Open Shortest Path (OSPF) E. Baccelli
Internet-Draft P. Jacquet
Intended status: Experimental INRIA
Expires: July 21, 2009 D. Nguyen
CRC
T. Clausen
LIX, Ecole Polytechnique, France
January 17, 2009
OSPF MPR Extension for Ad Hoc Networks
draft-ietf-ospf-manet-mpr-04
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Abstract
This document specifies an OSPFv3 interface type tailored for mobile
ad hoc networks. This interface type is derived from the broadcast
interface type, and denoted the "OSPFv3 MANET interface type".
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Applicability Statement . . . . . . . . . . . . . . . . . . . 6
3.1. MANET Characteristics . . . . . . . . . . . . . . . . . . 6
3.2. OSPFv3 MANET Interface Characteristics . . . . . . . . . . 6
4. Protocol Overview and Functioning . . . . . . . . . . . . . . 7
4.1. Efficient Flooding using MPRs . . . . . . . . . . . . . . 7
4.2. MPR Topology Reduction . . . . . . . . . . . . . . . . . . 7
4.3. Multicast Transmissions of Protocol Packets . . . . . . . 7
4.4. MPR Adjacency Reduction . . . . . . . . . . . . . . . . . 8
5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Data Structures . . . . . . . . . . . . . . . . . . . . . 8
5.1.1. N(i): Symmetric 1-hop Neighbor Set . . . . . . . . . . 8
5.1.2. N2(i): Symmetric strict 2-hop Neighbor Set . . . . . . 9
5.1.3. Flooding-MPR set . . . . . . . . . . . . . . . . . . . 9
5.1.4. Flooding-MPR-selector set . . . . . . . . . . . . . . 10
5.1.5. Path-MPR set . . . . . . . . . . . . . . . . . . . . . 10
5.1.6. Path-MPR-selector set . . . . . . . . . . . . . . . . 11
5.1.7. MPR set . . . . . . . . . . . . . . . . . . . . . . . 11
5.1.8. MPR-selector set . . . . . . . . . . . . . . . . . . . 11
5.2. Hello Protocol . . . . . . . . . . . . . . . . . . . . . . 11
5.2.1. Flooding-MPR Selection . . . . . . . . . . . . . . . . 12
5.2.2. Flooding-MPR Selection Signaling - FMPR TLV . . . . . 12
5.2.3. Neighbor Ordering . . . . . . . . . . . . . . . . . . 12
5.2.4. Metric Signaling - METRIC-MPR TLV and PMPR TLV . . . . 13
5.2.5. Path-MPR Selection . . . . . . . . . . . . . . . . . . 13
5.2.6. Path-MPR Selection Signaling - PMPR TLV . . . . . . . 13
5.2.7. Hello Packet Processing . . . . . . . . . . . . . . . 14
5.3. Adjacencies . . . . . . . . . . . . . . . . . . . . . . . 14
5.3.1. Packets over 2-Way Links . . . . . . . . . . . . . . . 15
5.3.2. Adjacency Conservation . . . . . . . . . . . . . . . . 15
5.4. Link State Advertisements . . . . . . . . . . . . . . . . 15
5.4.1. LSA Flooding . . . . . . . . . . . . . . . . . . . . . 16
5.4.2. Link State Acknowledgments . . . . . . . . . . . . . . 17
5.5. Hybrid Routers . . . . . . . . . . . . . . . . . . . . . . 18
5.6. Synch Routers . . . . . . . . . . . . . . . . . . . . . . 19
5.7. Routing Table Computation . . . . . . . . . . . . . . . . 19
6. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 19
6.1. Flooding-MPR TLV . . . . . . . . . . . . . . . . . . . . 20
6.2. Metric-MPR TLV . . . . . . . . . . . . . . . . . . . . . . 20
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6.3. Path-MPR TLV . . . . . . . . . . . . . . . . . . . . . . 22
7. Security Considerations . . . . . . . . . . . . . . . . . . . 25
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
9.1. Normative References . . . . . . . . . . . . . . . . . . . 27
9.2. Informative References . . . . . . . . . . . . . . . . . . 27
Appendix A. Flooding-MPR Selection Heuristic . . . . . . . . . . 28
Appendix B. Path-MPR Selection Heuristic . . . . . . . . . . . . 29
Appendix C. Contributors . . . . . . . . . . . . . . . . . . . . 30
Appendix D. Acknowledgments . . . . . . . . . . . . . . . . . . . 30
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1. Introduction
This document specifies an extension of OSPFv3 [RFC5340] adapted to
MANETs [RFC2501], and based on mechanisms providing:
Flooding reduction: only a subset of all routers will be involved in
(re)transmissions during a flooding operation.
Topology reduction: only a subset of links are advertised, hence
both the number and the size of LSAs are decreased.
Adjacency reduction: adjacencies are brought up only with a subset
of neighbors, for lower database synchronization overhead.
These mechanisms are based on multipoint relays (MPR), a technique
developed in OLSR [RFC3626].
The extension specified in this document integrates into the OSPF
framework by defining the OSPFv3 MANET interface type. While this
extension enables OSPFv3 to function efficiently on mobile ad hoc
networks, operation of OSPFv3 on other types of interfaces or
networks, or in areas without OSPFv3 MANET interfaces, remains
unaltered.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
This document uses OSPF terminology as defined in [RFC2328] and
[RFC5340], LLS terminology as defined in [RFC4813], and introduces
the following terminology to the OSPF nomenclature:
OSPFv3 MANET interface - the OSPFv3 interface type for MANETs, as
specified in this document.
Additionally, the following terms are used in this document:
MANET router - a router which has only OSPFv3 MANET interface(s).
Wired router - a router which has only OSPFv3 interface of types
other than OSPFv3 MANET interfaces.
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Hybrid router - a router which has OSPFv3 interfaces of several
types, including at least one of the OSPFv3 MANET interface type.
Neighbor - a router, reachable through an OSPFv3 interface (of any
type).
MANET neighbor - a neighbor, reachable through an OSPFv3 MANET
interface.
Symmetric 1-hop neighbor - a neighbor, in a state greater than or
equal to 2-Way (through an interface of any type).
