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Versions: 00 01 02 03 RFC 5820

Network Working Group                                M. Chandra (Editor)
Internet-Draft                                           A. Roy (Editor)
Intended status: Standards Track                           Cisco Systems
Expires: August 2008                                       February 2008


         Extensions to OSPF to Support Mobile Ad Hoc Networking
                    draft-ietf-ospf-manet-or-00

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Copyright Notice

   Copyright (C) The IETF Trust (2008).


Abstract

   This document describes extensions to OSPF to support mobile ad hoc
   networking.  Specifically, the document specifies a mechanism for
   link-local signaling, a OSPF-MANET interface, a simple technique to
   reduce the size of Hello packets by only transmitting incremental
   state changes, and a method for optimized flooding of routing
   updates.


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Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1  Problem Statement  . . . . . . . . . . . . . . . . . . . .   3
     1.2  Motivation for extending OSPF to support MANETs  . . . . .   4
   2.   Specification of Requirements  . . . . . . . . . . . . . . .   4
   3.   Proposed Enhancements  . . . . . . . . . . . . . . . . . . .   4
     3.1  OSPF-MANET Interface . . . . . . . . . . . . . . . . . . .   5
       3.1.1  Interface Operation  . . . . . . . . . . . . . . . . .   6
       3.1.2  LSA Formats and Examples . . . . . . . . . . . . . . .   6
     3.2  Incremental OSPF-MANET Hellos  . . . . . . . . . . . . . .  10
       3.2.1  The I Option Bit . . . . . . . . . . . . . . . . . . .  10
       3.2.2  State Check Sequence TLV . . . . . . . . . . . . . . .  11
       3.2.3  Neighbor Drop TLV  . . . . . . . . . . . . . . . . . .  12
       3.2.4  'Request From' TLV (RF-TLV)  . . . . . . . . . . . . .  12
       3.2.5  Full State For TLV (FSF-TLV) . . . . . . . . . . . . .  12
       3.2.6  Neighbor Adjacencies . . . . . . . . . . . . . . . . .  13
       3.2.7  Sending Hellos . . . . . . . . . . . . . . . . . . . .  14
       3.2.8  Receiving Hellos . . . . . . . . . . . . . . . . . . .  15
       3.2.9  Interoperability . . . . . . . . . . . . . . . . . . .  17
       3.2.10   Support for OSPF Graceful Restart  . . . . . . . . .  17
     3.3  Optimized Flooding (Overlapping Relays)  . . . . . . . . .  17
       3.3.1  Operation Overview . . . . . . . . . . . . . . . . . .  18
       3.3.2  Determination of Overlapping Relays  . . . . . . . . .  18
       3.3.3  Terminology  . . . . . . . . . . . . . . . . . . . . .  19
       3.3.4  Overlapping Relay Discovery Process  . . . . . . . . .  19
       3.3.5  The F Option Bit . . . . . . . . . . . . . . . . . . .  20
       3.3.6  Active Overlapping Relay Extension . . . . . . . . . .  20
       3.3.7  Willingness TLV  . . . . . . . . . . . . . . . . . . .  22
       3.3.8  Flooding and Relay Decisions . . . . . . . . . . . . .  22
       3.3.9  Intelligent Transmission of Link State
              Acknowledgements . . . . . . . . . . . . . . . . . . .  24
       3.3.10   Important Timers . . . . . . . . . . . . . . . . . .  24
       3.3.11   Miscellaneous Protocol Considerations  . . . . . . .  25
       3.3.12   Interoperability . . . . . . . . . . . . . . . . . .  26
     3.4  New Bits in OSPFv3 Option Field  . . . . . . . . . . . . .  26
     3.5  Smart Peering . . . . . . . . . . . . . . . . . . . . . . . 26
     3.5.1  Introduction . . . . . . . . . . . .. . . . . . . . . . . 26
     3.5.2  Previous Related Work  . . . . . . .. . . . . . . . . . . 27
     3.5.3  Proposed Solution  . . . . . . . . .. . . . . . . . . . . 27
   4.   Security Considerations  . . . . . . . . . . . . . . . . . .  30
   5.   IANA Considerations  . . . . . . . . . . . . . . . . . . . .  31
   6.   Contributors . . . . . . . . . . . . . . . . . . . . . . . .  31
   7.   Acknowledgements . . . . . . . . . . . . . . . . . . . . . .  32
        References . . . . . . . . . . . . . . . . . . . . . . . . .  32
            Normative References . . . . . . . . . . . . . . . . . .  32
            Informative References . . . . . . . . . . . . . . . . .  33
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  33
        Intellectual Property and Copyright Statements . . . . . . .  34


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1.  Introduction

   Mobile Ad Hoc Networks have been an area of study for some time,
   within various working groups and areas within the IETF, various
   Military branches, and various government agencies.  Recently,
   networks with mobile ad hoc requirements are being proposed and
   seriously considered for deployment in the near term, which means the
   concepts and research now needs to be applied to deployed networks.
   Towards that end, this draft applies many of the principles and
   concepts learned through prior work to [OSPFv3], along with new
   concepts based on current requirements.

1.1  Problem Statement

   MANETs are synonymous with packet radio networks, which have been
   around since the 1960s in a limited military capacity.  With the boom
   of mobile devices and wireless communications, MANETs are finding
   scope in commercial and military environments.  The aim of these
   networks is to support robust and efficient communication in a mobile
   wireless network by incorporating routing functionality into mobile
   nodes.

   A MANET is an autonomous set of nodes distributed over a wide
   geographical area that communicate over bandwidth-constrained
   wireless links.  Each node may represent a transmitter, receiver, or
   relay station with varying physical capabilities.  Packets may
   traverse through several intermediate (relay) nodes before reaching
   their destination.  These networks typically lack infrastructure:
   nodes are mobile, there is no central hub or controller, and thus
   there is no fixed network topology.  Moreover, MANETs must contend
   with a difficult and variable communication environment.  Packet
   transmissions are plagued by the usual problems of radio
   communication, which include propagation path loss, signal multipath
   and fading, and thermal noise.  These effects vary with terminal
   movement, which also induces Doppler spreading in the frequency of
   the transmitted signal.  Finally, transmissions from neighboring
   terminals, known as multi-access interference, hostile jammers, and
   impulsive interference, e.g., ignition systems, generators, and other
   non-similar in-band communications, may contribute additional
   interference.

   Given this nature of MANETs, the existence of a communication link
   between a pair of nodes is a function of their variable link quality,
   including signal strength and bandwidth.  Thus, routing paths vary
   based on environment, and the resulting network topology.  In such
   networks, the topology may be stable for periods of time, and then
   suddenly become unpredictable.  Since MANETs are typically
   decentralized systems, there are no central controllers or specially

   designated routers to determine the routing paths as the topology
   changes.  All of the routing decisions and forwarding (relaying) of
   packets must be done by the nodes themselves, and communication is on

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   a peer-to-peer basis.

1.2  Motivation for extending OSPF to support MANETs

   The motivation to extend a standard protocol, OSPF (described in
   [OSPF] and [OSPFv3]) to operate on MANET networks is twofold.  The
   primary reason is for interoperability--MANET devices need to be able
   to work when plugged into a wireline network in as many cases as
   possible.  The junction point between a MANET and wire-line network
   should also be as fluid as possible, allowing a MANET network to
   "plug in" to just about any location within a wire-line network, and
   find connectivity, etc., as needed.

   While routes could be redistributed between two routing protocols,
   one designed just for wire-line networks, and the other just for
   MANET networks, this adds complexity and overhead to the MANET/
   wireline interface, increases the odds of an error being introduced
   between the two domains, and decreases flexibility.

