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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 6130

Mobile Ad hoc Networking (MANET)                              T. Clausen
Internet-Draft                          LIX, Ecole Polytechnique, France
Expires: December 21, 2006                                   C. Dearlove
                                         BAE Systems Advanced Technology
                                                                  Centre
                                                                 J. Dean
                                               Naval Research Laboratory
                                                  The OLSRv2 Design Team
                                                     MANET Working Group
                                                           June 19, 2006


              MANET Neighborhood Discovery Protocol (NHDP)
                        draft-ietf-manet-nhdp-00

Status of this Memo

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document describes a neighborhood discovery protocol (NHDP) for
   a mobile ad hoc network (MANET).  The protocol provides each MANET



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   node with local topology up to two hops distant, describing a node's
   1-hop neighbors and symmetric 2-hop neighbors.  This is achieved
   through periodic message exchange.  This neighborhood discovery
   protocol may be used by any MANET protocols which need neighborhood
   information.

   The protocol imposes minimum requirements to the network by not
   requiring sequenced or reliable transmission of control traffic.











































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
     1.2.  Applicability Statement  . . . . . . . . . . . . . . . . .  5
   2.  Protocol Overview and Functioning  . . . . . . . . . . . . . .  7
   3.  Neighborhood Information Base  . . . . . . . . . . . . . . . .  9
     3.1.  Link Set . . . . . . . . . . . . . . . . . . . . . . . . .  9
     3.2.  Symmetric Neighbor Set . . . . . . . . . . . . . . . . . . 10
     3.3.  Neighborhood Address Association Set . . . . . . . . . . . 11
     3.4.  2-Hop Neighbor Set . . . . . . . . . . . . . . . . . . . . 11
   4.  Packets and Messages . . . . . . . . . . . . . . . . . . . . . 13
     4.1.  HELLO Messages . . . . . . . . . . . . . . . . . . . . . . 13
       4.1.1.  Local Interface Block  . . . . . . . . . . . . . . . . 14
       4.1.2.  Message TLVs . . . . . . . . . . . . . . . . . . . . . 14
       4.1.3.  Address Block TLVs . . . . . . . . . . . . . . . . . . 16
   5.  HELLO Message Generation . . . . . . . . . . . . . . . . . . . 17
     5.1.  HELLO Message: Transmission  . . . . . . . . . . . . . . . 18
   6.  HELLO Message Processing . . . . . . . . . . . . . . . . . . . 19
     6.1.  Populating the Link Set  . . . . . . . . . . . . . . . . . 19
     6.2.  Populating the Symmetric Neighbor Set  . . . . . . . . . . 20
     6.3.  Populating the Neighborhood Address Association Set  . . . 21
     6.4.  Populating the 2-Hop Neighbor Set  . . . . . . . . . . . . 22
     6.5.  Neighborhood Changes . . . . . . . . . . . . . . . . . . . 23
   7.  Proposed Values for Constants  . . . . . . . . . . . . . . . . 24
     7.1.  Message Intervals  . . . . . . . . . . . . . . . . . . . . 24
     7.2.  Holding Times  . . . . . . . . . . . . . . . . . . . . . . 24
     7.3.  Time . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 25
     8.1.  Multicast Addresses  . . . . . . . . . . . . . . . . . . . 25
     8.2.  Message Types  . . . . . . . . . . . . . . . . . . . . . . 25
     8.3.  TLV Types  . . . . . . . . . . . . . . . . . . . . . . . . 25
     8.4.  LINK_STATUS and OTHER_NEIGHB Values  . . . . . . . . . . . 26
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 27
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 27
   Appendix A.  Heuristics for Generating HELLO Messages  . . . . . . 28
   Appendix B.  HELLO Message Example . . . . . . . . . . . . . . . . 31
   Appendix C.  Security Considerations . . . . . . . . . . . . . . . 33
   Appendix D.  Flow and Congestion Control . . . . . . . . . . . . . 35
   Appendix E.  Contributors  . . . . . . . . . . . . . . . . . . . . 36
   Appendix F.  Acknowledgements  . . . . . . . . . . . . . . . . . . 37
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38
   Intellectual Property and Copyright Statements . . . . . . . . . . 39







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1.  Introduction

   This document describes a neighborhood discovery protocol (NHDP) for
   a mobile ad hoc network (MANET).  It was originally developed for the
   Optimized Link State Routing Protocol version 2 (OLSRv2) [3], based
   on that used in the Optimized Link State Routing Protocol version 1
   [4].  It uses an exchange of HELLO messages in order that each node
   can determine its neighborhood up to two hops distant.  This protocol
   is used by OLSRv2 to determine a node's 1-hop neighbors for routing,
   and to allow the selection of MultiPoint Relays (MPRs) for optimized
   flooding and topology reporting.  This specification however only
   describes the message exchange and information storage required for
   1-hop and symmetric 2-hop neighborhood discovery.  It may be used by
   any MANET protocols which need neighborhood information, and which
   may add an MPR mechanism, or an alternative to it, using appropriate
   TLVs (type-length-value objects) as specified in [1], using which
   this protocol's HELLO message format is defined.

   This protocol makes no assumptions about the underlying link layer,
   other than support of local multicast.  Link layer information and
   notifications may be used if available and applicable to qualify the
   neighborhood information.

1.1.  Terminology

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC2119 [2].

   Additionally, this document uses the following terminology:

   node - A MANET router which implements this neighborhood discovery
      protocol.

   MANET interface - A network device participating in a MANET and using
      this neighborhood discovery protocol.  A node may have several
      MANET interfaces, each interface being assigned one or more IP
      addresses.

   link - A link is a pair of MANET interfaces from two different nodes,
      where at least one interface is able to hear (i.e. receive traffic
      from) the other.

   symmetric link - A link where both MANET interfaces are able to hear
      (i.e. receive traffic from) the other.






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   asymmetric link - A link which is not symmetric.

   1-hop neighbor - A node X is a 1-hop neighbor of a node Y if node Y
      can hear node X (i.e. a link exists from a MANET interface on node
      X to a MANET interface on node Y).

   symmetric 1-hop neighbor - A node X is a symmetric 1-hop neighbor of
      a node Y if a symmetric link exists from a MANET interface on node
      X to a MANET interface on node Y.

   symmetric 2-hop neighbor - A node X is a symmetric 2-hop neighbor of
      a node Y if node X is a symmetric 1-hop neighbor of a symmetric
      1-hop neighbor of node Y, but is not node Y itself.

