Network Working Group C. Bormann
Internet-Draft Universitaet Bremen TZI
Intended status: Standards Track B. Carpenter, Ed.
Expires: August 27, 2016 Univ. of Auckland
B. Liu, Ed.
Huawei Technologies Co., Ltd
February 24, 2016
A Generic Autonomic Signaling Protocol (GRASP)
draft-ietf-anima-grasp-03
Abstract
This document establishes requirements for a signaling protocol that
enables autonomic devices and autonomic service agents to dynamically
discover peers, 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 . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. Specific Technical Requirements . . . . . . . . . . . . . 8
3. GRASP Protocol Overview . . . . . . . . . . . . . . . . . . . 10
3.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 10
3.2. High-Level Design Choices . . . . . . . . . . . . . . . . 11
3.3. GRASP Protocol Basic Properties and Mechanisms . . . . . 15
3.3.1. Required External Security Mechanism . . . . . . . . 15
3.3.2. Transport Layer Usage . . . . . . . . . . . . . . . . 16
3.3.3. Discovery Mechanism and Procedures . . . . . . . . . 16
3.3.4. Negotiation Procedures . . . . . . . . . . . . . . . 19
3.3.5. Synchronization and Flooding Procedure . . . . . . . 20
3.4. High Level Deployment Model . . . . . . . . . . . . . . . 21
3.5. GRASP Constants . . . . . . . . . . . . . . . . . . . . . 22
3.6. Session Identifier (Session ID) . . . . . . . . . . . . . 22
3.7. GRASP Messages . . . . . . . . . . . . . . . . . . . . . 23
3.7.1. Message Overview . . . . . . . . . . . . . . . . . . 23
3.7.2. GRASP Message Format . . . . . . . . . . . . . . . . 23
3.7.3. Discovery Message . . . . . . . . . . . . . . . . . . 24
3.7.4. Discovery Response Message . . . . . . . . . . . . . 25
3.7.5. Request Messages . . . . . . . . . . . . . . . . . . 25
3.7.6. Negotiation Message . . . . . . . . . . . . . . . . . 26
3.7.7. Negotiation End Message . . . . . . . . . . . . . . . 26
3.7.8. Confirm Waiting Message . . . . . . . . . . . . . 27
3.7.9. Synchronization Message . . . . . . . . . . . . . . . 27
3.7.10. Flood Synchronization Message . . . . . . . . . . . . 27
3.7.11. No Operation Message . . . . . . . . . . . . . . . . 28
3.8. GRASP Options . . . . . . . . . . . . . . . . . . . . . . 28
3.8.1. Format of GRASP Options . . . . . . . . . . . . . . . 28
3.8.2. Divert Option . . . . . . . . . . . . . . . . . . . . 28
3.8.3. Accept Option . . . . . . . . . . . . . . . . . . . . 29
3.8.4. Decline Option . . . . . . . . . . . . . . . . . . . 29
3.8.5. Locator Options . . . . . . . . . . . . . . . . . . . 29
3.9. Objective Options . . . . . . . . . . . . . . . . . . . . 31
3.9.1. Format of Objective Options . . . . . . . . . . . . . 31
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3.9.2. Objective flags . . . . . . . . . . . . . . . . . . . 32
3.9.3. General Considerations for Objective Options . . . . 32
3.9.4. Organizing of Objective Options . . . . . . . . . . . 33
3.9.5. Experimental and Example Objective Options . . . . . 34
4. Security Considerations . . . . . . . . . . . . . . . . . . . 34
5. CDDL Specification of GRASP . . . . . . . . . . . . . . . . . 36
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 40
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 40
8.1. Normative References . . . . . . . . . . . . . . . . . . 40
8.2. Informative References . . . . . . . . . . . . . . . . . 41
Appendix A. Open Issues . . . . . . . . . . . . . . . . . . . . 44
Appendix B. Closed Issues [RFC Editor: Please remove] . . . . . 45
Appendix C. Change log [RFC Editor: Please remove] . . . . . . . 51
Appendix D. Capability Analysis of Current Protocols . . . . . . 54
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 57
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 [RFC7575] and
[RFC7576].
One approach is to largely decentralize the logic of network
management by migrating it into network elements. A reference model
for autonomic networking on this basis is given in
[I-D.behringer-anima-reference-model]. In order to fulfil autonomy,
devices that embody autonomic service agents have specific signaling
requirements. In particular they need 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 non-autonomic
network. The atomic unit of synchronization or negotiation is
referred to as a technical objective, i.e, a configurable parameter
or set of parameters (defined more precisely in Section 3.1).
Following this Introduction, Section 2 describes the requirements for
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
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protocol intended to support discovery, synchronization and
negotiation. The design of GeneRic Autonomic Signaling Protocol
(GRASP) in Section 3 of this document is mainly based on this
behavior model. The relevant capabilities of various existing
protocols are reviewed in Appendix D.
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 managed networks.
However, when a device starts up with no pre-configuration, it has no
knowledge of the topology. The protocol itself is capable of being
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 GRASP can be used to perform a decision process among
distributed devices or between networks, it must run in a secure and
strongly authenticated environment.
It is understood that in realistic deployments, not all devices will
support GRASP. It is expected that some autonomic service agents
will directly 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. The primary user of the protocol
is an autonomic service agent (ASA), so the requirements are mainly
expressed as the features needed by an ASA. A single physical device
might contain several ASAs, and a single ASA might manage several
technical objectives.
Note that requirements for ASAs themselves, such as the processing of
Intent [RFC7575] or interfaces for coordination between ASAs are out
of scope for the present document.
2.1. Requirements for Discovery
D1. ASAs may be designed to manage anything, as required in
Section 2.2. A basic requirement is therefore that the protocol can
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represent and discover any kind of technical objective among
arbitrary subsets of participating nodes.
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. The ASA(s) inside the device are
in the same situation. In some cases, when a new application session
starts up within a device, the device or ASA may again lack
information about relevant peers. 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. The relevant
peers 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. From this background we derive the next
three requirements:
D2. When an ASA first starts up, it has no knowledge of the specific
network to which it is attached. Therefore the discovery process
must be able to support any network scenario, assuming only that the
device concerned is bootstrapped from factory condition.
D3. When an ASA starts up, it must require no information about any
peers in order to discover them.