Symmetric strict 2-hop neighbor - a symmetric 1-hop neighbor of a
symmetric 1-hop neighbor, which is not itself a symmetric 1-hop
neighbor of this router.
Symmetric strict 2-hop neighborhood - the set formed by all the
symmetric strict 2-hop neighbors of the considered router.
Synch router - a router which brings up adjacencies with all of its
MANET neighbors.
Flooding-MPR - A router which is selected by its symmetric 1-hop
neighbor, router X, to retransmit all broadcast protocol packets
that it receives from router X, provided that that broadcast
protocol packet is not a duplicate, and that the hop limit field
of the protocol packet is greater than one.
Path-MPR - A router, which is selected by a symmetric 1-hop
neighbor, X, as being on the shortest path from a router in the
symmetric strict 2-hop neighborhood of router X and to the router
X.
Multipoint Relay (MPR) - A router which is selected by its symmetric
1-hop neighbor as either Flooding-MPR or as Path-MPR, or as both.
Flooding-MPR Selector - A router which has selected its symmetric
1-hop neighbor, router X, as one of its Flooding-MPRs is a
Flooding-MPR selector of router X.
Path-MPR Selector - A router which has selected its symmetric 1-hop
neighbor, router X, as one of its Path-MPRs is a Path-MPR selector
of router X.
MPR Selector - A router which has selected its symmetric 1-hop
neighbor, router X, as either one of its Flooding-MPRs or as one
of its Path-MPRs or as both is an MPR selector of router X.
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3. Applicability Statement
The OSPFv3 MANET interface type, defined in this specification,
allows OSPFv3 to be deployed within an area where parts of that area
are a mobile ad hoc network (MANET) with moderate mobility
properties.
3.1. MANET Characteristics
MANETs [RFC2501] are networks in which a dynamic network topology is
a frequently expected condition, often due to router mobility and/or
to varying quality of wireless links - the latter of which also
generally entails bandwidth scarcity and interference issues between
neighbors.
Moreover, MANETs often exhibit "semi-broadcast" properties, i.e. that
a router R that makes a transmission within a MANET can only assume
that transmission to be received by a subset of the total number of
routers within that MANET. Further, if two routers, R1 and R2, each
make a transmission, each of these transmissions is not guaranteed to
be received by the same subset of routers within the MANET - and this
even if each of R1 and R2 can mutually receive transmissions from
each other.
These characteristics are incompatible with several OSPFv3
mechanisms, including, but not limited to, existing mechanisms for
control traffic reduction, such as flooding reduction, topology
reduction and adjacency reduction (e.g. Designated Router).
3.2. OSPFv3 MANET Interface Characteristics
An interface of the OSPFv3 MANET interface type is the point of
attachment of an OSPFv3 router to a network which may have MANET
characteristics. That is, an interface of the OSPFv3 MANET interface
type is able to accommodate the MANET characteristics described in
Section 3.1. An OSPFv3 MANET interface type is not prescribing a set
of behaviors or expectations that the network is required to have.
Rather, it is describing operating conditions under which protocols
on an interface towards that network must be able to function (i.e.
the protocols are required to be able to operate correctly when faced
with the characteristics as described in Section 3.1). As such, the
OSPFv3 MANET interface type is a generalization of other OSPFv3
interface types; for example a protocol operating correctly over an
OSPFv3 MANET interface would also operate correctly over an OSPFv3
broadcast interface (whereas the inverse would not necessarily be
true).
Efficient OSPFv3 operation over MANETs relies on control traffic
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reduction, and using mechanisms appropriate for semi-broadcast. The
OSPFv3 MANET interface type, defined in this document, allows
networks with MANET characteristics into the OSPFv3 framework by
integrating mechanisms (flooding reduction, topology reduction and
adjacency reduction) derived from solutions standardized by the MANET
working group.
4. Protocol Overview and Functioning
The OSPFv3 MANET interface type, defined in this specification, makes
use of flooding reduction, topology reduction and adjacency
reduction, all based on multipoint relaying (MPR) - a technique
derived from [RFC3626], as standardized in the MANET working group.
Multicast transmissions of protocol packets are used when possible.
4.1. Efficient Flooding using MPRs
OSPFv3 MANET interfaces use a flooding reduction mechanism denoted
MPR flooding [MPR], whereby only a subset of MANET neighbors (those
selected as Flooding-MPR) participate in a flooding operation. This
reduces the number of (re)transmissions necessary for a flooding
operation [MPR-analysis], while retaining resilience to transmission
errors (inherent when using wireless links), and obsolete two-hop
neighbor information (e.g. as caused by router mobility)
[MPR-robustness].
4.2. MPR Topology Reduction
OSPFv3 MANET interfaces use a topology reduction mechanism denoted
MPR topology reduction, whereby only necessary links to MANET
neighbors (those identified by Path-MPR selection as belonging to
shortest paths) are included in LSAs. Routers in a MANET
periodically generate and flood Router-LSAs describing their
selection of such links to their Path-MPRs. Such links are reported
as point-to-point links. This reduces the size of LSAs originated by
routers on a MANET [MPR-topology], while retaining classic OSPF
properties: optimal paths using synchronized adjacencies (if
synchronized paths are preferred over non-synchronized paths of equal
cost).
4.3. Multicast Transmissions of Protocol Packets
OSPFv3 MANET interfaces employ multicast transmissions, when
possible, thereby taking advantage of inherent broadcast capabilities
of the medium, if present (with wireless interfaces, this can often
be the case [RFC2501]). In particular, LSA acknowledgments are sent
via multicast over these interfaces, and retransmissions over the
same interfaces are considered as implicit acknowledgments. Jitter
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management, such as delaying packet (re)transmission, can be employed
in order to allow several packets to be bundled into a single
transmission, which may avoid superfluous retransmissions due to
packet collisions [RFC5148].
4.4. MPR Adjacency Reduction
Adjacencies over OSPFv3 MANET interfaces are required to be formed
only with a subset of the neighbors of that OSPFv3 MANET interface.
No Designated Router or Backup Designated Router are elected on an
OSPFv3 MANET interface. Rather, adjacencies are brought up over an
OSPFv3 MANET interface only with MPRs and MPR Selectors. Only a
small subset of routers in the MANET (called Synch routers) are
required to bring up adjacencies with all their MANET neighbors.