   1-hop neighborhood - The 1-hop neighborhood of a node X is the set of
      the 1-hop neighbors of node X.

   symmetric 1-hop neighborhood - The symmetric 1-hop neighborhood of a
      node X is the set of the symmetric 1-hop neighbors of node X.

   symmetric 2-hop neighborhood - The symmetric 2-hop neighborhood of a
      node X is the set of the symmetric 2-hop neighbors of node X.
      (This may include nodes in the 1-hop neighborhood, or even in the
      symmetric 1-hop neighborhood, of node X.)

1.2.  Applicability Statement

   This neighborhood discovery protocol supports nodes which have one or
   more interfaces which participate in the MANET.  It provides each
   node with local topology information up to two hops away.  This
   information is made available to other protocols through a collection
   of sets describing the node's 1-hop neighborhood and symmetric 2-hop
   neighborhood, collectively known as the neighborhood information
   base.

   The specification is designed specifically with IP (IPv4/IPv6) in
   mind.  All addresses within a control message are assumed to be of
   the same size, deduced from IP.  In the case of mixed IPv6 and IPv4
   addresses, IPv4 addresses are carried in IPv6 as specified in [5].

   The packets defined by this specification may use any transport
   protocol appropriate to the protocol using this specification.  When
   the diffusion mechanism enabled by this specification is employed,
   UDP may be most appropriate.

   This protocol uses the message exchange format specified in [1].
   This implies that the HELLO messages specified by this protocol may
   be extended using the TLV mechanisms described in [1], e.g. to signal



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   MPR selection as required by OLSRv2 [3].  This also implies that
   neighborhood discovery protocol messages can be transmitted in
   packets with messages from other protocols, so long as these
   protocols also use [1].















































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2.  Protocol Overview and Functioning

   This protocol consists of a specification of local signaling, which
   serves to:

   o  advertise the presence of a node and its MANET interfaces to
      adjacent nodes (1-hop neighbors);

   o  discover links to adjacent nodes;

   o  perform bidirectionality (symmetry) checks on the discovered
      links;

   o  advertise discovered links and whether each is symmetric to its
      1-hop neighbors and hence discover symmetric 2-hop neighbors;

   o  maintain an information base consisting of discovered links and
      their status, 1-hop neighbors and their MANET interfaces,
      symmetric 1-hop neighbors and symmetric 2-hop neighbors.

   Signaling consists of a single type of periodically transmitted
   message known as a HELLO message.  A HELLO message identifies its
   originator node and that node's MANET interfaces and addresses.  As a
   node receives HELLO messages and populates its information base, a
   list of 1-hop neighbors' MANET interface addresses and their link
   status is included in subsequent HELLO message content.  Thus, the
   periodic transmission allows nodes to continuously track changes in
   their 1-hop and symmetric 2-hop neighborhoods.

   Because each node sends HELLO messages periodically, the protocol can
   tolerate reasonable message loss without requiring reliable
   transmission.  Such losses can occur frequently in radio networks due
   to collisions or other transmission problems.

   The nominal time interval of a node's periodic HELLO transmission is
   known as HELLO_INTERVAL and MAY be included in the HELLO message.
   The HELLO message MUST include a validity time value that indicates
   the length of time for which the message content is to be considered
   valid and included in the receiving node's information base.  In some
   uses the validity time may be a multiple of HELLO_INTERVAL to allow
   for lossy exchange of HELLO messages.

   HELLO messages MAY, in addition to periodic transmissions, also be
   generated as a response to some event (e.g. a change in the
   advertised neighborhood indicated by a received HELLO message or by a
   layer 2 notification, if available, indicating a change in a link to
   a neighbor).  However a node MUST respect a minimum interval,
   HELLO_MIN_INTERVAL, between successive HELLO message transmissions in



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   order to maintain an upper bound on signaling traffic.

   This protocol is designed to work in a completely distributed manner
   and does not depend on any central entity.  This protocol does not
   require any changes to the format of IP packets, thus any existing IP
   stack can be used as is.

   Each MANET node will form estimates of its 1-hop and symmetric 2-hop
   neighborhoods as this protocol operates.  These estimates can be
   maintained in an information base comprised of the data sets listed
   below.  These are defined formally in Section 3 and can be summarized
   as follows:

   Link Set - This set records the status of all links from and, if
      symmetric, to 1-hop neighbors.  It also records as lost links
      which used to be symmetric but have since failed.  A node MUST
      record the Link Set in order to correctly send HELLO messages.

   Symmetric Neighbor Set - This set records the addresses of the MANET
      interfaces of symmetric 1-hop neighbors, or, as lost, those which
      used to be.  Note that if any of these nodes have more than one
      MANET interface then this set may record addresses that are not in
      the Link Set. A node MUST record the Symmetric Neighbor Set in
      order to correctly send HELLO messages.

   Neighborhood Address Association Set - This set allows the addresses
      of the MANET interfaces of each 1-hop neighbor to be associated
      with each other.  It is required for processes such as MPR
      selection as in [3].

   2-Hop Neighbor Set - This set records the addresses of the MANET
      interfaces of symmetric 2-hop neighbors.  It is required for
      processes such as MPR selection as in [3].


















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3.  Neighborhood Information Base

   The neighborhood information base stores information about the 1-hop
   neighborhood and the symmetric 2-hop neighborhood of a node.

   Note that it is possible for a node, X, to be present in both the
   1-hop and symmetric 2-hop neighborhoods of another node, Y,
   concurrently.  If the link between node X and node Y breaks, this
   allows node X to be taken into consideration as a symmetric 2-hop
   neighbor by node Y immediately, rather than waiting for a HELLO
   message exchange cycle.

   This specification assumes that all addresses have an associated
   prefix length.  The prefix length of an address is, in HELLO
   messages, indicated using the PREFIX_LENGTH TLV specified in [1].  If
   no PREFIX_LENGTH TLV is present for a given address, it is assumed
   that the prefix length for that address is equal to the length of the
   address.  Two addresses are identical if and only if both the
   addresses and their associated prefix lengths are identical.

   Addresses recorded in the neighborhood information base
   (L_local_iface_addr, L_neighbor_iface_addr, N_local_iface_addr,
   N_neighbor_iface_addr, N2_local_iface_addr, N2_neighbor_iface_addr,
   N2_2hop_iface_addr and those listed in NA_neighbor_iface_addr_list)
   MUST all be recorded with prefix lengths, in order to allow
   comparison with addresses received in HELLO messages.