D4. If an ASA supports multiple technical objectives, relevant peers
may be different for different discovery objectives, so discovery
needs to be repeated to find counterparts for each objective. Thus,
there must be a mechanism by which an ASA can separately discover
peer ASAs for each of the technical objectives that it needs to
manage, whenever necessary.
D5. Following discovery, an ASA will normally perform negotiation or
synchronization for the corresponding objectives. The design should
allow for this by associating discovery, negotiation and
synchronization objectives. It may provide an optional mechanism to
combine discovery and negotiation/synchronization in a single call.
D6. 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 peers 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 provide
both on-link and off-link discovery of ASAs supporting specific
technical objectives.
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D7. The discovery process should be flexible enough to allow for
special cases, such as the following:
o In some networks, as mentioned above, there will be some
hierarchical structure, at least for certain synchronization or
negotiation objectives, but this is unknown in advance. The
discovery protocol must therefore operate regardless of
hierarchical structure, which is an attribute of individual
technical objectives and not of the autonomic network as a whole.
This is part of the more general requirement to discover off-link
peers.
o 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.ietf-anima-bootstrapping-keyinfra]. We require that once
trust has been established for a device, all ASAs within the
device inherit the device's credentials and are also trusted.
o 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]. The protocol
must be capable of supporting such discovery during
initialisation, as well as discovery during ongoing operation.
D8. The discovery process must not generate excessive traffic and
must take account of sleeping nodes in the case of a constrained-node
network [RFC7228].
D9. There must be a mechanism for handling stale discovery results.
2.2. Requirements for Synchronization and Negotiation Capability
As background, consider the example of routing protocols, the closest
approximation to autonomic networking already in widespread use.
Routing protocols use a largely autonomic model based on distributed
devices that communicate repeatedly with each other. The focus is
reachability, so current routing protocols mainly 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 in order for
the routing algorithm to converge. Thus, routing is mainly based on
information synchronization between peers, rather than on bi-
directional negotiation. Other information, such as latency,
congestion, capacity, and particularly unused capacity, would be
helpful to get better path selection and utilization rate, but is not
normally used in distributed routing algorithms. Additionally,
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autonomic networks need to be able to manage many more dimensions,
such as security settings, power saving, load balancing, etc. 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. In general, these parameters do not apply to all
participating nodes, but only to a subset.
SN1. 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.
SN2. Negotiation is a request/response process that 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 these must be defined specifically for each use
case, the protocol should have some general mechanisms in support of
loop and deadlock prevention, such as hop count limits or timeouts.
SN3. Synchronization might concern small groups of nodes or very
large groups. Different solutions might be needed at different
scales.
SN4. To avoid "reinventing the wheel", the protocol should be able
to carry the message formats used by existing configuration protocols
(such as NETCONF/YANG) in cases where that is convenient.
SN5. 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
therefore follows that the protocol, as part of the Autonomic
Networking Infrastructure, must be capable of running in any device
that would otherwise need human intervention.
SN6. Human intervention in large networks is often replaced by use
of a top-down network management system (NMS). It therefore follows
that the protocol, as part of the Autonomic Networking
Infrastructure, must be capable of running in any device that would
otherwise be managed by an NMS, and that it can co-exist with an NMS,
and with protocols such as SNMP and NETCONF.
SN7. Some features are expected to be implemented by individual
ASAs, but the protocol must be general enough to allow them:
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o 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 ASAs involved. To allow this, there need to be
clear boundaries and convergence mechanisms for negotiations.
Also some mechanisms are needed to avoid loop dependencies. In
such a case, the protocol's role is limited to signaling between
ASAs.
o Recovery from faults and identification of faulty devices should
be as automatic as possible. The protocol's role is limited to
the ability to handle discovery, synchronization and negotiation
at any time, in case an ASA detects an anomaly such as a
negotiation counterpart failing.
o 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.
o Management logging, monitoring, alerts and tools for intervention
are required. However, these can only be features of individual
ASAs. 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.ietf-anima-autonomic-control-plane].
SN8. The protocol will 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 easily extensible
message format. One design consideration is whether to adopt an
existing information model or to design a new one.
2.3. Specific Technical Requirements
T1. It should be convenient for ASA designers to define new
technical objectives and for programmers to express them, without
excessive impact on run-time efficiency and footprint. The classes
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of device in which the protocol might run is discussed in
[I-D.behringer-anima-reference-model].
T2. The protocol should be easily extensible in case the initially
defined discovery, synchronization and negotiation mechanisms prove
to be insufficient.
T3. 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 on a link, might need to be IP version
dependent. In case of doubt, IPv6 should be preferred.
T4. The protocol must be able to access off-link counterparts via
routable addresses, i.e., must not be restricted to link-local
operation.
T5. It must also be possible for an external discovery mechanism to
be used, if appropriate for a given technical objective. In other
words, GRASP discovery must not be a prerequisite for GRASP
negotiation or synchronization; the prerequisite is discovering a
peer's locator by any method.
T6. ASAs and the signaling protocol need to run asynchronously when
wait states occur.
T7. Intent: There must be provision for general Intent rules to be
applied by all devices in the network (e.g., security rules, prefix
length, resource sharing rules). However, Intent distribution might
not use the signaling protocol itself, but its design should not
exclude such use.
T8. 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 might not use
the signaling protocol itself, but its design should not exclude such
use.
T9. The protocol needs to be fully secured against forged messages
and man-in-the middle attacks, and secured as much as reasonably
possible against denial of service attacks. It needs to be capable
of encryption in order to resist unwanted monitoring. However, it is
not required that the protocol itself provides these security
features; it may depend on an existing secure environment.
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3. GRASP 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 [RFC7575].
The following additional terms are used throughout this document:
o Autonomic Device: identical to Autonomic Node.
o Discovery: a process by which an ASA discovers peers according to
a specific discovery objective. The discovery results may be
different according to the different discovery objectives. The
discovered peers may later be used as negotiation counterparts or
as sources of synchronization data.
o Negotiation: a process by which two (or more) ASAs interact
iteratively to agree on parameter settings that best satisfy the
objectives of one or more ASAs.
o State Synchronization: a process by which two (or more) ASAs
interact to agree on the current state of parameter values stored
in each ASA. This is a special case of negotiation in which
information is sent but the ASAs do not request their peers to
change parameter settings. All other definitions apply to both
negotiation and synchronization.
o Technical Objective (usually abbreviated as Objective): A
technical objective is a configurable parameter or set of
parameters of some kind, which occurs in three contexts:
Discovery, Negotiation and Synchronization. In the protocol, an
objective is represented by an identifier 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 ASA may support multiple independent objectives.
