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
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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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