This reduces the amount of control traffic needed for database
synchronization, while ensuring that LSAs still describe only
synchronized adjacencies.
5. Protocol Details
This section complements [RFC5340] and specifies the information that
must be maintained, processed and transmitted by routers which
operate one or more OSPFv3 MANET interfaces.
5.1. Data Structures
In addition to the values used in [RFC5340], the type field in the
interface data structure can take a new value, "MANET". Furthermore,
and in addition to the protocol structures defined by [RFC5340],
routers which operate one or more MANET interfaces make use of the
data structures described below.
5.1.1. N(i): Symmetric 1-hop Neighbor Set
The Symmetric 1-hop Neighbor set N(i) records router IDs of the set
of symmetric 1-hop neighbors of the router on interface i. More
precisely, N(i) records tuples of the form:
(1_HOP_SYM_id, 1_HOP_SYM_time)
where:
1_HOP_SYM_id: is the router ID of the symmetric 1-hop neighbor of
this router over the interface i.
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1_HOP_SYM_time: specifies the time at which the tuple expires and
MUST be removed from the set.
For convenience throughout this document, N will denote the union of
all N(i) sets, for all MANET interfaces on the router.
5.1.2. N2(i): Symmetric strict 2-hop Neighbor Set
The Symmetric strict 2-hop Neighbor set N2(i) records links between
routers in N(i) and their symmetric 1-hop neighbors, excluding:
(i) the router performing the computation,
(ii) all routers in N(i).
More precisely, N2(i) records tuples of the form:
(2_HOP_SYM_id, 1_HOP_SYM_id, 2_HOP_SYM_time)
where:
2_HOP_SYM_id: is the router ID of a symmetric strict 2-hop neighbor.
1_HOP_SYM_id: is the router ID of the symmetric 1-hop neighbor of
this router through which the symmetric strict 2-hop neighbor can
be reached.
2_HOP_SYM_time: specifies the time at which the tuple expires and
MUST be removed from the set.
For convenience throughout this document, N2 will denote the union of
all N2(i) sets, for all MANET interfaces on the router.
5.1.3. Flooding-MPR set
The Flooding-MPR set on interface i records router IDs of a subset of
the routers listed in N(i), selected such that through this subset,
each router listed in N2(i) is reachable in 2 hops by this router.
There is one Flooding-MPR set per MANET interface. More precisely,
the Flooding-MPR set records tuples of the form:
(Flooding_MPR_id, Flooding_MPR_time)
where:
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Flooding_MPR_id: is the router ID of the symmetric 1-hop neighbor of
this router, selected as Flooding-MPR.
Flooding_MPR_time: specifies the time at which the tuple expires and
MUST be removed from the set.
Flooding-MPR selection is detailed in Section 5.2.1.
5.1.4. Flooding-MPR-selector set
The Flooding-MPR-selector set on interface i records router IDs of
the set of symmetric 1-hop neighbors of this router on interface i
that have selected this router as Flooding-MPR. There is one
Flooding-MPR-selector set per MANET interface. More precisely, the
Flooding-MPR-selector set records tuples of the form:
(Flooding_MPR_SELECTOR_id, Flooding_MPR_SELECTOR_time)
where:
Flooding_MPR_SELECTOR_id: is the router ID of the symmetric 1-hop
neighbor of this router, that has selected this router as
Flooding-MPR.
Flooding_MPR_SELECTOR_time: specifies the time at which the tuple
expires and MUST be removed from the set.
Flooding-MPR selection is detailed in Section 5.2.1.
5.1.5. Path-MPR set
The Path-MPR set records router IDs of routers in N, that provide
shortest paths from routers in N2 and to this router. There is one
Path-MPR set per router. More precisely, the Path-MPR set records
tuples of the form:
(Path_MPR_id, Path_MPR_time)
where:
Path_MPR_id: is the router ID of the symmetric 1-hop neighbor of
this router, selected as Path-MPR.
Path_MPR_time: specifies the time at which the tuple expires and
MUST be removed from the set.
Path-MPR selection is detailed in Section 5.2.5.
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5.1.6. Path-MPR-selector set
The Path-MPR-selector set records router IDs of the set of symmetric
1-hop neighbors over any MANET interface that have selected this
router as Path-MPR. There is one Path-MPR-selector set per router.
More precisely, the Path-MPR-selector set records tuples of the form:
(Path_MPR_SELECTOR_id, Path_MPR_SELECTOR_time)
where:
Path_MPR_SELECTOR_id: is the router ID of the symmetric 1-hop
neighbor of this router, that has selected this router as Path-
MPR.
Path_MPR_SELECTOR_time: specifies the time at which the tuple
expires and MUST be removed from the set.
Path-MPR selection is detailed in Section 5.2.5.
5.1.7. MPR set
The MPR set is the union of the Flooding-MPR set(s) and the Path-MPR
set. There is one MPR set per router.
5.1.8. MPR-selector set
The MPR-Selector Set is the union of the Flooding-MPR-selector set(s)
and the Path-MPR-selector set. There is one MPR-selector set per
router.
5.2. Hello Protocol
On OSPFv3 MANET interfaces, packets are sent, received and processed
as defined in [RFC5340] and [RFC2328], augmented for MPR selection as
detailed in this section.
All additional signaling for OSPFv3 MANET interfaces is done through
inclusion of TLVs within an LLS block [RFC4813], appended to Hello
packets. If an LLS block is not already present, an LLS block MUST
be created and appended to the Hello packets.
Hello packets sent over an OSPFv3 MANET interface MUST have the L bit
of the OSPF Options field set, as per [RFC4813], indicating the
presence of an LLS block.
This document defines and employs the following TLVs in Hello packets
sent over OSPFv3 MANET interfaces:
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FMPR - signaling Flooding-MPR selection;
PMPR - signaling Path-MPR selection;
METRIC-MPR - signaling metrics.
The layout and internal structure of these TLVs is detailed in
Section 6.
5.2.1. Flooding-MPR Selection
The objective of Flooding-MPR selection is for a router to select a
subset of its neighbors such that a packet, retransmitted by these
selected neighbors, will be received by all routers 2 hops away.
