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Versions: 00 01 02 03 04 draft-ietf-anima-grasp

Network Working Group                                       B. Carpenter
Internet-Draft                                         Univ. of Auckland
Intended status: Standards Track                                  B. Liu
Expires: October 22, 2015                   Huawei Technologies Co., Ltd
                                                          April 20, 2015


 A Generic Discovery and Negotiation Protocol for Autonomic Networking
                 draft-carpenter-anima-gdn-protocol-03

Abstract

   This document establishes requirements for a protocol that enables
   intelligent devices to dynamically discover peer devices, to
   synchronize state with them, and to negotiate parameter settings
   mutually with them.  The document then defines a general protocol for
   discovery, synchronization and negotiation, while the technical
   objectives for specific scenarios are to be described in separate
   documents.  An Appendix briefly discusses existing protocols with
   comparable features.

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 http://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 October 22, 2015.

Copyright Notice

   Copyright (c) 2015 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
   (http://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



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   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
   2.  Requirement Analysis of Discovery, Synchronization and
       Negotiation . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements for Discovery  . . . . . . . . . . . . . . .   4
     2.2.  Requirements for Synchronization and Negotiation
           Capability  . . . . . . . . . . . . . . . . . . . . . . .   5
     2.3.  Specific Technical Requirements . . . . . . . . . . . . .   7
   3.  GDNP Protocol Overview  . . . . . . . . . . . . . . . . . . .   8
     3.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   8
     3.2.  High-Level Design Choices . . . . . . . . . . . . . . . .   9
     3.3.  GDNP Protocol Basic Properties and Mechanisms . . . . . .  13
       3.3.1.  Required External Security Mechanism  . . . . . . . .  13
       3.3.2.  Transport Layer Usage . . . . . . . . . . . . . . . .  13
       3.3.3.  Discovery Mechanism and Procedures  . . . . . . . . .  13
       3.3.4.  Negotiation Procedures  . . . . . . . . . . . . . . .  15
       3.3.5.  Synchronization Procedure . . . . . . . . . . . . . .  16
     3.4.  GDNP Constants  . . . . . . . . . . . . . . . . . . . . .  17
     3.5.  Session Identifier (Session ID) . . . . . . . . . . . . .  17
     3.6.  GDNP Messages . . . . . . . . . . . . . . . . . . . . . .  18
       3.6.1.  GDNP Message Format . . . . . . . . . . . . . . . . .  18
       3.6.2.  Discovery Message . . . . . . . . . . . . . . . . . .  19
       3.6.3.  Response Message  . . . . . . . . . . . . . . . . . .  19
       3.6.4.  Request Message . . . . . . . . . . . . . . . . . . .  20
       3.6.5.  Negotiation Message . . . . . . . . . . . . . . . . .  20
       3.6.6.  Negotiation-ending Message  . . . . . . . . . . . . .  21
       3.6.7.  Confirm-waiting Message . . . . . . . . . . . . . . .  21
     3.7.  GDNP General Options  . . . . . . . . . . . . . . . . . .  21
       3.7.1.  Format of GDNP Options  . . . . . . . . . . . . . . .  21
       3.7.2.  Divert Option . . . . . . . . . . . . . . . . . . . .  22
       3.7.3.  Accept Option . . . . . . . . . . . . . . . . . . . .  22
       3.7.4.  Decline Option  . . . . . . . . . . . . . . . . . . .  23
       3.7.5.  Waiting Time Option . . . . . . . . . . . . . . . . .  23
       3.7.6.  Device Identity Option  . . . . . . . . . . . . . . .  24
       3.7.7.  Locator Options . . . . . . . . . . . . . . . . . . .  24
     3.8.  Objective Options . . . . . . . . . . . . . . . . . . . .  26
       3.8.1.  Format of Objective Options . . . . . . . . . . . . .  26
       3.8.2.  General Considerations for Objective Options  . . . .  27
       3.8.3.  Organizing of Objective Options . . . . . . . . . . .  27
       3.8.4.  Vendor Specific Objective Options . . . . . . . . . .  28
       3.8.5.  Experimental Objective Options  . . . . . . . . . . .  29
   4.  Items for Future Work . . . . . . . . . . . . . . . . . . . .  29



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   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  30
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  31
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  33
   8.  Change log [RFC Editor: Please remove]  . . . . . . . . . . .  33
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  34
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  35
   Appendix A.  Capability Analysis of Current Protocols . . . . . .  37
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  40

1.  Introduction

   The success of the Internet has made IP-based networks bigger and
   more complicated.  Large-scale ISP and enterprise networks have
   become more and more problematic for human based management.  Also,
   operational costs are growing quickly.  Consequently, there are
   increased requirements for autonomic behavior in the networks.
   General aspects of autonomic networks are discussed in
   [I-D.irtf-nmrg-autonomic-network-definitions] and
   [I-D.irtf-nmrg-an-gap-analysis].  In order to fulfil autonomy,
   devices that embody autonomic service agents need to be able to
   discover each other, to synchronize state with each other, and to
   negotiate parameters and resources directly with each other.  There
   is no restriction on the type of parameters and resources concerned,
   which include very basic information needed for addressing and
   routing, as well as anything else that might be configured in a
   conventional network.

   Following this Introduction, Section 2 describes the requirements for
   network device discovery, synchronization and negotiation.
   Negotiation is an iterative process, requiring multiple message
   exchanges forming a closed loop between the negotiating devices.
   State synchronization, when needed, can be regarded as a special case
   of negotiation, without iteration.  Section 3.2 describes a behavior
   model for a protocol intended to support discovery, synchronization
   and negotiation.  The design of Generic Discovery and Negotiation
   Protocol (GDNP) in Section 3 of this document is mainly based on this
   behavior model.  The relevant capabilities of various existing
   protocols are reviewed in Appendix A.

   The proposed discovery mechanism is oriented towards synchronization
   and negotiation objectives.  It is based on a neighbor discovery
   process, but also supports diversion to off-link peers.  Although
   many negotiations will occur between horizontally distributed peers,
   many target scenarios are hierarchical networks, which is the
   predominant structure of current large-scale networks.  However, when
   a device starts up with no pre-configuration, it has no knowledge of
   a hierarchical superior.  The protocol itself is capable of being



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   used in a small and/or flat network structure such as a small office
   or home network as well as a professionally managed network.
   Therefore, the discovery mechanism needs to be able to allow a device
   to bootstrap itself without making any prior assumptions about
   network structure.

   Because GDNP can be used to perform a decision process among
   distributed devices or between networks, it must run in a secure and
   strongly authenticatd environment.

   It is understood that in realistic deployments, not all devices will
   support GDNP.  It is expected that some autonomic service agents will
   manage a group of non-autonomic nodes, and that other non-autonomic
   nodes will be managed traditionally.  Such mixed scenarios are not
   discussed in this specification.

2.  Requirement Analysis of Discovery, Synchronization and Negotiation

   This section discusses the requirements for discovery, negotiation
   and synchronization capabilities.

2.1.  Requirements for Discovery

   In an autonomic network we must assume that when a device starts up
   it has no information about any peer devices, the network structure,
   or what specific role it must play.  In some cases, when a new
   application session starts up within a device, the device may again
   lack information about relevant peer devices.  It might be necessary
   to set up resources on multiple other devices, coordinated and
   matched to each other so that there is no wasted resource.  Security
   settings might also need updating to allow for the new device or
   user.  Therefore a basic requirement is that there must be a
   mechanism by which a device can separately discover peer devices for
   each of the technical objectives that it needs to manage.  Some
   objectives may only be significant on the local link, but others may
   be significant across the routed network and require off-link
   operations.  Thus, the relevant peer devices might be immediate
   neighbors on the same layer 2 link or they might be more distant and
   only accessible via layer 3.  The mechanism must therefore support
   both on-link discovery and off-link discovery of peers that support
   specific technical objectives.

   The relevant peer devices may be different for different technical
   objectives.  Therefore discovery needs to be repeated as often as
   necessary to find peers capable of acting as counterparts for each
   objective that a discovery initiator needs to handle.  In many
   scenarios, the discovery process may be followed by a synchronization
   or negotiation process.  Therefore, a discovery objective may be



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   associated with one or more synchronization or negotiation
   objectives.

