[Docs] [txt|pdf] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02

Internet Engineering Task Force                               T. Li, Ed.
Internet-Draft                                           Arista Networks
Intended status: Standards Track                          P. Psenak, Ed.
Expires: June 6, 2019                                        L. Ginsberg
                                                     Cisco Systems, Inc.
                                                           T. Przygienda
                                                  Juniper Networks, Inc.
                                                               D. Cooper
                                                             CenturyLink
                                                                L. Jalil
                                                                 Verizon
                                                              S. Dontula
                                                                     ATT
                                                        December 3, 2018


                    Dynamic Flooding on Dense Graphs
                    draft-li-lsr-dynamic-flooding-02

Abstract

   Routing with link state protocols in dense network topologies can
   result in sub-optimal convergence times due to the overhead
   associated with flooding.  This can be addressed by decreasing the
   flooding topology so that it is less dense.

   This document discusses the problem in some depth and an
   architectural solution.  Specific protocol changes for IS-IS, OSPFv2,
   and OSPFv3 are described in this document.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 6, 2019.





Li, et al.                Expires June 6, 2019                  [Page 1]


Internet-Draft              Dynamic Flooding               December 2018


Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Solution Requirements . . . . . . . . . . . . . . . . . . . .   5
   4.  Dynamic Flooding  . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Applicability . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  Leader election . . . . . . . . . . . . . . . . . . . . .   7
     4.3.  Computing the Flooding Topology . . . . . . . . . . . . .   8
     4.4.  Topologies on Complete Bipartite Graphs . . . . . . . . .   9
       4.4.1.  A Minimal Flooding Topology . . . . . . . . . . . . .   9
       4.4.2.  Xia Topologies  . . . . . . . . . . . . . . . . . . .   9
       4.4.3.  Optimization  . . . . . . . . . . . . . . . . . . . .  10
     4.5.  Encoding the Flooding Topology  . . . . . . . . . . . . .  11
   5.  Protocol Elements . . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  IS-IS TLVs  . . . . . . . . . . . . . . . . . . . . . . .  11
       5.1.1.  IS-IS Area Leader Sub-TLV . . . . . . . . . . . . . .  11
       5.1.2.  IS-IS Dynamic Flooding Sub-TLV  . . . . . . . . . . .  12
       5.1.3.  IS-IS Area System IDs TLV . . . . . . . . . . . . . .  13
       5.1.4.  IS-IS Flooding Path TLV . . . . . . . . . . . . . . .  14
       5.1.5.  IS-IS Flooding Request TLV  . . . . . . . . . . . . .  15
     5.2.  OSPF LSAs and TLVs  . . . . . . . . . . . . . . . . . . .  16
       5.2.1.  OSPF Area Leader Sub-TLV  . . . . . . . . . . . . . .  17
       5.2.2.  OSPF Dynamic Flooding Sub-TLV . . . . . . . . . . . .  17
       5.2.3.  OSPFv2 Dynamic Flooding Opaque LSA  . . . . . . . . .  18
       5.2.4.  OSPFv3 Dynamic Flooding LSA . . . . . . . . . . . . .  19
       5.2.5.  OSPF Area Router IDs TLV  . . . . . . . . . . . . . .  20
       5.2.6.  OSPF Flooding Path TLV  . . . . . . . . . . . . . . .  21
       5.2.7.  OSPF Flooding Request Bit . . . . . . . . . . . . . .  22
   6.  Behavioral Specification  . . . . . . . . . . . . . . . . . .  23
     6.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .  23
     6.2.  Flooding Topology . . . . . . . . . . . . . . . . . . . .  23



Li, et al.                Expires June 6, 2019                  [Page 2]


Internet-Draft              Dynamic Flooding               December 2018


     6.3.  Leader Election . . . . . . . . . . . . . . . . . . . . .  24
     6.4.  Area Leader Responsibilities  . . . . . . . . . . . . . .  24
     6.5.  Distributed Flooding Topology Calculation . . . . . . . .  24
     6.6.  Flooding Behavior . . . . . . . . . . . . . . . . . . . .  25
     6.7.  Treatment of Topology Events  . . . . . . . . . . . . . .  25
       6.7.1.  Temporary Addition of Link to Flooding Topology . . .  26
       6.7.2.  Local Link Addition . . . . . . . . . . . . . . . . .  26
       6.7.3.  Node Addition . . . . . . . . . . . . . . . . . . . .  27
       6.7.4.  Failures of Link Not on Flooding Topology . . . . . .  27
       6.7.5.  Failures of Link On the Flooding Topology . . . . . .  28
       6.7.6.  Node Deletion . . . . . . . . . . . . . . . . . . . .  28
       6.7.7.  Local Link Addition to the Flooding Topology  . . . .  28
       6.7.8.  Local Link Deletion from the Flooding Topology  . . .  29
       6.7.9.  Treatment of Disconnected Adjacent Nodes  . . . . . .  29
       6.7.10. Failure of the Area Leader  . . . . . . . . . . . . .  29
       6.7.11. Recovery from Multiple Failures . . . . . . . . . . .  30
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  30
     7.1.  IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . .  30
     7.2.  OSPF  . . . . . . . . . . . . . . . . . . . . . . . . . .  31
       7.2.1.  OSPF Dynamic Flooding LSA TLVs Registry . . . . . . .  32
     7.3.  IGP . . . . . . . . . . . . . . . . . . . . . . . . . . .  33
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  33
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  33
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  34
     10.2.  Informative References . . . . . . . . . . . . . . . . .  35
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  36

1.  Introduction

   In recent years, there has been increased focus on how to address the
   dynamic routing of networks that have a bipartite (a.k.a. spine-leaf
   or leaf-spine), Clos [Clos], or Fat Tree [Leiserson] topology.
   Conventional Interior Gateway Protocols (IGPs, i.e., IS-IS
   [ISO10589], OSPFv2 [RFC2328], and OSPFv3 [RFC5340]) under-perform,
   redundantly flooding information throughout the dense topology,
   leading to overloaded control plane inputs and thereby creating
   operational issues.  For practical considerations, network architects
   have resorted to applying unconventional techniques to address the
   problem, e.g., applying BGP in the data center [RFC7938].  However it
   is very clear that using an Exterior Gateway Protocol as an IGP is
   sub-optimal, if only due to the configuration overhead.

   The primary issue that is demonstrated when conventional mechanisms
   are applied is the poor reaction of the network to topology changes.
   Normal link state routing protocols rely on a flooding algorithm for
   state distribution within an area.  In a dense topology, this
   flooding algorithm is highly redundant, resulting in unnecessary



Li, et al.                Expires June 6, 2019                  [Page 3]


Internet-Draft              Dynamic Flooding               December 2018


   overhead.  Each node in the topology receives each link state update
   multiple times.  Ultimately, all of the redundant copies will be
   discarded, but only after they have reached the control plane and
   been processed.  This creates issues because significant link state
   database updates can become queued behind many redundant copies of
   another update.  This delays convergence as the link state database
   does not stabilize promptly.

   In a real world implementation, the packet queues leading to the
   control plane are necessarily of finite size, so if the flooding rate
   exceeds the update processing rate for long enough, the control plane
   will be obligated to drop incoming updates.  If these lost updates
   are of significance, this will further delay stabilization of the
   link state database and the convergence of the network.

   This is not a new problem.  Historically, when routing protocols have
   been deployed in networks where the underlying topology is a complete
   graph, there have been similar issues.  This was more common when the
   underlying link layer fabric presented the network layer with a full
   mesh of virtual connections.  This was addressed by reducing the
   flooding topology through IS-IS Mesh Groups [RFC2973], but this
   approach requires careful configuration of the flooding topology.

   Thus, the root problem is not limited to massively scalable data
   centers.  It exists with any dense topology at scale.