3.1.  Link Set

   A node records a set of "Link Tuples", recording information about
   its 1-hop neighborhood:

     (L_local_iface_addr, L_neighbor_iface_addr, L_SYM_time,
      L_ASYM_time, L_time)

   each describing a link between a MANET interface of this node and a
   MANET interface of one of its 1-hop neighbors, where:

   L_local_iface_addr is the address of the MANET interface of the local
      node on which the 1-hop neighbor is or was heard;

   L_neighbor_iface_addr is the address of the MANET interface of the
      1-hop neighbor;

   L_SYM_time is the time until which the link to the 1-hop neighbor is
      considered symmetric;





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   L_ASYM_time is the time until which the MANET interface of the 1-hop
      neighbor is considered heard;

   L_time specifies when this Link Tuple expires and MUST be removed.

   The status of the link, denoted L_STATUS, can be derived based on the
   fields L_SYM_time and L_ASYM_time as defined in Table 1.

                 +-------------+-------------+-----------+
                 | L_SYM_time  | L_ASYM_time | L_STATUS  |
                 +-------------+-------------+-----------+
                 | Expired     | Expired     | LOST      |
                 |             |             |           |
                 | Not Expired | Expired     | SYMMETRIC |
                 |             |             |           |
                 | Not Expired | Not Expired | SYMMETRIC |
                 |             |             |           |
                 | Expired     | Not Expired | HEARD     |
                 +-------------+-------------+-----------+

                                  Table 1

   In a node, the set of Link Tuples is denoted the "Link Set".

3.2.  Symmetric Neighbor Set

   A node records a set of "Symmetric Neighbor Tuples", recording
   information about its symmetric 1-hop neighborhood:

     (N_local_iface_addr, N_neighbor_iface_addr, N_SYM_time, N_time)

   each describing an address of a MANET interface of this node and an
   address of a MANET interface of one of its symmetric 1-hop neighbors,
   where:

   N_local_iface_addr is the address of the MANET interface of the local
      node to which the 1-hop neighbor has or had a symmetric link;

   N_neighbor_iface_addr is an address of a MANET interface of a 1-hop
      neighbor which is or was in this node's symmetric 1-hop
      neighborhood;

   N_SYM_time is the time until which the 1-hop neighbor is considered
      to be in this node's symmetric 1-hop neighborhood;







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   N_time specifies when this Symmetric Neighborhood Tuple expires and
      MUST be removed.

   The status of the 1-hop neighbor, denoted N_STATUS, can be derived
   based on the field L_SYM_time as defined in Table 2.

                        +-------------+-----------+
                        | N_SYM_time  | N_STATUS  |
                        +-------------+-----------+
                        | Expired     | LOST      |
                        |             |           |
                        | Not Expired | SYMMETRIC |
                        +-------------+-----------+

                                  Table 2

   In a node, the set of Symmetric Neighbor Tuples is denoted the
   "Symmetric Neighbor Set".

3.3.  Neighborhood Address Association Set

   A node records a set of "Neighborhood Address Association Tuples",
   recording information about the MANET interface configuration of its
   1-hop neighbors:

       (NA_neighbor_iface_addr_list, NA_time)

   NA_neighbor_iface_addr_list is a list of interface addresses of a
      single 1-hop neighbor;

   NA_time specifies when this Neighborhood Address Association Tuple
      expires and MUST be removed.

   In a node, the set of Neighborhood Address Association Tuples is
   denoted the "Neighborhood Address Association Set".

3.4.  2-Hop Neighbor Set

   A node records a set of "2-Hop Neighbor Tuples", recording
   information about a its symmetric 2-hop neighborhood:

     (N2_local_iface_addr, N2_neighbor_iface_addr, N2_2hop_iface_addr,
      N2_time)

   each describing a symmetric link between an address of a MANET
   interface of one of this node's symmetric 1-hop neighbors and an
   address of a MANET interface of a node in this node's symmetric 2-hop
   neighborhood.



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   N2_local_iface_addr is the address of the local MANET interface over
      which the information defining this 2-Hop Neighbor Tuple was
      received;

   N2_neighbor_iface_addr is the address of the MANET interface address
      of a symmetric 1-hop neighbor;

   N2_2hop_iface_addr is the address of a MANET interface of a symmetric
      2-hop neighbor which has a symmetric link (not necessarily using
      this address) to the node with MANET interface address
      N2_neighbor_iface_addr;

   N2_time specifies the time at which this 2-Hop Neighbor Tuple expires
      and MUST be removed.

   In a node, the set of 2-Hop Neighbor Tuples is denoted the "2-Hop
   Neighbor Set".


































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4.  Packets and Messages

   The packet and message format used by this neighborhood discovery
   protocol is defined in [1], which is used with the following
   considerations:

   o  this protocol specifies one message type, the HELLO message, in
      Section 4.1;

   o  HELLO message header options may be used as specified by the
      protocol which uses this neighborhood discovery protocol;

   o  HELLO messages are transmitted only one hop, i.e.  MUST NOT be
      forwarded;

   o  multi-message packets may be created using other messages as
      specified by the protocol which uses this neighborhood discovery
      protocol;

   o  packet header options may be used as specified by the protocol
      which uses this neighborhood discovery protocol.

4.1.  HELLO Messages

   A HELLO message MUST contain:

   o  a message TLV with Type == VALIDITY_TIME and Value == H_HOLD_TIME,
      as specified in Section 4.1.2.1

   o  an address block known as the Local Interface Block, as specified
      in Section 4.1.1; other addresses MUST NOT be added to this
      address block.

   A HELLO message MAY contain:

   o  a message TLV with Type == INTERVAL_TIME and Value ==
      HELLO_INTERVAL, as specified in Section 4.1.2.2;

   o  one or more address blocks with associated address block TLVs as
      specified in Section 4.1.3; these address blocks contain current
      or former 1-hop neighbors' MANET interface addresses with
      associated TLVs.  Other addresses (i.e. addresses of non-neighbor
      nodes) MAY be added to these address blocks, however if they are
      then these addresses MUST NOT have associated TLVs from the
      address block TLVs specified in Section 4.1.3.

   This protocol specifies two message TLVs and three address block TLVs
   used in HELLO messages in Section 4.1.2 and Section 4.1.3; other TLVs



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   MAY be included as specified by the protocol which uses this
   neighborhood discovery protocol.

4.1.1.  Local Interface Block

   The first address block, plus following TLV block, in a HELLO message
   is known as the Local Interface Block.  The Local Interface Block is
   not distinguished in any way other than by being the first address
   block in the message.

   The first address of the Local Interface Block MUST contain the used
   address of the interface over which the HELLO message is transmitted.
   If that interface has an associated prefix different from the length
   of the address, a PREFIX_LENGTH TLV MUST be associated with this
   address.  This first address, with associated prefix length, of the
   Local Interface Block is henceforth denoted the "Source Address".