   When a device first starts up, it has no knowledge of the network
   structure.  Therefore the discovery process must be able to support
   any network scenario, assuming only that the device concerned is
   bootstrapped from factory condition.

   In some networks, as mentioned above, there will be some hierarchical
   structure, at least for certain synchronization or negotiation
   objectives.  A special case of discovery is that each device must be
   able to discover its hierarchical superior for each such objective
   that it is capable of handling.  This is part of the more general
   requirement to discover off-link devices.

   During initialisation, a device must be able to establish mutual
   trust with the rest of the network and join an authentication
   mechanism.  Although this will inevitably start with a discovery
   action, it is a special case precisely because trust is not yet
   established.  This topic is the subject of
   [I-D.pritikin-anima-bootstrapping-keyinfra].  In addition, depending
   on the type of network involved, discovery of other central functions
   might be needed, such as the Network Operations Center (NOC)
   [I-D.eckert-anima-stable-connectivity].  GDNP must be capable of
   supporting such discovery during initialisation, as well as discovery
   during ongoing operation.

2.2.  Requirements for Synchronization and Negotiation Capability

   We start by considering routing protocols, the closest approximation
   to autonomic networking in widespread use.  Routing protocols use a
   largely autonomic model based on distributed devices that communicate
   repeatedly with each other.  However, routing is mainly based on one-
   way information synchronization (in either direction), rather than on
   bi-directional negotiation.  The focus is reachability, so current
   routing protocols only consider simple link status, i.e., up or down,
   and an underlying assumption is that all nodes need a consistent view
   of the network topology.  Other information, such as latency,
   congestion, capacity, and particularly unused capacity, would be
   helpful to get better path selection and utilization rate, but are
   not normally used in distributed routing algorithms.  Also, autonomic
   networks need to be able to manage many more dimensions, such as
   security settings, power saving, load balancing, etc.  In general,
   these items do not apply to all participating nodes, but only to a
   subset.  A basic requirement for the protocol is therefore the
   ability to represent, discover, synchronize and negotiate almost any
   kind of network parameter among arbitrary subsets of participating
   nodes.



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   Human intervention in complex situations is costly and error-prone.
   Therefore, synchronization or negotiation of parameters without human
   intervention is desirable whenever the coordination of multiple
   devices can improve overall network performance.  It follows that a
   requirement for the protocol is to be capable of running in any
   device that would otherwise need human intervention.

   Human intervention in large networks is often replaced by use of a
   top-down network management system (NMS).  It therefore follows that
   a requirement for the protocol is to be capable of running in any
   device that would otherwise be managed by an NMS, and that it can co-
   exist with an NMS.

   Since the goal is to minimize human intervention, it is necessary
   that the network can in effect "think ahead" before changing its
   parameters.  In other words there must be a possibility of
   forecasting the effect of a change by a "dry run" mechanism before
   actually installing the change.  This will be an application of the
   protocol rather than a feature of the protocol itself.

   Status information and traffic metrics need to be shared between
   nodes for dynamic adjustment of resources and for monitoring
   purposes.  While this might be achieved by existing protocols when
   they are available, the new protocol needs to be able to support
   parameter exchange, including mutual synchronization, even when no
   negotiation as such is required.

   Recovery from faults and identification of faulty devices should be
   as automatic as possible.  However, the protocol's role is limited to
   the ability to handle discovery, synchronization and negotiation at
   any time, in case an autonomic service agent detects an anomaly such
   as a negotiation counterpart failing.

   Management logging, monitoring, alerts and tools for intervention are
   required.  However, these can only be features of individual
   autonomic service agents.  Another document
   [I-D.eckert-anima-stable-connectivity] discusses how such agents may
   be linked into conventional OAM systems via an Autonomic Control
   Plane [I-D.behringer-anima-autonomic-control-plane].

   The protocol needs to be able to deal with a wide variety of
   technical objectives, covering any type of network parameter.
   Therefore the protocol will need either an explicit information model
   describing its messages, or at least a flexible and extensible
   message format.  One design consideration is whether to adopt an
   existing information model or to design a new one.  Another
   consideration is whether it should be able to carry some or all of
   the message formats used by existing configuration protocols.



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2.3.  Specific Technical Requirements

   To be a generic platform, the protocol payload format should be
   independent of the transport protocol or IP version.  In particular,
   it should be able to run over IPv6 or IPv4.  However, some functions,
   such as multicasting or broadcasting on a link, might need to be IP
   version dependent.  In case of doubt, IPv6 should be preferred.

   The protocol must be able to access off-link counterparts via
   routable addresses, i.e., must not be restricted to link-local
   operation.

   The negotiation process must be guaranteed to terminate (with success
   or failure) and if necessary it must contain tie-breaking rules for
   each technical objective that requires them.  While this must be
   defined specifically for each use case, the protocol should have some
   general mechanisms in support of loop and deadlock prevention.

   Dependencies and conflicts: In order to decide a configuration on a
   given device, the device may need information from neighbors.  This
   can be established through the negotiation procedure, or through
   synchronization if that is sufficient.  However, a given item in a
   neighbor may depend on other information from its own neighbors,
   which may need another negotiation or synchronization procedure to
   obtain or decide.  Therefore, there are potential dependencies and
   conflicts among negotiation or synchronization procedures.  Resolving
   dependencies and conflicts is a matter for the individual autonomic
   service agents involved.  To allow this, there need to be clear
   boundaries and convergence mechanisms for negotiations.  Also some
   mechanisms are needed to avoid loop dependencies.

   Policy constraints: There must be provision for general policy intent
   rules to be applied by all devices in the network (e.g., security
   rules, prefix length, resource sharing rules).  However, policy
   intent distribution might not use the negotiation protocol itself.

   Management monitoring, alerts and intervention: Devices should be
   able to report to a monitoring system.  Some events must be able to
   generate operator alerts and some provision for emergency
   intervention must be possible (e.g.  to freeze synchronization or
   negotiation in a mis-behaving device).  These features may not use
   the negotiation protocol itself.

   The protocol needs to be fully secure against forged messages and
   man-in-the middle attacks, and as secure as reasonably possible
   against denial of service attacks.  It needs to be capable of
   encryption in order to resist unwanted monitoring, although this
   capability may not be required in all deployments.  However, it is



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   not required that the protocol itself provides these security
   features; it may depend on an existing secure environment.

3.  GDNP Protocol Overview

3.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119] when they appear in ALL CAPS.  When these words are not in
   ALL CAPS (such as "should" or "Should"), they have their usual
   English meanings, and are not to be interpreted as [RFC2119] key
   words.

   This document uses terminology defined in
   [I-D.irtf-nmrg-autonomic-network-definitions].

   The following additional terms are used throughout this document:

   o  Discovery: a process by which a device discovers peer devices
      according to a specific discovery objective.  The discovery
      results may be different according to the different discovery
      objectives.  The discovered peer devices may later be used as
      negotiation counterparts or as sources of synchronization data.

   o  Negotiation: a process by which two (or more) devices interact
      iteratively to agree on parameter settings that best satisfy the
      objectives of one or more devices.

   o  State Synchronization: a process by which two (or more) devices
      interact to agree on the current state of parameter values stored
      in each device.  This is a special case of negotiation in which
      information is sent but the devices do not request their peers to
      change parameter settings.  All other definitions apply to both
      negotiation and synchronization.

   o  Objective: An objective in GDNP is a configurable state of some
      kind, which occurs in three contexts: Discovery, Negotiation and
      Synchronization.  In the protocol, an objective is represented by
      an identifier (actually a GDNP option number) and if relevant a
      value.  Normally, a given objective will occur during discovery
      and negotiation, or during discovery and synchronization, but not
      in all three contexts.

      *  One device may support multiple independent objectives.





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      *  The parameter described by a given objective is naturally based
         on a specific service or function or action.  It may in
         principle be anything that can be set to a specific logical,
         numerical or string value, or a more complex data structure, by
         a network node.  That node is generally expected to be an
         autonomic service agent which may itself manage other nodes.

      *  Discovery Objective: if a node needs to synchronize or
         negotiate a specific objective but does not know a peer that
         supports this objective, it starts a discovery process.  The
         objective is called a Discovery Objective during this process.