   This problem is not entirely surprising.  Link state routing
   protocols were conceived when links were very expensive and
   topologies were sparse.  The fact that those same designs are sub-
   optimal in a dense topology should not come as a huge surprise.  The
   fundamental premise that was addressed by the original designs was an
   environment of extreme cost and scarcity.  Technology has progressed
   to the point where links are cheap and common.  This represents a
   complete reversal in the economic fundamentals of network
   engineering.  The original designs are to be commended for continuing
   to provide correct operation to this point, and optimizations for
   operation in today's environment are to be expected.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].








Li, et al.                Expires June 6, 2019                  [Page 4]


Internet-Draft              Dynamic Flooding               December 2018


2.  Problem Statement

   In a dense topology, the flooding algorithm that is the heart of
   conventional link state routing protocols causes a great deal of
   redundant messaging.  This is exacerbated by scale.  While the
   protocol can survive this combination, the redundant messaging is
   unnecessary overhead and delays convergence.  Thus, the problem is to
   provide routing in dense, scalable topologies with rapid convergence.

3.  Solution Requirements

   A solution to this problem must then meet the following requirements:

   Requirement 1    Provide a dynamic routing solution.  Reachability
       must be restored after any topology change.

   Requirement 2    Provide a significant improvement in convergence.

   Requirement 3    The solution should address a variety of dense
       topologies.  Just addressing a complete bipartite topology such
       as K5,8 is insufficient.  Multi-stage Clos topologies must also
       be addressed, as well as topologies that are slight variants.
       Addressing complete graphs is a good demonstration of generality.

   Requirement 4    There must be no single point of failure.  The loss
       of any link or node should not unduly hinder convergence.

   Requirement 5    Dense topologies are subgraphs of much larger
       topologies.  Operational efficiency requires that the dense
       subgraph not operate in a radically different manner than the
       remainder of the topology.  While some operational differences
       are permissible, they should be minimized.  Changes to nodes
       outside of the dense subgraph are not acceptable.  These
       situations occur when massively scaled data centers are part of
       an overall larger wide-area network.  Having a second protocol
       operating just on this subgraph would add much more complexity at
       the edge of the subgraph where the two protocols would have to
       inter-operate.

4.  Dynamic Flooding

   We have observed that the combination of the dense topology and
   flooding on the physical topology in a scalable network is sub-
   optimal.  However, if we decouple the flooding topology from the
   physical topology and only flood on a greatly reduced portion of that
   topology, we can have efficient flooding and retain all of the
   resilience of existing protocols.  A node that supports flooding on
   the decoupled flooding topology is said to support dynamic flooding.



Li, et al.                Expires June 6, 2019                  [Page 5]


Internet-Draft              Dynamic Flooding               December 2018


   In this idea, the flooding topology is computed within an IGP area
   with the dense topology either centrally on an elected node, termed
   the Area Leader, or in a distributed manner on all nodes that are
   supporting Dynamic Flooding.  If the flooding topology is computed
   centrally, it is encoded into and distributed as part of the normal
   link state database.  We call this the centralized mode of operation.
   If the flooding topology is computed in a distributed fashion, we
   call this the distributed mode of operation.  Nodes within such an
   IGP area would only flood on the flooding topology.  On links outside
   of the normal flooding topology, normal database synchronization
   mechanisms (i.e., OSPF database exchange, IS-IS CSNPs) would apply,
   but flooding may not.  Details are described in Section 6.  New link
   state information that arrives from outside of the flooding topology
   suggests that the sender has a different or no flooding topology
   information and that the link state update should be flooded on the
   flooding topology as well.

   The flooding topology covers the full set of nodes within the area,
   but excludes some of the links that standard flooding would employ.

   Since the flooding topology is computed prior to topology changes, it
   does not factor into the convergence time and can be done when the
   topology is stable.  The speed of the computation and its
   distribution, in the case of a centralized mode, is not a significant
   issue.

   If a node does not have any flooding topology information when it
   receives new link state information, it should flood according to
   standard flooding rules.  This situation will occur when the dense
   topology is first established, but is unlikely to recur.

   When centralized mode is used and if, during a transient, there are
   multiple flooding topologies being advertised, then nodes should
   flood link state updates on all of the flooding topologies.  Each
   node should locally evaluate the election of the Area Leader for the
   IGP area and first flood on its flooding topology.  The rationale
   behind this is straightforward: if there is a transient and there has
   been a recent change in Area Leader, then propagating topology
   information promptly along the most likely flooding topology should
   be the priority.

   During transients, it is possible that loops will form in the
   flooding topology.  This is not problematic, as the legacy flooding
   rules would cause duplicate updates to be ignored.  Similarly, during
   transients, it is possible that the flooding topology may become
   disconnected.  Section 6.7.11 discusses how such conditions are
   handled.




Li, et al.                Expires June 6, 2019                  [Page 6]


Internet-Draft              Dynamic Flooding               December 2018


4.1.  Applicability

   In a complete graph, this approach is appealing because it
   drastically decreases the flooding topology without the manual
   configuration of mesh groups.  By controlling the diameter of the
   flooding topology, as well as the maximum degree node in the flooding
   topology, convergence time goals can be met and the stability of the
   control plane can be assured.

   Similarly, in a massively scaled data center, where there are many
   opportunities for redundant flooding, this mechanism ensures that
   flooding is redundant, with each leaf and spine well connected, while
   ensuring that no update need make too many hops and that no node
   shares an undue portion of the flooding effort.

   In a network where only a portion of the nodes support Dynamic
   Flooding, the remaining nodes will continue to perform standard
   flooding.  This is not an issue for correctness, as no node can
   become isolated.

   Flooding that is initiated by nodes that support Dynamic Flooding
   will remain within the flooding topology until it reaches a legacy
   node, which will resume legacy flooding.  Standard flooding will be
   bounded by nodes supporting Dynamic Flooding, which can help limit
   the propagation of unnecessary flooding.  Whether or not the network
   can remain stable in this condition is unknown and may be very
   dependent on the number and location of the nodes that support
   Dynamic Flooding.

   During incremental deployment of dynamic flooding an area will
   consist of one or more sets of connected nodes that support dynamic
   flooding and one or more sets of connected nodes that do not, i.e.,
   nodes that support standard flooding.  The flooding topology is the
   union of these sets of nodes.  Each set of nodes that does not
   support dynamic flooding needs to be part of the flooding topology
   and such a set of nodes may provide connectivity between two or more
   sets of nodes that support dynamic flooding.

4.2.  Leader election

   A single node within the dense topology is elected as an Area Leader.

   A generalization of the mechanisms used in existing Designated Router
   (OSPF) or Designated Intermediate-System (IS-IS) elections suffices.
   The elected node is known as the Area Leader.

   In the case of centralized mode, the Area Leader is responsible for
   computing and distributing the flooding topology.  When a new Area



Li, et al.                Expires June 6, 2019                  [Page 7]


Internet-Draft              Dynamic Flooding               December 2018


   Leader is elected and has distributed new flooding topology
   information, then any prior Area Leaders should withdraw any of their
   flooding topology information from their link state database entries.

   In the case of distributed mode, the distributed algorithm advertised
   by the Area Leader MUST be used by all nodes that participate in
   Dynamic Flooding.

   Not every node needs to be a candidate to be Area Leader within an
   area, as a single candidate is sufficient for correct operation.  For
   redundancy, however, it is strongly RECOMMENDED that there be
   multiple candidates.

4.3.  Computing the Flooding Topology

   There is a great deal of flexibility in how the flooding topology may
   be computed.  For resilience, it needs to at least contain a cycle of
   all nodes in the dense subgraph.  However, additional links could be
   added to decrease the convergence time.  The trade-off between the
   density of the flooding topology and the convergence time is a matter
   for further study.  The exact algorithm for computing the flooding
   topology in the case of the centralized computation need not be
   standardized, as it is not an interoperability issue.  Only the
   encoding of the result needs to be documented.  In the case of
   distributed mode, all nodes in the IGP area need to use the same
   algorithm to compute the flooding topology.  It is possible to use
   private algorithms to compute flooding topology, so long as all nodes
   in the IGP area use the same algorithm.