* The parameter described by a given objective is naturally based
on a specific service or function or action. It may in
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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 contain an
ASA 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
ASAs.
* Negotiation Objective: an objective whose specific technical
content needs to be decided in coordination with another ASA.
o Discovery Initiator: an ASA that spontaneously starts discovery by
sending a discovery message referring to a specific discovery
objective.
o Discovery Responder: a peer ASA which responds to the discovery
objective initiated by the discovery initiator.
o Synchronization Initiator: an ASA that spontaneously starts
synchronization by sending a request message referring to a
specific synchronization objective.
o Synchronization Responder: a peer ASA which responds with the
value of a synchronization objective.
o Negotiation Initiator: an ASA that spontaneously starts
negotiation by sending a request message referring to a specific
negotiation objective.
o Negotiation Counterpart: a peer 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 signaling protocol initially supporting
discovery, synchronization and negotiation, which can act as a
platform for different technical objectives.
o A generic platform
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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
technical objectives and the different pairs of counterparts.
o The protocol is expected to form part of an Autonomic Networking
Infrastructure [I-D.behringer-anima-reference-model]. It will
provide services to ASAs via a suitable application programming
interface, which will reflect the protocol elements but will not
necessarily be in one-to-one correspondence to them. It is
expected that a single instance of GRASP will exist in an
autonomic node, and that the protocol engine and each ASA will run
as independent asynchronous processes.
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, ASAs might also exchange limited
information and negotiate some particular configurations based on
a limited conventional or contractual trust relationship.
o Discovery, synchronization and negotiation are 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.
* GRASP discovery is always available for efficient discovery of
GRASP peers and allows a rapid mode of operation described in
Section 3.3.3. For some objectives, especially those concerned
with application layer services, another discovery mechanism
such as the future DNS Service Discovery [RFC7558] or Service
Location Protocol [RFC2608] MAY be used. The choice is left to
the designers of individual ASAs.
o A uniform pattern for technical contents
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The synchronization and negotiation contents are defined according
to a uniform pattern. They could be carried either in simple
binary format or in payloads described by a flexible language.
The basic protocol design uses the Concise Binary Object
Representation (CBOR) [RFC7049]. The format is extensible for
unknown future requirements.
o A flexible model for synchronization
GRASP supports bilateral synchronization, which could be used to
perform synchronization among a small number of nodes. It also
supports an unsolicited flooding mode when large groups of nodes,
possibly including all autonomic nodes, need data for the same
technical objective.
* There may be some network parameters for which a more
traditional flooding mechanism such as DNCP
[I-D.ietf-homenet-dncp] is considered more appropriate. GRASP
can coexist with DNCP.
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 multi-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 autonomic device will be pre-loaded with various functions
and ASAs and will be aware of its own capabilities, typically
decided by the hardware, firmware or pre-installed software. Its
exact role may depend on Intent and on the surrounding network
behaviors, which may include forwarding behaviors, aggregation
properties, topology location, bandwidth, tunnel or translation
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properties, etc. The surrounding 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 ASAs, 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
ASAs.
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 ASA for each negotiation objective. It may be
an implementation choice, a pre-configurable parameter, or
network Intent. These choices might vary between different
types of ASA. 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 network Intent.
3.3. GRASP 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.ietf-anima-autonomic-control-plane]. The ACP is assumed to
carry all messages securely, including link-local multicast if
possible. A GRASP implementation MUST verify whether the ACP is
operational.
If there is no ACP, the protocol MUST use another form of strong
authentication and SHOULD use a form of strong encryption. TLS
[RFC5246] is RECOMMENDED for this purpose, based on a local Public
Key Infrastructure (PKI) [RFC5280] managed within the autonomic
network itself. The details of such a PKI and how its boundary is
established are out of scope for this document. DTLS [RFC6347] MAY
be used but since GRASP operations usually involve several messages
this is not expected to be advantageous.
The ACP, or in its absence the local PKI, sets the boundary within
which nodes are trusted as GRASP peers. A GRASP implementation MUST
refuse to execute any GRASP functions except discovery if there is
neither an operational ACP nor an operational TLS environment.
As mentioned in Section 3.2, limited GRASP operations might be
performed across an administrative domain boundary by mutual
agreement. Such operations MUST be authenticated and SHOULD be
encrypted. TLS is RECOMMENDED for this purpose.
Link-local multicast is used for discovery messages. Responses to
discovery messages MUST be secured, with one exception.
The exception is that during initialisation, before a node has joined
the applicable trust infrastructure, e.g.,
[I-D.ietf-anima-bootstrapping-keyinfra], or before the ACP is fully
established, it might be impossible to secure messages. Indeed, both
the security bootstrap process and the ACP creation process might use
insecure GRASP discovery and response messages. Such usage MUST be
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limited to the strictly necessary minimum. A full analysis of the
initialisation process is out of scope for the present document.
3.3.2. Transport Layer Usage
GRASP discovery and flooding messages are designed for use over link-
local multicast UDP. They MUST NOT be fragmented, and therefore MUST
NOT exceed the link MTU size. Nothing in principle prevents them
from working over some other method of sending packets to all on-link
neighbors, but this is out of scope for the present specification.
All other GRASP messages are unicast and could in principle run over
any transport protocol. An implementation MUST support use of TCP.
It MAY support use of another transport protocol. However, GRASP
itself does not provide for error detection or retransmission. Use
of an unreliable transport protocol is therefore NOT RECOMMENDED.
When running within a secure ACP on reliable infrastructure, UDP MAY
be used for unicast messages not exceeding the minimum IPv6 path MTU;
however, TCP MUST be used for longer messages. In other words, IPv6
fragmentation is avoided. If a node receives a UDP message but the
reply is too long, it MUST open a TCP connection to the peer for the
reply. Note that when the network is under heavy load or in a fault
condition, UDP might become unreliable. Since this is when autonomic
functions are most necessary, automatic fallback to TCP MUST be
implemented. The simplest implementation is therefore to use only
TCP.