This property is called the Flooding-MPR "coverage criterion". The
Flooding-MPR set of a router is computed such that, for each OSPFv3
MANET interface, it satisfies this criterion. The information
required to perform this calculation (i.e. link sensing and
neighborhood information) is acquired through periodic exchange of
OSPFv3 Hello packets.
Flooding-MPRs are computed by each router which operates at least one
OSPFv3 MANET interface. The smaller the Flooding-MPR set is, the
lower the overhead will be. However, while it is not essential that
the Flooding-MPR set is minimal, the "coverage criterion" MUST be
satisfied by the selected Flooding-MPR set.
The willingness of a neighbor router to act as Flooding-MPR MAY be
taken into consideration by a heuristic for Flooding-MPR selection.
An example heuristic taking willingness into account is given in
Appendix A.
5.2.2. Flooding-MPR Selection Signaling - FMPR TLV
A router MUST signal its Flooding-MPRs set to its neighbors, through
including an FMPR TLV in generated Hello packets. Inclusion of this
FMPR TLV signals the list of symmetric 1-hop neighbors that the
sending router has selected as Flooding-MPR, as well as the
willingness of the sending router to be elected Flooding-MPR by other
routers. The FMPR TLV structure is detailed in Section 6.1.
5.2.3. Neighbor Ordering
Neighbors listed in the Hello packets sent over OSPFv3 MANET
interfaces MUST be included in the order as given below:
1. symmetric 1-hop neighbors which are selected as Flooding-MPRs;
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2. other symmetric 1-hop neighbors;
3. other 1-hop neighbors.
This ordering allows correct interpretation of an included FMPR TLV.
5.2.4. Metric Signaling - METRIC-MPR TLV and PMPR TLV
Hello packets sent over OSPFv3 MANET interfaces MUST advertise the
costs of links towards ALL the symmetric MANET neighbors of the
sending router. If the sending router has more than one OSPFv3 MANET
interfaces, links to ALL the symmetric MANET neighbors over ALL the
OSPFv3 MANET interfaces of that router MUST have their costs
advertised.
The costs of the links between the router and each of its MANET
neighbors on the OSPFv3 MANET interface over which the Hello packet
is sent MUST be signaled through including METRIC-MPR TLVs. The
METRIC-MPR TLV structure is detailed in Section 6.2.
Moreover, the lowest cost from each MANET neighbor towards the router
(regardless of over which interface) MUST be specified in the
included PMPR TLV. Note that the lowest cost can be over an
interface which is not an OSPFv3 MANET interface.
5.2.5. Path-MPR Selection
A router which has one or more OSPFv3 MANET interface(s) MUST select
a Path-MPR set from among routers in N. Routers in the Path-MPR set
of a router are those which take part in the shortest (with respect
to the metrics used) path from routers in N2 and to this router. A
heuristic for Path-MPR selection is given in Appendix B.
5.2.6. Path-MPR Selection Signaling - PMPR TLV
A router MUST signal its Path-MPR set to its neighbors, through
including a PMPR TLV in generated Hello packets.
A PMPR TLV MUST contain a list of IDs of all symmetric 1-hop
neighbors of all OSPFv3 MANET interfaces of the router. These IDs
MUST be included in the PMPR TLV in the order as given below:
1. Neighbors which are both adjacent AND are selected as Path-MPR
for any OSPFv3 MANET interface of the router generating the Hello
packet.
2. Neighbors which are adjacent over any OSPFv3 MANET interface of
the router generating the Hello packet.
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3. Symmetric 1-hop neighbors on any OSPFv3 MANET interface of the
router generating the Hello packet, which have not been
previously included in this PMPR TLV.
The list of neighbor IDs is followed by a list of costs for the links
from these neighbors and to the router generating the Hello packet
containing this PMPR TLV, as detailed in Section 5.2.4. The PMPR TLV
structure is detailed in Section 6.3.
5.2.7. Hello Packet Processing
In addition to the processing specified in [RFC5340], N and N2 MUST
be updated when received Hello packets indicate changes to the
neighborhood of an OSPFv3 MANET interface i. In particular, if a
received Hello packet signals that a tuple in N (or N2) is to be
deleted, the deletion is done immediately, without waiting for the
tuple to expire. Note that N2 records not only 2-hop neighbors
listed in received Hellos, but also 2-hop neighbors listed in the
appended PMPR TLVs.
The Flooding-MPR set MUST be recomputed when either of N(i) or N2(i)
has changed. The Path-MPR set MUST be recomputed when either of N or
N2 has changed. Moreover, the Path-MPR set MUST be recomputed if
appended LLS information signals change with respect to one or more
link cost(s).
The Flooding-MPR selector set and the Path-MPR selector set MUST be
updated upon receipt of a Hello packet containing LLS information
indicating changes in the list of neighbors that has selected the
router as MPR.
If a Hello with the S bit set is received on a OSPFv3 MANET interface
of a router, from a non-adjacent neighbor, the router MUST transition
this neighbor's state to ExStart.
5.3. Adjacencies
Adjacencies are brought up between OSPFv3 MANET interfaces as
described in [RFC5340] and [RFC2328]. However, in order to reduce
the control traffic overhead over the OSPFv3 MANET interfaces, a
router which has one or more such OSPFv3 MANET interface(s) MAY bring
up adjacencies with only subset of its MANET neighbors.
Over an OSPFv3 MANET interface, a router MUST bring up adjacencies
with all MANET neighbors which are included in its MPR set and its
MPR Selector set; this ensures that beyond the first hop, routes use
synchronized links (if synchronized paths are preferred over non-
synchronized paths of equal cost). A router MAY bring up adjacencies
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with other MANET neighbors, at the expense of additional
synchronization overhead.
5.3.1. Packets over 2-Way Links
When a router does not form a full adjacency with a MANET neighbor,
the state of that neighbor does not progress beyond 2-Way (as defined
in [RFC2328]). A router can send protocol packets, such as LSAs, to
a MANET neighbor in 2-Way state. Therefore, any packet received from
a symmetric MANET neighbor MUST be processed.