   The Local Interface Block MUST contain all of the addresses of all of
   the MANET interfaces of the originating node, using the standard
   <address-block> syntax specified in [1].  Those addresses, if any,
   which correspond to MANET interfaces other than that on which the
   HELLO message is transmitted MUST have a corresponding OTHER_IF TLV
   as specified in Section 4.1.3, other addresses MUST NOT use this TLV.

   Note that a Local Interface Block MAY include more than one address
   for each MANET interface, and hence a HELLO message MAY contain more
   than one address without an OTHER_IF TLV.  A Local Interface Block
   MUST NOT contain any addresses which are not of MANET interfaces of
   the originating node.

4.1.2.  Message TLVs

   This section specifies two message TLVs: VALIDITY_TIME and
   INTERVAL_TIME.

4.1.2.1.  VALIDITY_TIME TLV

   All HELLO messages MUST include a VALIDITY_TIME TLV, specifying for
   how long a node may, upon receiving a message, consider the message
   content to be valid.  The VALIDITY_TIME TLV, described in this
   document, contains a single value since HELLO messages are
   transmitted only one hop.  Note that [1] specifies an extended
   version of this VALIDITY_TIME TLV, which is compatible with the
   format of the VALIDITY_TIME TLV in this specification.

   The VALIDITY_TIME message TLV specification is given in Table 3.





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   +----------------+------+-------------------+----------------------+
   |      Name      | Type |       Length      | Value                |
   +----------------+------+-------------------+----------------------+
   |  VALIDITY_TIME |  TBD |       8 bits      | <t_default>          |
   +----------------+------+-------------------+----------------------+

                                  Table 3

   where <t_default> is the period for which the information is valid,
   represented as specified in Section 4.1.2.3.

4.1.2.2.  INTERVAL_TIME TLV

   HELLO messages MAY include an INTERVAL_TIME message TLV, specifying
   the interval at which HELLO messages are being generated by the
   originator node.  Note that HELLO messages which are not part of a
   regular schedule SHALL be ignored in defining the interval.  If, for
   whatever reason, HELLO messages are sent in an irregular pattern,
   then this SHALL be the longest interval in that pattern.

   The INTERVAL_TIME message TLV specification is given in Table 4.

   +----------------+------+-------------------+----------------------+
   |      Name      | Type |       Length      | Value                |
   +----------------+------+-------------------+----------------------+
   |  INTERVAL_TIME |  TBD |       8 bits      | <time>               |
   +----------------+------+-------------------+----------------------+

                                  Table 4

   where <time> is the scheduled maximum time until the next
   transmission of a HELLO message by the originator node on the same
   interface, represented as specified in Section 4.1.2.3.

4.1.2.3.  Representing Time

   Section 4.1.2.1 and Section 4.1.2.2 specify TLVs where time is
   represented as a single octet.  This is defined by the lowest four
   bits of the octet representing the mantissa (a) and the highest four
   bits of the octet representing the exponent (b) of the time as a
   multiple of a fixed constant C, yielding that:

   o  time = C * (1 + a/16) * 2^b

   where a is the integer represented by the four lowest bits of the
   time field and b the integer represented by the four highest bits of
   the time field.  All nodes in the network MUST use the same value of
   C, which will be specified in seconds, hence so will be all times



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   (see Section 7).  Note that ascending values of the octet represent
   ascending values of time, times may thus be compared by comparison of
   octets.

   An algorithm for computing the representation of time t is the
   following:

   1.  find the largest integer b such that t/C >= 2^b;

   2.  set a = 16 * (t / (C * 2^b) - 1), rounded up to the nearest
       integer;

   3.  if a == 16 then set b = b + 1 and set a = 0;

   4.  if a and b are in the range 0 and 15 then t can be represented by
       an octet holding the value 16*b + a, otherwise it can not.

   As examples, the values of 2 seconds and 6 seconds are represented by
   (a=0, b=5) and (a=8, b=6), respectively, i.e., by the octets 80 and
   104 (hexadecimal 50 and 68).

4.1.3.  Address Block TLVs

   The three address block TLVs used in HELLO messages are specified in
   Table 5.

   +----------------+------+-------------------+-----------------------+
   |      Name      | Type |       Length      | Value                 |
   +----------------+------+-------------------+-----------------------+
   |    OTHER_IF    |  TBD |       0 bits      | Not Applicable        |
   |                |      |                   |                       |
   |   LINK_STATUS  |  TBD |       8 bits      | One of LOST,          |
   |                |      |                   | SYMMETRIC or HEARD.   |
   |                |      |                   |                       |
   |  OTHER_NEIGHB  |  TBD |       8 bits      | One of LOST or        |
   |                |      |                   | SYMMETRIC             |
   +----------------+------+-------------------+-----------------------+

                                  Table 5












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5.  HELLO Message Generation

   HELLO messages MUST be generated and transmitted independently on
   each MANET interface.  The maximum interval between HELLO
   transmissions on the same MANET interface MUST NOT exceed
   HELLO_MIN_INTERVAL.  Two successive HELLO message transmissions on
   the same MANET interface MUST be separated by at least
   HELLO_MIN_INTERVAL.

   Each HELLO message MUST include a Local Interface Block as specified
   in Section 4.1.1 as its first address block.

   On its MANET interface with address Sending Address, a node MUST
   report appropriate addresses with associated TLVs from the Link Set
   and Symmetric Neighbor Set. These addresses, with their associated
   TLVs, MAY be reported in any HELLO messages transmitted on that MANET
   interface.  All such addresses, with their associated TLVs, MUST be
   reported in at least one HELLO message transmitted on that MANET
   interface within every interval of length REFRESH_INTERVAL.  These
   addresses MUST NOT be included in the Local Interface Block, they MAY
   be included in any other address block.

   The addresses, with their associated TLVs, which MUST be included in
   HELLO messages over the local MANET interface with address Sending
   Address, are computed thus:

   1.  For each Link Tuple with L_local_iface_addr == Sending Address,
       include:

       *  L_neighbor_iface_addr with an associated TLV with:

          +  Type = LINK_STATUS; AND

          +  Value = L_STATUS.

