 1-hop symmetric
neighbor,<list style="letters">
<t>A DPD entry is made for that packet for the
<srcIface>, but the packet is not forwarded.</t>
</list></t>
<t>Otherwise, no action is taken.</t>
</list></t>
<t>Case number two in the above table is non-intuitive, but important
to ensure correctness of S-MPR SMF operation. The selection of
source-based relays does not result in a common set among neighboring
nodes, so relays MUST mark in their DPD state, packets received from
non-selector, symmetric, one-hop neighbors (for a given interface) and
not forward subsequent duplicates of that packet if received on that
interface. Deviation here can result in unnecessary, repeated packet
forwarding throughout the network, or incomplete flooding.</t>
<t>Nodes not participating in neighborhood discovery and relay set
selection will not be able to source multicast packets into the area
and have SMF forward them, unlike E-CDS or MPR-CDS where forwarding
may occur dependent on topology. Correct S-MPR relay behavior will
occur with the introduction of repeaters (non-NHDP/SMF participants
that relay multicast packets using duplicate detection and CF) but the
repeaters will not efficiently contribute to S-MPR forwarding as these
nodes will not be identified as neighbors (symmetric or otherwise) in
the S-MPR forwarding process. NHDP/SMF participants MUST NOT provide
extra forwarding, forwarding packets which are not selected by the
algorithm, as this can disrupt network-wide S-MPR flooding, resulting
in incomplete or inefficient flooding.</t>
</section>
<section title="S-MPR Neighborhood Discovery Requirements">
<t>Nodes may optionally signal "Router Priority" or "WILLINGNESS" to
become MPR nodes for their one hop neighbors by using the
SMF_TYPE:S-MPR message block TLV value field defined as such:</t>
<texttable anchor="smprMsgTLVValueDef"
title="S-MPR Message TLV Values">
<ttcol>Length(bytes)</ttcol>
<ttcol>Value</ttcol>
<ttcol>Router Priority</ttcol>
<c>0</c>
<c>N/A</c>
<c>64</c>
<c>1</c>
<c><value></c>
<c>0-127</c>
</texttable>
<t>Where <value> is a one byte bit field which is defined
as:</t>
<t>bit 0: is reserved and SHOULD be set to 0.</t>
<t>bit 1-7: contain the priority value, 0-127, which is associated
with the originator address.</t>
<t>Router priority values for S-MPR work similarly to "WILLINGNESS"
values as described in <xref target="OLSRv2"></xref> with value 0
indicating a node will NEVER forward and value 127 indicating a node
will ALWAYS forward. Combinations of value field lengths and values
other than specified here are NOT permitted and SHOULD be ignored.
Below is an example SMF_TYPE:S-MPR message TLV.</t>
<t><figure anchor="smprMsgTLVExample"
title="S-MPR Message TLV Example">
<artwork><![CDATA[ 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... | SMF_NBR_TYPE |1|0|0|1|0|0| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-MPR |0|0|0|0|0|0|0|1|R| priority | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
</figure></t>
<t>S-MPR election operation requires 2-hop neighbor knowledge as
provided by the NHDP protocol <xref target="NHDP"></xref> or from
external sources. MPRs are dynamically selected by each node and
selections MUST be advertised and dynamically updated within NHDP or
an equivalent protocol or mechanism. For NHDP use, the
SMF_NBR_TYPE:S-MPR address block TLV value field is defined as
such:</t>
<texttable anchor="smprAddrTLVValueDef"
title="E-CDS Address Block TLV Values">
<ttcol>Length(bytes)</ttcol>
<ttcol># Addr</ttcol>
<ttcol>Value</ttcol>
<ttcol>Meaning</ttcol>
<c>0</c>
<c>Any</c>
<c>N/A</c>
<c>Addresses are NOT MPRs</c>
<c>1</c>
<c>Any</c>
<c><value></c>
<c><value> is for all addresses</c>
<c>N</c>
<c>N</c>
<c><value>*</c>
<c>Each address gets its own <value></c>
</texttable>
<t>Where <value> is a one byte field whcih is defined as:</t>
<t>bit 0: Is the M bit which when set indicates MPR selection of
associated address(es) by the originator node of the NHDP HELLO
message. When unset indicates the originator of the NHDP HELLO message
has not selected the relevant address as an MPR.</t>
<t>bit 1-7: are reserved and SHOULD be set to 0.</t>
<t>Combinations of value field lengths and # of addresses other than
specified here are NOT permitted and SHOULD be ignored. All bits,
excepting the leftmost bit, are RESERVED and SHOULD be set to 0.</t>
<figure anchor="smprAddrTLVExample1"
title="S-MPR Address Block TLV Example 1">
<artwork><![CDATA[ 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... | SMF_NBR_TYPE |1|1|0|1|0|0| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-MPR | start-index |0|0|0|0|0|0|0|1|M| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
</figure>
<t>This single index example TLV indicates that the address specified
by the <start-index> field is running SMF using S-MPR and has
been selected by the originator of the NHDP HELLO message as an MPR
forwarder if the M bit is set. Multivalue TLVs may also be used to
specify MPR selection status of multiple addresses using only one TLV.