      *  Synchronization Objective: an objective whose specific
         technical content needs to be synchronized among two or more
         devices.

      *  Negotiation Objective: an objective whose specific technical
         content needs to be decided in coordination with another
         network device.

   o  Discovery Initiator: a device that spontaneously starts discovery
      by sending a discovery message referring to a specific discovery
      objective.

   o  Discovery Responder: a peer device which responds to the discovery
      objective initiated by the discovery initiator.

   o  Synchronization Initiator: a device that spontaneously starts
      synchronization by sending a request message referring to a
      specific synchronization objective.

   o  Synchronization Responder: a peer device which responds with the
      value of a synchronization objective.

   o  Negotiation Initiator: a device that spontaneously starts
      negotiation by sending a request message referring to a specific
      negotiation objective.

   o  Negotiation Counterpart: a peer device with which the Negotiation
      Initiator negotiates a specific negotiation objective.

3.2.  High-Level Design Choices

   This section describes a behavior model and some considerations for
   designing a generic discovery, synchronization and negotiation
   protocol, which can act as a platform for different technical
   objectives.




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   NOTE: This protocol is described here in a stand-alone fashion as a
   proof of concept.  An early version was prototyped by Huawei and the
   Beijing University of Posts and Telecommunications.  However, this is
   not yet a definitive proposal for IETF adoption.  In particular,
   adaptation and extension of one of the protocols discussed in
   Appendix A might be an option.  This whole specification is subject
   to change as a result.

   o  A generic platform

      The protocol is designed as a generic platform, which is
      independent from the synchronization or negotiation contents.  It
      takes care of the general intercommunication between counterparts.
      The technical contents will vary according to the various
      synchronization or negotiation objectives and the different pairs
      of counterparts.


   o  Security infrastructure and trust relationship

      Because this negotiation protocol may directly cause changes to
      device configurations and bring significant impacts to a running
      network, this protocol is assumed to run within an existing secure
      environment with strong authentication.

      On the other hand, a limited negotiation model might be deployed
      based on a limited trust relationship.  For example, between two
      administrative domains, devices might also exchange limited
      information and negotiate some particular configurations based on
      a limited conventional or contractual trust relationship.


   o  Discovery, synchronization and negotiation designed together

      The discovery method and the synchronization and negotiation
      methods are designed in the same way and can be combined when this
      is useful.  These processes can also be performed independently
      when appropriate.

      *  GDNP discovery is appropriate for efficient discovery of GDNP
         peers and allows a rapid mode of operation described in
         Section 3.3.3.  For some parameters, especially those concerned
         with application layer services, a text-based discovery
         mechanism such as DNS Service Discovery
         [I-D.ietf-dnssd-requirements] or Service Location Protocol
         [RFC2608] might be more appropriate.  The choice is left to the
         designers of individual Autonomic Service Agents.




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   o  A uniform pattern for technical contents

      The synchronization and negotiation contents are defined according
      to a uniform pattern.  They could be carried either in simple TLV
      (Type, Length and Value) format or in payloads described by a
      flexible language.  The initial protocol design uses the TLV
      approach.  The format is extensible for unknown future
      requirements.


   o  A conservative model for synchronization

      GDNP supports bilateral synchronization, which could be used to
      perform synchronization among a small number of nodes.

      *  For some parameters, synchronization across large groups of
         nodes, possibly including all autonomic nodes, might be needed.
         For such cases, a flooding mechanism such as ADNCP
         [I-D.stenberg-anima-adncp] is considered more appropriate.
         GDNP is designed to coexist with ADNCP.  The choice is left to
         the designers of individual Autonomic Service Agents.

   o  A simple initiator/responder model for negotiation

      Multi-party negotiations are too complicated to be modeled and
      there might be too many dependencies among the parties to converge
      efficiently.  A simple initiator/responder model is more feasible
      and can complete multiple-party negotiations by indirect steps.


   o  Organizing of synchronization or negotiation content

      Naturally, the technical content will be organized according to
      the relevant function or service.  The content from different
      functions or services is kept independent from each other.  They
      are not combined into a single option or single session because
      these contents may be negotiated or synchronized with different
      counterparts or may be different in response time.


   o  Self aware network device

      Every network device will be pre-loaded with various functions and
      be aware of its own capabilities, typically decided by the
      hardware, firmware or pre-installed software.  Its exact role may
      depend on the surrounding network behaviors, which may include
      forwarding behaviors, aggregation properties, topology location,
      bandwidth, tunnel or translation properties, etc.  The surrounding



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      topology will depend on the network planning.  Following an
      initial discovery phase, the device properties and those of its
      neighbors are the foundation of the synchronization or negotiation
      behavior of a specific device.  A device has no pre-configuration
      for the particular network in which it is installed.


   o  Requests and responses in negotiation procedures

      The initiator can negotiate with its relevant negotiation
      counterpart devices, which may be different according to the
      specific negotiation objective.  It can request relevant
      information from the negotiation counterpart so that it can decide
      its local configuration to give the most coordinated performance.
      It can request the negotiation counterpart to make a matching
      configuration in order to set up a successful communication with
      it.  It can request certain simulation or forecast results by
      sending some dry run conditions.

      Beyond the traditional yes/no answer, the responder can reply with
      a suggested alternative if its answer is 'no'.  This would start a
      bi-directional negotiation ending in a compromise between the two
      devices.


   o  Convergence of negotiation procedures

      To enable convergence, when a responder makes a suggestion of a
      changed condition in a negative reply, it should be as close as
      possible to the original request or previous suggestion.  The
      suggested value of the third or later negotiation steps should be
      chosen between the suggested values from the last two negotiation
      steps.  In any case there must be a mechanism to guarantee
      convergence (or failure) in a small number of steps, such as a
      timeout or maximum number of iterations.



      *  End of negotiation

         A limited number of rounds, for example three, or a timeout, is
         needed on each device for each negotiation objective.  It may
         be an implementation choice, a pre-configurable parameter, or a
         network-wide policy intent.  These choices might vary between
         different types of autonomic service agent.  Therefore, the
         definition of each negotiation objective MUST clearly specify
         this, so that the negotiation can always be terminated
         properly.



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      *  Failed negotiation

         There must be a well-defined procedure for concluding that a
         negotiation cannot succeed, and if so deciding what happens
         next (deadlock resolution, tie-breaking, or revert to best-
         effort service).  Again, this MUST be specified for individual
         negotiation objectives, as an implementation choice, a pre-
         configurable parameter, or a network-wide policy intent.

3.3.  GDNP Protocol Basic Properties and Mechanisms

3.3.1.  Required External Security Mechanism

   The protocol SHOULD run within a secure Autonomic Control Plane (ACP)
   [I-D.behringer-anima-autonomic-control-plane].  If this is
   impossible, it MUST use TLS [RFC5246] or DTLS [RFC6347] for all
   messages, based on a local Public Key Infrastructure (PKI) [RFC5280]
   managed within the autonomic network itself.

   Link-local multicast is used for discovery messages.  These cannot be
   secured, but responses to discovery messages MUST be secured.
   However, during initialisation, before a node has joined the
   applicable trust infrastructure, e.g.,
   [I-D.pritikin-anima-bootstrapping-keyinfra], it will be impossible to
   secure certain messages.  Such messages MUST be limited to the
   strictly necessary minimum.

3.3.2.  Transport Layer Usage

   The protocol is capable of running over UDP or TCP, except for
   multicast discovery messages which can only run over UDP.  When
   running within an ACP, UDP SHOULD be used for messages not exceeding
   the minimum IPv6 path MTU, and TCP SHOULD be used for longer
   messages.  In other words, IPv6 fragmentation should be avoided.
   When running without an ACP, TLS MUST be used by default, except for
   multicast discovery messages.  DTLS MAY be supported as an
   alternative.

3.3.3.  Discovery Mechanism and Procedures

   o  Separated discovery and negotiation mechanisms

         Although discovery and negotiation or synchronization are
         defined together in the GDNP, they are separated mechanisms.
         The discovery process could run independently from the
         negotiation or synchronization process.  Upon receiving a
         discovery (Section 3.6.2) or request (Section 3.6.4) message,
         the recipient device should return a message in which it either



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         indicates itself as a discovery responder or diverts the
         initiator towards another more suitable device.