   2.  For each address which appears as an N_neighbor_iface_addr in one
       or more Symmetric Neighbor Tuples:

       1.  if this address has already been included with an associated
           TLV with Type == LINK_STATUS and Value == SYMMETRIC, do not
           add an associated TLV with Type == OTHER_NEIGHB;

       2.  otherwise if, for one or more of these Symmetric Neighbor
           Tuples, N_STATUS == SYMMETRIC, then include this address with
           associated TLV with:

           +  Type = OTHER_NEIGHB; AND




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           +  Value = SYMMETRIC;

       3.  otherwise if, for all of these Symmetric Neighbor Tuples,
           N_STATUS == LOST, and this address has not already been
           included with an associated TLV with Type == LINK_STATUS and
           Value == LOST, then include this address with associated TLV
           with:

           +  Type = OTHER_NEIGHB; AND

           +  Value = LOST.

   If an address is specified as included with more than one associated
   TLV, then these TLVs MAY be independently included or excluded from
   HELLO messages as long as all are included with any interval of
   length REFRESH_INTERVAL.  TLVs applying to the same address MAY be
   applied to the same or different copies of the address in a given
   HELLO message.

5.1.  HELLO Message: Transmission

   Messages are transmitted in the packet/message format specified by
   [1] using the ALL-MANET-NEIGHBORS multicast address as destination IP
   address and with the HELLO message Hop Limit = 1.



























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6.  HELLO Message Processing

   On receiving a HELLO message, a node will update its neighborhood
   information base according to the specification given in this
   section.

   For the purpose of this section, note the following definitions:

   o  the "validity time" of a message is calculated from the
      VALIDITY_TIME TLV of the message as specified in Section 4.1.2.1;

   o  the "Source Address" is the first address, including prefix
      length, of the Local Interface Block in the HELLO message;

   o  the "Receiving Address" is the address, including prefix length,
      of the MANET interface on which the HELLO message was received;

   o  the word EXPIRED indicates that a timer is set to a value clearly
      preceding the current time (e.g. current time - 1).

6.1.  Populating the Link Set

   On receiving a HELLO message, a node SHOULD update its Link Set:

   1.  If there is no Link Tuple with:

       *  L_local_iface_addr == Receiving Address; AND

       *  L_neighbor_iface_addr == Source Address,

       then create a new Link Tuple with

       *  L_local_iface_addr = Receiving Address;

       *  L_neighbor_iface_addr = Source Address;

       *  L_SYM_time = EXPIRED;

       *  L_time = current time + validity time.

   2.  This Link Tuple (existing or new) is then modified as follows:

       1.  If the node finds the Receiving Address in one of the address
           blocks included in the HELLO message, other than the Local
           Interface Block, then the Link Tuple is modified as follows:

           1.  If the Receiving Address in that address block is
               associated with a TLV with Type == LINK_STATUS and Value



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               == LOST then:

               1.  if L_STATUS == SYMMETRIC:

                   o  L_time = current time + max(validity time,
                      L_HOLD_TIME),

                   o  L_SYM_time = EXPIRED.

           2.  Otherwise if the Receiving Address in that address block
               is associated with a TLV with Type == LINK_STATUS and
               (Value == HEARD or Value == SYMMETRIC) then:

               -  L_SYM_time = current time + validity time;

               -  L_time = L_SYM_time + L_HOLD_TIME.

       2.  L_ASYM_time = current time + validity time;

       3.  L_time = max(L_time, L_ASYM_time).

6.2.  Populating the Symmetric Neighbor Set

   On receiving a HELLO message, a node SHOULD update its Symmetric
   Neighbor Set:

   1.  If the Receiving Address is in an address block of the HELLO
       message, other than the Local Interface Block, with an associated
       TLV with Type == LINK_STATUS and (Value == HEARD or Value ==
       SYMMETRIC) then:

       1.  For each address (henceforth neighbor address) in the HELLO
           message's Local Interface Block:

           1.  If there is a Symmetric Neighbor Tuple with:

               -  N_local_iface_addr == Receiving Address; AND

               -  N_neighbor_iface_addr == neighbor address,

               then update this Symmetric Neighbor Tuple to have:

               -  N_SYM_time = current time + validity time;

               -  N_time = N_SYM_time + N_HOLD_TIME.






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           2.  Otherwise create a new Symmetric Neighbor Tuple with:

               -  N_local_iface_addr = Receiving Address;

               -  N_neighbor_iface_addr = neighbor address;

               -  N_SYM_time = current time + validity time;

               -  N_time = N_SYM_time + N_HOLD_TIME.

   2.  Otherwise if the Receiving Address is in an address block of the
       HELLO message, other than the Local Interface Block, with an
       associated TLV with Type == LINK_STATUS and Value == LOST, then:

       1.  For each address (henceforth neighbor address) in the HELLO
           message Local Interface Block, if there exists a Symmetric
           Neighbor Tuple with:

           +  N_local_iface_addr == Receiving Address; AND

           +  N_neighbor_iface_addr == neighbor address,

           update this Symmetric Neighbor Tuple to have:

           +  N_SYM_time = EXPIRED;

           +  N_time = min(N_time, current time + N_HOLD_TIME).

6.3.  Populating the Neighborhood Address Association Set

   On receiving a HELLO message, the node SHOULD update its Neighborhood
   Address Association Set:

   1.  Remove all Neighborhood Address Association Tuples where:

       *  NA_neighbor_iface_addr_list contains at least one address
          which is contained in the Local Interface Block of the
          received HELLO message,

       and create a new Neighborhood Address Association Tuple with:

       *  NA_neighbor_iface_addr_list = list of all addresses contained
          in the Local Interface Block of the received HELLO message;

       *  NA_time = current time + validity time.






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6.4.  Populating the 2-Hop Neighbor Set

   On receiving a HELLO message the node SHOULD update its 2-Hop
   Neighbor Set:

   1.  If there exists a Link Tuple with L_local_iface_addr == Source
       Address and L_STATUS == SYMMETRIC then:

       1.  For each address (henceforth 2-hop neighbor address) in an
           address block of the HELLO message, other than the Local
           Interface Block, which is not an interface address of the
           receiving node:

           1.  If the 2-hop neighbor address has an associated TLV with:

               -  Type == LINK_STATUS and Value == SYMMETRIC; OR

               -  Type == OTHER_NEIGHB and Value == SYMMETRIC,

               then, if there is no 2-Hop Neighbor Tuple with:

               -  N2_local_iface_addr == Receiving Address;

               -  N2_neighbor_iface_addr == Source Address;

               -  N2_2hop_iface_addr == 2-hop neighbor address;

               create a 2-Hop Neighbor Tuple with:

               -  N2_local_iface_addr = Receiving Address; AND

               -  N2_neighbor_iface_addr = Source Address; AND

               -  N2_2hop_iface_addr = 2-hop neighbor address.

               This 2-Hop Neighbor Tuple (existing or new) is then
               modified as follows:

               -  N2_time = current time + validity time.