   The second motivation is that OSPF is a well understand and widely
   deployed routing protocol.  This provides a strong basis of
   experience and skills from which to work.  A protocol which is known
   to work can be extended, rather than developing a new protocol, which
   must then be completely troubleshoot, tested, and modified over a
   number of years.  Working with a well known protocol allows
   development effort to be placed in a narrowly focused area, rather
   than rebuilding, from scratch, many things which are already known to
   work.

2.  Requirements notation

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

3.  Proposed Enhancements

   This document proposes modifications to [OSPFv3] to support mobile ad
   hoc networks (MANETs).  Note that it is possible to use the mechanism
   defined in Section "Incremental OSPF-MANET Hellos" and the mechanism
   defined in Section "Optimized Flooding (Overlapping Relays)"
   independently of one another.

   The challenges with deploying standard [OSPFv3] in a MANET
   environment fit into two categories.  First, traditional link-state
   routing protocols are designed for a statically configured
   environment.  As a result, most of the configuration is done manually
   when a new router is placed in the network.  Thus, OSPF will not
   function in an environment where routers interconnect and disconnect
   in somewhat random topologies and combinations.  There are
   modifications that must be made in order for routers running the same
   protocol to communicate in a heterogeneous and dynamic environment.
   Second, a MANET network must transmit more state information to

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   maintain reachability.  Therefore, OSPF will need scalability
   enhancements to support MANETs.

   Currently there is no defined interface type that describes a
   wireless network.  Wireless links have characteristics of both multi-
   access and point-to-multipoint links.  Treating wireless links as
   multi-access does not take into account that not all nodes on the
   same Layer 2 link have bi-directional connectivity.  However, any
   transmission on a link will reach nodes that are within transmission
   range.  In this way, the link is multi-access due to the fact that
   two simultaneous transmissions may collide.  A new interface type
   needs to be defined in order to accurately describe this behavior.

   The second category of challenges fall into is scalability.  While
   some flooding optimizations are present in OSPF, such as designated
   router (DR) election, many of these were built under the assumption
   of a true multi-access network.  Wireless networks are not true
   multi-access because it cannot be assumed that there is two-way
   connectivity between everyone on the same Layer 2 link.  Therefore,
   optimizations such as DR election will not perform correctly in MANET
   networks.  Without any further optimizations in link-state flooding,
   current OSPF would not be able to operate in a highly dynamic
   environment in which links are constantly being formed and broken.
   The amount of information that would need to be flooded would
   overload the network.

   Another scalability issue is the periodic transmission of Hello
   messages.  Currently, even if there are no changes in a router's
   neighbor list, the Hello messages still list all the neighbors on a
   particular link.  For a MANET router, where saving bandwidth and
   transmission power is a critical issue, the transmission of
   potentially large Hello messages is particularly wasteful.

   Finally, current routing protocols will form a neighbor relationship
   with any router on a Layer 2 link that is correctly configured.  For
   MANET routers in a wireless network, this may lead to an excessive
   number of parallel links between two routers if communication is
   achieved via multiple interfaces.  In a statically configured
   network, this is not a problem, since the physical topology can be
   built to prevent excessive redundancy.  However, in a dynamic
   network, there must exist additional mechanisms to prevent too many
   redundant links.  (Note that links between two nodes on different
   radio types, different antenna, different channels, etc., are
   considered different links and not redundant links.)  In scalability
   tests, it has been demonstrated that the presence of too many
   redundant links will increase both the size of routing updates and
   cause extra flooding resulting in even relatively small networks not
   converging.

3.1  OSPF-MANET Interface

   Interfaces are defined as the connection between a router and one of
   its attached networks [OSPF].  Four types of interfaces have been

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   defined and supported in [OSPF] and [OSPFv3]: broadcast, NBMA, point-
   to-point, and point-to-multipoint.

   Point-to-multipoint model has been chosen to represent MANET
   interfaces.  (The features designed in this document MAY be included
   on other interface types as appropriate.)  The MANET interface allows
   the following:

   o  OSPF treats all router-to-router connections over the MANET
      interface as if they were point-to-point links.
   o  Link metric can be set on a per neighbor basis.
   o  Broadcast and multicast can be accomplished through Layer-2
      broadcast or Layer-2 pseudo-broadcast.
      *  The MANET interface supports Layer-2 broadcast if it is able to
         address a single physical message to all of the attached
         neighbors.  One such example is 802.11.
      *  The MANET interface supports Layer-2 pseudo-broadcast if it is
         able to pick up a packet from the broadcast queue, replicate
         the packet, and send a copy over each point-to-point link.  One
         such example is Frame Relay.
   o  An API must be provided for Layer-3 to determine the layer-2
      broadcast capability.  Based on the return of the API, OSPF
      classifies the MANET interfaces into the following three types:
      MANET broadcast, MANET pseudo-broadcast, and MANET non- broadcast.
   o  Multicast SHOULD be used for OSPF packets.  When the MANET
      interface supports Layer-2 broadcast or pseudo-broadcast, the
      multicast process is transparent to OSPF.  Otherwise, OSPF MUST
      replicate multicast packets by itself.

3.1.1  Interface Operation

   A MANET node has at least one MANET interface.  MANET nodes can
   communicate with each other through MANET interfaces.  MANET nodes
   can communicate with non-MANET routers only through normal
   interfaces, such as Ethernet, ATM and etc.

   For scalability reasons, it is not required to configure IPv6 global
   unicast addresses on MANET interfaces.  Instead, a management
   loopback interface, with an IPv6 global unicast address, MAY be
   configured on each MANET node.

   The LSAs associated with a MANET interface SHOULD have the DC-bit set
   in the OSPFv3 Options Field and the DoNotAge bit set in the LS Age
   field as described in [OSPFv3].

3.1.2  LSA Formats and Examples

   LSA formats are specified in [OSPFv3].



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   In order to display example LSAs, a network map is included below.
   Router names are prefixed with the letters RT, network names with the
   letter N, and router interface names with the letter I.
   o  Four MANET nodes, RT1, RT2, RT3, and RT4, reside in area 2.
   o  RT1 has one MANET interface I11.  Through the interface, RT1 is
      full adjacent to RT2, RT3, and RT4.
   o  RT2 has two MANET interfaces, I21 and I22, and one Ethernet
      interface I23.  RT2 is full adjacent to RT1 and RT4 through the
      interface I21, and full adjacent to RT4 through the interface I22.
      Stub network N1 is attached with RT2 through the interface I23.
   o  RT3 has one MANET interface I31, and is full adjacent to RT1
      through the interface.
   o  RT4 has two MANET interfaces, I41 and I42.  It is full adjacent to
      RT2 through the interface I41, and full adjacent to RT1 and RT2
      through the interface I42.
   o  Moreover, each MANET node is configured with a management loop-
      back interface.

      +---+I11        I21+---+I23   |
      |RT1|-+----------+-|RT2|------|N1
      +---+ |          | +---+      |
      |                |   VI22
      |                |   +
      |                |   |
      |                |   |
      |                |   |
      |                |   |
      |                |   +
      |                |   ^I41
      +---+ |          +---+
      |RT3|-+        +-|RT4|
      +---+I31      I42+---+

   The assignment of IPv6 global unicast prefixes to network links is
   shown below.  (Note: No IPv6 global unicast addresses are configured
   on the MANET interfaces)


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      Node     Interface     IPv6 global unicast prefix
      -----------------------------------------------------------
      RT1      LOOPBACK      5f00:0001::/64
               I11           n/a
      RT2      LOOPBACK      5f00:0002::/64
               I21           n/a
               I22           n/a
               I23           5f00:0012::/60
      RT3      LOOPBACK      5f00:0003::/64
               I31           n/a
      RT4      LOOPBACK      5f00:0004::/64
               I41           n/a
               I42           n/a

   The OSPF interface IDs and the link local addresses for the router
   interfaces in the network illustrated above below.  EUIxy represents
   the 64-bit interface identifier of the interface Ixy, in Modified
   EUI-64 format [IPV6ADD].