As with the OSPF broadcast interface [RFC2328], the next hop in the
forwarding table MAY be a neighbor that is not adjacent. However,
when a data packet has travelled beyond its first hop, the MPR
selection process guarantees that subsequent hops in the SPT will be
over adjacencies (if synchronized paths are preferred over non-
synchronized paths of equal cost).
5.3.2. Adjacency Conservation
Adjacencies are torn down according to [RFC2328]. When the MPR set
or MPR selector set is updated (due to changes in the neighborhood),
and when a neighbor was formerly, but is no longer, in the MPR set or
the MPR selector set, then the adjacency with that neighbor is kept,
unless the change causes the neighbor to cease being a symmetric
1-hop neighbor.
When a router receives Hello packets from a symmetric 1-hop neighbor
which ceases to list this router as being adjacent (see
Section 5.2.6), the state of that neighbor MUST be changed to (i)
2-Way if the neighbor is not in the MPR set or the MPR selector set,
or (ii) ExStart if the neighbor is in the MPR set or the MPR selector
set, or if the neighbor or the router itself is a Synch router.
5.4. Link State Advertisements
Routers generate Router-LSAs periodically, using the format specified
in [RFC5340] and [RFC2328].
Routers which have one or more OSPFv3 MANET interface(s) MUST include
the following links in the Router-LSAs that they generate:
o links to all neighbors that are in the Path-MPR set; AND
o links to all neighbors that are in the Path-MPR Selector set.
Routers which have one or more OSPFv3 MANET interface(s) MAY list
other links they have through those OSPFv3 MANET interfaces, at the
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expense of larger LSAs.
In addition, routers which have one or more OSPFv3 MANET interface(s)
MUST generate updated Router-LSAs when either of the following
occurs:
o a new adjacency has been brought up, reflecting a change in the
MPR set;
o a new adjacency has been brought up, reflecting a change in the
MPR Selector set;
o a formerly adjacent and advertised neighbor ceases to be adjacent;
o the cost of a link to (or from) an advertised neighbor has
changed.
5.4.1. LSA Flooding
An originated LSA is flooded according to [RFC5340], out all
interfaces concerned by the scope of this LSA.
Link State Updates received on an interface of a type other than
OSPFv3 MANET interface are processed and flooded according to
[RFC2328] and [RFC5340], over every interface. If a Link State
Update was received on an OSPFv3 MANET interface, it is processed as
follows:
1. Consistency checks are performed on the received packet according
to [RFC2328] and [RFC5340], and the Link State Update packet is
thus associated with a particular neighbor and a particular area.
2. If the Link State Update was received from a router other than a
symmetric 1-hop neighbor, the Link State Update MUST be discarded
without further processing.
3. Otherwise, for each LSA contained in Link State Updates received
over an OSPFv3 MANET interface, the following steps replace steps
1 to 5 of section 13.3 of [RFC2328].
1. If an LSA exists in the Link State Database, with the same
Link State ID, LS Type and Advertising Router values as the
received LSA, and if the received LSA is not newer (see
section 13.1 of [RFC2328]), then the received LSA MUST NOT be
processed, except for acknowledgment as described in
Section 5.4.2.
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2. Otherwise, the LSA MUST be attributed a scope according to
its type, as specified in section 3.5 of [RFC5340].
3. If the scope of the LSA is link local or reserved, the LSA
MUST NOT be flooded on any interface.
4. Otherwise:
+ If the scope of the LSA is the area, the LSA MUST be
flooded on all the OSPFv3 interfaces of the router in that
area according to the default flooding algorithm described
in Section 5.4.1.1.
+ Otherwise, the LSA MUST be flooded on all the OSPFv3
interfaces of the router according to the default flooding
algorithm described in Section 5.4.1.1.
5.4.1.1. Default LSA Flooding Algorithm
The default LSA flooding algorithm is as follows:
1. The LSA MUST be installed in the Link State Database.
2. The Age of the LSA MUST be increased by InfTransDelay.
3. The LSA MUST be retransmitted over all OSPFv3 interfaces of types
other than OSPFv3 MANET interface.
4. If the sending OSPFv3 interface is a Flooding-MPR selector of
this router, then the LSA MUST also be retransmitted over all
OSPFv3 MANET interfaces concerned by the scope, with the
multicast address all_SPF_Routers.
Note that MinLSArrival SHOULD be set to a value that is appropriate
to dynamic topologies: LSA updating may need to be more frequent in
MANET parts of an OSPF network than in other parts of an OSPF
network.
5.4.2. Link State Acknowledgments
When a router receives an LSA over an OSPFv3 MANET interface, the
router MUST proceed to acknowledge the LSA as follows:
1. If the LSA was not received from an adjacent neighbor, the router
MUST NOT acknowledge it.
2. Otherwise, if the LSA was received from an adjacent neighbor and
if the LSA is already in the Link State Database (i.e. the LSA
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has already been received and processed), then the router MUST
send an acknowledgment for this LSA on all OSPFv3 MANET
interfaces, to the multicast address all_SPF_Routers.
3. Otherwise, if the LSA is not already in the Link State Database:
1. If the router decides to retransmit the LSA (as part of the
flooding procedure), the router MUST NOT acknowledge it, as
this retransmission will be considered as an implicit
acknowledgment.
2. Otherwise, if the router decides to not retransmit the LSA
(as part of the flooding procedure), the router MUST send an
explicit acknowledgment for this LSA on all OSPFv3 MANET
interfaces, to the multicast address all_SPF_Routers.
If a router sends an LSA on an OSPFv3 MANET interface, it expects
acknowledgments (explicit or implicit) from all adjacent neighbors.
In the case where the router did not generate, but simply relays, the
LSA, then the router MUST expect acknowledgments (explicit or
implicit) only from adjacent neighbors that have not previously
acknowledged this LSA. If a router detects that some adjacent
neighbor has not acknowledged the LSA, then that router MUST
retransmit the LSA.
If, due to the MPR flooding reduction mechanism employed for LSA
Flooding as described in Section 5.4.1, a router decides to not relay
an LSA, the router MUST still expect acknowledgments of this LSA
(explicit or implicit) from adjacent neighbors that have not
previously acknowledged this LSA. If a router detects that some
adjacent neighbor has not acknowledged the LSA, then the router MUST
retransmit the LSA.