           2.  Otherwise if the 2-hop neighbor address has a TLV with:

               -  Type == LINK_STATUS and (Value == LOST or Value ==
                  HEARD); OR

               -  Type == OTHER_NEIGHB and Value == LOST;

               then remove all 2-Hop Neighbor Tuples with:



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               -  N2_local_iface_addr == Receiving Address; AND

               -  N2_neighbor_iface_addr == Source Address; AND

               -  N2_2hop_iface_addr == 2-hop neighbor address.

6.5.  Neighborhood Changes

   If the L_SYM_time field of a Link Tuple expires (either due to timing
   out, or as a result of processing a TLV with Type == LINK_STATUS and
   Value == LOST) then all 2-Hop Neighbor Tuples with:

   o  N2_local_iface_addr == L_local_iface_addr from the Link Tuple,
      AND;

   o  N2_neighbor_iface_addr == L_neighbor_iface_addr from the Link
      Tuple,

   MUST be deleted.

   In this, or any other case of neighborhood change, a node MAY send a
   HELLO message reporting updated information.  If a node does send
   such a HELLO message the node MUST ensure that any two successive
   HELLO messages are separated by at least HELLO_MIN_INTERVAL.



























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7.  Proposed Values for Constants

   This section list the values for the constants used in the
   description of the protocol.

7.1.  Message Intervals

   o  HELLO_INTERVAL = 2 seconds

   o  REFRESH_INTERVAL = HELLO_INTERVAL

   o  HELLO_MIN_INTERVAL = HELLO_INTERVAL/4

7.2.  Holding Times

   o  H_HOLD_TIME = 3 x REFRESH_INTERVAL

   o  L_HOLD_TIME = H_HOLD_TIME

   o  N_HOLD_TIME = H_HOLD_TIME

7.3.  Time

   o  C = 0.0625 seconds (1/16 second)

   In order to achieve interoperability, C MUST be the same on all
   nodes.
























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8.  IANA Considerations

8.1.  Multicast Addresses

   A well-known multicast address, ALL-MANET-NEIGHBORS, must be
   registered and defined for both IPv6 and IPv4.  The addressing scope
   is link-local, i.e. this address is similar to the all nodes/routers
   multicast address of IPv6 in that it targets all MANET nodes adjacent
   to the originator of an IP datagram.

8.2.  Message Types

   This specification defines one message type, which must be allocated
   from the "Assigned Message Types" repository of [1]

   +--------------------+-------+--------------------------------------+
   |      Mnemonic      | Value | Description                          |
   +--------------------+-------+--------------------------------------+
   |        HELLO       |  TBD  | Local Signaling                      |
   +--------------------+-------+--------------------------------------+

                                  Table 6

8.3.  TLV Types

   This specification defines two Message TLV types, which must be
   allocated from the "Assigned Message TLV Types" repository of [1]

   +--------------------+-------+--------------------------------------+
   |      Mnemonic      | Value | Description                          |
   +--------------------+-------+--------------------------------------+
   |    VALIDITY_TIME   |  TBD  | The time (in seconds) from receipt   |
   |                    |       | of the message during which the      |
   |                    |       | information contained in the message |
   |                    |       | is to be considered valid            |
   |                    |       |                                      |
   |    INTERVAL_TIME   |  TBD  | The maximum time (in seconds)        |
   |                    |       | between two successive transmissions |
   |                    |       | of messages of the appropriate type  |
   +--------------------+-------+--------------------------------------+

                                  Table 7

   This specification defines three Address Block TLV types, which must
   be allocated from the "Assigned Address Block TLV Types" repository
   of [1]





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   +--------------------+-------+--------------------------------------+
   |      Mnemonic      | Value | Description                          |
   +--------------------+-------+--------------------------------------+
   |      OTHER_IF      |  TBD  | Specifies that the address, in the   |
   |                    |       | Local Interface Block of the         |
   |                    |       | message, is an address associated    |
   |                    |       | with a MANET interface other than    |
   |                    |       | the one on which the message is      |
   |                    |       | transmitted                          |
   |                    |       |                                      |
   |     LINK_STATUS    |  TBD  | Specifies a given link's status      |
   |                    |       | (LOST, SYMMETRIC or HEARD)           |
   |                    |       |                                      |
   |    OTHER_NEIGHB    |  TBD  | Specifies that the address is, or    |
   |                    |       | was, of a MANET interface of a       |
   |                    |       | symmetric 1-hop neighbor of the node |
   |                    |       | transmitting the HELLO message, but  |
   |                    |       | does not have a matching or better   |
   |                    |       | LINK_STATUS TLV                      |
   +--------------------+-------+--------------------------------------+

                                  Table 8

8.4.  LINK_STATUS and OTHER_NEIGHB Values

   The values which the LINK_STATUS TLV can use are the following:

   o  LOST = 0

   o  SYMMETRIC = 1

   o  HEARD = 2

   The values which the OTHER_NEIGHB TLV can use are the following:

   o  LOST = 0

   o  SYMMETRIC = 1













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9.  References

9.1.  Normative References

   [1]  Clausen, T., Dean, J., Dearlove, C., and C. Adjih, "Generalized
        MANET Packet/Message Format", Work In
        Progress draft-ietf-manet-packetbb-01.txt, June 2006.

   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", RFC 2119, BCP 14, March 1997.

9.2.  Informative References

   [3]  Clausen, T., Dearlove, C., and P. Jacquet, "The Optimized Link
        State Routing Protocol version 2", Work In
        Progress draft-ietf-manet-olsrv2-02.txt, June 2006.

   [4]  Clausen, T. and P. Jacquet, "The Optimized Link State Routing
        Protocol", RFC 3626, October 2003.

   [5]  Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6)
        Addressing Architecture", RFC 3513, April 2003.





























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Appendix A.  Heuristics for Generating HELLO Messages

   The algorithm for generating HELLO messages in Section 5 specifies
   which addresses MAY be included in the address blocks after the Local
   Interface Block, and with which associated TLVs.  These TLVs may have
   Type == LINK_STATUS or Type == OTHER_NEIGHB, or both.  TLVs with Type
   == LINK_STATUS may have three possible values (Value == HEARD, Value
   == SYMMETRIC or Value == LOST), and TLVs of TYPE == OTHER_NEIGHB may
   have two possible values (Value == SYMMETRIC or Value == LOST).  When
   both TLVs are associated with the same address only certain
   combinations of these TLV values are necessary, and are the only
   combinations generated by the algorithm in Section 5.  These
   combinations are indicated in Table 9.