      Node    Interface    Interface ID    Link Local address
      -----------------------------------------------------------
      RT1     LOOPBACK     1               n/a
              I11          2               fe80:0002::EUI11
      RT2     LOOPBACK     1               n/a
              I21          2               fe80:0002::EUI21
              I22          3               fe80:0003::EUI22
              I23          4               fe80:0004::EUI23
      RT3     LOOPBACK     1               n/a
              I31          2               fe80:0002::EUI31
      RT4     LOOPBACK     1               n/a
              I41          2               fe80:0002::EUI41
              I42          3               fe80:0003::EUI42


3.1.2.1  Router LSAs

   As an example, consider the router LSAs that node RT2 would
   originate.  Two MANET interfaces, consisting of 3 point-to-point
   links, are presented.


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      RT2's router-LSA

      LS age = DoNotAge+0              ;newly originated
      LS type = 0x2001                 ;router-LSA
      Link State ID = 0                ;first fragment
      Advertising Router = 192.0.2.2   ;RT2's Router ID
      bit E = 0                        ;not an AS boundary router
      bit B = 0                        ;not an area border router
      Options = (V6-bit|E-bit|R-bit)
       Type = 1                        ;p2p link to RT1 over I21
       Metric = 10                     ;cost to RT1
       Interface ID = 2                ;Interface ID of I21
       Neighbor Interface ID = 2       ;Interface ID of I11
       Neighbor Router ID = 192.0.2.1  ;RT1's Router ID
       Type = 1                        ;p2p link to RT4 over I21
       Metric = 25                     ;cost to RT4
       Interface ID = 2                ;Interface ID of I21
       Neighbor Interface ID = 3       ;Interface ID of I42
       Neighbor Router ID = 192.0.2.4  ;RT4's Router ID
       Type = 1                        ;p2p link to RT4 over I22
       Metric = 15                     ;cost to RT4
       Interface ID = 3                ;Interface ID of I22
       Neighbor Interface ID = 2       ;Interface ID of I41
       Neighbor Router ID = 192.0.2.4  ;RT4's Router ID


3.1.2.2  Link LSAs

   A MANET node originates a separate Link-LSA for each attached
   interface.  As an example, consider the Link-LSA that RT3 will build
   for its MANET interface I31.

      RT3's Link-LSA for MANET interface I31

      LS age = DoNotAge+0              ;newly originated
      LS type = 0x0008                 ;Link-LSA
      Link State ID = 2                ;Interface ID of I31
      Advertising Router = 192.0.2.3   ;RT3's Router ID
      Rtr Pri = 1                      ;default priority
      Options = (V6-bit|E-bit|R-bit)
      Link-local Interface Address = fe80:0002::EUI31
      # prefixes = 0                   ;no global unicast address


3.1.2.3  Intra Area Prefix LSAs

   A MANET node originates an intra area prefix LSA to advertise its own
   prefixes, and those of its attached stub links.  As an example,



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   consider the intra area prefix LSA that RT2 will build.

      RT2's intra area prefix LSA for its own prefixes

      LS age = DoNotAge+0              ;newly originated
      LS type = 0x2009                 ;intra area prefix LSA
      Link State ID = 177              ;or something else
      Advertising Router = 192.0.2.2   ;RT2's Router ID
      # prefixes = 2
      Referenced LS type = 0x2001      ;router LSA reference
      Referenced Link State ID = 0     ;always 0 for router-LSA
                                       ;reference
      Referenced Advertising Router = 192.0.2.2
                                       ;RT2's Router ID
       PrefixLength = 64               ;prefix on RT2's LOOPBACK
       PrefixOptions = 0
       Metric = 0                      ;cost of RT2's LOOPBACK
       Address Prefix = 5f00:0002::
       PrefixLength = 60               ;prefix on I23
       PrefixOptions = 0
       Metric = 10                     ;cost of I23
       Address Prefix = 5f00:0012::    ;pad to 64-bit

   Note: MANET nodes may originate Intra-Area-Prefix-LSAs for attached
   transit (broadcast/NBMA) networks.  This is normal behavior defined
   in [OSPFv3], which is irrelevant to MANET interfaces.  Please consult
   [OSPFv3] for details.

3.2  Incremental OSPF-MANET Hellos

   In MANETs, reducing the size of periodically transmitted packets can
   be very important in decreasing the total amount of overhead associ-
   ated with routing.  Towards this end, removing the list of neighbors
   from Hello packets unless that information changes can reduce routing
   protocol overhead.  While the reduction for each hello packet is
   small, over time it will be significant.

   A new option bit is defined in this document to facilitate the
   operation of incremental Hello packets.  A new SCS-TLV and Neighbor
   Drop TLV are also defined, transmitted using LLS [LLS].

3.2.1  The I Option Bit

   A new I bit is defined in the OSPFv3 option field.  The bit is
   defined for Hello packets and indicates that only incremental
   information is present.  See Section "New Bits in OSPFv3 Options
   Field" for placement of the I bit within the OSPFv3 options field.



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3.2.2  State Check Sequence TLV

   A new TLV is defined that indicates the current state, which is
   represented by an State Check Sequence (SCS) number of the
   transmitting router.

    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               |           Length                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+--+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         SCS Number            |R|FS|N |   Reserved              |
   +-----------------------------------------------------------------+

   o  Type: Type,  set to 2.
   o  Length: Set to 4.
   o  SCS Number: A circular two octet unsigned integer indicating the
      current state of the transmitting device.  Note that when the
      incremental Hello mechanism is invoked (or re-started), an initial
      SCS value of '1' SHOULD be used for the first incremental Hello
      packet.  This sequence number is referred to as InitialSCS.  Note
      that InitialSCS also implies a full state.
   o  R: Request bit.  If set, this is a request for current state.  The
      list of routers who should respond to this request are listed in
      the 'Request From' TLV defined below.  If the 'Request From' TLV
      is not present, it is assumed that the request is meant for all
      nodes.
   o  FS: Full State bit.  If set, the Hello packet contains full state
      as far as the neighbor(s) in the 'Full State For' TLV (defined
      below) are concerned.  If the 'Full State For' TLV is not present,
      the Hello packet contains full state for all neighbors.
   o  N: InComplete bit.  If NOT set, the complete state associated with
      the SCS number is included in the Hello packet.  If set, indicates
      that the appended TLVs are being sent 'persistently', and that
      there is more state associated with the SCS number that was sent
      originally, but is not included in this Hello packet.  This bit
      allows any desired TLVs to be sent 'persistently' for a number of
      Hellos with the same SCS number without requiring all of the TLVs
      associated with that SCS number to be transmitted.  The first time
      an SCS number is sent, the entire state associated with that SCS
      number is transmitted, and the 'N' bit MUST NOT be set.
   o  Reserved: Set to 0.  Reserved for future use.

   A Hello with the State Check Sequence TLV appended with the R bit set
   will be referred to as a Hello request.


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3.2.3  Neighbor Drop TLV

   A new TLV is defined in this document which indicates neighbor(s)
   that have been removed from the list of known neighbors.

    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               |           Length              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Dropped Neighbor(s)                                           |
   +---------------------------------------------------------------+
   | ....
   +--------------------

   o  Type: Type, set to 3.
   o  Length: Set to the number of dropped neighbors included in the TLV
      multiplied by 4.
   o  Dropped Neighbor(s) - Router ID of the neighbor being dropped.

3.2.4  'Request From' TLV (RF-TLV)

   A new TLV is defined in this document which indicates neighbor(s)
   from which the latest Hello state is being requested.