See <xref target="ecdsAddrTLVExample2"></xref> for an example on how
this may be done.</t>
</section>
<section anchor="smprAlgorithm" title="S-MPR Selection Algorithm">
<t>This section describes a basic algorithm for the S-MPR selection
process. Note that the selection is with respect to a specific
interface of the node performing selection and other node interfaces
referenced are reachable from this reference node interface. This is
consistent with the S-MPR forwarding rules described above. When
multiple interfaces per node are used, it is possible to enhance the
overall selection process across multiple interfaces such that common
nodes are selected as MPRs for each interface to avoid unnecessary
inefficiencies in flooding. This is described further in <xref
target="OLSRv2"></xref>. The following steps describe a basic
algorithm for conducting S-MPR selection for a node interface "n0":
<list style="numbers">
<t>Initialize the set "MPR" to empty.</t>
<t>Initialize the set "N1" to include all 1-hop neighbors of
"n0".</t>
<t>Initialize the set "N2" to include all 2-hop neighbors,
excluding "n0" and any nodes in "N1". Nodes which are only
reachable via "N1" nodes with router priority values of NEVER are
also excluded.</t>
<t>For each interface "y" in "N1", initialize a set "N2(y)" to
include any interfaces in "N2" that are 1-hop neighbors of
"y".</t>
<t>For each interface "x" in "N1" with a router priority value of
"ALWAYS" (or using CF relay algorithm), select "x" as a MPR:<list
style="letters">
<t>Add "x" to the set "MPR" and remove "x" from "N1".</t>
<t>For each interface "z" in "N2(x)", remove "z" from "N2"</t>
<t>For each interface "y" in "N1", remove any interfaces in
"N2(x)" from "N2(y)"</t>
</list></t>
<t>For each interface "z" in "N2", initialize the set "N1(z)" to
include any interfaces in "N1" that are 1-hop neighbors of
"z".</t>
<t>For each interface "x" in "N2" where "N1(x)" has only one
member, select "x" as a MPR:<list style="letters">
<t>Add "x" to the set "MPR" and remove "x" from "N1".</t>
<t>For each interface "z" in "N2(x)", remove "z" from "N2" and
delete "N1(z)"</t>
<t>For each interface "y" in "N1", remove any interfaces in
"N2(x)" from "N2(y)"</t>
</list></t>
<t>While "N2" is not empty, select the interface "x" in "N1" with
the largest router priority which has the number of members in
"N_2(x)" as a MPR:<list style="letters">
<t>Add "x" to the set "MPR" and remove "x" from "N1".</t>
<t>For each interface "z" in "N2(x)", remove "z" from "N2"</t>
<t>For each interface "y" in "N1", remove any interfaces in
"N2(x)" from "N2(y)"</t>
</list></t>
</list>After the set of nodes "MPR" is selected, node "n_0" must
signal its selections to its neighbors. With NHDP, this is done by
using the MPR address block TLV to mark selected neighbor addresses in
NHDP_HELLO messages. Neighbors MUST record their MPR selection status
and the previous hop address (e.g., link or MAC layer) of the
selector. Note these steps are re-evaluated upon neighborhood status
changes.</t>
</section>
</section>
<section anchor="mprcdsAppendix"
title="Multipoint Relay Connected Dominating Set (MPR-CDS) Algorithm">
<t>The MPR-CDS algorithm is an extension to the basic S-MPR election
algorithm that results in a shared (non source-specific) SMF CDS. Thus
its forwarding rules are not dependent upon previous hop information
similar to E-CDS. An overview of the MPR-CDS selection algorithm is
provided in <xref target="MPR-CDS"></xref>.</t>
<t>It is RECOMMENDED that the SMF_RELAY_ALG message TLV be included in
NHDP_HELLO messages that are generated by nodes conducting MPR-CDS SMF
operation.</t>
<section title="MPR-CDS Relay Set Selection Overview">