   Cells labeled with "Yes" indicate the possible combinations which are
   generated by the algorithm in Section 5.  Cells labeled with "No"
   indicate combinations not generated by the algorithm in Section 5,
   but which are correctly parsed and interpreted by the algorithm in
   Section 6.

   +----------------+----------------+----------------+----------------+
   |                |     Type ==    |     Type ==    |     Type ==    |
   |                |  OTHER_NEIGHB  |  OTHER_NEIGHB, |  OTHER_NEIGHB, |
   |                |    (absent)    |    Value ==    |  Value == LOST |
   |                |                |    SYMMETRIC   |                |
   +----------------+----------------+----------------+----------------+
   | Type ==        |       No       |       Yes      |       Yes      |
   | LINK_STATUS    |                |                |                |
   | (absent)       |                |                |                |
   |                |                |                |                |
   | Type ==        |       Yes      |       Yes      |       Yes      |
   | LINK_STATUS,   |                |                |                |
   | Value == HEARD |                |                |                |
   |                |                |                |                |
   | Type ==        |       Yes      |       No       |       No       |
   | LINK_STATUS,   |                |                |                |
   | Value ==       |                |                |                |
   | SYMMETRIC      |                |                |                |
   |                |                |                |                |
   | Type ==        |       Yes      |       Yes      |       No       |
   | LINK_STATUS,   |                |                |                |
   | Value == LOST  |                |                |                |
   +----------------+----------------+----------------+----------------+

                                  Table 9

   In creating the HELLO message there are three stages:




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   1.  collect the addresses into groups, each of which will form an
       address block (this heuristic assumes that each address will be
       included only once in a HELLO message, and that all TLVs
       associated with it are included);

   2.  order the addresses in each group for most efficient TLV
       association;

   3.  add the TLVs in the most efficient manner, whether single or
       multiple value.

   There is no straightforward way to perform these steps to create the
   most optimal (smallest) HELLO message.  Instead the following
   heuristics may be considered:

   1.  The easiest approach to grouping addresses is to put them all in
       a single address block.  Separate address blocks are appropriate
       when addresses have significantly different initial (head) bit
       sequences, and the address compression in the address block
       construction can be more efficient when addresses with different
       initial sequences can be compressed separately, gaining more than
       the overhead of multiple address blocks.  Separate address blocks
       have a lower overhead when either they use different TLVs, or
       when they use multivalue TLVs.  The simplest heuristic is to use
       a single address block, unless addresses may be divided into one
       or more subnets, especially if these are associated with
       different MANET interfaces and hence each uses either LINK_STATUS
       or OTHER_NEIGHB TLVs, but not both.

   2.  Grouping addresses that use a single TLV is straightforward, so
       that each TLV type and value may be applied to a continuous
       sequence of addresses.  This can be extended to cover the case
       where addresses have more than one TLV.  An example of how to
       order all TLV combinations so that each TLV type and value is
       applied to a continuous sequence of addresses is given.  (This
       order is not unique.)

       *  Type == LINK_STATUS, Value == LOST.

       *  Type == LINK_STATUS, Value == LOST and Type == OTHER_NEIGHB,
          Value == SYMMETRIC.

       *  Type == OTHER_NEIGHB, Value == SYMMETRIC.

       *  Type == LINK_STATUS, Value == HEARD and Type == OTHER_NEIGHB,
          Value == SYMMETRIC.





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       *  Type == LINK_STATUS, Value == HEARD.

       *  Type == LINK_STATUS, Value == HEARD and Type == OTHER_NEIGHB,
          Value == LOST.

       *  Type == OTHER_NEIGHB, Value == LOST.

       *  Type == LINK_STATUS, Value == SYMMETRIC.

       This order is not appropriate when multiple value TLVs are to be
       used, then it is more important to group all TLVs of the same
       type together, even when having different values.  A possible
       ordering is

       *  Type == LINK_STATUS, Value == HEARD.

       *  Type == LINK_STATUS, Value == SYMMETRIC.

       *  Type == LINK_STATUS, Value == LOST.

       *  Type == LINK_STATUS, Value == HEARD and Type == OTHER_NEIGHB,
          Value == SYMMETRIC.

       *  Type == LINK_STATUS, Value == HEARD and Type == OTHER_NEIGHB,
          Value == LOST.

       *  Type == LINK_STATUS, Value == LOST and Type == OTHER_NEIGHB,
          Value == SYMMETRIC.

       *  Type == OTHER_NEIGHB, Value == SYMMETRIC.

       *  Type == OTHER_NEIGHB, Value == LOST.

       Where one TLV type uses single values and the other multiple
       values, appropriate orderings can be devised.

   3.  When there are many addresses in an address block, the most
       efficient way to add TLVs is as up to five single value TLVs,
       each with a single octet value field.  When there are few
       addresses in an address block, the most efficient way to add TLVs
       is as up to two multiple value TLVs, with one octet of value per
       address each.  It may be appropriate to use one approach for each
       TLV type.  It is relatively straightforward to estimate the cost
       of each approach (adding TLV type, semantics, length and index
       overheads per TLV, and either one octet per value or per address
       as appropriate) and to select the probably lower cost approach.
       Alternatively a single decision based on the expected number of
       1-hop neighbor addresses may be made.



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Appendix B.  HELLO Message Example

   A simple example HELLO message, sent by an originator node with a
   single MANET interface, is as follows.  The message uses IPv4 (four
   octet) addresses without prefix TLVs, i.e. with all addresses having
   maximum length prefixes.  The message is sent with a full message
   header (message semantics octet is 0) with a hop limit of 1 and a hop
   count of 0.  The overall message length is 48 octets (it does not
   need padding).

   The message has a message TLV block with content length 8 octets
   containing two message TLVs, of types VALIDITY_TIME and
   INTERVAL_TIME.  Each uses a TLV with semantics value 4, indicating no
   start and stop indexes are included, and each has a value length of 1
   octet.  The values included (0x68 and 0x50) represent the default
   values of 6 seconds and 2 seconds, respectively.

   The first address block contains 1 local interface address, with head
   length 4 and no address tail or mid parts.  This address block has no
   TLVs (TLV block content length 0 octets).

   The second, and last, address block contains 4 neighbor interface
   addresses, with head length 3 octets, no address tail part and each
   address mid part having length one octet.  The following TLV block
   (content length 7 octets) includes one TLV which reports the link
   status of all neighbors in a single multivalue TLV: the first two
   addresses are HEARD, the third address is SYMMETRIC and the fourth
   address is LOST.  The TLV semantics value of 12 indicates, in
   addition to that this is a multivalue TLV, that no start and stop
   indexes are included, since values for all addresses are included.
   The TLV value length of 4 octets indicates one octet per value per
   address.



