   While the flooding topology should be a covering cycle, it need not
   be a Hamiltonian cycle where each node appears only once.  In fact,
   in many relevant topologies this will not be possible e.g., K5,8.
   This is fortunate, as computing a Hamiltonian cycle is known to be
   NP-complete.

   A simple algorithm to compute the topology for a complete bipartite
   graph is to simply select unvisited nodes on each side of the graph
   until both sides are completely visited.  If the number of nodes on
   each side of the graph are unequal, then revisiting nodes on the less
   populated side of the graph will be inevitable.  This algorithm can
   run in O(N) time, so is quite efficient.

   While a simple cycle is adequate for correctness and resiliency, it
   may not be optimal for convergence.  At scale, a cycle may have a
   diameter that is half the number of nodes in the graph.  This could
   cause an undue delay in link state update propagation.  Therefore it
   may be useful to have a bound on the diameter of the flooding
   topology.  Introducing more links into the flooding topology would



Li, et al.                Expires June 6, 2019                  [Page 8]


Internet-Draft              Dynamic Flooding               December 2018


   reduce the diameter, but at the trade-off of possibly adding
   redundant messaging.  The optimal trade-off between convergence time
   and graph diameter is for further study.

   Similarly, if additional redundancy is added to the flooding
   topology, specific nodes in that topology may end up with a very high
   degree.  This could result in overloading the control plane of those
   nodes, resulting in poor convergence.  Thus, it may be optimal to
   have an upper bound on the degree of nodes in the flooding topology.
   Again, the optimal trade-off between graph diameter, node degree, and
   convergence time, and topology computation time is for further study.

   If the leader chooses to include a multi-node broadcast LAN segment
   as part of the flooding topology, all of the connectivity to that LAN
   segment should be included as well.  Once updates are flooded onto
   the LAN, they will be received by every attached node.

4.4.  Topologies on Complete Bipartite Graphs

   Complete bipartite graph topologies have become popular for data
   center applications and are commonly called leaf-spine or spine-leaf
   topologies.  In this section, we discuss some flooding topologies
   that are of particular interest in these networks.

4.4.1.  A Minimal Flooding Topology

   We define a Minimal Flooding Topology on a complete bipartite graph
   as one in which the topology is connected and each node has at least
   degree two.  This is of interest because it guarantees that the
   flooding topology has no single points of failure.

   In practice, this implies that every leaf node in the flooding
   topology will have a degree of two.  As there are usually more leaves
   than spines, the degree of the spines will be higher, but the load on
   the individual spines can be evenly distributed.

   This type of flooding topology is also of interest because it scales
   well.  As the number of leaves increases, we can construct flooding
   topologies that perform well.  Specifically, for n spines and m
   leaves, if m >= n(n/2-1), then there is a flooding topology that has
   a diameter of four.

4.4.2.  Xia Topologies

   We define a Xia Topology on a complete bipartite graph as one in
   which all spine nodes are bi-connected through leaves with degree
   two, but the remaining leaves all have degree one and are evenly
   distributed across the spines.



Li, et al.                Expires June 6, 2019                  [Page 9]


Internet-Draft              Dynamic Flooding               December 2018


   Constructively, we can create a Xia topology by iterating through the
   spines.  Each spine can be connected to the next spine by selecting
   any unused leaf.  Since leaves are connected to all spines, all
   leaves will have a connection to both the first and second spine and
   we can therefore choose any leaf without loss of generality.
   Continuing this iteration across all of the spines, selecting a new
   leaf at each iteration, will result in a path that connects all
   spines.  Adding one more leaf between the last and first spine will
   produce a cycle of n spines and n leaves.

   At this point, m-n leaves remain unconnected.  These can be
   distributed evenly across the remaining spines, connected by a single
   link.

   Xia topologies represent a compromise that trades off increased risk
   and decreased performance for lower flooding amplification.  Xia
   topologies will have a larger diameter.  For m spines, the diameter
   will be m + 2.

   In a Xia topology, some leaves are singly connected.  This represents
   a risk in that in some failures, convergence may be delayed.
   However, there may be some alternate behaviors that can be employed
   to mitigate these risks.  If a leaf node sees that its single link on
   the flooding topology has failed, it can compensate by performing a
   database synchronization check with a different spine.  Similarly, if
   a leaf determines that its connected spine on the flooding topology
   has failed, it can compensate by performing a database
   synchronization check with a different spine.  In both of these
   cases, the synchronization check is intended to ameliorate any delays
   in link state propagation due to the fragmentation of the flooding
   topology.

   The benefit of this topology is that flooding load is easily
   understood.  Each node in the spine cycle will never receive an
   update more than twice.  For m leaves and n spines, a spine never
   transmits more than (m/n +1) updates.

4.4.3.  Optimization

   If two nodes are adjacent on the flooding topology and there are a
   set of parallel links between them, then any given update MUST be
   flooded over a single one of those links.  Selection of the specific
   link is implementation specific.








Li, et al.                Expires June 6, 2019                 [Page 10]


Internet-Draft              Dynamic Flooding               December 2018


4.5.  Encoding the Flooding Topology

   There are a variety of ways that the flooding topology could be
   encoded efficiently.  If the topology was only a cycle, a simple list
   of the nodes in the topology would suffice.  However, this is
   insufficiently flexible as it would require a slightly different
   encoding scheme as soon as a single additional link is added.
   Instead, we choose to encode the flooding topology as a set of
   intersecting paths, where each path is a set of connected edges.

   Other encodings are certainly possible.  We have attempted to make a
   useful trade off between simplicity, generality, and space.

5.  Protocol Elements

5.1.  IS-IS TLVs

   The following TLVs/sub-TLVs are added to IS-IS:

   1.  A sub-TLV that an IS may inject into its LSP to indicate its
       preference for becoming Area Leader.

   2.  A sub-TLV that an IS may inject into its LSP to indicate that it
       supports Dynamic Flooding and the algorithms that it supports for
       distributed mode, if any.

   3.  A TLV to carry the list of system IDs that compromise the
       flooding topology for the area.

   4.  A TLV to carry a path which is part of the flooding topology

   5.  A TLV that requests flooding from the adjacent node

5.1.1.  IS-IS Area Leader Sub-TLV

   The Area Leader Sub-TLV allows a system to:

   1.  Indicate its eligibility and priority for becoming Area Leader.

   2.  Indicate whether centralized or distributed mode is to be used to
       compute the flooding topology in the area.

   3.  Indicate the algorithm identifier for the algorithm that is used
       to compute the flooding topology in distributed mode.

   Intermediate Systems (nodes) that are not advertising this Sub-TLV
   are not eligible to become Area Leader.




Li, et al.                Expires June 6, 2019                 [Page 11]


Internet-Draft              Dynamic Flooding               December 2018


   The Area Leader is the node with the numerically highest Area Leader
   priority in the area.  In the event of ties, the node with the
   numerically highest system ID is the Area Leader.  Due to transients
   during database flooding, different nodes may not agree on the Area
   Leader.

   The Area Leader Sub-TLV is advertised as a Sub-TLV of the IS-IS
   Router Capability TLV-242 that is defined in [RFC7981] and has the
   following format:

            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    | Priority      |   Algorithm   |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type: TBD1

      Length: 2

      Priority: 0-255, unsigned integer

      Algorithm: a numeric identifier in the range 0-255 that identifies
      the algorithm used to calculate the flooding topology.  The
      following values are defined:

         0: Centralized computation by the Area Leader.

         1-127: Standardized distributed algorithms.  Individual values
         are are to be assigned according to the "Specification
         Required" policy defined in [RFC8126] (see Section 7.3).

         128-254: Private distributed algorithms.  Individual values are
         are to be assigned according to the "Private Use" policy
         defined in [RFC8126] (see Section 7.3).