<t>The MPR-CDS relay set selection process is based upon the MPR
selection process of the S-MPR algorithm with the added refinement of
a distributed technique for subsequently down-selecting to a common
reduced, shared relay set. A node ordering (or "prioritization")
metric is used as part of this down-selection process Like the E-CDS
algorithm, this metric can be based upon node address or some other
unique router identifier ("Router ID") as well as an additional
"Router Priority" measure, if desired. The process for MPR-CDS relay
selection is as follows: <list style="numbers">
<t>First, MPR selection per the S-MPR algorithm is conducted, with
selectors informing their MPRs (via NHDP) of their selection.</t>
<t>Then, the following rules are used on a distributed basis by
selected nodes to possibly unselect themselves and thus jointly
establish a common set of shared SMF relays:<list style="letters">
<t>If a selected node has a larger "RtrPri()" than all of its
1-hop symmetric neighbors, then it acts as a relay for all
multicast traffic, regardless of the previous hop</t>
<t>Else, if the 1-hop symmetric neighbor with the largest
"RtrPri()" value has selected the node, then it also acts as a
relay for all multicast traffic, regardless of the previous
hop.</t>
<t>Otherwise, it unselects itself as a relay and does not
forward any traffic unless changes occur that require
re-evaluation of the above steps.</t>
</list></t>
</list>This technique shares many of the desirable properties of the
E-CDS technique with regards to compatibility with multicast sources
not participating in NHDP and the opportunity for statically-configure
CF nodes to be present, regardless of their participation in NHDP.</t>
</section>
<section title="MPR-CDS Forwarding Rules">
<t>The forwarding rules for MPR-CDS are common with those of E-CDS.
Any SMF node that has selected itself as a relay performs DPD and
forward all non-duplicative multicast traffic allowed by the present
forwarding policy. Packet previous hop knowledge is not needed for
forwarding decisions when using MPR-CDS.</t>
<t><list style="numbers">
<t>Upon packet reception, DPD is performed. Note MPR-CDS require
one duplicate table for the set of interfaces associated with the
relay set selection.</t>
<t>If the packet is a duplicate, no further action is taken.</t>
<t>If the packet is non-duplicative:<list style="letters">
<t>A DPD entry is made for the packet identifier</t>
<t>The packet is forwarded out all interfaces associated with
the relay set selection</t>
</list></t>
</list>As previously mentioned, even packets sourced (or relayed) by
nodes not participating in NHDP and/or the MPR-CDS relay set selection
may be forwarded by E-CDS forwarders without problem. A particular
deployment MAY choose to not forward packets from sources or relays
that have been explicitly identified via NHDP or other means as
operating as part of a different relay set algorithm (e.g. S-MPR) to
allow coexistent deployments to operate correctly. Also, MPR-CDS relay
set selection may be configured to be influenced by
statically-configured CF relays that are identified via NHDP or other
means.</t>
</section>
<section title="MPR-CDS Neighborhood Discovery Requirements">
<t>The neighborhood discovery requirements for MPR-CDS have
commonality with both the S-MPR and E-CDS algorithms. MPR-CDS
selection operation requires 2-hop neighbor knowledge as provided by
the NHDP protocol <xref target="NHDP"></xref> or from external
sources. Unlike S-MPR operation, there is no need for associating
link-layer address information with 1-hop neighbors since MPR-CDS
forwarding is independent of the previous hop similar to E-CDS
forwarding.</t>