When running without an ACP, TLS MUST be supported and used by
default, except for link-local multicast messages. DTLS MAY be
supported as an alternative but the details are out of scope for this
document.
For all transport protocols, the GRASP protocol listens to the GRASP
Listen Port (Section 3.5).
3.3.3. Discovery Mechanism and Procedures
o Separated discovery and negotiation mechanisms
Although discovery and negotiation or synchronization are
defined together in the GRASP, they are separated mechanisms.
The discovery process could run independently from the
negotiation or synchronization process. Upon receiving a
Discovery (Section 3.7.3) message, the recipient ASA should
return a response message in which it either indicates itself
as a discovery responder or diverts the initiator towards
another more suitable ASA.
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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 ASA the
initiator will negotiate with.
It is entirely possible to use GRASP discovery without a
subsequent negotiation or synchronization action. In this
case, the discovered objective is simply used as a name during
the discovery process and any subsequent operations between the
peers are outside the scope of GRASP.
o Discovery Procedures
Discovery starts as an on-link operation. The Divert option
can tell the discovery initiator to contact an off-link ASA for
that discovery objective. Every Discovery message is sent by a
discovery initiator via UDP to the ALL_GRASP_NEIGHBOR multicast
address (Section 3.5). Every network device that supports the
GRASP always listens to a well-known UDP port to capture the
discovery messages.
If an ASA in the neighbor device supports the requested
discovery objective, it MAY respond with a Discovery Response
message (Section 3.7.4) with locator option(s). Otherwise, if
the neighbor has cached information about an ASA that supports
the requested discovery objective (usually because it
discovered the same objective before), it SHOULD respond with a
Discovery Response message with a Divert option pointing to the
appropriate Discovery Responder.
If no discovery response is received within a reasonable
timeout (default GRASP_DEF_TIMEOUT milliseconds, Section 3.5),
the Discovery message MAY be repeated, with a newly generated
Session ID (Section 3.6). An exponential backoff SHOULD be
used for subsequent repetitions, in order to mitigate possible
denial of service attacks.
After a GRASP 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 that MAY be
modified by network Intent.
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
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responders is an implementation choice. This choice MUST be
available to each ASA but the GRASP implementation SHOULD
provide a default choice.
Because Discovery Responders will be cached in a finite cache,
they might be deleted at any time. In this case, discovery
will need to be repeated. If an ASA exits for any reason, its
locator might still be cached for some time, and attempts to
connect to it will fail. ASAs need to be robust in these
circumstances.
A GRASP device with multiple link-layer interfaces (typically a
router) MUST support discovery on all interfaces. If it
receives a Discovery message on a given interface for a
specific objective that it does not support and for which it
has not previously cached a Discovery Responder, it MUST relay
the query by re-issuing a Discovery message on its other
interfaces. The relayed message MUST have a new Session ID.
Before this, it MUST decrement the loop count within the
objective, and MUST NOT relay the Discovery message if the
result is zero. Also, 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. These precautions avoid discovery
loops and mitigate potential overload.
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 a multicast on the
local link. On-link neighbors supporting the discovery objective
will respond directly. A neighbor with multiple interfaces will
respond with a cached discovery response if any. If not, it will
relay the discovery on its other interfaces, for example reaching
a higher-level gateway in a hierarchical network. If a node
receiving the relayed discovery supports the discovery objective,
it will respond to the relayed discovery. If it has a cached
response, it will respond with that. If not, it will repeat the
discovery process, which thereby becomes recursive. The loop
count and timeout will ensure that the process ends.
o Rapid Mode (Discovery/Negotiation binding)
A Discovery message MAY include a Negotiation Objective option.
This allows a rapid mode of negotiation described in
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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
ASA, 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 no reply message of any kind is received within a reasonable
timeout (default GRASP_DEF_TIMEOUT milliseconds, Section 3.5), the
negotiation request MAY be repeated, with a newly generated Session
ID (Section 3.6). An exponential backoff SHOULD be used for
subsequent repetitions.
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-
directional negotiation to reach a compromise between the two ASAs.
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 ASAs, or in simultaneous negotiations
about different objectives. Thus, GRASP 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.
Some configuration actions, for example wavelength switching in
optical networks, might take considerable time to execute. The ASA
concerned needs to allow for this by design, but GRASP does allow for
a peer to insert latency in a negotiation process if necessary
(Section 3.7.8).
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3.3.4.1. 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 Negotiation
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 Intent.
3.3.5. Synchronization and Flooding Procedure
A synchronization initiator sends a synchronization request to a
counterpart, including a specific synchronization objective. The
counterpart responds with a Synchronization message (Section 3.7.9)
containing the current value of the requested synchronization
objective. No further messages are needed.
If no reply message of any kind is received within a reasonable
timeout (default GRASP_DEF_TIMEOUT milliseconds, Section 3.5), the
synchronization request MAY be repeated, with a newly generated
Session ID (Section 3.6). An exponential backoff SHOULD be used for
subsequent repetitions.
3.3.5.1. Flooding
In the case just described, the message exchange is unicast and
concerns only one synchronization objective. For large groups of
nodes requiring the same data, synchronization flooding is available.
For this, a flooding initiator MAY send an unsolicited Flood
Synchronization message containing one or more Synchronization
Objective option(s), if and only if the specification of those
objectives permits it. This is sent as a multicast message to the
ALL_GRASP_NEIGHBOR multicast address (Section 3.5). To ensure that
flooding does not result in a loop, the originator of the Flood
Synchronization message MUST set the loop count in the objectives to
a suitable value (the default is GRASP_DEF_LOOPCT). In this case a
suitable mechanism is needed to avoid excessive multicast traffic.
This mechanism MUST be defined as part of the specification of the
synchronization objective(s) concerned. It might be a simple rate
limit or a more complex mechanism such as the Trickle algorithm
[RFC6206].
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A GRASP device with multiple link-layer interfaces (typically a
router) MUST support synchronization flooding on all interfaces. If
it receives a multicast Flood Synchronization message on a given
interface, it MUST relay it by re-issuing a Flood Synchronization
message on its other interfaces. The relayed message MUST have a new
Session ID. Before this, it MUST decrement the loop count within the
objective, and MUST NOT relay the Flood Synchronization message if
the result is zero. Also, it MUST limit the total rate at which it
relays Flood Synchronization messages to a reasonable value, in order
to mitigate possible denial of service attacks. It MUST cache the
Session ID value of each relayed Flood Synchronization message and,
to prevent loops, MUST NOT relay a Flood Synchronization message
which carries such a cached Session ID. These precautions avoid
synchronization loops and mitigate potential overload.