         255: Reserved

5.1.2.  IS-IS Dynamic Flooding Sub-TLV

   The Dynamic Flooding Sub-TLV allows a system to:

   1.  Indicate that it supports Dynamic Flooding.  This is indicated by
       the advertisement of this Sub-TLV.

   2.  Indicate the set of algorithms that it supports for distributed
       mode, if any.




Li, et al.                Expires June 6, 2019                 [Page 12]


Internet-Draft              Dynamic Flooding               December 2018


   In incremental deployments, understanding which nodes support Dynamic
   Flooding can be used to optimize the flooding topology.  In
   distributed mode, knowing the capabilities of the nodes can allow the
   Area Leader to select the optimal algorithm.

   The Dynamic Flooding Sub-TLV is advertised as a Sub-TLV of the IS-IS
   Router Capability TLV (242) [RFC7981] and has the following format:

            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    | Algorithm...  |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type: TBD7

      Length: 0-255; number of Algorithms

      Algorithm: zero or more numeric identifiers in the range 0-255
      that identifies the algorithm used to calculate the flooding
      topology, as described in Section 5.1.1.

5.1.3.  IS-IS Area System IDs TLV

   IS-IS Area System IDs TLV is only used in centralized mode.

   The Area System IDs TLV is used by the Area Leader to enumerate the
   system IDs that it has used in computing the flooding topology.
   Conceptually, the Area Leader creates a list of system IDs for all
   nodes in the area, assigning indices to each system, starting with
   index 0.

   Because the space in a single TLV is small, more than one TLV may be
   required to encode all of the system IDs in the area.  This TLV may
   be present in multiple LSPs.

   The format of the Area System IDs TLV is:

            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    | Starting Index                |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |L| Reserved    | System IDs ...
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           System IDs continued ....
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




Li, et al.                Expires June 6, 2019                 [Page 13]


Internet-Draft              Dynamic Flooding               December 2018


      Type: TBD2

      Length: 3 + (System ID length * (number of System IDs))

      Starting index: The index of the first system ID that appears in
      this TLV.

      L (Last): This bit is set if the index of the last system ID that
      appears in this TLV is equal to the last index in the full list of
      system IDs for the area.

      System IDs: A concatenated list of system IDs for the area.

   If there are multiple IS-IS Area System IDs TLVs with the L bit set
   advertised by the same node, the TLV which specifies the smaller
   maximum index is used and the other TLV(s) with L bit set are
   ignored.  TLVs which specify system IDs with indices greater than
   that specified by the TLV with the L bit set are also ignored.

5.1.4.  IS-IS Flooding Path TLV

   IS-IS Flooding Path TLV is only used in centralized mode.

   The Flooding Path TLV is used to denote a path in the flooding
   topology.  The goal is an efficient encoding of the links of the
   topology.  A single link is a simple case of a path that only covers
   two nodes.  A connected path may be described as a sequence of
   indices: (I1, I2, I3, ...), denoting a link from the system with
   index 1 to the system with index 2, a link from the system with index
   2 to the system with index 3, and so on.

   If a path exceeds the size that can be stored in a single TLV, then
   the path may be distributed across multiple TLVs by the replication
   of a single system index.

   Complex topologies that are not a single path can be described using
   multiple TLVs.

   The Flooding Path TLV contains a list of system indices relative to
   the systems advertised through the Area System IDs TLV.  At least 2
   indices must be included in the TLV.  Due to the length restriction
   of TLVs, this TLV can contain at most 126 system indices.

   The Flooding Path TLV has the format:







Li, et al.                Expires June 6, 2019                 [Page 14]


Internet-Draft              Dynamic Flooding               December 2018


            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    | Starting Index                |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           | Index 2                       | Additional indices ...
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type: TBD3

      Length: 2 * (number of indices in the path)

      Starting index: The index of the first system in the path.

      Index 2: The index of the next system in the path.

      Additional indices (optional): A sequence of additional indices to
      systems along the path.

5.1.5.  IS-IS Flooding Request TLV

   The Flooding Request TLV allows a system to request an adjacent node
   to enable flooding towards it on a specific link in the case where
   the connection to adjacent node is not part of the existing flooding
   topology.

   Nodes that support Dynamic Flooding MAY include the Flooding Request
   TLV in its IIH PDUs.

   The Flooding Request TLV has the format:

            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    | Circuit Type  |R|  Scope      |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |R|  ...        |
           -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type: TBD9

      Length: 1 + number of advertised Flooding Scopes

      Circuit Type - circuit type as specified in IS-IS [ISO10589]

      R bit: MUST be 0 and is ignored on receipt.





Li, et al.                Expires June 6, 2019                 [Page 15]


Internet-Draft              Dynamic Flooding               December 2018


      Scope: Flooding Scope for which the flooding is requested as
      defined by LSP Flooding Scope Identifier Registry defined by
      [RFC7356].  Inclusion of flooding scopes is optional and is only
      necessary if [RFC7356] is supported.

   Circuit Flooding Scope MUST NOT be sent in the Flooding Request TLV
   and MUST be ignore if received.

   If flooding was disabled on the received link due to Dynamic
   Flooding, then flooding MUST be temporarily enabled over the link for
   the specified Circuit Type(s) and Flooding Scope(s) received in the
   in the Flooding Request TLV.  Flooding MUST be enabled until the
   Circuit Type or Flooding Scope is no longer advertised in the
   Flooding Request TLV or the TLV no longer appears in IIH PDUs
   received on the link.

   When the flooding is temporarily enabled on the link for any Circuit
   Type or Flooding Scope due to received Flooding Request TLV, the
   receiver MUST perform standard database synchronization for the
   corresponding Circuit Type(s) and Flooding Scope(s) on the link.  In
   the case of IS-IS, this results in setting SRM bit for all related
   LSPs on the link and sending CSNPs.

   So long as the Flooding Request TLV is being received flooding MUST
   not be disabled for any of the Circuit Types or Flooding Scopes
   present in the Flooding Request TLV even if the connection between
   the neighbors is removed from the flooding topology.  Flooding for
   such Circuit Types or Flooding Scopes MUST continue on the link and
   be considered as temporarily enabled.

5.2.  OSPF LSAs and TLVs

   This section defines new LSAs and TLVs for both OSPFv2 and OSPFv3.

   Following objects are added:

   1.  A TLV that is used to advertise the preference for becoming Area
       Leader.

   2.  A TLV that is used to indicate the support for Dynamic Flooding
       and the algorithms that the advertising node supports for
       distributed mode, if any.

   3.  OSPFv2 Opaque LSA and OSPFv3 LSA to advertise the flooding
       topology for centralized mode.

   4.  A TLV to carry the list of system IDs that compromise the
       flooding topology for the area.



Li, et al.                Expires June 6, 2019                 [Page 16]


Internet-Draft              Dynamic Flooding               December 2018


   5.  A TLV to carry a path which is part of the flooding topology.

   6.  The bit in the LLS Type 1 Extended Options and Flags requests
       flooding from the adjacent node.

5.2.1.  OSPF Area Leader Sub-TLV

   The usage of the OSPF Area Leader Sub-TLV is identical to IS-IS and
   is described in Section 5.1.1.

   The OSPF Area Leader Sub-TLV is used by both OSPFv2 and OSPFv3.

   The OSPF Area Leader Sub-TLV is advertised as a top-level TLV of the
   RI LSA that is defined in [RFC7770] and has the following format:


       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Priority   |   Algorithm   |            Reserved           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type: TBD4

      Length: 4 octets

      Priority: 0-255, unsigned integer

      Algorithm: as defined in Section 5.1.1.

5.2.2.  OSPF Dynamic Flooding Sub-TLV

   The usage of the OSPF Dynamic Flooding Sub-TLV is identical to IS-IS
   and is described in Section 5.1.2.

   The OSPF Dynamic Flooding Sub-TLV is used by both OSPFv2 and OSPFv3.

   The OSPF Dynamic Flooding Sub-TLV is advertised as a top-level TLV of
   the RI LSA that is defined in [RFC7770] and has the following format:










Li, et al.                Expires June 6, 2019                 [Page 17]


Internet-Draft              Dynamic Flooding               December 2018


       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Algorithm ... |                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type: TBD8

      Length: number of Algorithms

      Algorithm: as defined in Section 5.1.1.