    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               |           Length              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Request From Neighbor(s)                    |
   +---------------------------------------------------------------+
   | ....
   +--------------------

   o  Type: set to 4
   o  Length: Set to the number of neighbors included in the TLV
      multiplied by 4.
   o  Request From Neighbor(s) - Router ID of the neighbor(s) from which
   o  Hello state is being requested.

3.2.5  Full State For TLV (FSF-TLV)

   A new TLV is defined in this document which indicates neighbor(s) to
   which the transmitting node is responding with full state.


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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               |           Length              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Full State For Neighbor(s)                  |
   +---------------------------------------------------------------+
   | ....
   +--------------------

   o  Type: set to 5
   o  Length: Set to the number of neighbors included in the TLV
      multiplied by 4.
   o  Full State For Neighbor(s) - Router ID of the neighbor(s) should
      process this packet.

3.2.6  Neighbor Adjacencies

   This section describes building neighbor adjacencies and the failure
   of such adjacencies using the incremental Hello signaling.

3.2.6.1  Building Neighbor Adjacencies

   Hello packets are sent periodically in accordance with [OSPF] and
   [OSPFv3].  An OSPF implementation which supports sending only partial
   neighbor information in Hello packets SHOULD always set the I bit in
   its transmitted Hello packets, except as described elsewhere in this
   document.  Hello packets MAY be suppressed from being transmitted
   every HelloInterval if other packet transmissions are sent by the
   router during that time.

   On receiving a Hello packet from a new neighbor (in this context, a
   new neighbor is a neighbor in less than Init state as defined in
   Section 10.1 [OSPF]), if the Hello has the I bit set, a router will:
   o  Place the new neighbor in the neighbor list described in [OSPFv3],
      A.3.2.
   o  Increment the router's SCS number that it will use in its next
      Hello (indicated in the State Check Sequence TLV).
   o  When the neighbor has reached the EXCHANGE state, described in
      [OSPF], 10.1, it is removed from the list of neighbors described
      in [OSPFv3], A.3.2.
   o  If the neighbor is not a DR or backup designated router (BDR) on
      an OSPF broadcast link, and the neighbor is advertised as
      connected in the Network LSA advertised by the DR, it is removed
      from the list of neighbors described in [OSPFv3], A.3.2.


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3.2.6.2  Adjacency Failure

   On discovering an adjacency failure (going to state less than
   EXCHANGE), a router using I bit signaling SHOULD:
   o  Remove the adjacent router from local tables, and take the
      appropriate actions for a failed adjacency described in [OSPF] and
      [OSPFv3].
   o  Add the formerly adjacent router to a Neighbor Drop TLV.
   o  Increment the router's SCS number that it will transmit in its
      next Hello.
   o  Transmit Hellos with this Neighbor Drop TLV  - It may be desirable
      to send the Neighbor Drop TLV in three consecutive Hellos to
      increase the probability of reception.  In this case, 'persistent'
      Hello packets would be sent with the same SCS number, the Neighbor
      Drop TLV, and the 'N' bit set.  Thus, the receiver knows that the
      Neighbor Drop TLV is being sent persistently and there is more
      state associated with the SCS in case it must request missing
      state presumably transmitted in a previous Hello.

3.2.7  Sending Hellos

   When a device is first attached to a network (whether through being
   brought into range of another device, powering the device on, or
   enabling the device's radio interface, etc.), it will need to obtain
   complete neighbor state from each of its neighbors before it can
   utilize the incremental Hello mechanism.  Thus, upon initialization,
   a device MAY send a multicast Hello request (and omit the 'Request
   From' TLV).  Neighbors will receive the request and respond with a
   Hello with their complete neighbor state.

   If a device is in INIT state with a neighbor and receives a Hello
   from the neighbor without its router ID listed in the neighbor list,
   the device SHOULD request the current state from the neighbor.  Note
   that this is to avoid a race condition since the received Hello can
   either mean that the device is NOT SEEN by the neighbor, or that the
   device is adjacent and not listed in the incremental list.  Thus, by
   receiving a Hello request, the neighbor will respond with its
   neighbor state for the neighbor.

   The first Hello packet with a particular SCS number MUST contain the
   full state associated with that SCS number, i.e., all state changes
   since the last SCS number.  The 'N' bit MUST NOT be set in the State
   Check Sequence TLV.

   Incremental Hello packets can be sent persistently (sent in k
   successive Hello packets), with flexibility in the actual amount of
   information being sent.  The three options include:


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   o  The entire incremental Hello packet is sent persistently.  This is
      accomplished by simply sending the entire state associated with a
      SCS number for k successive Hellos.  Since the SCS number remains
      the same, the 'N' bit is not set in these incremental Hello
      packets.
   o  Partial information for a particular SCS number is sent
      persistently.  After the first Hello packet with a particular SCS
      number is sent, only the TLVs that are desired to be sent
      persistently are sent in subsequent Hellos with the same SCS
      number and the 'N' bit set.
   o  No information is sent persistently.  This is simply the default
      behavior where an incremental Hello packet with a particular SCS
      number is only sent once.

3.2.8  Receiving Hellos

   Each OSPF device supporting incremental Hello signaling, as described
   in this document, MUST keep the last known SCS number from each
   neighbor it has received Hellos from as long as the neighbor
   adjacency structure is maintained.

   If a device receives a Hello from an adjacent neighbor with an SCS
   number less than the last known SCS number from that neighbor, it
   MUST first check if the SCS number is a wrap around.  If it is NOT a
   wrap around, then the device MUST send a Hello request to the
   neighbor.

   If it is a wrap around or if a device receives a Hello from an
   adjacent neighbor with an SCS number one greater than the last known
   SCS number from that neighbor, it MUST:
   o  Examine the neighbor list described in [OSPFv3], A.3.2.  If any
      neighbors are contained in this list, increment the SCS number
      contained in the adjacent neighbor's data structure.
   o  Examine the Neighbor-Drop TLV as described in the section
      Adjacency Failure.  If this list contains a neighbor other than
      the local router, increment the SCS number contained in the
      adjacent neighbor's data structure.
   o  Examine the Neighbor Drop TLV as described in the section
      Adjacency Failure.  If the local router identifier is contained in
      this list, destroy the transmitting adjacent neighbor's data
      structures.
   o  Examine any other TLVs incrementally signaled, as described in
      drafts referring to this document.  If there are other state
      changes indicated, increment the SCS number contained in the
      adjacent neighbor's data structure.
   o  If no state change information is contained in the received Hello,
      a request for current state (by setting the 'R' bit) is sent in
      the next Hello.


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   If a device receives a Hello from an adjacent neighbor with an SCS
   number greater than the last known SCS number + 1 from that neighbor,
   it MUST send a Hello request to the neighbor since it may be missing
   some neighbor state.

3.2.8.1  Receiving Hellos with the N Bit Set

   If a device receives a Hello with the State Check Sequence TLV
   included, and the 'N' bit set in this TLV, it MUST verify that it has
   already received the SCS number with the 'N' bit NOT set from the
   neighbor.  If the device determines that this is the first reception
   of the SCS number from this neighbor, then it MUST send a Hello
   request to the neighbor since it missed the initial Hello packet with
   the SCS number, and thus is missing state.

3.2.8.2  Receiving Hellos with the R Bit Set

   If a device receives a Hello with the State Check Sequence TLV
   included, and the R bit set, it looks for the 'Request From' TLV.  If
   it's router ID is listed in the 'Request From' TLV or the TLV is not
   found, it includes its full state in the next Hello.  This MUST
   include:
   o  The neighbor ID of the requesting neighbor(s) in the list of
      neighbors described in [OSPFv3], A.3.2.,
   o  An State Check Sequence TLV with the transmitter's current SCS
      number, and the FS bit set.  Note that the transmitter's SCS
      number is NOT incremented.
   o  Any other TLVs, defined in other drafts referencing this document,
      indicating the current state of the local system.
   o  The neighbor ID of all the neighbors who have requested current
      state, in the 'Full State For' TLV.