Note that it may be beneficial to aggregate several acknowledgments
in the same transmission, taking advantage of native multicasting (if
available). A timer wait MAY thus be used before any acknowledgment
transmission.
Additionally, jitter [RFC5148] on packet (re)transmission MAY be used
in order to increase the opportunities to bundle several packets
together in each transmission.
5.5. Hybrid Routers
In addition to the operations described in Section 5.2, Section 5.3
and Section 5.4, hybrid routers MUST:
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o select ALL their MANET neighbors as Path-MPRs.
o list adjacencies over OSPFv3 interfaces of types other than OSPFv3
MANET interface, as specified in [RFC5340] and [RFC2328], in
generated Router-LSAs.
5.6. Synch Routers
In a network with no hybrid routers, at least one Synch router MUST
be selected. A Synch router MUST:
o set the S bit in the PMPR TLV appended to the Hello packets it
generates; AND
o become adjacent with ALL MANET neighbors.
A proposed heuristic for selection of Sync routers is as follows:
o A router which has a MANET interface and an ID that is higher than
the ID of all of its current neighbors, and whose ID is higher
than any other ID present in Router-LSAs currently in its Link
State Database selects itself as Synch router.
Other heuristics are possible, however any heuristic for selecting
Synch routers MUST ensure the presence of at least one sync or hybrid
router in the network.
5.7. Routing Table Computation
When routing table (re)computation occurs, in addition to the
processing of the Link State Database defined in [RFC5340] and
[RFC2328], routers which have one or more MANET interfaces MUST take
into account links between themselves and MANET neighbors that are in
state 2-Way or higher (as data and protocol packets may be sent,
received and processed over these links too). Thus, the connectivity
matrix used to compute routes MUST reflect links between the root and
all its neighbors in state 2-Way and higher, as well as links
described in the Link State Database.
6. Packet Formats
OSPFv3 packets are as defined by [RFC5340] and [RFC2328]. Additional
LLS signaling [RFC4813] is used in Hello packets sent over OSPFv3
MANET interfaces, as detailed in this section.
This specification uses network byte order (most significant octet
first) for all fields.
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6.1. Flooding-MPR TLV
A TLV of Type FMPR is defined for signaling Flooding-MPR selection,
shown in Figure 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=FMPR | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Willingness | # Sym. Neigh. | # Flood MPR | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Flooding-MPR TLV (FMPR)
where:
Willingness - is an 8 bit unsigned integer field which specifies the
willingness of the router to flood link state information on
behalf of other routers. It can be set to any integer value from
1 to 6. By default, a router SHOULD advertise a willingness of
WILL_DEFAULT = 3.
# Sym. Neigh. - is an 8 bit unsigned integer field which specifies
the number of symmetric 1-hop neighbors. These symmetric 1-hop
neighbors are listed first among the neighbors in a Hello packet.
# Flood MPR - is an 8 bit unsigned integer field which specifies the
number of neighbors selected as Flooding-MPR. These Flooding-MPRs
are listed first among the symmetric 1-hop neighbors.
Reserved - is an 8 bit field which SHOULD be cleared ('0') on
transmission and SHOULD be ignored on reception.
6.2. Metric-MPR TLV
A TLV of Type METRIC-MPR is defined for signaling costs of links to
neighbors, shown in Figure 2.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=METRIC-MPR | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |U|R| Cost 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cost 1 | Cost 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cost n | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Metric TLV (METRIC-MPR).
where:
Reserved - is a 14 bit field which SHOULD be cleared ('0') on
transmission and SHOULD be ignored on reception.
R - is a binary flag, cleared ('0') if the costs advertised in the
TLV are direct (i.e. the costs of the links from the router to the
neighbors), set ('1') if the costs advertised are reverse (i.e.
the costs of the links from the neighbors to the router).
U - is a binary flag, cleared ('0') if each the cost for each link
from the sending router and to each advertised neighbor is
explicitly included (shown in Figure 3), set ('1') if a single
metric value is included which applies to all links (shown in
Figure 4).
Cost n - is an 8 bit unsigned integer field which specifies the cost
of the link, in the direction specified by the R flag, between
this router and the neighbor listed at the n-th position in the
Hello packet, when counting from the beginning of the Hello packet
and with the first neighbor being at position 0.
Padding - is a 16 bit field which SHOULD be cleared ('0') on
transmission and SHOULD be ignored on reception. Padding is
included in order that the TLV is 32bit aligned. Padding MUST be
included when the TLV contains an even number of Cost fields, and
MUST NOT be included otherwise.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=METRIC-MPR | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |0|R| Cost 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cost 1 | Cost 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Metric Advertisement TLV (METRIC-MPR) example with
explicit individual link costs (U=0) and an odd number of Costs (and,
hence, no padding).
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=METRIC-MPR | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |1|R| Cost |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Metric Advertisement TLV (METRIC-MPR) example with a
single and uniform link cost (U=1) (and, hence, no padding).
6.3. Path-MPR TLV
A TLV of Type PMPR is defined for signaling Path-MPR selection, shown
in Figure 1, as well as the link cost associated with these Path-
MPRs.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=PMPR | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| # Sym Neigh | # Adj. Neigh | # Path-MPR | Reserved |U|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Neighbor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Neighbor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cost 0 | Cost 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cost n | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Path-MPR TLV (PMPR)
# Sym Neigh. - is an 8 bit unsigned integer field which specifies
the number of symmetric 1-hop MANET neighbors of all OSPFv3 MANET
interfaces of the router, listed in the PMPR TLV.
# Adj. Neigh. - is an 8 bit unsigned integer field which specifies
the number of adjacent neighbors. These adjacent neighbors are
listed first among the symmetric 1-hop MANET neighbors of all
OSPFv3 MANET interface of the router in the PMPR TLV.
# Path-MPR - is an 8 bit unsigned integer field which specifies the
number of MANET neighbors selected as Path-MPR. These Path-MPRs
are listed first among the adjacent MANET neighbors in the PMPR
TLV.
Reserved - is a 6 bit field which SHOULD be cleared ('0') on
transmission and SHOULD be ignored on reception.