5.2.3.  OSPFv2 Dynamic Flooding Opaque LSA

   The OSPFv2 Dynamic Flooding Opaque LSA is only used in centralized
   mode.

   The OSPFv2 Dynamic Flooding Opaque LSA is used to advertise
   additional data related to the dynamic flooding in OSPFv2.  OSPFv2
   Opaque LSAs are described in [RFC5250].

   Multiple OSPFv2 Dynamic Flooding Opaque LSAs can be advertised by an
   OSPFv2 router.  The flooding scope of the OSPFv2 Dynamic Flooding
   Opaque LSA is area-local.

   The format of the OSPFv2 Dynamic Flooding Opaque LSA is as follows:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            LS age             |     Options   |   LS Type     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      TBD5     |                 Opaque ID                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Advertising Router                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     LS sequence number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         LS checksum           |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +-                            TLVs                             -+
      |                             ...                               |

                    OSPFv2 Dynamic Flooding Opaque LSA




Li, et al.                Expires June 6, 2019                 [Page 18]


Internet-Draft              Dynamic Flooding               December 2018


   The opaque type used by OSPFv2 Dynamic Flooding Opaque LSA is TBD.
   The opaque type is used to differentiate the various type of OSPFv2
   Opaque LSAs and is described in section 3 of [RFC5250].  The LS Type
   is 10.  The LSA Length field [RFC2328] represents the total length
   (in octets) of the Opaque LSA including the LSA header and all TLVs
   (including padding).

   The Opaque ID field is an arbitrary value used to maintain multiple
   Dynamic Flooding Opaque LSAs.  For OSPFv2 Dynamic Flooding Opaque
   LSAs, the Opaque ID has no semantic significance other than to
   differentiate Dynamic Flooding Opaque LSAs originated by the same
   OSPFv2 router.

   The format of the TLVs within the body of the OSPFv2 Dynamic Flooding
   Opaque LSA is the same as the format used by the Traffic Engineering
   Extensions to OSPF [RFC3630].

   The Length field defines the length of the value portion in octets
   (thus a TLV with no value portion would have a length of 0).  The TLV
   is padded to 4-octet alignment; padding is not included in the length
   field (so a 3-octet value would have a length of 3, but the total
   size of the TLV would be 8 octets).  Nested TLVs are also 32-bit
   aligned.  For example, a 1-octet value would have the length field
   set to 1, and 3 octets of padding would be added to the end of the
   value portion of the TLV.  The padding is composed of zeros.

5.2.4.  OSPFv3 Dynamic Flooding LSA

   The OSPFv3 Dynamic Flooding Opaque LSA is only used in centralized
   mode.

   The OSPFv3 Dynamic Flooding LSA is used to advertise additional data
   related to the dynamic flooding in OSPFv3.

   The OSPFv3 Dynamic Flooding LSA has a function code of TBD.  The
   flooding scope of the OSPFv3 Dynamic Flooding LSA is area-local.  The
   U bit will be set indicating that the OSPFv3 Dynamic Flooding LSA
   should be flooded even if it is not understood.  The Link State ID
   (LSID) value for this LSA is the Instance ID.  OSPFv3 routers MAY
   advertise multiple Dynamic Flooding Opaque LSAs in each area.

   The format of the OSPFv3 Dynamic Flooding LSA is as follows:









Li, et al.                Expires June 6, 2019                 [Page 19]


Internet-Draft              Dynamic Flooding               December 2018


        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |            LS age             |1|0|1|          TBD6           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    Link State ID                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    Advertising Router                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    LS sequence number                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |        LS checksum            |            Length             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +-                            TLVs                             -+
       |                             ...                               |


                        OSPFv3 Dynamic Flooding LSA

5.2.5.  OSPF Area Router IDs TLV

   The OSPF Area Router IDs TLV is a top level TLV of the OSPFv2 Dynamic
   Flooding Opaque LSA and OSPFv3 Dynamic Flooding LSA.

   The OSPF Area Router IDs TLV is used by the Area Leader to enumerate
   the Router IDs that it has used in computing the flooding topology.
   Conceptually, the Area Leader creates a list of Router IDs for all
   routers in the area, assigning indices to each router, starting with
   index 0.

   Because the space in a single OSPF Area Router IDs TLV is limited,
   more than one TLV may be required to encode all of the Router IDs in
   the area.  This TLV may also recur in multiple OSPFv2 Dynamic
   Flooding Opaque LSAs or OSPFv3 Dynamic Flooding LSA, so that all
   Router IDs can be advertised.

   The format of the Area Router IDs TLV is:













Li, et al.                Expires June 6, 2019                 [Page 20]


Internet-Draft              Dynamic Flooding               December 2018


        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            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Starting Index             |L| Flags       |   Reserved    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +-                        Router IDs                           -+
       |                           ...                                 |

                         OSPF Area Router IDs TLV

      TLV Type: 1

      TLV Length: 4 + (Router ID length * (number of Router IDs))

      Starting index: The index of the first Router ID that appears in
      this TLV.

      L (Last): This bit is set if the index of the last system ID that
      appears in this TLV is equal to the last index in the full list of
      Rourer IDs for the area.

      Router IDs: A concatenated list of Router IDs for the area.

   If there are multiple OSPF Area Router IDs TLVs with the L bit set
   advertised by the same router, the TLV which specifies the smaller
   maximum index is used and the other TLV(s) with L bit set are
   ignored.  TLVs which specify Router IDs with indices greater than
   that specified by the TLV with the L bit set are also ignored.

5.2.6.  OSPF Flooding Path TLV

   The OSPF Flooding Path TLV is a top level TLV of the OSPFv2 Dynamic
   Flooding Opaque LSAs and OSPFv3 Dynamic Flooding LSA.

   The usage of the OSPF Flooding Path TLV is identical to IS-IS and is
   described in Section 5.1.4.

   The OSPF Flooding Path TLV contains a list of Router ID indices
   relative to the Router IDs advertised through the OSPF Area Router
   IDs TLV.  At least 2 indices must be included in the TLV.

   Multiple OSPF Flooding Path TLVs can be advertised in a single OSPFv2
   Dynamic Flooding Opaque LSA or OSPFv3 Dynamic Flooding LSA.  OSPF
   Flooding Path TLVs can also be advertised in multiple OSPFv2 Dynamic




Li, et al.                Expires June 6, 2019                 [Page 21]


Internet-Draft              Dynamic Flooding               December 2018


   Flooding Opaque LSAs or OSPFv3 Dynamic Flooding LSA, if they all can
   not fit in a single LSA.

   The Flooding Path TLV has the format:


        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            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Starting Index             |       Index 2                 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +-                        Additional Indices                   -+
       |                           ...                                 |



                          OSPF Flooding Path TLV

      TLV Type: 2

      TLV Length: 2 * (number of indices in the path)

      Starting index: The index of the first Router ID in the path.

      Index 2: The index of the next Router ID in the path.

      Additional indices (optional): A sequence of additional indices to
      Router IDs along the path.

5.2.7.  OSPF Flooding Request Bit

   A single new option bit, the Flooding-Request (FR-bit), is defined in
   the LLS Type 1 Extended Options and Flags field [RFC2328].  The FR-
   bit allows a router to request an adjacent node to enable flooding
   towards it on a specific link in the case where the connection to
   adjacent node is not part of the current flooding topology.

   Nodes that support Dynamic Flooding MAY include FR-bit in its OSPF
   LLS Extended Options and Flags TLV.

   If FR-bit is signalled for an area for which the flooding on the link
   was disabled due to Dynamic Flooding, the flooding MUST be
   temporarily enabled over such link and area.  Flooding MUST be
   enabled until FR-bit is no longer advertised in the OSPF LLS Extended




Li, et al.                Expires June 6, 2019                 [Page 22]


Internet-Draft              Dynamic Flooding               December 2018


   Options and Flags TLV or the OSPF LLS Extended Options and Flags TLV
   no longer appears in the OSPF Hellos.