   If the full state is being sent to a large number of existing
   neighbors, and implementation could choose to instead generate a full
   state for all neighbors and omit the 'Full State For' TLV.

3.2.8.3  Receiving Hellos with the FS Bit Set

   When a device receives a Hello with the State Check Sequence TLV
   included, and the FS bit set, the Hello packet contains the
   neighbor's full state for the device.  The packet SHOULD be processed
   as follows:
   o  If the received SCS number is equal to the last known SCS number,
      the packet SHOULD be ignored since the device already has the
      latest state information.
   o  If the received SCS number is different than the last known SCS
      number, this Hello has new information and MUST be parsed.


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   o  If it is listed in the 'Full State For' TLV or if the 'Full State
      For' TLV is not present, the device MUST save the SCS number,
      process the Hello as described in the Receiving Hellos section,
      and process any other appended TLVs.

3.2.9  Interoperability

   On receiving a Hello packet from a new neighbor without the I bit
   set, the local router will continue to place that router's identifier
   in transmitted Hellos on this link as described in [OSPFv3], A.3.2.

3.2.10  Support for OSPF Graceful Restart

   OSPF graceful restart, as described in [OSPFREST] and [OSPFGR],
   relies on the lack of neighbors in the list of neighbors described in
   [OSPFv3], A.3.2, to determine that an adjacent router has restarted,
   and other signaling to determine the adjacency should not be torn
   down.  If all Hello packets transmitted by a given router have an
   empty Hello list, reliance on an empty Hello packet to signal a
   restart (or to reliably tear down an OSPF adjacency) is no longer
   possible.  Hence, this signaling must be slightly altered.

   When a router would like to tear down all adjacencies, or signal it
   has restarted:
   o  On initially restarting, during the first RouterDeadInterval after
      restart, the router will transmit Hello packets with an empty
      neighbor list, and the I bit cleared.  Any normal restart or other
      signaling may be included in these initial Hello packets.
   o  As adjacencies are learned, these newly learned adjacent routers
      are included in the multicast Hellos transmitted on the link.
   o  After one RouterDeadInterval has passed, the incremental Hello
      mechanism is invoked.  An incremental Hello packet with full state
      is sent with the 'I' bit set, and the SCS TLV included with the
      'A' bit set and the InitialSCS value, e.g., SCS of '1'.
      Subsequent Hello packets will include only incremental state.

   Routers which are neighboring with a restarting router MUST continue
   sending their Hello packets with the I bit set.

3.3  Optimized Flooding (Overlapping Relays)

   A component that may influence the scalability and convergence
   characteristics of OSPF [OSPF],[OSPFv3] in a MANET environment is how
   much information needs to be flooded.  The ideal solution is that a
   router will only receive a particular routing update only once.
   However, there must be a tradeoff between protocol complexity and
   ensuring that every speaker in the network receives all of the
   information.  Note that a speaker refers to any node in the network


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   that is running the routing protocol and transmitting routing updates
   and Hello messages.

   Controlling the amount of information on the link has increased
   importance in a MANET environment due to the potential transmission
   costs and resource availability in general.

   In some environments, a group of speakers that share the same logical
   segment may not be directly visible to each other; some of the
   possible causes are the following: low signal strength, long distance
   separation, environmental disruptions, partial VC meshing, etc.  In
   these networks, a logical segment refers to the local flooding domain
   dynamically determined by transmission radius.  In these situations,
   some speakers (the ones not able to directly reach the sender) may
   never be able to synchronize their databases.  To solve the
   synchronization issues encountered in these environments, a mechanism
   is needed through which all the nodes on the same logical segment can
   receive the routing information, regardless of the state of their
   adjacency to the source.

3.3.1  Operation Overview

   The optimized flooding operation relies on the ability of a speaker
   to advertise all of its locally connected neighbors.  In OSPF, this
   ability is realized through the use of link state advertisements
   (LSA)s [OSPF],[OSPFv3].

   A speaker receives router LSAs from its adjacent neighbors.  A
   speaker's router LSA conveys the list of the adjacent speakers of the
   originator ("neighbor list").  The local speaker can compare the
   neighbor list reported by each speaker to its own neighbor list.  If
   the local neighbor list contains adjacent speakers that the
   originator cannot reach directly (i.e. those speakers that are not in
   the originator's neighbor list), then these speakers are locally
   known as non-overlapping neighbors for the originator.

   The local speaker should relay any routing information to non-
   overlapping neighbors of the sender based on the algorithm outlined
   in the Flooding and Relay Decisions section.  Because more than one
   such speaker may exist, the mechanism is called "overlapping relays."
   The algorithm, however, does select the set of overlapping relays
   that should transmit first.  This set is known as the active set of
   overlapping relays for a speaker.

3.3.2  Determination of Overlapping Relays

   The first step in the process is for each speaker to build and
   propagate their neighbor lists in router LSAs packets.  Every speaker


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   is then in a position to determine their two-hop neighborhood, i.e.,
   those nodes that are neighbors of the speaker's one-hop neighbors.  A
   neighbor is considered an overlapping relay for a speaker if it can
   reach a node in the two-hop neighborhood of the neighbor, i.e., if it
   has one-hop neighbors.

   The set of active overlapping relays for a speaker is the minimum set
   of direct neighbors such that every node in the two-hop neighborhood
   of the speaker is a neighbor of a least one overlapping relay in the
   active set.  Each speaker SHOULD select a set of active overlapping
   relays based on a selection algorithm (one such algorithm is
   suggested in the "Overlapping Relay Discovery Process" Section and is
   based on the MPR selection algorithm described in [OLSR]).  Note that
   a speaker MUST NOT choose a neighbor to serve as an active
   overlapping relay if that neighbor set the 'N' bit in its Active
   Overlapping Relay TLV as defined in Section "Active Overlapping Relay
   Extension", unless the neighbor is the only neighbor to reach a two-
   hop neighbor.  Election of active overlapping relays is done across
   interfaces, and thus, it is node-based and not link-based.

3.3.3  Terminology

   The following heuristic and terminology for active overlapping relay
   selection is largely taken from [OLSR]:
   o  FULL: Neighbor state FULL as defined in [OSPF] & [OSPFv3].  Note
      that all neighbor references in this document are assumed to be
      FULL neighbors.
   o  2-hop FULL neighbors: The list of 2-hop neighbors of the node that
      are FULL and that can be reached from direct neighbors, excluding
      any directly connected neighbors.
   o  Active Set: A (sub)set of the neighbors selected such that through
      these selected nodes, all 2-hop FULL neighbors are reachable.
   o  N: N is the set of FULL neighbors of the node.
   o  N2: A subset of 2-hop FULL neighbors excluding the nodes only
      reachable by members of N.
   o  D(y): The degree of a one hop neighbor node y (where y is a member
      of N), is defined as the number of FULL neighbors of node y,
      EXCLUDING all the members of N and EXCLUDING the node performing
      the computation.

3.3.4  Overlapping Relay Discovery Process

   A possible algorithm for discovering overlapping relays is the
   following:
   1.  Start with an active set made of all members of N that have set
       the 'A' bit in their Active Overlapping Relays TLV as defined in
       Section "Active Overlapping Relays Extension".