Note that this mechanism is unreliable in the case of sleeping nodes.
Sleeping nodes that require an objective subject to flooding SHOULD
periodically request unicast synchronization for that objective.
The multicast messages for synchronization flooding are subject to
the security rules in Section 3.3.1. In practice this means that
they MUST NOT be transmitted and MUST be ignored on receipt unless
there is an operational ACP. However, because of the security
weakness of link-local multicast (Section 4), synchronization
objectives that are flooded SHOULD NOT contain unencrypted sensitive
information and SHOULD be validated by the recipient ASA.
3.3.5.2. Rapid Mode (Discovery/Synchronization Linkage)
A Discovery message MAY include a Synchronization Objective option.
In this case the Discovery message also acts as a Request
Synchronization message to indicate to the Discovery Responder that
it could directly reply to the Discovery Initiator with a
Synchronization message Section 3.7.9 with synchronization data for
rapid processing, if the discovery target supports the corresponding
synchronization objective. 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 Intent.
3.4. High Level Deployment Model
It is expected that a GRASP implementation will reside in an
autonomic node that also contains both the appropriate security
environment (preferably the ACP) and one or more Autonomic Service
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Agents (ASAs). In the minimal case of a single-purpose device, these
three components might be fully integrated. A more common model is
expected to be a multi-purpose device capable of containing several
ASAs. In this case it is expected that the ACP, GRASP and the ASAs
will be implemented as separate processes, which are probably multi-
threaded to support asynchronous operation. It is expected that
GRASP will access the ACP by using a typical socket interface. Well
defined Application Programming Interfaces (APIs) will be needed
between GRASP and the ASAs. For further details of possible
deployment models, see [I-D.behringer-anima-reference-model].
3.5. GRASP Constants
o ALL_GRASP_NEIGHBOR
A link-local scope multicast address used by a GRASP-enabled
device to discover GRASP-enabled neighbor (i.e., on-link) devices
. All devices that support GRASP are members of this multicast
group.
* IPv6 multicast address: TBD1
* IPv4 multicast address: TBD2
o GRASP_LISTEN_PORT (TBD3)
A UDP and TCP port that every GRASP-enabled network device always
listens to.
o GRASP_DEF_TIMEOUT (60000 milliseconds)
The default timeout used to determine that a discovery etc. has
failed to complete.
o GRASP_DEF_LOOPCT (6)
The default loop count used to determine that a negotiation has
failed to complete, and to avoid looping messages.
3.6. Session Identifier (Session ID)
This is an up to 24-bit opaque value used to distinguish multiple
sessions between the same two devices. A new Session ID MUST be
generated by the initiator for every new Discovery, Flood
Synchronization or Request message. All responses and follow-up
messages in the same discovery, synchronization or negotiation
procedure MUST carry the same Session ID.
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The Session ID SHOULD have a very low collision rate locally. It
MUST be generated by a pseudo-random algorithm using a locally
generated seed which is unlikely to be used by any other device in
the same network [RFC4086].
However, there is a finite probability that two nodes might generate
the same Session ID value. For that reason, when a Session ID is
communicated via GRASP, the receiving node MUST tag it with the
initiator's IP address to allow disambiguation. Multicast GRASP
messages, which may be relayed between links, therefore require a new
Session ID each time they are relayed.
3.7. GRASP Messages
3.7.1. Message Overview
This section defines the GRASP message format and message types.
Message types not listed here are reserved for future use.
The messages currently defined are:
Discovery and Discovery Response.
Request Negotiation, Negotiation, Confirm Waiting and Negotiation
End.
Request Synchronization, Synchronization, and Flood
Synchronization.
No Operation.
3.7.2. GRASP Message Format
GRASP messages share an identical header format and a variable format
area for options. GRASP message headers and options are transmitted
in Concise Binary Object Representation (CBOR) [RFC7049]. In this
specification, they are described using CBOR data definition language
(CDDL) [I-D.greevenbosch-appsawg-cbor-cddl]. Fragmentary CDDL is
used to describe each item in this section. A complete and normative
CDDL specification of GRASP is given in Section 5, including
constants such as message types.
Every GRASP message, except the No Operation message, carries a
Session ID (Section 3.6). Options are then presented serially in the
options field.
In fragmentary CDDL, every GRASP message follows the pattern:
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grasp-message = (message .within message-structure) / noop-message
message-structure = [MESSAGE_TYPE, session-id, +grasp-option]
MESSAGE_TYPE = 1..255
session-id = 0..16777215 ;up to 24 bits
grasp-option = any
The MESSAGE_TYPE indicates the type of the message and thus defines
the expected options. Any options received that are not consistent
with the MESSAGE_TYPE SHOULD be silently discarded.
The No Operation (noop) message is described in Section 3.7.11.
The various MESSAGE_TYPE values are defined in Section 5.
All other message elements are described below and formally defined
in Section 5.
3.7.3. Discovery Message
In fragmentary CDDL, a Discovery message follows the pattern:
discovery-message = [M_DISCOVERY, session-id, objective]
A discovery initiator sends a Discovery message to initiate a
discovery process for a particular objective option.
The discovery initiator sends the Discovery messages to the link-
local ALL_GRASP_NEIGHBOR multicast address for discovery, and stores
the discovery results (including responding discovery objectives and
corresponding unicast addresses, FQDNs or URIs).
A Discovery message MUST include exactly one of the following:
o a discovery objective option (Section 3.9.1). Its loop count MUST
be set to a suitable value to prevent discovery loops (default
value is GRASP_DEF_LOOPCT).
o a negotiation objective option (Section 3.9.1). This is used both
for the purpose of discovery and 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 Negotiation message
(Section 3.7.5).
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o a synchronization objective option (Section 3.9.1). This is used
both for the purpose of discovery and to indicate to the discovery
target that it MAY directly reply to the discovery initiator with
a Synchronization message for rapid processing, if it could act as
the corresponding synchronization counterpart. Its loop count
MUST be set to a suitable value to prevent discovery loops
(default value is GRASP_DEF_LOOPCT).