   When the flooding is temporarily enabled on the link for any area due
   to received FR-bit in OSPF LLS Extended Options and Flags TLV, the
   receiver MUST perform standard database synchronization for the
   corresponding area(s) on the link.  If the adjacency is already in
   the FULL state, mechanism specified in [RFC4811] MUST be used for
   database resynchronization.

   So long as the FR-bit is being received in the OSPF LLS Extended
   Options and Flags TLV for an area, flooding MUST not be disabled in
   such area even if the connection between the neighbors is removed
   from the flooding topology.  Flooding for such area MUST continue on
   the link and be considered as temporarily enabled.

6.  Behavioral Specification

   In this section, we specify the detailed behaviors of the nodes
   participating in the IGP.

6.1.  Terminology

   We define some terminology here that is used in the following
   sections:

      A node is considered reachable if it is part of the connected
      network graph.  Note that this is independent of any constraints
      which may be considered when performing IGP SPT calculation (e.g.,
      link metrics, OL bit state, etc.).  Two-way-connectivity check
      MUST be performed before including an edge in the connected
      network graph.

      Node is connected to the flooding topology, if it has at least one
      local link, which is part of the flooding topology.

      Node is disconnected from the flooding topology when it is not
      connected to the flooding topology.

      Current flooding topology - latest version of the flooding
      topology received (in case of the centralized mode) or calculated
      locally (in case of the distributed mode).

6.2.  Flooding Topology

   The flooding topology MUST include all reachable nodes in the area.





Li, et al.                Expires June 6, 2019                 [Page 23]


Internet-Draft              Dynamic Flooding               December 2018


   If a node's reachability changes, the flooding topology MUST be
   recalculated.  In centralized mode, the Area Leader MUST advertise a
   new flooding topology.

   If a node becomes disconnected from the current flooding topology but
   is still reachable then a new flooding topology MUST be calculated.
   In centralized mode the Area Leader MUST advertise the new flooding
   topology.

   The flooding topology SHOULD be bi-connected.

6.3.  Leader Election

   Any node that is capable MAY advertise its eligibility to become Area
   Leader.

   Nodes that are not reachable are not eligible as Area Leader.  Nodes
   that do not advertise their eligibility to become Area Leader are not
   eligible.  Amongst the eligible nodes, the node with the numerically
   highest priority is the Area Leader.  If multiple nodes all have the
   highest priority, then the node with the numerically highest system
   identifier in the case of IS-IS, or Router-ID in the case of OSPFv2
   and OSPFv3 is the Area Leader.

6.4.  Area Leader Responsibilities

   If the Area Leader operates in centralized mode, it MUST advertise
   algorithm 0 in its Area Leader Sub-TLV.  It also MUST compute and
   advertise a flooding topology for the area.  The Area Leader may
   update the flooding topology at any time, however, it should not
   destabilize the network with undue or overly frequent topology
   changes.

   If the Area Leader operates in centralized mode and needs to
   advertises a new flooding topology, it floods a new flooding topology
   on both the new and old flooding topologies.

6.5.  Distributed Flooding Topology Calculation

   If the Area Leader advertises a non-zero algorithm in its Area Leader
   Sub-TLV, all nodes in the area that support Dynamic Flooding and the
   value of algorithm advertised by the Area Leader MUST compute the
   flooding topology based on the Area Leader's advertised algorithm.

   Nodes that do not support the value of algorithm advertised by the
   Area Leader MUST continue to use standard flooding mechanism as
   defined by the protocol.




Li, et al.                Expires June 6, 2019                 [Page 24]


Internet-Draft              Dynamic Flooding               December 2018


   Nodes that do not support the value of algorithm advertised by the
   Area Leader MUST be considered as Dynamic Flooding incapable nodes by
   the Area Leader.

   If the value of the algorithm advertised by the Area Leader is from
   the range 128-254 (private distributed algorithms), it is the
   responsibility of the network operator to guarantee that all nodes in
   the area have a common understanding of what the given algorithm
   value represents.

6.6.  Flooding Behavior

   Nodes that support Dynamic Flooding MUST use the flooding topology
   for flooding when possible, and MUST NOT revert to standard flooding
   when a valid flooding topology is available.

   In some cases a node that supports Dynamic Flooding may need to add a
   local link(s) to the flooding topology temporarily, even though the
   link(s) is not part of the calculated flooding topology.  This is
   termed "temporary flooding" and is discussed in Section 6.7.1.

   The flooding topology is calculated locally in the case of
   distributed mode.  In centralized mode the flooding topology is
   advertised in the area link state database.  Received link state
   updates, whether received on a link that is in the flooding topology
   or on a link that is not in the flooding topology, MUST be flooded on
   all links that are in the flooding topology, except for the link on
   which the update was received.

   In centralized mode, if multiple flooding topologies are present in
   the area link state database, the node SHOULD flood on the on each of
   these topologies.

   When the flooding topology changes on a node, either as a result of
   the local computation in distributed mode or as a result of the
   advertisement from the Area Leader in centralized mode, the node MUST
   continue to flood on both the old and new flooding topology for a
   limited amount of time.  This is required to provide all nodes
   sufficient time to migrate to the new flooding topology.

6.7.  Treatment of Topology Events

   In this section, we explicitly consider a variety of different
   topological events in the network and how Dynamic Flooding should
   address them.






Li, et al.                Expires June 6, 2019                 [Page 25]


Internet-Draft              Dynamic Flooding               December 2018


6.7.1.  Temporary Addition of Link to Flooding Topology

   In some cases a node that supports Dynamic Flooding may need to add a
   local link(s) to the flooding topology temporarily, even though the
   link(s) is not part of the calculated flooding topology.  We refer to
   this as "temporary flooding" on the link.

   When temporary flooding is enabled on the link, the flooding needs to
   be enabled from both directions on such link.  To achieve that, the
   following steps MUST be performed:

      Link State Database needs to be re-synchronised on the link.  This
      is done using the standard protocol mechanisms.  In the case of
      IS-IS, this results in setting SRM bit for all LSPs on the circuit
      and sending compete set of CSNPs on it.  In OSPF, the mechanism
      specified in [RFC4811] is used.

      Flooding is enabled locally on the link.

      Flooding is requested from the neighbor using the mechanism
      specified in section Section 5.1.5 or Section 5.2.7.

   The request for temporary flooding is withdrawn on the link when all
   of the following conditions are met:

      Node itself is connected to the current flooding topology.

      Adjacent node is connected to the current flooding topology.

   Any change in the flooding topology MUST result in evaluation of the
   above conditions for any link on which the temporary flooding was
   enabled.

   Temporary flooding is stopped on the link when both adjacent nodes
   stop requesting temporary flooding on the link.

6.7.2.  Local Link Addition

   If a local link is added to the topology, the protocol will form a
   normal adjacency on the link and update the appropriate link state
   advertisements for the nodes on either end of the link.  These link
   state updates will be flooded on the flooding topology.

   In centralized mode, the Area Leader, upon receiving these updates,
   may choose to retain the existing flooding topology or may choose to
   modify the flooding topology.  If it elects to change the flooding
   topology, it will update the flooding topology in the link state
   database and flood it using the new flooding topology.



Li, et al.                Expires June 6, 2019                 [Page 26]


Internet-Draft              Dynamic Flooding               December 2018


   In distributed mode, any change in the topology, including the link
   addition, MUST trigger the flooding topology recalculation.  This is
   done to ensure that all nodes converge to the same flooding topology,
   regardless of the time of the calculation.

   Temporary flooding MUST be enabled on the newly added local link, if
   at least one of the following conditions are met:

      The node on which the local link was added is not connected to the
      current flooding topology.

      The new adjacent node is not connected to the current flooding
      topology.