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   2.  Calculate D(y), where y is a member of N, for all nodes in N.
   3.  Add to the active set those nodes in N, which are the *only*
       nodes to provide reachability to a node in N2, i.e., if node-b in
       N2 can be reached only through a symmetric link to node-a in N,
       then add node-a to the active set.  Remove the nodes from N2
       which are now covered by a node in the active set.
   4.  While there exist nodes in N2 which are not covered by at least
       one node in the active set:
       1.  For each node in N, calculate the reachability, i.e., the
           number of nodes in N2 which are not yet covered by at least
           one node in the active set, and which are reachable through
           this one hop neighbor;
       2.  Select as an active overlapping relay the node with highest
           Willingness among the nodes in N with non-zero reachability.
           In case of multiple choice select the node which provides
           reachability to the maximum number of nodes in N2.  In case
           of multiple nodes providing the same amount of reachability,
           select the node as active whose D(y) is greater.  As a final
           tie breaker, the node with the highest router ID should be
           chosen.  Remove the nodes from N2 which are now covered by a
           node in the active set.
   5.  As an optimization, process each node, y, in the active set in
       increasing order of Willingness.  If all nodes in N2 are still
       covered by at least one node in the active set excluding node y,
       and if Willingness of node y is smaller than MAX_WILLINGNESS,
       then node y should be removed from the active set.

   Note that the active overlapping relays selection algorithm is
   implementation specific, and the above is simply a suggested
   algorithm.  However, the behavior of the overlapping relays MUST
   follow that specified in the "Flooding and Relay Decisions" Section.
   Moreover, the same selection algorithm MUST be used by all nodes
   within an area.

3.3.5  The F Option Bit

   A single new option bit, the F bit, is defined in the OSPFv3 option
   field.  The F bit indicates that the node supports the Optimized
   Flooding mechanism as specified in this draft.  See Section "New Bits
   in OSPFv3 Options Field" for placement of the F bit.

3.3.6  Active Overlapping Relay Extension

   A new TLV is defined so that each speaker can convey its set of
   active overlapping relays in the Hello messages.  The TLV is
   transmitted using the Link Local Signaling method described in "Link
   Local Signaling" Section.


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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                  |        Length                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Relays Added |A|N|           Reserved                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Router ID(s) of Active Overlapping Relay(s)                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: Type, set to 4.
   o  Length - variable; Length of TLV in bytes NOT including Type and
      Length.
   o  Relays Added - variable; Number of active overlapping relays that
      are being added.  Note that the number of active overlapping
      relays that are being dropped is then given by: [(Length - 4)/4 -
      Relays Added].
   o  A bit - If this bit is set, the node is specifying that it will
      always flood routing updates that it receives, regardless of
      whether it is selected as an Active Overlapping Relay.
   o  N bit - If this bit is set, the node is specifying that it most
      likely will not flood routing updates.  The node SHOULD NOT be
      chosen to be an active overlapping relay unless it is the *only*
      neighbor that can reach two-hop neighbor(s).  Note that if the
      node is selected as an Active Overlapping relay and the node can
      not perform the required duties, network behavior is not
      compromised since it results in the same behavior as if the node
      was not chosen as an active overlapping relay.
   o  Reserved - Reserved for future use and MUST be ignored upon
      reception.
   o  Router ID(s) of Active Overlapping Relay(s) - The router ID(s) of
      neighbor(s) that are either chosen to serve as an active
      overlapping relay, or removed from serving as an active
      overlapping relay.  The active overlapping relays that are being
      added MUST be listed first, and the number of such relays MUST
      equal Add Length.  The remaining list of relays are being dropped
      as active overlapping relays, and the number of such relays MUST
      equal [(Length - 4)/4 - Relays Added].

   Note that the 'A' bit and 'N' bit are independent of any particular
   selection algorithm to determine the set of Active Overlapping
   Relays.  However, the bits SHOULD be considered as input into the
   selection algorithm.

   If a node is selected as an active overlapping relay and it does not
   support the Incremental Hello mechanism defined in the "Incremental


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   OSPF-MANET Hellos" Section, then it SHOULD always be included as an
   Active Overlapping Relay in the TLV.  Note that while a node needs to
   know whether it is an active overlapping relay, it does not
   necessarily have to know the identities of the other active
   overlapping relays.

3.3.7  Willingness TLV

   A new TLV is defined so that each speaker can convey its willingness
   to serve as an active overlapping relay in the Hello meassage.  The
   TLV is transmitted using the Link Local Signaling method described in
   the "Link Local Signaling" Section.

       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                  |        Length                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Willingness |                       Reserved                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: Type, set to 5.
   o  Length - 4 bytes.  It does not include the Type and Length fields.
   o  Willingness - 1 byte to indicate the willingness of the node to
      serve as an active overlapping relay for its neighbors.
      *  0: MIN_WILLINGNESS
      *  128: DEFAULT_WILLINGNESS
      *  255: MAX_WILLINGNESS

   The TLV is optional and MUST be silently ignored if not understood.
   If the Willingness TLV is not included in the Hello packet, the
   Willingness value SHOULD be taken as DEFAULT_WILLINGNESS.

3.3.8  Flooding and Relay Decisions

   The decision whether to relay any received LSAs and when to relay
   such information, is made depending on the topology and whether the
   node is part of the set of active overlapping relays.

   Upon receiving an LSA from an adjacent speaker, a node makes flooding
   decisions based on the following algorithm:
   1.  If the node is an active overlapping relay for the adjacent
       speaker, then the router SHOULD immediately relay any information
       received from the adjacent speaker.
   2.  If the node is a non-active overlapping relay for the adjacent
       speaker, then the router SHOULD wait a specified amount of time
       (PushbackInterval plus jitter, see "Important Timers" Section) to
       decide whether to transmit.  [Jitter is used to try to avoid


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       several non-active overlapping relays from propagating redundant
       information.]  Note that a node with the 'N' bit set in the
       'Active Overlapping Relays' Extension will not be chosen as an
       active overlapping relay unless it is the only node to provide
       reachability to a two-hop neighbor.  However, it MUST perform the
       duties of a non-active overlapping relay as required.  Non-active
       overlapping relays MUST follow the acknowledgment mechanism
       outlined in the section 'Intelligent Transmission of Link State
       Acknowledgements.'
       1.  During this time, if the node determines that flooding the
           LSA will only result in a redundant transmission, the node
           MUST suppress its transmission.  Otherwise, it MUST transmit
           upon expiration of PushbackInterval plus jitter.
       2.  If a non-active overlapping relay hears a re-flood from
           another node that covers its non-overlapping neighbors before
           its timer to transmit expires, it SHOULD reset its
           PushbackInterval plus jitter timer.  (Note that the
           implementation should take care to avoid resetting the
           PushbackInterval timer based on transmissions from active
           overlapping relays.)  During this time, if the node
           determines that flooding the update will only result in a
           redundant transmission, the node MUST suppress its
           transmission.  Otherwise, it MUST transmit upon expiration of
           PushbackInterval + jitter.
       3.  If a non-active overlapping relay hears an old instance of
           the LSA during this time, it SHOULD ignore the LSA and it
           SHOULD NOT send a unicast packet to the neighbor with the
           most recent LSA as specified in [OSPFv3].
   3.  For LSAs that are received unicast because of retransmission by
       the originator, the node MUST determine whether it has already
       received the LSA from another speaker.  If it already has the
       current instance of the LSA in its database, it MUST do nothing
       further in terms of flooding the LSA (since it would have taken
       appropriate behavior when it initially received the LSA.)
       However, if it does not have the current instance of the LSA in
       its database, it MUST take action according to the rules above,
       just as if it received the multicast LSA.  The acknowledgement
       mechanism outlined in the section 'Intelligent Transmission of
       Link State Acknowledgements' MUST be followed, and any timeout
       mechanism for unicast LSAs MAY be followed.

   Note that a node can determine whether further flooding a LSA will
   only result in a redundant transmission by already having heard link
   state acknowledgements (ACKs) or floods for the LSA from all of its
   neighbors.