3.7.4. Discovery Response Message
In fragmentary CDDL, a Discovery Response message follows the
pattern:
response-message = [M_RESPONSE, session-id,
(+locator-option // divert-option), ?objective)]
A node which receives a Discovery message SHOULD send a Discovery
Response message if and only if it can respond to the discovery. 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 3.8.5) to indicate its own location. A sequence of multiple
kinds of locator options (e.g. IP address option and 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 3.8.2) embedding a locator option or a combination of
multiple kinds of locator options which indicate the locator(s) of
the discovery objective.
3.7.5. Request Messages
In fragmentary CDDL, Request Negotiation and Request Synchronization
messages follow the patterns:
request-negotiation-message = [M_REQ_NEG, session-id, objective]
request-synchronization-message = [M_REQ_SYN, session-id, objective]
A negotiation or synchronization requesting node sends the
appropriate Request message to the unicast address (directly stored
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or resolved from an FQDN) of the negotiation or synchronization
counterpart (selected from the discovery results).
A Request message MUST include the relevant objective option. In the
case of Request Negotiation, the objective option MUST include the
requested value.
When an initiator sends a Request Negotiation message, it MUST
initialize a negotiation timer for the new negotiation thread with
the value GRASP_DEF_TIMEOUT milliseconds. Unless this timeout is
modified by a Confirm Waiting message (Section 3.7.8), 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
GRASP_DEF_LOOPCT.
If a node receives a Request message for an objective for which no
ASA is currently listening, it MUST immediately close the relevant
socket to indicate this to the initiator.
3.7.6. Negotiation Message
In fragmentary CDDL, a Negotiation message follows the pattern:
discovery-message = [M_NEGOTIATE, session-id, objective]
A negotiation counterpart sends a Negotiation message in response to
a Request Negotiation 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 the message MUST NOT be sent. In this case
the negotiation session has failed and will time out.
3.7.7. Negotiation End Message
In fragmentary CDDL, a Negotiation End message follows the pattern:
end-message = [M_END, session-id, accept-option / decline-option]
A negotiation counterpart sends an Negotiation End message to close
the negotiation. It MUST contain either an accept or a decline
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option, defined in Section 3.8.3 and Section 3.8.4. It could be sent
either by the requesting node or the responding node.
3.7.8. Confirm Waiting Message
In fragmentary CDDL, a Confirm Waiting message follows the pattern:
wait-message = [M_WAIT, session-id, waiting-time]
waiting-time = 0..4294967295 ; in milliseconds
A responding node sends a Confirm Waiting message to ask 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. When received, the waiting time value
overwrites and restarts the current negotiation timer
(Section 3.7.5).
The responding node SHOULD send a Negotiation, Negotiation End 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.
3.7.9. Synchronization Message
In fragmentary CDDL, a Synchronization message follows the pattern:
synch-message = [M_SYNCH, session-id, objective]
A node which receives a Request Synchronization, or a Discovery
message in Rapid Mode, sends back a unicast Synchronization message
with the synchronization data, in the form of a GRASP Option for the
specific synchronization objective present in the Request
Synchronization.
3.7.10. Flood Synchronization Message
In fragmentary CDDL, a Flood Synchronization message follows the
pattern:
flood-message = [M_FLOOD, session-id, +objective]
A node MAY initiate flooding by sending an unsolicited Flood
Synchronization Message with synchronization data. This MAY be sent
to the link-local ALL_GRASP_NEIGHBOR multicast address, in accordance
with the rules in Section 3.3.5. The synchronization data will be in
the form of GRASP Option(s) for specific synchronization
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objective(s). The loop count(s) MUST be set to a suitable value to
prevent flood loops (default value is GRASP_DEF_LOOPCT).
A node that receives a Flood Synchronization message SHOULD cache the
received objectives for use by local ASAs.
3.7.11. No Operation Message
In fragmentary CDDL, a No Operation message follows the pattern:
noop-message = [M_NOOP]
This message MAY be sent by an implementation that for practical
reasons needs to activate a socket. It MUST be silently ignored by a
recipient.
3.8. GRASP Options
This section defines the GRASP options for the negotiation and
synchronization protocol signaling. Additional options may be
defined in the future.
3.8.1. Format of GRASP Options
GRASP options are CBOR objects that MUST start with an unsigned
integer identifying the specific option type carried in this option.
These option types are formally defined in Section 5. Apart from
that the only format requirement is that each option MUST be a well-
formed CBOR object. In general a CBOR array format is RECOMMENDED to
limit overhead.
GRASP options are usually scoped by using encapsulation. However,
this is not a requirement
3.8.2. Divert Option
The Divert option is used to redirect a GRASP 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 Discovery Response messages. If found elsewhere, it
SHOULD be silently ignored.
In fragmentary CDDL, the Divert option follows the pattern:
divert-option = [O_DIVERT, +locator-option]
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The embedded Locator Option(s) (Section 3.8.5) point to diverted
destination target(s) in response to a Discovery message.
3.8.3. 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 End
messages. If found elsewhere, it SHOULD be silently ignored.
In fragmentary CDDL, the Accept option follows the pattern:
accept-option = [O_ACCEPT]
3.8.4. 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 End
messages. If found elsewhere, it SHOULD be silently ignored.
In fragmentary CDDL, the Decline option follows the pattern:
decline-option = [O_DECLINE, ?reason]
reason = text ;optional error message
Note: 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 a
data field set to indicate a meaningless initial value, or a specific
objective option that provides further conditions for convergence.
3.8.5. Locator Options
These locator options are used to present reachability information
for an ASA, a device or an interface. They are Locator IPv4 Address
Option, Locator IPv6 Address Option, Locator FQDN (Fully Qualified
Domain Name) Option and Uniform Resource Identifier Option.
Note: It is assumed that all locators are in scope throughout the
GRASP domain. GRASP is not intended to work across disjoint
addressing or naming realms.
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3.8.5.1. Locator IPv4 address option
In fragmentary CDDL, the IPv4 address option follows the pattern:
ipv4-locator-option = bytes .size 4
The content of this option is a binary IPv4 address.
Note: If an operator has internal network address translation for
IPv4, this option MUST NOT be used within the Divert option.
3.8.5.2. Locator IPv6 address option
In fragmentary CDDL, the IPv6 address option follows the pattern:
ipv6-locator-option = bytes .size 16
The content of this option is a binary IPv6 address.