   Note that in this case there is no need to perform a database
   synchronization as part of the enablement of the temporary flooding,
   because it has been part of the adjacency bring-up itself.

   If multiple local links are added to the topology before the flooding
   topology is updated, temporary flooding MUST be enabled on a subset
   of these links.

6.7.3.  Node Addition

   If a node is added to the topology, then at least one link is also
   added to the topology.  Section 6.7.2 applies.

6.7.4.  Failures of Link Not on Flooding Topology

   If a link that is not part of the flooding topology fails, then the
   adjacent nodes will update their link state advertisements and flood
   them on the flooding topology.

   In centralized mode, the Area Leader, upon receiving these updates,
   may choose to retain the existing flooding topology or may choose to
   modify the flooding topology.  If it elects to change the flooding
   topology, it will update the flooding topology in the link state
   database and flood it using the new flooding topology.

   In distributed mode, any change in the topology, including the
   failure of the link that is not part of the flooding topology MUST
   trigger the flooding topology recalculation.  This is done to ensure
   that all nodes converge to the same flooding topology, regardless of
   the time of the calculation.







Li, et al.                Expires June 6, 2019                 [Page 27]


Internet-Draft              Dynamic Flooding               December 2018


6.7.5.  Failures of Link On the Flooding Topology

   If there is a failure on the flooding topology, the adjacent nodes
   will update their link state advertisements and flood them.  If the
   original flooding topology is bi-connected, the flooding topology
   should still be connected despite a single failure.

   If the failed local link represented the only connection to the
   flooding topology on the node where the link failed, the node MUST
   enable temporary flooding on a subset of its local links.  This
   allows the node to send its updated link state advertisement(s) and
   also keep receiving link state updates from other nodes in the
   network before the new flooding topology is calculated and
   distributed (in the case of centralized mode).

   In centralized mode, the Area Leader will notice the change in the
   flooding topology, recompute the flooding topology, and flood it
   using the new flooding topology.

   In distributed mode, all nodes supporting dynamic flooding will
   notice the change in the topology and recompute the new flooding
   topology.

6.7.6.  Node Deletion

   If a node is deleted from the topology, then at least one link is
   also removed from the topology.  The two sections above apply.

6.7.7.  Local Link Addition to the Flooding Topology

   If the new flooding topology is received in the case of centralized
   mode, or calculated locally in the case of distributed mode and the
   local link on the node that was not part of the flooding topology has
   been added to the flooding topology, the node MUST:

      Re-synchronize the Link State Database over the link.  This is
      done using the standard protocol mechanisms.  In the case of IS-
      IS, this results in setting SRM bit for all LSPs on the circuit
      and sending a complete set of CSNPs.  In OSPF, the mechanism
      specified in [RFC4811] is used.

      Make the link part of the flooding topology and start flooding
      over it








Li, et al.                Expires June 6, 2019                 [Page 28]


Internet-Draft              Dynamic Flooding               December 2018


6.7.8.  Local Link Deletion from the Flooding Topology

   If the new flooding topology is received in the case of centralized
   mode, or calculated locally in the case of distributed mode and the
   local link on the node that was part of the flooding topology has
   been removed from the flooding topology, the node MUST remove the
   link from the flooding topology.

   The node MUST keep flooding on such link for a limited amount of time
   to allow other nodes to migrate to the new flooding topology.

   If the removed local link represented the only connection to the
   flooding topology on the node, the node MUST enable temporary
   flooding on a subset of its local links.  This allows the node to
   send its updated link state advertisement(s) and also keep receiving
   link state updates from other nodes in the network before the new
   flooding topology is calculated and distributed (in the case of
   centralized mode).

6.7.9.  Treatment of Disconnected Adjacent Nodes

   Every time there is a change in the flooding topology a node MUST
   check if there are any adjacent nodes that are disconnected from the
   current flooding topology.  Temporary flooding MUST be enabled
   towards a subset of the disconnected nodes.

6.7.10.  Failure of the Area Leader

   The failure of the Area Leader can be detected by observing that it
   is no longer reachable.  In this case, the Area Leader election
   process is repeated and a new Area Leader is elected.

   In the centralized mode, the new Area Leader will compute a new
   flooding topology and flood it using the new flooding topology.

   As an optimization, applicable to centralized mode, the new Area
   Leader MAY compute a new flooding topology that has as much in common
   as possible with the old flooding topology.  This will minimize the
   risk of over-flooding.

   In the distributed mode, the new flooding topology will be calculated
   on all nodes that support the algorithm that is advertised by the new
   Area Leader.  Nodes that do not support the algorithm advertised by
   the new Area Leader will no longer participate in Dynamic Flooding
   and will revert to standard flooding.






Li, et al.                Expires June 6, 2019                 [Page 29]


Internet-Draft              Dynamic Flooding               December 2018


6.7.11.  Recovery from Multiple Failures

   In the unlikely event of multiple failures on the flooding topology,
   it may become partitioned.  The nodes that remain active on the edges
   of the flooding topology partitions will recognize this and will try
   to repair the flooding topology locally by enabling temporary
   flooding towards the nodes that they consider disconnected from the
   flooding topology until a new flooding topology becomes connected
   again.

   Nodes where local failure was detected update their own link state
   advertisements and flood them on the remainder of the flooding
   topology.

   In centralized mode, the Area Leader will notice the change in the
   flooding topology, recompute the flooding topology, and flood it
   using the new flooding topology.

   In distributed mode, all nodes that actively participate in Dynamic
   Flooding will compute the new flooding topology.

   Note that this is very different from the area partition because
   there is still a connected network graph between the nodes in the
   area.  The area may remain connected and forwarding may still be
   effective.

7.  IANA Considerations

7.1.  IS-IS

   This document requests the following code point from the "sub-TLVs
   for TLV 242" registry (IS-IS Router CAPABILITY TLV).

      Type: TBD1

      Description: IS-IS Area Leader Sub-TLV

      Reference: This document (Section 5.1.1)

      Type: TBD7

      Description: IS-IS Dynamic Flooding Sub-TLV

      Reference: This document (Section 5.1.2)

   This document requests that IANA allocate and assign two code points
   from the "IS-IS TLV Codepoints" registry.  One for each of the
   following TLVs:



Li, et al.                Expires June 6, 2019                 [Page 30]


Internet-Draft              Dynamic Flooding               December 2018


      Type: TBD2

      Description: IS-IS Area System IDs TLV

      Reference: This document (Section 5.1.3)

      Type: TBD3

      Description: IS-IS Flooding Path TLV

      Reference: This document (Section 5.1.4)

      Type: TBD9

      Description: IS-IS Flooding Request TLV

      Reference: This document (Section 5.1.5)

7.2.  OSPF

   This document requests the following code points from the "OSPF
   Router Information (RI) TLVs" registry:

      Type: TBD4

      Description: OSPF Area Leader Sub-TLV

      Reference: This document (Section 5.2.1)

      Type: TBD8

      Description: OSPF Dynamic Flooding Sub-TLV

      Reference: This document (Section 5.2.2)

   This document requests the following code point from the "Opaque
   Link-State Advertisements (LSA) Option Types" registry:

      Type: TBD5

      Description: OSPFv2 Dynamic Flooding Opaque LSA

      Reference: This document (Section 5.2.3)

   This document requests the following code point from the "OSPFv3 LSA
   Function Codes" registry:

      Type: TBD6



Li, et al.                Expires June 6, 2019                 [Page 31]


Internet-Draft              Dynamic Flooding               December 2018


      Description: OSPFv3 Dynamic Flooding LSA

      Reference: This document (Section 5.2.4)

   This document requests a new bit in LLS Type 1 Extended Options and
   Flags registry:

      Bit Position: TBD10

      Description: Flooding Request bit

      Reference: This document (Section 5.2.7)

7.2.1.  OSPF Dynamic Flooding LSA TLVs Registry

   This specification also requests one new registry - "OSPF Dynamic
   Flooding LSA TLVs".  New values can be allocated via IETF Review or
   IESG Approval

   The "OSPF Dynamic Flooding LSA TLVs" registry will define top-level
   TLVs for the OSPFv2 Dynamic Flooding Opaque LSA and OSPFv3 Dynamic
   Flooding LSAs.  It should be added to the "Open Shortest Path First
   (OSPF) Parameters" registries group.