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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     HELLO     |0 0 0 0 0 0 0 0|0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Originator Address                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 1|0 0 0 0 0 0 0 0|    Message Sequence Number    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0| VALIDITY_TIME |0 0 0 0 0 1 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 1|0 1 1 0 1 0 0 0| INTERVAL_TIME |0 0 0 0 0 1 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 1|0 1 0 1 0 0 0 0|0 0 0 0 0 0 0 1|0 0 0 0 0 1 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             Head                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0|0 0 0 0 0 1 0 0|0 0 0 0 0 0 1 1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Head                      |      Mid      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Mid      |      Mid      |      Mid      |0 0 0 0 0 0 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 1 1 1|  LINK_STATUS  |0 0 0 0 1 1 0 0|0 0 0 0 0 1 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     HEARD     |     HEARD     |   SYMMETRIC   |     LOST      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
























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Appendix C.  Security Considerations

   The objective of this protocol is to allow each node in the network
   to acquire information describing its 1-hop and symmetric 2-hop
   neighborhoods.  This is acquired through periodic message exchange
   between neighboring nodes, and the information is made available
   through a collection of sets, describing the node's 1-hop
   neighborhood and symmetric 2-hop neighborhood.

   Under normal circumstances, the information recorded in these sets is
   correct - i.e. corresponds to the actual network topology, apart from
   any changes which have not (yet) been tracked by the HELLO message
   exchanges.  If some node for some reason, malice or malfunction,
   inject invalid HELLO messages, incorrect information may be recorded
   in the sets maintained.

   A correctly formed, but still invalid, HELLO message may take any of
   the following forms:

   1.   The Local Interface Block of the HELLO message may contain
        addresses which do not correspond to addresses of MANET
        interfaces of the local node which transmits the HELLO message;

   2.   The Local Interface Block of the HELLO message may omit
        addresses of MANET interfaces of the local node which transmits
        the HELLO message;

   3.   The Local Interface Block may contain OTHER_IF TLVs, indicating
        incorrectly that an address is associated with a MANET interface
        other than the one over which the HELLO message is being
        transmitted;

   4.   The Local Interface Block may omit OTHER_IF TLVs, thereby
        indicating incorrect addresses associated with the MANET
        interface over which the HELLO message is being transmitted;

   5.   A present or absent address in an address block, other than in
        the Local Interface Block, does not in and by itself cause a
        problem.  It is the presence, absence or incorrectness of
        associated LINK_STATUS and OTHER_NEIGHB TLVs that cause
        problems;

   6.   A present LINK_STATUS TLV may, incorrectly, identify an address
        as being of a node which is or was in the sending node's 1-hop
        neighborhood;

   7.   A consistently absent LINK_STATUS TLV may, incorrectly, fail to
        identify an address as being of a node which is or was in the



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        sending node's 1-hop neighborhood;

   8.   A present OTHER_NEIGHB TLV may, incorrectly, identify an address
        as being of a node which is or was in the sending node's
        symmetric 1-hop neighborhood;

   9.   A consistently absent OTHER_NEIGHB TLV may, incorrectly, fail to
        identify an address as being of a node which is or was in the
        sending node's symmetric 1-hop neighborhood;

   10.  The value of a LINK_STATUS or OTHER_NEIGHB TLV may incorrectly
        indicate the status (LOST, SYMMETRIC, HEARD) of a 1-hop
        neighbor.






































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Appendix D.  Flow and Congestion Control

   This document specifies one message type, HELLO messages.  The size
   of each complete HELLO message is proportional to the size of the
   transmitting node's 1-hop neighborhood (this information may be sent
   distributed across multiple interfaces).  HELLO messages MUST NOT be
   forwarded.

   A node MUST report its 1-hop neighborhood in HELLO messages on each
   of its MANET interfaces at least each REFRESH_INTERVAL.  Thus, this
   puts a lower bound on the control traffic, which each node employing
   this neighborhood discovery protocol in the network generates.

   A node MUST ensure that two successive HELLO messages sent on the
   same MANET interface are separated by at least HELLO_MIN_INTERVAL.
   Thus, this puts an upper bound on the control traffic, which each
   node employing this neighborhood discovery protocol in the network
   generates.

   In order for the protocol to function, each node in the network MUST
   employ the HELLO signaling as described in this specification.






























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Appendix E.  Contributors

   This specification is the result of the joint efforts of the
   following contributors -- listed alphabetically.

   o  Brian Adamson, NRL, USA, <adamson@itd.nrl.navy.mil>

   o  Cedric Adjih, INRIA, France, <Cedric.Adjih@inria.fr>

   o  Emmanuel Baccelli, Hitachi Labs Europe, France,
      <Emmanuel.Baccelli@inria.fr>

   o  Thomas Heide Clausen, PCRI, France, <T.Clausen@computer.org>

   o  Justin Dean, NRL, USA, <jdean@itd.nrl.navy.mil>

   o  Christopher Dearlove, BAE Systems, UK,
      <Chris.Dearlove@baesystems.com>

   o  Philippe Jacquet, INRIA, France, <Philippe.Jacquet@inria.fr>































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Appendix F.  Acknowledgements

   The authors would like to acknowledge the team behind OLSRv1,
   specified in RFC3626, including Anis Laouiti, Pascale Minet, Laurent
   Viennot (all at INRIA, France), and Amir Qayuum (Center for Advanced
   Research in Engineering, Pakistan) for their contributions.

   The authors would like to gratefully acknowledge the following people
   for intense technical discussions, early reviews and comments on the
   specification and its components: Joe Macker (NRL), Alan Cullen (BAE
   Systems), Song-Yean Cho (Samsung Software Center) and the entire IETF
   MANET working group.







































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Authors' Addresses

   Thomas Heide Clausen
   LIX, Ecole Polytechnique, France

   Phone: +33 6 6058 9349
   Email: T.Clausen@computer.org
   URI:   http://www.lix.polytechnique.fr/Labo/Thomas.Clausen/


   Christopher M. Dearlove
   BAE Systems Advanced Technology Centre

   Phone: +44 1245 242194
   Email: chris.dearlove@baesystems.com
   URI:   http://www.baesystems.com/ocs/sharedservices/atc/


   Justin W. Dean
   Naval Research Laboratory

   Phone: +1 202 767 3397
   Email: jdean@itd.nrl.navy.mil
   URI:   http://pf.itd.nrl.navy.mil/


   The OLSRv2 Design Team
   MANET Working Group























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