Note 1: The IPv6 address MUST normally have global scope.
Exceptionally, during node bootstrap, a link-local address MAY be
used for specific objectives only.
Note 2: A link-local IPv6 address MUST NOT be used when this option
is included in a Divert option.
3.8.5.3. Locator FQDN option
In fragmentary CDDL, the FQDN option follows the pattern:
fqdn-locator-option = [O_FQDN_LOCATOR, text]
The content of this option is the Fully Qualified Domain Name of the
target.
Note 1: 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.
Note 2: Normal GRASP operations are not expected to use this option.
It is intended for special purposes such as discovering external
services.
3.8.5.4. Locator URI option
In fragmentary CDDL, the URI option follows the pattern:
uri-locator-option = [O_URI_LOCATOR, text]
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The content of this option is the Uniform Resource Identifier of the
target [RFC3986].
Note 1: Any URI which might not be valid throughout the network in
question, such as one based on a Multicast DNS name [RFC6762], MUST
NOT be used when this option is used within the Divert option.
Note 2: Normal GRASP operations are not expected to use this option.
It is intended for special purposes such as discovering external
services.
3.9. Objective Options
3.9.1. Format of Objective Options
An objective option is used to identify objectives for the purposes
of discovery, negotiation or synchronization. All objectives MUST be
in the following format, described in fragmentary CDDL:
objective = [objective-name, objective-flags, loop-count, ?any]
objective-name = text
loop-count = 0..255
All objectives are identified by a unique name which is a case-
sensitive UTF-8 string.
The names of generic objectives MUST NOT include a colon (":") and
MUST be registered with IANA (Section 6).
The names of privately defined objectives MUST include at least one
colon (":"). The string preceding the last colon in the name MUST be
globally unique and in some way identify the entity or person
defining the objective. The following three methods MAY be used to
create such a globally unique string:
1. The unique string is a decimal number representing a registered
32 bit Private Enterprise Number (PEN) [I-D.liang-iana-pen] that
uniquely identifies the enterprise defining the objective.
2. The unique string is a fully qualified domain name that uniquely
identifies the entity or person defining the objective.
3. The unique string is an email address that uniquely identifies
the entity or person defining the objective.
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The GRASP protocol treats the objective name as an opaque string.
For example, "EX1", "411:EX1", "example.com:EX1", "example.org:EX1
and "user@example.org:EX1" would be five different objectives.
The 'objective-flags' field is described below.
The 'loop-count' field is used for terminating negotiation as
described in Section 3.7.6. It is also used for terminating
discovery as described in Section 3.3.3, and for terminating flooding
as described in Section 3.3.5.1.
The 'any' 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. It is optional because it is optional in a
Discovery or Discovery Response message.
3.9.2. Objective flags
An objective may be relevant for discovery only, for discovery and
negotiation, or for discovery and synchronization. This is expressed
in the objective by logical flags:
objective-flags = uint .bits objective-flag
objective-flag = &(
F_DISC: 0 ; valid for discovery only
F_NEG: 1 ; valid for discovery and negotiation
F_SYNCH: 2 ; valid for discovery and synchronization
)
3.9.3. General Considerations for Objective Options
As mentioned above, Objective Options MUST be assigned a unique name.
As long as privately defined Objective Options obey the rules above,
this document does not restrict their choice of name, but the entity
or person concerned SHOULD publish the names in use.
All Objective Options MUST respect the CBOR patterns defined above as
"objective" and MUST replace the "any" field with a valid CBOR data
definition for the relevant use case and application.
An Objective Option that contains no additional fields beyond its
"loop-count" can only be a discovery objective and MUST only be used
in Discovery and Discovery Response messages.
The Negotiation Objective Options contain negotiation objectives,
which vary according to different functions/services. They MUST be
carried by Discovery, Request Negotiation or Negotiation messages
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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 GRASP_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 Negotiation 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 indicate a
meaningless value, unless this is inappropriate for the specific
negotiation objective.
Synchronization Objective Options are similar, but MUST be carried by
Discovery, Discovery Response, Request Synchronization, or Flood
Synchronization messages only. They include value fields only in
Synchronization or Flood Synchronization messages.
3.9.4. Organizing of Objective Options
Generic objective options MUST be specified in documents available to
the public and SHOULD be designed to use either the negotiation or
the synchronization mechanism described above.
As noted earlier, one negotiation objective is handled by each GRASP
negotiation thread. Therefore, a negotiation objective, which is
based on a specific function or action, SHOULD be organized as a
single GRASP 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.
It is important to understand that GRASP negotiation does not support
transactional integrity. If transactional integrity is needed for a
specific objective, this must be ensured by the ASA. For example, an
ASA might need to ensure that it only participates in one negotiation
thread at the same time. Such an ASA would need to stop listening
for incoming negotiation requests before generating an outgoing
negotiation request.
A synchronization objective SHOULD be organized as a single GRASP
option.
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 flags indicating the applicable mode(s).
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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 CBOR sub-options or some
other form of data structure embedded in CBOR. 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 GRASP 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.
All objectives MUST support GRASP discovery. However, as mentioned
in Section 3.2, it is acceptable for an ASA to use an alternative
method of discovery.
Normally, a GRASP objective will refer to specific technical
parameters as explained in Section 3.1. However, it is acceptable to
define an abstract objective for the purpose of managing or
coordinating ASAs. It is also acceptable to define a special-purpose
objective for purposes such as trust bootstrapping or formation of
the ACP.
3.9.5. Experimental and Example Objective Options
The names "EX0" through "EX9" have been reserved for experimental
options. Multiple names 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 names are also RECOMMENDED for use in documentation examples.
4. 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. GRASP nodes and messages therefore require full
protection.
- Authentication
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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 node MUST be
capable of proving its identity and authenticating its messages.
GRASP relies on a separate external certificate-based security
mechanism to support authentication, data integrity protection,
and anti-replay protection.
Since GRASP 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.
If GRASP is used temporarily without an external security
mechanism, for example during system bootstrap (Section 3.3.1),
the Session ID (Section 3.6) will act as a nonce to provide
limited protection against third parties injecting responses. A
full analysis of the secure bootstrap process is out of scope for
the present document.