   The following initial values are allocated:

      Type: 0

      Description: Reserved

      Reference: This document

      Type: 1

      Description: OSPF Area Router IDs TLV

      Reference: This document (Section 5.2.5)

      Type: 2

      Description: OSPF Flooding Path TLV

      Reference: This document (Section 5.2.6)

   Types in the range 32768-33023 are for experimental use; these will
   not be registered with IANA, and MUST NOT be mentioned by RFCs.





Li, et al.                Expires June 6, 2019                 [Page 32]


Internet-Draft              Dynamic Flooding               December 2018


   Types in the range 33024-65535 are not to be assigned at this time.
   Before any assignments can be made in the 33024-65535 range, there
   MUST be an IETF specification that specifies IANA Considerations that
   covers the range being assigned.

7.3.  IGP

   IANA is requested to set up a registry called "IGP Algorithm Type For
   Computing Flooding Topology" under an existing "Interior Gateway
   Protocol (IGP) Parameters" IANA registries.

   Values in this registry come from the range 0-255.

   The initial values in the IGP Algorithm Type For Computing Flooding
   Topology registry are:

      0: Reserved for centralized mode.  Individual values are are to be
      assigned according to the "Specification Required" policy defined
      in [RFC8126]

      1-127: Available for standards action.Individual values are are to
      be assigned according to the "Private Use" policy defined in
      [RFC8126]

      128-254: Reserved for private use.

      255: Reserved.

8.  Security Considerations

   This document introduces no new security issues.  Security of routing
   within a domain is already addressed as part of the routing protocols
   themselves.  This document proposes no changes to those security
   architectures.

   It is possible that an attacker could become Area Leader and
   introduce a flawed flooding algorithm into the network thus
   compromising the operation of the protocol.  Authentication methods
   as describe in [RFC5304] and [RFC5310] for IS-IS, [RFC2328] and
   [RFC7474] for OSPFv2 and [RFC5340] and [RFC4552] for OSPFv3 SHOULD be
   used to prevent such attack.

9.  Acknowledgements

   The authors would like to thank Sarah Chen for her contribution to
   this work.





Li, et al.                Expires June 6, 2019                 [Page 33]


Internet-Draft              Dynamic Flooding               December 2018


   The authors would like to thank Zeqing (Fred) Xia, Naiming Shen, Adam
   Sweeney and Olufemi Komolafe for their helpful comments.

   The authors would like to thank Tom Edsall for initially introducing
   them to the problem.

10.  References

10.1.  Normative References

   [ISO10589]
              International Organization for Standardization,
              "Intermediate System to Intermediate System Intra-Domain
              Routing Exchange Protocol for use in Conjunction with the
              Protocol for Providing the Connectionless-mode Network
              Service (ISO 8473)", ISO/IEC 10589:2002, Nov. 2002.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/info/rfc2328>.

   [RFC4552]  Gupta, M. and N. Melam, "Authentication/Confidentiality
              for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
              <https://www.rfc-editor.org/info/rfc4552>.

   [RFC5250]  Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
              OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250,
              July 2008, <https://www.rfc-editor.org/info/rfc5250>.

   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
              Authentication", RFC 5304, DOI 10.17487/RFC5304, October
              2008, <https://www.rfc-editor.org/info/rfc5304>.

   [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
              and M. Fanto, "IS-IS Generic Cryptographic
              Authentication", RFC 5310, DOI 10.17487/RFC5310, February
              2009, <https://www.rfc-editor.org/info/rfc5310>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.





Li, et al.                Expires June 6, 2019                 [Page 34]


Internet-Draft              Dynamic Flooding               December 2018


   [RFC5613]  Zinin, A., Roy, A., Nguyen, L., Friedman, B., and D.
              Yeung, "OSPF Link-Local Signaling", RFC 5613,
              DOI 10.17487/RFC5613, August 2009,
              <https://www.rfc-editor.org/info/rfc5613>.

   [RFC7120]  Cotton, M., "Early IANA Allocation of Standards Track Code
              Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
              2014, <https://www.rfc-editor.org/info/rfc7120>.

   [RFC7356]  Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
              Scope Link State PDUs (LSPs)", RFC 7356,
              DOI 10.17487/RFC7356, September 2014,
              <https://www.rfc-editor.org/info/rfc7356>.

   [RFC7474]  Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
              "Security Extension for OSPFv2 When Using Manual Key
              Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
              <https://www.rfc-editor.org/info/rfc7474>.

   [RFC7770]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
              February 2016, <https://www.rfc-editor.org/info/rfc7770>.

   [RFC7981]  Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions
              for Advertising Router Information", RFC 7981,
              DOI 10.17487/RFC7981, October 2016,
              <https://www.rfc-editor.org/info/rfc7981>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

10.2.  Informative References

   [Clos]     Clos, C., "A Study of Non-Blocking Switching Networks",
              The Bell System Technical Journal Vol. 32(2), DOI
              10.1002/j.1538-7305.1953.tb01433.x, March 1953,
              <http://dx.doi.org/10.1002/j.1538-7305.1953.tb01433.x>.

   [Leiserson]
              Leiserson, C., "Fat-Trees: Universal Networks for
              Hardware-Efficient Supercomputing", IEEE Transactions on
              Computers 34(10):892-901, 1985.






Li, et al.                Expires June 6, 2019                 [Page 35]


Internet-Draft              Dynamic Flooding               December 2018


   [RFC2973]  Balay, R., Katz, D., and J. Parker, "IS-IS Mesh Groups",
              RFC 2973, DOI 10.17487/RFC2973, October 2000,
              <https://www.rfc-editor.org/info/rfc2973>.

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,
              <https://www.rfc-editor.org/info/rfc3630>.

   [RFC4811]  Nguyen, L., Roy, A., and A. Zinin, "OSPF Out-of-Band Link
              State Database (LSDB) Resynchronization", RFC 4811,
              DOI 10.17487/RFC4811, March 2007,
              <https://www.rfc-editor.org/info/rfc4811>.

   [RFC7938]  Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of
              BGP for Routing in Large-Scale Data Centers", RFC 7938,
              DOI 10.17487/RFC7938, August 2016,
              <https://www.rfc-editor.org/info/rfc7938>.

Authors' Addresses

   Tony Li (editor)
   Arista Networks
   5453 Great America Parkway
   Santa Clara, California  95054
   USA

   Email: tony.li@tony.li


   Peter Psenak (editor)
   Cisco Systems, Inc.
   Eurovea Centre, Central 3
   Pribinova Street 10
   Bratislava  81109
   Slovakia

   Email: ppsenak@cisco.com


   Les Ginsberg
   Cisco Systems, Inc.
   510 McCarthy Blvd.
   Milpitas, California  95035
   USA

   Email: ginsberg@cisco.com




Li, et al.                Expires June 6, 2019                 [Page 36]


Internet-Draft              Dynamic Flooding               December 2018


   Tony Przygienda
   Juniper Networks, Inc.
   1194 N. Mathilda Ave
   Sunnyvale, California  94089
   USA

   Email: prz@juniper.net


   Dave Cooper
   CenturyLink
   1025 Eldorado Blvd
   Broomfield, Colorado  80021
   USA

   Email: Dave.Cooper@centurylink.com


   Luay Jalil
   Verizon
   Richardson, Texas  75081
   USA

   Email: luay.jalil@verizon.com


   Srinath Dontula
   ATT
   200 S Laurel Ave
   Middletown, New Jersey  07748
   USA

   Email: sd947e@att.com


















Li, et al.                Expires June 6, 2019                 [Page 37]


Html markup produced by rfcmarkup 1.129b, available from https://tools.ietf.org/tools/rfcmarkup/