   Due to the dynamic nature of a network, the set of active overlapping
   relays may not be up to date at the time the relay decision is made


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   or may not be able to perform the flooding duties, e.g., due to poor
   link quality.  The non-active overlapping relays prevent this
   situation from causing database synchronization issues and thus,
   packet loss.

   Since the originator of the information, the relay, and the receiver
   are all in the same dynamically determined local flooding domain, the
   relay MUST NOT change the routing update information.  In general,
   LSAs SHOULD be sent to a well-known multicast address.  In some
   cases, routing updates MAY be sent using unicast packets.

3.3.9  Intelligent Transmission of Link State Acknowledgements

   In order to optimize the bandwidth utilization on the link, a speaker
   MUST follow these recommendations related to ACK transmissions:
   1.  All ACKs MUST be sent via multicast.
   2.  Typically, LSAs are acknowledged by all of the adjacent speakers.
       In the case of relayed information, the relay MUST only expect
       either explicit or implicit acknowledgements from neighbors that
       have not previously acknowledged this LSA.
   3.  Because routing updates are sent via multicast, the set of
       overlapping speakers will usually receive the same update more
       than once.  A speaker SHOULD only acknowledge the first update
       received on the link.
   4.  An active overlapping relay SHOULD NOT explicitly acknowledge
       information that it is relaying.  The relayed information will
       serve as an acknowledgement to the sender.  If no information is
       being relayed, than an explicit ACK MUST be sent.
   5.  Several ACKs MAY be bundled into a single packet.  The wait
       (AckInterval) before sending one such packet reduces the number
       of packet transmissions required in acknowledging multiple LSAs.
   6.  All ACK packets SHOULD reset the RouterDeadInterval at the
       receiver.  If there is no state waiting to be transmitted in a
       Hello packet at the sender, then the HelloInterval at the sender
       SHOULD be reset.  Note that an ACK serves as a Hello packet with
       no state change.
   7.  Any LSA received via unicast MUST be acknowledged.  (Note that
       acknowledgment is via multicast as specified in rule (1) above.)

   An ACK received from a non-overlapping neighbor should prevent
   redundant transmission of the information to it by another
   overlapping relay.

3.3.10  Important Timers

   This section details the timers that are introduced in the Flooding
   and Relay Decisions and Intelligent Transmission of Link State
   Acknowledgements sections.


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   o  PushbackInterval: The length of time in seconds that a non-active
      overlapping relay SHOULD wait before further flooding an LSA if
      needed.  This timer MUST be less than 1/2 of the RxmtInterval
      [OSPF],[OSPFv3] minus propagation delays, i.e., (PushbackInterval
      + propagation delay) < RxmtInterval/2.  The PushbackInterval is
      set by a non-active overlapping relay upon reception of an LSA.
   o  AckInterval: After a node determines that it must transmit an ACK
      and the AckInterval timer is not already set, the node SHOULD set
      the AckInterval timer.  The AckInterval is the length of time in
      seconds that a node should wait in order to transmit many ACKs in
      the acknowledgement packet.  This wait reduces the number of
      packet transmissions required in acknowledging multiple LSAs.  The
      AckInterval MUST be less than the PushbackInterval minus
      propagation delays, i.e., (AckInterval + propagation delay) <
      PushbackInterval.

3.3.11  Miscellaneous Protocol Considerations

   The mechanism described refers to the operation of relays on a common
   media segment.  In other words, an LSA is only relayed out the same
   interface through which it was received.  However, the concept of
   information relay may be extended to the flooding of all link state
   advertisements received on any interface (and forwarded on any other
   interface).  OSPF works on the premise that all of the nodes in a
   flooding domain will receive all of the routing information.  Note
   that one of the important properties is that the routing information
   is not altered when relayed.

   If each speaker advertised all of its adjacent neighbors on all
   interfaces, then the overlap check would result in the determination
   of which speakers are adjacent to both speakers.  As a result, link
   state information should only be flooded to non-overlapping neighbors
   (taking all of the interfaces into account).

   The flooding mechanism in OSPF relies on a designated router to
   guarantee that any new LSA received by one router attached to the
   broadcast network will be reflooded properly to all the other routers
   attached to the broadcast network.  Such desginated routers must be
   able to reach all of the other speakers on the same subnet.  A
   designated router SHOULD NOT be elected if overlapping relays are
   used.

   If such designated routers already exist, then the relays MUST be
   capable of differentiating them, and then making the relaying
   decisions based on the OSPF's normal operation.  As a result, there
   may be groups of neighbors to which some information should not be
   relayed.  This mode of operation is NOT RECOMMENDED as it adds to the
   complexity of the system.


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   The intent of the overlapping relay mechanism is to optimize flooding
   of routing control information.  However, other information (such as
   data) may also be relayed in some networks using the same mechanism.

3.3.12  Interoperability

   On receiving a Hello packet from a new neighbor without the F bit
   set, the local router will assume that the new neighbor will flood
   normally as described in [OSPFv3].  Thus, the local router SHOULD
   include the neighbor in its overlapping relay set since the neighbor
   will flood by default.  This will allow the local router to more
   optimally select its entire overlapping relay set.

   If the F bit is set and the I bit as defined in Section "Incremental
   OSPF-MANET Hellos" is not set in the neighbor's Hello and the
   neighbor is selected as an overlapping relay by the local router, the
   local router will continue to include the neighbor's identifier in
   its active relay set.

3.4  New Bits in OSPFv3 Option Field

   Three new option bits are defined in the OSPFv3 Options Field
   (defined in [OSPFv3], A.2) as follows:

       0                   1                         2
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7  8  9  0  1  2  3
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+--+--+--+--+--+--+
      | | | | | | | | | | | | |F|I|L|AF|*|*|DC| R| N|MC| E|V6|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+--+--+--+--+--+--+

   o  I bit - defined in Section "I Option Bit": The I bit is only
      defined for Hello packets and indicates that only incremental
      information is present.
   o  F bit - defined in Section "F Option Bit": The F bit indicates
      that the node supports the Optimized Flooding mechanism as
      specified in this draft.

3.5  Smart Peering

   There is a significant overhead in OSPF if a router has to establish
   adjacencies with every peer it can verify 2-way connectivity with.
   OSPF supports a broadcast network type for these scenarios, where you
   only have to peer with a designated router (DR). But a full mesh of
   connectivity is required for proper DR election, so this doesn't help
   in networks with overlapping partial meshes of connectivity. This
   draft proposes an optional technique to reduce the number of
   adjacencies based on the shortest path tree (SPT) reachability
   information.

3.5.1  Introduction

   In OSPF [OSPF] [OSPFv3], nodes establish an adjacency by first

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   verifying 2-way connectivity between them and then synchronizing
   their link state databases. Once the peering relationship is complete
   and the adjacency is established, the nodes will continue to
   advertise each other in their periodic Hellos and LSAs. As a result,
   the peers are maintained in the link state database and are included
   in all SPF calculations. During the reliable flooding process, a node
   must ensure that each peer has indeed received the flooded routing
   update via an acknowledgement and retransmission mechanism.

   Consequently, maintaining an adjacency for a particular peer is a
   tradeoff between the added redundancy in routing paths and network
   reachability versus the overhead (memory consumption, SPF
   computations, routing overhead, and network convergence).

   Consider the possibility of reducing the number of adjacencies that a
   node maintains without compromising reachability and redundancy.
   This will have direct implications on network scalability and is
   especially attractive in environments where the network topology is
   dynamic. For example, in a Mobile Ad-Hoc Network (MANET) where nodes
   are mobile and the topology is constantly changing, it seems highly
   desirable to 'intelligently' become adjacent with only selected peers
   and thus, not establish a peering session with every node that comes
   within transmission range. Selective peering can be particularly
   useful in avoiding the peering process for unstable nodes, i.e.,
   nodes that come in and out of transmission range.