<t>To advertise an optional "Router Priority" value or "WILLINGNESS"
an originating node may use the message TLV of type SMF_TYPE:MPR-CDS
which shares a common <value> format with both SMF_TYPE:E-CDS
<xref target="ecdsMsgTLVValueDef"></xref> and SMF_TYPE:S-MPR <xref
target="smprMsgTLVValueDef"></xref>.</t>
<t>MPR-CDS only requires 1-hop knowledge of "Router Priority" for
correct operation. In the S-MPR phase of MPR-CDS selection, MPRs are
dynamically determined by each node and selections MUST be advertised
and dynamically updated using NHDP or an equivalent protocol or
mechanism. Therefore the <value> field of the
SMF_NBR_TYPE:MPR-CDS type TLV shares a common format with
SMF_NBR_TYPE:S-MPR <xref target="smprAddrTLVValueDef"></xref> to
convey MPR selection.</t>
</section>
<section title="MPR-CDS Selection Algorithm">
<t>This section describes an algorithm for the MPR-CDS selection
process. Note that the selection described is with respect to a
specific interface of the node performing selection and other node
interfaces referenced are reachable from this reference node
interface. An ordered tuple of "Router Priority" and "Router ID" is
used in MPR-CDS relay set selection. The "Router ID" value should be
set to the largest advertised address of a given node, this
information is provided to one hop neighbors via NHDP by default.
Precedence is given to the "Router Priority" portion and the "Router
ID" value is used as a tie-breaker. The evaluation of this tuple is
referred to as "RtrPri(n)" in the description below where "n"
references a specific node. Note it is possible that the "Router
Priority" portion may be optional and the evaluation of "RtrPri()" be
solely based upon the unique "Router ID". Since there MUST NOT be any
duplicate address values among SMF nodes, a comparison of RtrPri(n)
between any two nodes will always be an inequality. The following
steps, repeated upon any changes detected within the 1-hop and 2-hop
neighborhood, describe a basic algorithm for conducting MPR-CDS
selection for a node interface "n0": <list style="numbers">
<t>Perform steps 1-8 of <xref target="smprAlgorithm"></xref> to
select MPRs from the set of 1-hop neighbors of "n0" and
notify/update neighbors of selections.</t>
<t>Upon being selected as an MPR (or any change in the set of
nodes selecting "n0" as an MPR):<list style="letters">
<t>If no neighbors have selected "n0" as an MPR, "n0" does not
act as a relay and no further steps are taken until a change
in neighborhood topology or selection status occurs.</t>
<t>Determine the node "n1_max" that has the maximum "RtrPri()"
of all 1-hop neighbors.</t>
<t>If "RtrPri(n0)" is greater than "RtrPri(n1_max)", then "n0"
selects itself as a relay for all multicast packets,</t>
<t>Else, if "n1_max" has selected "n0" as an MPR, then "0"
selects itself as a relay for all multicast packets.</t>
<t>Otherwise, "n0" does not act as a relay.</t>
</list></t>
</list>It is possible to extend this algorithm to consider
neighboring SMF nodes that are known to be statically configured for
CF (always relaying). The modification to the above algorithm is to
process such nodes as having a maximum possible "Router Priority"
value. This is the same as the case for participating nodes that have
been configured with a S-MPR "WILLINGNESS" value of "WILL_ALWAYS". It
is expected that nodes configured for CF and participating in NHDP
would indicate their status with use of the SMF_RELAY_ALG TLV type in
their NHDP_HELLO message TLV block. It is important to note however
that CF nodes will not select MPR nodes and therefore cannot guarantee
connectedness.</t>
</section>
</section>
</back>
</rfc>| PAFTECH AB 2003-2026 | 2026-04-24 03:00:33 |