S - is a binary flag, cleared ('0') if the router brings up
adjacencies only with neighbors in its MPR set and MPR selector
set as per Section 5.3, set ('1') if the router brings up
adjacencies with all MANET neighbors as a Synch router -- as per
Section 5.6.
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U - is a binary flag, cleared ('0') if the cost for each link from
each advertised neighbor in the PMPR TLV and to the sending router
is explicitly included (as shown in Figure 6), set ('1') if a
single metric value is included which applies to all links (as
shown in Figure 7).
Neighbor ID - is a 32 bit field which specifies the router ID of a
symmetric 1-hop neighbor of an OSPFv3 MANET interface of the
router.
Cost n - is a 16 bit unsigned integer field which specifies the cost
of the link in the direction from the nth listed advertised
neighbor in the PMPR TLV and towards this router. A default value
of 0xFFFF (i.e. infinity) MUST be advertised, unless information
received via Hello packets from the neighbor specifies otherwise,
in which case the received information MUST be advertised. If a
neighbor is reachable via more than one interface, the cost
advertised MUST be the minimum of the costs by which that neighbor
can be reached.
Padding - is a 16 bit field which SHOULD be cleared ('0') on
transmission and SHOULD be ignored on reception. Padding is
included in order that the PMPR TLV is 32bit aligned. Padding
MUST be included when the TLV contains an odd number of Cost
fields, and MUST NOT be included otherwise.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=PMPR | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| # Adj. Neigh | # Path-MPR | Reserved |0|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Neighbor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Neighbor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cost 1 | Cost 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: ....... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cost n-1 | Cost n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Path-MPR TLV (PMPR) with explicit individual link costs
(U=0) and an even number of Cost fields (hence, no padding).
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=PMPR | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| # Adj. Neigh | # Path-MPR | Reserved |1|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Neighbor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Neighbor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cost | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Path-MPR TLV (PMPR) with a single and uniform link cost
(U=1) (hence, padding included).
7. Security Considerations
[RFC4593] describes generic threats to routing protocols, whose
applicability to OSPFv3 [RFC5340] is not altered by the presence of
OSPFv3 MANET interfaces. As such, the OSPFv3 MANET interface type
does not introduce new security threats to [RFC5340].
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However, the use of a wireless medium and the lack of infrastructure,
as enabled by the use of the OSPFv3 MANET interface type, may render
some of the attacks described in [RFC4593] easier to undertake.
For example, control traffic sniffing and control traffic analysis
are simpler tasks with wireless than with wires, as it is sufficient
to be somewhere within radio range in order to "listen" to wireless
traffic. Inconspicuous wiretapping of the right cable(s) is not
necessary.
In a similar fashion, physical signal interference is also a simpler
task with wireless than with wires, as it is sufficient to emit from
somewhere within radio range in order to be able to disrupt the
communication medium. No complex wire connection is required.
Other types of interference (including not forwarding packets),
spoofing, and different types of falsification or overloading (as
described in [RFC4593]) are also threats to which routers using
OSPFv3 MANET interfaces may be subject. In these cases, the lack of
pre-determined infrastructure or authority, enabled by the use of
OSPFv3 MANET interfaces, may facilitate such attacks by making it
easier to forge legitimacy.
Moreover, the consequence zone of a given threat, and its consequence
period (as defined in [RFC4593]), may also be slightly altered over
the wireless medium, compared to the same threat over wired networks.
Indeed, mobility and the fact that radio range spans "further" than a
mere cable may expand the consequence zone in some cases, while the
more dynamic nature of MANET topologies may decrease the consequence
period, as harmful information (or lack of information) will tend to
be replaced quicker by legitimate information.
8. IANA Considerations
This document defines three LLS TLVs, for which allocation of type
values are requested from the LLS TLV type registry defined in
[RFC4813].
+------------+------------+--------------+
| Mnemonic | Type Value | Name |
+------------+------------+--------------+
| FMPR | tbd | Flooding-MPR |
| METRIC-MPR | tbd | Metric-MPR |
| PMPR | tbd | Path-MPR |
+------------+------------+--------------+
Table 1: LLS TLV Type Assignments
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9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997.
[RFC2328] Moy, J., "OSPF version 2", RFC 2328, 1998.
[RFC5340] Moy, J., Coltun, R., Ferguson, D., and A. Lindem,
"OSPF for IPv6", RFC 5340, 2008.
[RFC4813] Zinin, A., Friedman, B., Roy, A., Nguyen, L., and
D. Yeung, "OSPF Link Local Signaling", RFC 4813,
2007.
9.2. Informative References
[RFC2501] Macker, J. and S. Corson, "MANET Routing Protocol
Performance Issues and Evaluation Considerations",
RFC 2501, January 1999.
[RFC3626] Clausen, T. and P. Jacquet, "The Optimized Link
State Routing Protocol", RFC 3626, October 2003.
[RFC5148] Adamson, B., Dearlove, C., and T. Clausen, "Jitter
Considerations in MANETs", RFC 5148, 2008.
[MPR] Qayyum, A., Viennot, L., and A. Laouiti,,
"Multipoint Relaying for Flooding Broadcast
Messages in Mobile Wireless Networks", Proceedings
of HICSS , 2002.
[MPR-robustness] Adjih, C., Baccelli, E., Clausen, T., and P.
Jacquet, "On the Robustness and Stability of
Connected Dominated Sets", INRIA Research
Report RR-5609, 2005.
[MPR-analysis] Ngyuen, D. and P. Minet, "Analysis of MPR Selection
in the OLSR Protocol", 2nd Int. Workshop on
Performance Analysis and Enhancement of Wireless
Networks , 2007.
[MPR-topology] Baccelli, E., Clausen, T., and P. Jacquet, "Partial
Topology in an MPR-based Solution for Wireless OSPF
on Mobile Ad Hoc Networks", INRIA Research
Report RR-5619, 2005.
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[RFC4593] Barbir, A., Murphy, S., and Y. Yang, "Generic
Threats to Routing Protocols", RFC 4593, 2006.