3.5.2  Previous Related Work

   The formation of a FULL adjacency requires the discovery (2-way
   relationship) and the database synchronization. To prevent from
   achieving the FULL state, others have taken the approach of modifying
   link state protocols to use periodic advertisements (instead of a
   database exchange).  The result is that neighbor discovery is still
   required, but the routing information is learned over time.  An
   example of this approach is:

   - OSPFv2 Wireless Interface Type [WINTF]
     - where the use of periodic advertisements "eliminates the
       formation of full adjacencies on wireless interfaces; all
       neighbor states beyond 2-Way are not reached,and no database
       synchronization is performed".

   What we propose below, goes a step further by not requiring the
   formation and maintenance of neighbor state (2-way, or other) *and*
   without changing the route distribution mechanisms in the link state
   protocols. In other words, the mechanism described is completely
   backwards compatible.

3.5.3  Proposed Solution

   Two routers are called synchronized when they have identical link
   state database. To limit the number of neighbors that are formed, an
   algorithm is needed to select which neighbors to peer with.

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   The algorithm MUST provide reachability to every possible destination
   in the network, just like when normal adjacency formation processes
   are used. We should always peer with a neighbor if it provides our
   only path to currently unreachable destinations.

3.5.3.1  SPT Reachability Heuristics

   The peering decision is really a local matter to a router. If a
   router can ensure that the reachability to other nodes is available
   without bringing up a new adjacency, it can choose to not bring up
   the new adjacency.

   We propose an algorithm which uses the already existing information
   about a new neighbor's reachability in the SPT. If the two routers
   can already reach each other in the SPT, it is not necessary to build
   up the adjacency between them.

   The decision to peer or not, is made when a hello is received. When a
   hello is received from a new neighbor or a neighbor in a state lower
   than Exchange:

   - A check is made in the link state database to see if the peer is
     already reachable in the SPT.

     - If the peer is either not known in the SPT or is not reachable,
       we start the Exchange process.

     - If the peer is reachable than bringing up adjacency with this
       neighbor does not provide reachability to any new destinations.

   Lets take an example of a single OSPF area. This check would look for
   the neighbor's Router LSA. If the LSA is present in the database and
   is reachable in the SPT, we have a chance to keep this adjacency from
   going to Exchange.

   It's worth noting that as the number of links and redundancy in the
   network is reduced, there may be an increase in suboptimal routing.

3.5.3.2  State Machine

   The state machine of a basic implementation of this algorithm is
   provided below: An implementation MAY use some heuristics below
   (step (3)), beyond the SPT reachability to decide if it considers a
   new adjacacency to be of value or not.


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                     ......................
                     |Receive a hello     |
                 (1) |from a new potential|
                     |neighbor            |
                     '`''''''''''''''''''''
                               |
                               |
                               |
                     ,''''''''''''''''''''''|
                     |Check to see if there |
                 (2) |is a router LSA from  |----no--(4)form a
                     |the new potential     |          new
                     |neighbor in the link  |          neighbor
                     |state database, which |
                     |is reachable in SPT   |
                     '`''''''''''''''''''''''
                               |
                               |yes
      (3)                      |
   ,'''''''''''''''''''''''''''''''''''''''''''''''''''''''''|
   |                            (3b)........................ |
   |(3a),______________________     |Determine if the      | |
   |    |Determine if the new |     |number of redundant   | |
   |    |link cost is better  |     |paths to the potential| |
   |    |than the current path|     |neighbor is < the     | |
   |    |cost by a configured |     |maximum configured    | |
   |    |amount               |     |value                 | |
   |    '`'''''''''''''''''''''     '`'''''''''''''''''''''' |
   |                       \             /                   |
   |                   .....\.........../....                |
   |                   |User configurable   |                |
   |                   |selection algorithm |                |
   |                   '`'''/'''''''\''''''''                |
   |                       /         \                       |
   '`'''''''''''''''''''''/'''''''''''\'''''''''''''''''''''''
                         /             \
                  requirements     requirements
                     met              not met
                     /                    \
                    /                      \
        (4) form a new neighbor      (5) do not become
                                         neighbors


3.5.3.3  Announce the 2-way link in Router-LSA

   While the technique described above minimizes the number of
   adjacencies in highly meshed einvironments, it may lead to the
   undesirable result of limiting the number of transit links available
   on which to forward traffic.

   An implementation may choose to allow some (or even all) of these
   2-way state neighbors to be announced in the Router-LSA. Since the

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   state remains 2-way, we don't incur control plan (database sync and
   flooding) overhead. But at the same time, announcing the link in the
   Router-LSA makes the link available to the data plane.

4.  Security Considerations

   In a MANET network, security is both more difficult and important due
   to the wireless nature of the medium.  Controlling the ability of
   devices to connect to a MANET network at Layer 2 will be relegated to
   Layer 2 security mechanisms, such as 802.1x, and others.  Controlling
   the ability of attached devices to transit traffic will require some


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   type of security system (outside the scope of this document) which
   can authenticate and provide authorization for individual members of
   the routing domain.

5.  IANA Considerations

   IANA will make assignments as explained below using the policies
   outlined in [IANA].

   o  An option bit value for the I-bit and F-bit as defined in the "New
      Bits in OSPFv3 Options Field" section above.

   o  TLV type codes for SCS-TLV, Neighbor Drop TLV, Request From TLV,
      Full State For TLV and Willingness TLV as defined in this
      document. This allocation comes from LLS [LLS] TLV types values.


6.  Contributors

   The following persons are contributing authors to the document:


      Fred Baker
      Cisco Systems
      1121 Via Del Rey
      Santa Barbara, CA 93117
      USA
      Email: fred@cisco.com

      Alvaro Retana
      Cisco Systems
      7025-4 Kit Creek Road
      RTP, NC 27709
      USA
      Email: aretana@cisco.com

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      Russ White
      Cisco Systems
      7025-4 Kit Creek Road
      RTP, NC 27709
      USA
      Email: riw@cisco.com

      Dave Cook
      Cisco Systems
      7025-4 Kit Creek Road
      RTP, NC 27709
      USA
      Email: dacook@cisco.com

      Yi Yang
      Cisco Systems
      7025-4 Kit Creek Road
      RTP, NC 27709
      USA
      Email: yiya@cisco.com


7.  Acknowledgements

   The authors and contributors would like to thank Pratap Pellakuru and
   Stan Ratliff for their feedback and implementation of the document.

References

Normative References

   [OSPF]     Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

   [OSPFv3]   Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6",
              RFC 2740, December 1999.

   [IANA]     Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

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


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Informative References

   [IPV6ADD]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [OSPFGR]   Moy, J., Pillay-Esnault, P., and A. Lindem, "Graceful OSPF
              Restart", RFC 3623, November 2003.

   [OSPFREST] Zinin, A., Roy, A., and L. Nguyen, "OSPF Restart
              Signaling", RFC 4812, March 2007.

   [LLS]      Zinin, A., Roy, A., Nguyen, L., Friedman, B., and D.
              Yeung, "OSPF Link-local Signaling",
              draft-ietf-ospf-lls-03.txt (work in progress),
              February 2008.

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

   [WINTF]   Ahrenholz J. et al, "OSPFv2 Wireless Interface Type",
             draft-spagnolo-manet-ospf-wireless-interface
             (work in progress)


Authors' Addresses

      Madhavi W. Chandra (Editor)
      Email: mw.chandra@gmail.com

      Abhay Roy (Editor)
      Cisco Systems
      170 W. Tasman Drive
      San Jose, CA 95134
      USA
      Email: akr@cisco.com



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Full Copyright Statement

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   This document is subject to the rights, licenses and restrictions
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Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).








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