         The discovery action will normally be followed by a negotiation
         or synchronization action.  The discovery results could be
         utilized by the negotiation protocol to decide which device the
         initiator will negotiate with.

   o  Discovery Procedures

         Discovery starts as an on-link operation.  The Divert option
         can tell the discovery initiator to contact an off-link
         discovery objective device.  Every DISCOVERY message is sent by
         a discovery initiator via UDP to the ALL_GDNP_NEIGHBOR
         multicast address (Section 3.4).  Every network device that
         supports the GDNP always listens to a well-known UDP port to
         capture the discovery messages.

         If the neighbor device supports the requested discovery
         objective, it MAY respond with a Response message
         (Section 3.6.3) with locator option(s).  Otherwise, if the
         neigbor device has cached information about a device that
         supports the requested discovery objective (usually because it
         discovered the same objective before), it SHOULD respond with a
         Response message with a Divert option pointing to the
         appropriate Discovery Responder.

         If no discovery response is received within a reasonable
         timeout (default GDNP_DEF_TIMEOUT milliseconds, Section 3.4),
         the DISCOVERY message MAY be repeated, with a newly generated
         Session ID (Section 3.5).  An exponential backoff SHOULD be
         used for subsequent repetitions, in order to mitigate possible
         denial of service attacks.

         After a GDNP device successfully discovers a Discovery
         Responder supporting a specific objective, it MUST cache this
         information.  This cache record MAY be used for future
         negotiation or synchronization, and SHOULD be passed on when
         appropriate as a Divert option to another Discovery Initiator.
         The cache lifetime is an implementation choice.

         If multiple Discovery Responders are found for the same
         objective, they SHOULD all be cached, unless this creates a
         resource shortage.  The method of choosing between multiple
         responders is an implementation choice.

         A GDNP device with multiple link-layer interfaces (typically a
         router) MUST support discovery on all interfaces.  If it



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         receives a DISCOVERY message on a given interface for a
         specific objective that it does not support and for which it
         has not previously discovered a Discovery Responder, it MUST
         relay the query by re-issuing the same DISCOVERY message on its
         other interfaces.  However, it MUST limit the total rate at
         which it relays discovery messages to a reasonable value, in
         order to mitigate possible denial of service attacks.  It MUST
         cache the Session ID value of each relayed discovery message
         and, to prevent loops, MUST NOT relay a DISCOVERY message which
         carries such a cached Session ID.

         This relayed discovery mechanism, with caching of the results,
         should be sufficient to support most network bootstrapping
         scenarios.

   o  A complete discovery process will start with multicast on the
      local link; a neighbor might divert it to an off-link destination,
      which could be a default higher-level gateway in a hierarchical
      network.  Then discovery would continue with a unicast to that
      gateway; if that gateway is still not the right counterpart, it
      should divert to another device, which is in principle closer to
      the right counterpart.  Finally the right counterpart responds to
      start the negotiation or synchronization process.

   o  Rapid Mode (Discovery/Negotiation binding)

         A Discovery message MAY include one or more Negotiation
         Objective option(s).  This allows a rapid mode of negotiation
         described in Section 3.3.4.  A similar mechanism is defined for
         synchronization in Section 3.3.5.

3.3.4.  Negotiation Procedures

   A negotiation initiator sends a negotiation request to a counterpart
   device, including a specific negotiation objective.  It may request
   the negotiation counterpart to make a specific configuration.
   Alternatively, it may request a certain simulation or forecast result
   by sending a dry run configuration.  The details, including the
   distinction between dry run and an actual configuration change, will
   be defined separately for each type of negotiation objective.

   If the counterpart can immediately apply the requested configuration,
   it will give an immediate positive (accept) answer.  This will end
   the negotiation phase immediately.  Otherwise, it will negotiate.  It
   will reply with a proposed alternative configuration that it can
   apply (typically, a configuration that uses fewer resources than
   requested by the negotiation initiator).  This will start a bi-




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   directional negotiation to reach a compromise between the two network
   devices.

   The negotiation procedure is ended when one of the negotiation peers
   sends a Negotiation Ending message, which contains an accept or
   decline option and does not need a response from the negotiation
   peer.  Negotiation may also end in failure (equivalent to a decline)
   if a timeout is exceeded or a loop count is exceeded.

   A negotiation procedure concerns one objective and one counterpart.
   Both the initiator and the counterpart may take part in simultaneous
   negotiations with various other devices, or in simultaneous
   negotiations about different objectives.  Thus, GDNP is expected to
   be used in a multi-threaded mode.  Certain negotiation objectives may
   have restrictions on multi-threading, for example to avoid over-
   allocating resources.

   Rapid Mode (Discovery/Negotiation linkage)

      A Discovery message MAY include a Negotiation Objective option.
      In this case the Discovery message also acts as a Request message
      to indicate to the Discovery Responder that it could directly
      reply to the Discovery Initiator with a Negotiation message for
      rapid processing, if it could act as the corresponding negotiation
      counterpart.  However, the indication is only advisory not
      prescriptive.

      This rapid mode could reduce the interactions between nodes so
      that a higher efficiency could be achieved.  This rapid
      negotiation function SHOULD be configured off by default and MAY
      be configured on or off by policy intent.

3.3.5.  Synchronization Procedure

   A synchronization initiator sends a synchronization request to a
   counterpart device, including a specific synchronization objective.
   The counterpart responds with a Response message containing the
   current value of the requested synchronization objective.  No further
   messages are needed.  If no Response message is received, the
   synchronization request MAY be repeated after a suitable timeout.

   In the case just described, the message exchange is unicast and
   concerns only one synchronization objective.  For large groups of
   nodes requiring mutual synchronization, ADNCP
   [I-D.stenberg-anima-adncp] is considered more appropriate.  In the
   following case, several synchronization objectives may be combined.

   Rapid Mode (Discovery/Synchronization linkage)



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      A Discovery message MAY include one or more Synchronization
      Objective option(s).  In this case the Discovery message also acts
      as a Request message to indicate to the Discovery Responder that
      it could directly reply to the Discovery Initiator with a Response
      message with synchronization data for rapid processing, if the
      discovery target supports the corresponding synchronization
      objective(s).  However, the indication is only advisory not
      prescriptive.

      This rapid mode could reduce the interactions between nodes so
      that a higher efficiency could be achieved.  This rapid
      synchronization function SHOULD be configured off by default and
      MAY be configured on or off by policy intent.

3.4.  GDNP Constants

   o  ALL_GDNP_NEIGHBOR

      A link-local scope multicast address used by a GDNP-enabled device
      to discover GDNP-enabled neighbor (i.e., on-link) devices . All
      devices that support GDNP are members of this multicast group.

      *  IPv6 multicast address: TBD1

      *  IPv4 multicast address: TBD2

   o  GDNP Listen Port (TBD3)

      A UDP and TCP port that every GDNP-enabled network device always
      listens to.

   o  GDNP_DEF_TIMEOUT (60000 milliseconds)

      The default timeout used to determine that a discovery or
      negotiation has failed to complete.

   o  GDNP_DEF_LOOPCT (6)

      The default loop count used to determine that a negotiation has
      failed to complete.

3.5.  Session Identifier (Session ID)

   A 24-bit opaque value used to distinguish multiple sessions between
   the same two devices.  A new Session ID MUST be generated for every
   new Discovery or Request message, and for every unsolicited Response
   message.  All follow-up messages in the same discovery,




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   synchronization or negotiation procedure, which is initiated by the
   request message, MUST carry the same Session ID.

   The Session ID SHOULD have a very low collision rate locally.  It is
   RECOMMENDED to be generated by a pseudo-random algorithm using a seed
   which is unlikely to be used by any other device in the same network
   [RFC4086].

3.6.  GDNP Messages

   This document defines the following GDNP message format and types.
   Message types not listed here are reserved for future use.  The
   numeric encoding for each message type is shown in parentheses.

3.6.1.  GDNP Message Format

   GDNP messages share an identical fixed format header and a variable
   format area for options.  GDNP message headers and options are in the
   type-length-value (TLV) format defined in DNCP (see Section "Type-
   Length-Value Objects" in [I-D.ietf-homenet-dncp]).