Appendix A. Flooding-MPR Selection Heuristic
The following specifies a proposed heuristic for selection of
Flooding-MPRs on interface i. It constructs a Flooding-MPR set that
enables a router to reach routers in the 2-hop neighborhood through
relaying by one Flooding-MPR router.
The following terminology will be used in describing the heuristics:
D(Y) is the degree of a 1-hop neighbor, router Y (where Y is a member
of N(i), defined as the number of neighbors of router Y, EXCLUDING
all the members of N(i) and EXCLUDING the router performing the
computation. The proposed heuristic can then be described as
follows. Begin with an empty Flooding-MPR set. Then:
1. Calculate D(Y), where Y is a member of N(i), for all routers in
N(i).
2. Add to the Flooding-MPR set those routers in N(i), which are the
only routers to provide reachability to a router in N2(i). For
example, if router B in N2(i) can be reached only through a
router A in N(i), then add router A to the Flooding-MPR set.
Remove the routers from N2(i) which are now covered by a router
in the Flooding-MPR set.
3. While there exist routers in N2(i) which are not covered by at
least one router in the Flooding-MPR set:
1. For each router in N(i), calculate the reachability, i.e. the
number of routers in N2(i) which are not yet covered by at
least one router in the Flooding-MPR set, and which are
reachable through this 1-hop neighbor;
2. Select as a Flooding-MPR the neighbor with highest
willingness among the routers in N(i) with non-zero
reachability. In case of a tie among routers with same
willingness, select the router which provides reachability to
the maximum number of routers in N2(i). In case of another
tie between routers also providing the same amount of
reachability, select as Flooding-MPR the router whose D(Y) is
greater. Remove the routers from N2(i) which are now covered
by a router in the Flooding-MPR set.
4. As an optimization, consider in increasing order of willingness
each router Y in the Flooding-MPR set: if all routers in N2(i)
are still covered by at least one router in the Flooding-MPR set
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when excluding router Y, then router Y MAY be removed from the
Flooding-MPR set.
Other algorithms, as well as improvements over this algorithm, are
possible. Different routers may use different algorithms
independently. However, the algorithm used MUST provide the router
with a Flooding-MPR set that fulfills the flooding coverage
criterion, i.e. it MUST select a Flooding-MPR set such that any 2-hop
neighbor is covered by at least one Flooding-MPR router.
Appendix B. Path-MPR Selection Heuristic
The following specifies a proposed heuristic for calculating a Path-
MPR set that enables a router to reach routers in the 2-hop
neighborhood through shortest paths via routers in its Path-MPR set.
The following terminology will be used for describing this heuristic:
A - The router performing the Path-MPR set calculation.
B, C, D, .... - Other routers in the network.
cost(A, B) - The cost of the path through the direct link, from A to
B.
dist(C, A) - The cost of the shortest path from C to A.
A cost matrix is populated with the values of the costs of links
originating from router A (available locally) and by values listed in
Hello packets received from neighbor routers. More precisely, the
cost matrix is populated as follows:
1. The coefficients of the cost matrix are set by default to 0xFFFF
(maximal value, i.e. infinity).
2. The coefficient cost(A,B) of the cost matrix for a link from
router A to a neighbor B (the direct cost for this link) is set
to the minimum cost over all interfaces that feature router B as
a symmetric 1-hop neighbor. The reverse cost for this link,
cost(B,A), is set at the value received in Hello packets from
router B. If router B is reachable through several interfaces at
the same time, cost(B,A) is set as the minimum cost advertised by
router B for its links towards router A.
3. The coefficients of the cost matrix concerning the link between
two neighbors of A, routers C and B, are populated at the
reception of their Hello packets. The cost (B,C) is set to the
value advertised by the Hello packets from B, and respectively,
the cost (C,B) is set to the value advertised in Hello packets
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from C.
4. The coefficients of the cost matrix, cost(B,C) for a link that
connects a neighbor B to a 2-hop neighbor C is obtained via the
Hello packets received from router B. In this case cost(B,C) and
cost(C,B) are respectively set to the values advertised by router
B for the direct cost and reverse cost for node C.
Once the cost matrix is populated, the proposed heuristic can then be
described as follows. Begin with an empty Path-MPR set. Then:
1. Using the cost matrix and the Dijkstra algorithm, compute the
router distance vector, i.e. the shortest distance for each pair
(X,A) where X is in N or N2 minimizing the sum of the cost of the
path between X and A.
2. Compute N' as the subset of N made of the elements X such that
cost(X,A)=dist(X,A).
3. Compute N2' as the subset of N and N2 made of the elements Y that
do not belong to N' and such that there exist X in N' such
cost(Y,X)+cost(X,A)=dist(Y,A).
4. Compute the MPR selection algorithm presented in Appendix A with
N' instead of N(i) and N2' instead of N2(i). The resulting MPR
set is the Path-MPR set.
Other algorithms, as well as improvements over this algorithm, are
possible. Different routers may use different algorithms
independently. However, the algorithm used MUST provide the router
with a Path-MPR set that fulfills the path coverage criterion, i.e.
it MUST select a Path-MPR set such that for any element of N or N2
that is not in the Path-MPR set, there exists a shortest path that
goes from this element to the router through a neighbor selected as
Path-MPR (unless the shortest path is only one hop).
Appendix C. Contributors
The authors would like to thank Cedric Adjih, Acee Lindem, Padma
Pillay-Esnault and Laurent Viennot for their contributions to this
document.
Appendix D. Acknowledgments
The authors would like to thank Juan Antonio Cordero Fuertes, Ulrich
Herberg and Richard Ogier for reviewing this document.
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Authors' Addresses
Emmanuel Baccelli
INRIA
Phone: +33 1 69 33 55 11
EMail: Emmanuel.Baccelli@inria.fr
URI: http://www.emmanuelbaccelli.org/
Philippe Jacquet
INRIA
Phone: +33 1 3963 5263
EMail: Philippe.Jacquet@inria.fr
Dang-Quan Nguyen
CRC
Phone: +1-613-949-8216
EMail: dang.nguyen@crc.ca
Thomas Heide Clausen
LIX, Ecole Polytechnique, France
Phone: +33 6 6058 9349
EMail: T.Clausen@computer.org
URI: http://www.thomasclausen.org/
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