   Every GDNP message carries a Session ID.  Options are presented
   serially in the options field, with padding to 4-byte alignment.

   The following diagram illustrates the format of GDNP messages:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          MESSAGE_TYPE         |                4              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Reserved   |                Session ID                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Options  (variable length)             |
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   MESSAGE_TYPE:  Identifies the GDNP message type. 16-bit.

   Reserved:  Set to zero, ignored on receipt. 8-bit.

   Session ID:  Identifies this GDNP session, as defined in Section 3.5.
      24-bit.

   Options:  GDNP Options carried in this message.  Options are defined
      starting at Section 3.7.





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3.6.2.  Discovery Message

   DISCOVERY (MESSAGE_TYPE = G1):

   A discovery initiator sends a DISCOVERY message to initiate a
   discovery process.

   The discovery initiator sends the DISCOVERY messages to the link-
   local ALL_GDNP_NEIGHBOR multicast address for discovery, and stores
   the discovery results (including responding discovery objectives and
   corresponding unicast addresses or FQDNs).

   A DISCOVERY message MUST include exactly one of the following:

   o  a discovery objective option (Section 3.8.1).

   o  a negotiation objective option (Section 3.8.1) to indicate to the
      discovery target that it MAY directly reply to the discovery
      initiatior with a NEGOTIATION message for rapid processing, if it
      could act as the corresponding negotiation counterpart.  The
      sender of such a DISCOVERY message MUST initialize a negotiation
      timer and loop count in the same way as a REQUEST message
      (Section 3.6.4).

   o  one or more synchronization objective options (Section 3.8.1) to
      indicate to the discovery target that it MAY directly reply to the
      discovery initiator with a RESPONSE message for rapid processing,
      if it could act as the corresponding synchronization counterpart.

3.6.3.  Response Message

   RESPONSE (MESSAGE_TYPE = G2):

   A node which receives a DISCOVERY message sends a Response message to
   respond to a discovery.  It MUST contain the same Session ID as the
   DISCOVERY message.  It MAY include a copy of the discovery objective
   from the DISCOVERY message.

   If the responding node supports the discovery objective of the
   discovery, it MUST include at least one kind of locator option
   (Section 3.7.7) to indicate its own location.  A combination of
   multiple kinds of locator options (e.g.  IP address option + FQDN
   option) is also valid.

   If the responding node itself does not support the discovery
   objective, but it knows the locator of the discovery objective, then
   it SHOULD respond to the discovery message with a divert option
   (Section 3.7.2) embedding a locator option or a combination of



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   multiple kinds of locator options which indicate the locator(s) of
   the discovery objective.

   A node which receives a synchronization request sends a Response
   message with the synchronization data, in the form of GDNP Option(s)
   for the specific synchronization objective(s).

3.6.4.  Request Message

   REQUEST (MESSAGE_TYPE = G3):

   A negotiation or synchronization requesting node sends the REQUEST
   message to the unicast address (directly stored or resolved from the
   FQDN) of the negotiation or synchronization counterpart (selected
   from the discovery results).

   A request message MUST include the relevant objective option, with
   the requested value in the case of negotiation.

   When an initiator sends a REQUEST message, it MUST initialize a
   negotiation timer for the new negotiation thread with the value
   GDNP_DEF_TIMEOUT milliseconds.  Unless this timeout is modified by a
   CONFIRM-WAITING message (Section 3.6.7), the initiator will consider
   that the negotiation has failed when the timer expires.

   When an initiator sends a REQUEST message, it MUST initialize the
   loop count of the objective option with a value defined in the
   specification of the option or, if no such value is specified, with
   GDNP_DEF_LOOPCT.

3.6.5.  Negotiation Message

   NEGOTIATION (MESSAGE_TYPE = G4):

   A negotiation counterpart sends a NEGOTIATION message in response to
   a REQUEST message, a NEGOTIATION message, or a DISCOVERY message in
   Rapid Mode.  A negotiation process MAY include multiple steps.

   The NEGOTIATION message MUST include the relevant Negotiation
   Objective option, with its value updated according to progress in the
   negotiation.  The sender MUST decrement the loop count by 1.  If the
   loop count becomes zero both parties will consider that the
   negotiation has failed.








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3.6.6.  Negotiation-ending Message

   NEGOTIATION-ENDING (MESSAGE_TYPE = G5):

   A negotiation counterpart sends an NEGOTIATION-ENDING message to
   close the negotiation.  It MUST contain one, but only one of accept/
   decline option, defined in Section 3.7.3 and Section 3.7.4.  It could
   be sent either by the requesting node or the responding node.

3.6.7.  Confirm-waiting Message

   CONFIRM-WAITING (MESSAGE_TYPE = G6):

   A responding node sends a CONFIRM-WAITING message to indicate the
   requesting node to wait for a further negotiation response.  It might
   be that the local process needs more time or that the negotiation
   depends on another triggered negotiation.  This message MUST NOT
   include any other options than the Waiting Time Option
   (Section 3.7.5).

3.7.  GDNP General Options

   This section defines the GDNP general options for the negotiation and
   synchronization protocol signalling.  Additional option types are
   reserved for GDNP general options defined in the future.

3.7.1.  Format of GDNP Options

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          option-code          |           option-len          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          option-data                          |
   |                      (option-len octets)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Option-code:  An unsigned integer identifying the specific option
      type carried in this option.

   Option-len:  An unsigned integer giving the length of the option-data
      field in this option in octets.

   Option-data:  The data for the option; the format of this data
      depends on the definition of the option.

   GDNP options are scoped by using encapsulation.  If an option
   contains other options, the outer Option-len includes the total size



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   of the encapsulated options, and the latter apply only to the outer
   option.

3.7.2.  Divert Option

   The divert option is used to redirect a GDNP request to another node,
   which may be more appropriate for the intended negotiation or
   synchronization.  It may redirect to an entity that is known as a
   specific negotiation or synchronization counterpart (on-link or off-
   link) or a default gateway.  The divert option MUST only be
   encapsulated in Response messages.  If found elsewhere, it SHOULD be
   silently ignored.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         OPTION_DIVERT         |           option-len          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Locator Option(s) of Diversion Device(s)          |
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Option-code:  OPTION_DIVERT (G32).

   Option-len:  The total length of diverted destination sub-option(s)
      in octets.

   Locator Option(s) of Diversion Device(s):  Embedded Locator Option(s)
      (Section 3.7.7) that point to diverted destination device(s).

3.7.3.  Accept Option

   The accept option is used to indicate to the negotiation counterpart
   that the proposed negotiation content is accepted.

   The accept option MUST only be encapsulated in Negotiation-ending
   messages.  If found elsewhere, it SHOULD be silently ignored.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        OPTION_ACCEPT          |           option-len          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Option-code:  OPTION_ACCEPT (G33)

   Option-len:  0




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3.7.4.  Decline Option

   The decline option is used to indicate to the negotiation counterpart
   the proposed negotiation content is declined and end the negotiation
   process.

   The decline option MUST only be encapsulated in Negotiation-ending
   messages.  If found elsewhere, it SHOULD be silently ignored.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        OPTION_DECLINE         |           option-len          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Option-code:  OPTION_DECLINE (G34)

   Option-len:  0

   Notes: there are scenarios where a negotiation counterpart wants to
   decline the proposed negotiation content and continue the negotiation
   process.  For these scenarios, the negotiation counterpart SHOULD use
   a Negotiate message, with either an objective option that contains at
   least one data field with all bits set to 1 to indicate a meaningless
   initial value, or a specific objective option that provides further
   conditions for convergence.

3.7.5.  Waiting Time Option

   The waiting time option is used to indicate that the negotiation
   counterpart needs to wait for a further negotiation response, since
   the processing might need more time than usual or it might depend on
   another triggered negotiation.

   The waiting time option MUST only be encapsulated in Confirm-waiting
   messages.  If found elsewhere, it SHOULD be silently ignored.  When
   received, its value overwrites the negotiation timer (Section 3.6.4).

   The counterpart SHOULD send a Negotiation, Negotiation-Ending or
   another Confirm-waiting message before the negotiation timer expires.
   If not, the initiator MUST abandon or restart the negotiation
   procedure, to avoid an indefinite wait.









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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       OPTION_WAITING          |           option-len          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              Time                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Option-code:  OPTION_WAITING (G35)

   Option-len:  4, in octets

   Time:  Time in milliseconds

3.7.6.  Device Identity Option

   The Device Identity option carries the identities of the sender and
   of the domain(s) that it belongs to.  The format of the Device
   Identity option 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       OPTION_DEVICE_ID        |           option-len          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                    Identities (variable length)               .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Option-code:  OPTION_DEVICE_ID (G36)

   Option-len:  Length of identities in octets

   Identities:  A variable-length field containing the device identity
      and one or more domain identities.  The format is not yet defined.

   Note:  Currently this option is a placeholder.  It might be removed
      or modified.

3.7.7.  Locator Options

   These locator options are used to present a device's or interface's
   reachability information.  They are Locator IPv4 Address Option,
   Locator IPv6 Address Option and Locator FQDN (Fully Qualified Domain
   Name) Option.




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   Note that it is assumed that all locators are in scope throughout the
   GDNP domain.  GDNP is not intended to work across disjoint addressing
   or naming realms.

3.7.7.1.  Locator IPv4 address option

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    OPTION_LOCATOR_IPV4ADDR    |           option-len          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          IPv4-Address                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Option-code:  OPTION_LOCATOR_IPV4ADDR (G37)

   Option-len:  4, in octets

   IPv4-Address:  The IPv4 address locator of the device/interface

   Note: If an operator has internal network address translation for
   IPv4, this option MUST NOT be used within the Divert option.

3.7.7.2.  Locator IPv6 address option

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   OPTION_LOCATOR_IPV6ADDR     |           option-len          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                          IPv6-Address                         |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Option-code:  OPTION_LOCATOR_IPV6ADDR (G38)

   Option-len:  16, in octets

   IPv6-Address:  The IPv6 address locator of the device/interface

   Note: A link-local IPv6 address MUST NOT be used when this option is
   used within the Divert option.







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3.7.7.3.  Locator FQDN option

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         OPTION_FQDN           |           option-len          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Fully Qualified Domain Name                 |
   |                       (variable length)                       |
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Option-code:  OPTION_FQDN (G39)

   Option-len:  Length of Fully Qualified Domain Name in octets

   Domain-Name:  The Fully Qualified Domain Name of the entity

   Note: Any FQDN which might not be valid throughout the network in
   question, such as a Multicast DNS name [RFC6762], MUST NOT be used
   when this option is used within the Divert option.

3.8.  Objective Options

3.8.1.  Format of Objective Options

   An objective option is used to identify objectives for the purposes
   of discovery, negotiation or synchronization.  All objectives must
   follow a common format 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         OPTION_XXX            |           option-len          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   loop-count  |    flags      |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+          value                |
   .                                    (variable length)          .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Option-code:  OPTION_XXX: The option code assigned in the
      specification of the XXX objective.

   option-len:  The total length in octets.

   loop-count:  The loop count.  This field is present if and only if
      the objective is a negotiation objective.




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   flags:  Flag bits.  This field is present if and only if defined in
      the specification of the objective.

   value:  This field is to express the actual value of a negotiation or
      synchronization objective.  Its format is defined in the
      specification of the objective and may be a single value or a data
      structure of any kind.

3.8.2.  General Considerations for Objective Options

   Objective Options MUST be assigned an option type greater than G63 in
   the GDNP option table.

   An Objective Option that contains no additional fields, i.e., has a
   length of 4 octets, is a discovery objective and MUST only be used in
   Discovery and Response messages.

   The Negotiation Objective Options contain negotiation objectives,
   which are various according to different functions/services.  They
   MUST be carried by Discovery, Request or Negotiation Messages only.
   The negotiation initiator MUST set the initial "loop-count" to a
   value specified in the specification of the objective or, if no such
   value is specified, to GDNP_DEF_LOOPCT.

   For most scenarios, there should be initial values in the negotiation
   requests.  Consequently, the Negotiation Objective options MUST
   always be completely presented in a Request message, or in a
   Discovery message in rapid mode.  If there is no initial value, the
   bits in the value field SHOULD all be set to 1 to indicate a
   meaningless value, unless this is inappropriate for the specific
   negotiation objective.

   Synchronization Objective Options are similar, but MUST be carried by
   Discovery, Request or Response messages only.  They include value
   fields only in Response messages.

3.8.3.  Organizing of Objective Options

   As noted earlier, one negotiation objective is handled by each GDNP
   negotiation thread.  Therefore, a negotiation objective, which is
   based on a specific function or action, SHOULD be organized as a
   single GDNP option.  It is NOT RECOMMENDED to organize multiple
   negotiation objectives into a single option, nor to split a single
   function or action into multiple negotiation objectives.

   A synchronization objective SHOULD also be organized as a single GDNP
   option.




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   Some objectives will support more than one operational mode.  An
   example is a negotiation objective with both a "dry run" mode (where
   the negotiation is to find out whether the other end can in fact make
   the requested change without problems) and a "live" mode.  Such modes
   will be defined in the specification of such an objective.  These
   objectives SHOULD include a "flags" octet, with bits indicating the
   applicable mode(s).

   An objective may have multiple parameters.  Parameters can be
   categorized into two classes: the obligatory ones presented as fixed
   fields; and the optional ones presented in TLV sub-options or some
   other form of data structure.  The format might be inherited from an
   existing management or configuration protocol, the objective option
   acting as a carrier for that format.  The data structure might be
   defined in a formal language, but that is a matter for the
   specifications of individual objectives.  There are many candidates,
   according to the context, such as ABNF, RBNF, XML Schema, possibly
   YANG, etc.  The GDNP protocol itself is agnostic on these questions.

   It is NOT RECOMMENDED to split parameters in a single objective into
   multiple options, unless they have different response periods.  An
   exception scenario may also be described by split objectives.

3.8.4.  Vendor Specific Objective Options

   Option codes G128~159 have been reserved for vendor specific options.
   Multiple option codes have been assigned because a single vendor
   might use multiple options simultaneously.  These vendor specific
   options are highly likely to have different meanings when used by
   different vendors.  Therefore, they SHOULD NOT be used without an
   explicit human decision and SHOULD NOT be used in unmanaged networks
   such as home networks.

   There is one general requirement that applies to all vendor specific
   options.  They MUST start with a field that uniquely identifies the
   enterprise that defines the option, in the form of a registered 32
   bit Private Enterprise Number (PEN) [I-D.liang-iana-pen].  There is
   no default value for this field.  Note that it is not used during
   discovery.  It MUST be verified during negotiation or
   synchronization.

   In the case of a vendor-specific objective, the loop count and flags,
   if present, follow the PEN.








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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         OPTION_vendor         |           option-len          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              PEN                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   loop-count  |    flags      |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+          value                |
   .                                    (variable length)          .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Option-code:  OPTION_vendor (G128~159)

   Option-len:  The total length in octets.

   PEN:  Private Enterprise Number.

   loop-count:  The loop count.  This field is present if and only if
      the objective is a negotiation objective.

   flags:  Flag bits.  This field is present if and only if defined in
      the specification of the objective.

   value:  This field is to express the actual value of a negotiation or
      synchronization objective.  Its format is defined in the vendor's
      specification of the objective.

3.8.5.  Experimental Objective Options

   Option codes G176~191 have been reserved for experimental options.
   Multiple option codes have been assigned because a single experiment
   may use multiple options simultaneously.  These experimental options
   are highly likely to have different meanings when used for different
   experiments.  Therefore, they SHOULD NOT be used without an explicit
   human decision and SHOULD NOT be used in unmanaged networks such as
   home networks.

   These option codes are also RECOMMENDED for use in documentation
   examples.

4.  Items for Future Work

   There are various design questions that are worthy of more work in
   the near future, as listed below (statically numbered for reference
   purposes):





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   o  5.  Need to expand description of the minimum requirements for the
      specification of an individual discovery, synchronization or
      negotiation objective.

   o  6.  Use case and protocol walkthrough.  A description of how a
      node starts up, performs discovery, and conducts negotiation and
      synchronisation for a sample use case would help readers to
      understand the applicability of this specification.  Maybe it
      should be an artificial use case or maybe a simple real one.
      However, the authors have not yet decided whether to have a
      separate document or have it in this document.

   o  7.  Cross-check against other ANIMA WG documents for consistency
      and gaps.

5.  Security Considerations

   It is obvious that a successful attack on negotiation-enabled nodes
   would be extremely harmful, as such nodes might end up with a
   completely undesirable configuration that would also adversely affect
   their peers.  GDNP nodes and messages therefore require full
   protection.

   - Authentication

      A cryptographically authenticated identity for each device is
      needed in an autonomic network.  It is not safe to assume that a
      large network is physically secured against interference or that
      all personnel are trustworthy.  Each autonomic device MUST be
      capable of proving its identity and authenticating its messages.
      GDNP relies on a separate certificate-based security mechanism to
      support authentication, data integrity protection, and anti-replay
      protection.

      Since GDNP is intended to be deployed in a single administrative
      domain operating its own trust anchor and CA, there is no need for
      a trusted public third party.  In a network requiring "air gap"
      security, such a dependency would be unacceptable.

   - Privacy and confidentiality

      Generally speaking, no personal information is expected to be
      involved in the negotiation protocol, so there should be no direct
      impact on personal privacy.  Nevertheless, traffic flow paths,
      VPNs, etc. could be negotiated, which could be of interest for
      traffic analysis.  Also, operators generally want to conceal
      details of their network topology and traffic density from
      outsiders.  Therefore, since insider attacks cannot be excluded in



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      a large network, the security mechanism for the protocol MUST
      provide message confidentiality.

   - DoS Attack Protection

      GDNP discovery partly relies on insecure link-local multicast.
      Since routers participating in GDNP sometimes relay discovery
      messages from one link to another, this could be a vector for
      denial of service attacks.  Relevant mitigations are specified in
      Section 3.3.3.  Additionally, it is of great importance that
      firewalls prevent any GDNP messages from entering the domain from
      an untrusted source.

   - Security during bootstrap and discovery

      A node cannot authenticate GDNP traffic from other nodes until it
      has identified the trust anchor and can validate certificates for
      other nodes.  Also, until it has succesfully enrolled
      [I-D.pritikin-anima-bootstrapping-keyinfra] it cannot assume that
      other nodes are able to authenticate its own traffic.  Therefore,
      GDNP discovery during the bootstrap phase for a new device will
      inevitably be insecure and GDNP synchronization and negotiation
      will be impossible until enrollment is complete.

6.  IANA Considerations

   Section 3.4 defines the following link-local multicast addresses,
   which have been assigned by IANA for use by GDNP:

   ALL_GDNP_NEIGHBOR multicast address  (IPv6): (TBD1).  Assigned in the
      IPv6 Link-Local Scope Multicast Addresses registry.

   ALL_GDNP_NEIGHBOR multicast address  (IPv4): (TBD2).  Assigned in the
      IPv4 Multicast Local Network Control Block.

      (Note in draft: alternatively, we could use 224.0.0.1, currently
      defined as All Systems on this Subnet.)

   Section 3.4 defines the following UDP and TCP port, which has been
   assigned by IANA for use by GDNP:

   GDNP Listen Port:  (TBD3)

   This document defines the General Discovery and Negotiation Protocol
   (GDNP).  The IANA is requested to create a GDNP registry within the
   unused portion of the DNCP registry [I-D.ietf-homenet-dncp].  The
   IANA is also requested to add two new registry tables to the newly-




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   created GDNP registry.  The two tables are the GDNP Messages table
   and GDNP Options table.

   Initial values for these registries are given below.  Future
   assignments are to be made through Standards Action or Specification
   Required [RFC5226].  Assignments for each registry consist of a type
   code value, a name and a document where the usage is defined.

   Note to the RFC Editor: In the following tables and in the body of
   this document, the values G0, G1, etc., should be replaced by the
   assigned values.

   GDNP Messages table.  The values in this table are 16-bit unsigned
   integers.  The following initial values are assigned in Section 3.6
   in this document:

         Type  |          Name               |   RFCs
      ---------+-----------------------------+------------
           G0  |Reserved                     | this document
           G1  |Discovery Message            | this document
           G2  |Response Message             | this document
           G3  |Request Message              | this document
           G4  |Negotiation Message          | this document
           G5  |Negotiation-ending Message   | this document
           G6  |Confirm-waiting Message      | this document
        G7~31  |reserved for future messages |

   GDNP Options table.  The values in this table are 16-bit unsigned
   integers.  The following initial values are assigned in Section 3.7
   and Section 3.8.1 in this document:





















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         Type  |          Name               |   RFCs
      ---------+-----------------------------+------------
          G32  |Divert Option                | this document
          G33  |Accept Option                | this document
          G34  |Decline Option               | this document
          G35  |Waiting Time Option          | this document
          G36  |Device Identity Option       | this document
          G37  |Device IPv4 Address Option   | this document
          G38  |Device IPv6 Address Option   | this document
          G39  |Device FQDN Option           | this document
       G40~63  |Reserved for future GDNP     |
               |General Options              |
       G64~127 |Reserved for future GDNP     |
               |Objective Options            |
       G128~159|Vendor Specific Options      | this document
       G160~175|Reserved for future use      |
       G176~191|Experimental Options         | this document
       G192~???|Reserved for future use      |

7.  Acknowledgements

   A major contribution to the original version of this document was
   made by Sheng Jiang.

   Valuable comments were received from Michael Behringer, Zongpeng Du,
   Yu Fu, Zhenbin Li, Dimitri Papadimitriou, Michael Richardson, Markus
   Stenberg, Rene Struik, Dacheng Zhang, and other participants in the
   NMRG research group and the ANIMA working group.

   This document was produced using the xml2rfc tool [RFC2629].

8.  Change log [RFC Editor: Please remove]

   draft-carpenter-anima-discovery-negotiation-protocol-03, 2015-04-20:

   Removed intrinsic security, required external security

   Format changes to allow ADNCP co-existence

   Recognized DNS-SD as alternative discovery method

   Editorial improvements

   draft-carpenter-anima-discovery-negotiation-protocol-02, 2015-02-19:

   Tuned requirements to clarify scope,

   Clarified relationship between types of objective,



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   Clarified that objectives may be simple values or complex data
   structures,

   Improved description of objective options,

   Added loop-avoidance mechanisms (loop count and default timeout,
   limitations on discovery relaying and on unsolicited responses),

   Allow multiple discovery objectives in one response,

   Provided for missing or multiple discovery responses,

   Indicated how modes such as "dry run" should be supported,

   Minor editorial and technical corrections and clarifications,

   Reorganized future work list.

   draft-carpenter-anima-discovery-negotiation-protocol-01, restructured
   the logical flow of the document, updated to describe synchronization
   completely, add unsolicited responses, numerous corrections and
   clarifications, expanded future work list, 2015-01-06.

   draft-carpenter-anima-discovery-negotiation-protocol-00, combination
   of draft-jiang-config-negotiation-ps-03 and draft-jiang-config-
   negotiation-protocol-02, 2014-10-08.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4086]  Eastlake, D., Schiller, J., and S. Crocker, "Randomness
              Requirements for Security", BCP 106, RFC 4086, June 2005.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.




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9.2.  Informative References

   [I-D.behringer-anima-autonomic-control-plane]
              Behringer, M., Bjarnason, S., BL, B., and T. Eckert, "An
              Autonomic Control Plane", draft-behringer-anima-autonomic-
              control-plane-02 (work in progress), March 2015.

   [I-D.chaparadza-intarea-igcp]
              Behringer, M., Chaparadza, R., Petre, R., Li, X., and H.
              Mahkonen, "IP based Generic Control Protocol (IGCP)",
              draft-chaparadza-intarea-igcp-00 (work in progress), July
              2011.

   [I-D.eckert-anima-stable-connectivity]
              Eckert, T. and M. Behringer, "Using Autonomic Control
              Plane for Stable Connectivity of Network OAM", draft-
              eckert-anima-stable-connectivity-01 (work in progress),
              March 2015.

   [I-D.ietf-dnssd-requirements]
              Lynn, K., Cheshire, S., Blanchet, M., and D. Migault,
              "Requirements for Scalable DNS-SD/mDNS Extensions", draft-
              ietf-dnssd-requirements-06 (work in progress), March 2015.

   [I-D.ietf-homenet-dncp]
              Stenberg, M. and S. Barth, "Distributed Node Consensus
              Protocol", draft-ietf-homenet-dncp-01 (work in progress),
              March 2015.

   [I-D.ietf-homenet-hncp]
              Stenberg, M., Barth, S., and P. Pfister, "Home Networking
              Control Protocol", draft-ietf-homenet-hncp-04 (work in
              progress), March 2015.

   [I-D.ietf-netconf-restconf]
              Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", draft-ietf-netconf-restconf-04 (work in
              progress), January 2015.

   [I-D.irtf-nmrg-an-gap-analysis]
              Jiang, S., Carpenter, B., and M. Behringer, "General Gap
              Analysis for Autonomic Networking", draft-irtf-nmrg-an-
              gap-analysis-05 (work in progress), March 2015.








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   [I-D.irtf-nmrg-autonomic-network-definitions]
              Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
              Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
              Networking - Definitions and Design Goals", draft-irtf-
              nmrg-autonomic-network-definitions-07 (work in progress),
              March 2015.

   [I-D.liang-iana-pen]
              Liang, P., Melnikov, A., and D. Conrad, "Private
              Enterprise Number (PEN) practices and Internet Assigned
              Numbers Authority (IANA) registration considerations",
              draft-liang-iana-pen-05 (work in progress), March 2015.

   [I-D.pritikin-anima-bootstrapping-keyinfra]
              Pritikin, M., Behringer, M., and S. Bjarnason,
              "Bootstrapping Key Infrastructures", draft-pritikin-anima-
              bootstrapping-keyinfra-01 (work in progress), February
              2015.

   [I-D.stenberg-anima-adncp]
              Stenberg, M., "Autonomic Distributed Node Consensus
              Protocol", draft-stenberg-anima-adncp-00 (work in
              progress), March 2015.

   [RFC2205]  Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

   [RFC2608]  Guttman, E., Perkins, C., Veizades, J., and M. Day,
              "Service Location Protocol, Version 2", RFC 2608, June
              1999.

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)", RFC
              2865, June 2000.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, December 2001.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.





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   [RFC3416]  Presuhn, R., "Version 2 of the Protocol Operations for the
              Simple Network Management Protocol (SNMP)", STD 62, RFC
              3416, December 2002.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5971]  Schulzrinne, H. and R. Hancock, "GIST: General Internet
              Signalling Transport", RFC 5971, October 2010.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)", RFC
              6241, June 2011.

   [RFC6733]  Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
              "Diameter Base Protocol", RFC 6733, October 2012.

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              February 2013.

   [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
              Discovery", RFC 6763, February 2013.

   [RFC6887]  Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)", RFC 6887, April
              2013.

Appendix A.  Capability Analysis of Current Protocols

   This appendix discusses various existing protocols with properties
   related to the above negotiation and synchronisation requirements.
   The purpose is to evaluate whether any existing protocol, or a simple
   combination of existing protocols, can meet those requirements.

   Numerous protocols include some form of discovery, but these all
   appear to be very specific in their applicability.  Service Location
   Protocol (SLP) [RFC2608] provides service discovery for managed
   networks, but requires configuration of its own servers.  DNS-SD
   [RFC6763] combined with mDNS [RFC6762] provides service discovery for
   small networks with a single link layer.
   [I-D.ietf-dnssd-requirements] aims to extend this to larger
   autonomous networks.  However, both SLP and DNS-SD appear to target
   primarily application layer services, not the layer 2 and 3



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   objectives relevant to basic network configuration.  Both SLP and
   DNS-SD are text-based protocols.

   Routing protocols are mainly one-way information announcements.  The
   receiver makes independent decisions based on the received
   information and there is no direct feedback information to the
   announcing peer.  This remains true even though the protocol is used
   in both directions between peer routers; there is state
   synchronization, but no negotiation, and each peer runs its route
   calculations independently.

   Simple Network Management Protocol (SNMP) [RFC3416] uses a command/
   response model not well suited for peer negotiation.  Network
   Configuration Protocol (NETCONF) [RFC6241] uses an RPC model that
   does allow positive or negative responses from the target system, but
   this is still not adequate for negotiation.

   There are various existing protocols that have elementary negotiation
   abilities, such as Dynamic Host Configuration Protocol for IPv6
   (DHCPv6) [RFC3315], Neighbor Discovery (ND) [RFC4861], Port Control
   Protocol (PCP) [RFC6887], Remote Authentication Dial In User Service
   (RADIUS) [RFC2865], Diameter [RFC6733], etc.  Most of them are
   configuration or management protocols.  However, they either provide
   only a simple request/response model in a master/slave context or
   very limited negotiation abilities.

   There are also signalling protocols with an element of negotiation.
   For example Resource ReSerVation Protocol (RSVP) [RFC2205] was
   designed for negotiating quality of service parameters along the path
   of a unicast or multicast flow.  RSVP is a very specialised protocol
   aimed at end-to-end flows.  However, it has some flexibility, having
   been extended for MPLS label distribution [RFC3209].  A more generic
   design is General Internet Signalling Transport (GIST) [RFC5971], but
   it is complex, tries to solve many problems, and is also aimed at
   per-flow signalling across many hops rather than at device-to-device
   signalling.  However, we cannot completely exclude extended RSVP or
   GIST as a synchronization and negotiation protocol.  They do not
   appear to be directly useable for peer discovery.

   We now consider two protocols that are works in progress at the time
   of this writing.  Firstly, RESTCONF [I-D.ietf-netconf-restconf] is a
   protocol intended to convey NETCONF information expressed in the YANG
   language via HTTP, including the ability to transit HTML
   intermediaries.  While this is a powerful approach in the context of
   centralised configuration of a complex network, it is not well
   adapted to efficient interactive negotiation between peer devices,
   especially simple ones that are unlikely to include YANG processing
   already.



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   Secondly, we consider Distributed Node Consensus Protocol (DNCP)
   [I-D.ietf-homenet-dncp].  This is defined as a generic form of state
   synchronization protocol, with a proposed usage profile being the
   Home Networking Control Protocol (HNCP) [I-D.ietf-homenet-hncp] for
   configuring Homenet routers.  A specific application of DNCP for
   autonomic networking was proposed in [I-D.stenberg-anima-adncp].

   Specific features of DNCP include:

   o  Every participating node has a unique node identifier.

   o  DNCP messages are encoded as a sequence of TLV objects, sent over
      unicast UDP or TCP, with or without (D)TLS security.

   o  Multicast is used only for discovery of DNCP neighbors when lower
      security is acceptable.

   o  Synchronization of state is maintained by a flooding process using
      the Trickle algorithm.  There is no bilateral synchronization or
      negotiation capability.

   o  The HNCP profile of DNCP is designed to operate between directly
      connected neighbors on a shared link using UDP and link-local IPv6
      addresses.

   Clearly DNCP does not meet the needs of a general negotiation
   protocol, especially in its HNCP profile due to the limitation to
   link-local messages and its strict dependency on IPv6.  However, at
   the minimum it is a very interesting test case for this style of
   interaction between devices without needing a central authority, and
   it is a proven method of network-wide state synchronization by
   flooding.

   A proposal was made some years ago for an IP based Generic Control
   Protocol (IGCP) [I-D.chaparadza-intarea-igcp].  This was aimed at
   information exchange and negotiation but not directly at peer
   discovery.  However, it has many points in common with the present
   work.

   None of the above solutions appears to completely meet the needs of
   generic discovery, state synchronization and negotiation in a single
   solution.  Neither is there an obvious combination of protocols that
   does so.  Therefore, this document proposes the design of a protocol
   that does meet those needs.  However, this proposal needs to be
   compared with alternatives such as extension and adaptation of GIST
   or DNCP, or combination with IGCP.





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Authors' Addresses

   Brian Carpenter
   Department of Computer Science
   University of Auckland
   PB 92019
   Auckland  1142
   New Zealand

   Email: brian.e.carpenter@gmail.com


   Bing Liu
   Huawei Technologies Co., Ltd
   Q14, Huawei Campus
   No.156 Beiqing Road
   Hai-Dian District, Beijing  100095
   P.R. China

   Email: leo.liubing@huawei.com































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