- Authorization and Roles
The GRASP protocol is agnostic about the role of individual ASAs
and about which objectives a particular ASA is authorized to
support. It SHOULD apply obvious precautions such as allowing
only one ASA in a given node to modify a given objective, but
otherwise authorization is out of scope.
- Privacy and confidentiality
Generally speaking, no personal information is expected to be
involved in the signaling 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
a large network, the security mechanism for the protocol MUST
provide message confidentiality. This is why Section 3.3.1
requires either an ACP or the use of TLS.
- Link-local multicast security
GRASP has no reasonable alternative to using link-local multicast
for Discovery or Flood Synchronization messages and these messages
are sent in clear and with no authentication. They are therefore
available to on-link eavesdroppers, and could be forged by on-link
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attackers. In the case of Discovery, the Discovery Responses are
unicast and will therefore be protected (Section 3.3.1), and an
untrusted forger will not be able to receive responses. In the
case of Flood Synchronization, an on-link eavesdropper will be
able to receive the flooded objectives but there is no response
message to consider. Some precautions for Flood Synchronization
messages are suggested in Section 3.3.5.1.
- DoS Attack Protection
GRASP discovery partly relies on insecure link-local multicast.
Since routers participating in GRASP 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 GRASP messages from entering the domain from
an untrusted source.
- Security during bootstrap and discovery
A node cannot authenticate GRASP 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.ietf-anima-bootstrapping-keyinfra] it cannot assume that
other nodes are able to authenticate its own traffic. Therefore,
GRASP discovery during the bootstrap phase for a new device will
inevitably be insecure and GRASP synchronization and negotiation
will be impossible until enrollment is complete.
- Security of discovered locators
When GRASP discovery returns an IP address, it MUST be that of a
node within the secure environment (Section 3.3.1). If it returns
an FQDN or a URI, the ASA that receives it MUST NOT assume that
the target of the locator is within the secure environment.
5. CDDL Specification of GRASP
<CODE BEGINS>
grasp-message = (message .within message-structure) / noop-message
message-structure = [MESSAGE_TYPE, session-id, *grasp-option]
MESSAGE_TYPE = 0..255
session-id = 0..16777215 ;up to 24 bits
grasp-option = any
message /= discovery-message
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discovery-message = [M_DISCOVERY, session-id, objective]
message /= response-message ;response to Discovery
response-message = [M_RESPONSE, session-id,
(+locator-option // divert-option), ?objective]
message /= synch-message ;response to Synchronization request
synch-message = [M_SYNCH, session-id, objective]
message /= flood-message
flood-message = [M_FLOOD, session-id, +objective]
message /= request-negotiation-message
request-negotiation-message = [M_REQ_NEG, session-id, objective]
message /= request-synchronization-message
request-synchronization-message = [M_REQ_SYN, session-id, objective]
message /= negotiation-message
negotiation-message = [M_NEGOTIATE, session-id, objective]
message /= end-message
end-message = [M_END, session-id, accept-option / decline-option ]
message /= wait-message
wait-message = [M_WAIT, session-id, waiting-time]
noop-message = [M_NOOP]
divert-option = [O_DIVERT, +locator-option]
accept-option = [O_ACCEPT]
decline-option = [O_DECLINE, ?reason]
reason = text ;optional error message
waiting-time = 0..4294967295 ; in milliseconds
locator-option /= ipv4-locator-option
ipv4-locator-option = bytes .size 4
; this is simpler than [O_IPv4_LOCATOR, bytes .size 4]
locator-option /= ipv6-locator-option
ipv6-locator-option = bytes .size 16
locator-option /= fqdn-locator-option
fqdn-locator-option = [O_FQDN_LOCATOR, text]
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locator-option /= uri-locator-option
uri-locator-option = [O_URI_LOCATOR, text]
objective-flags = uint .bits objective-flag
objective-flag = &(
F_DISC: 0 ; valid for discovery only
F_NEG: 1 ; valid for discovery and negotiation
F_SYNCH: 2) ; valid for discovery and synchronization
objective = [objective-name, objective-flags, loop-count, ?any]
objective-name = text ;see specification for uniqueness rules
loop-count = 0..255
; Constants for message types and option types
M_NOOP = 0
M_DISCOVERY = 1
M_RESPONSE = 2
M_REQ_NEG = 3
M_REQ_SYN = 4
M_NEGOTIATE = 5
M_END = 6
M_WAIT = 7
M_SYNCH = 8
M_FLOOD = 9
O_DIVERT = 100
O_ACCEPT = 101
O_DECLINE = 102
O_FQDN_LOCATOR = 103
O_URI_LOCATOR = 104
<CODE ENDS>
6. IANA Considerations
This document defines the General Discovery and Negotiation Protocol
(GRASP).
Section 3.5 explains the following link-local multicast addresses,
which IANA is requested to assign for use by GRASP:
ALL_GRASP_NEIGHBOR multicast address (IPv6): (TBD1). Assigned in
the IPv6 Link-Local Scope Multicast Addresses registry.
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ALL_GRASP_NEIGHBOR multicast address (IPv4): (TBD2). Assigned in
the IPv4 Multicast Local Network Control Block.
Section 3.5 explains the following UDP and TCP port, which IANA is
requested to assign for use by GRASP:
GRASP_LISTEN_PORT: (TBD3)
The IANA is requested to create a GRASP Parameter Registry including
two registry tables. These are the GRASP Messages and Options
Table and the GRASP Objective Names Table.
GRASP Messages and Options Table. The values in this table are names
paired with decimal integers. Future values MUST be assigned using
the Standards Action policy defined by [RFC5226]. The following
initial values are assigned by this document:
M_NOOP = 0
M_DISCOVERY = 1
M_RESPONSE = 2
M_REQUEST = 3
M_NEGOTIATE = 4
M_END = 5
M_WAIT = 6
O_DIVERT = 100
O_ACCEPT = 101
O_DECLINE = 102
O_FQDN_LOCATOR = 103
O_URI_LOCATOR = 104
O_DEVICE_ID = 105
GRASP Objective Names Table. The values in this table are UTF-8
strings. Future values MUST be assigned using the Specification
Required policy defined by [RFC5226]. The following initial values
are assigned by this document:
EX0
EX1
EX2
EX3
EX4
EX5
EX6
EX7
EX8
EX9
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7. Acknowledgements
A major contribution to the original version of this document was
made by Sheng Jiang.
Valuable comments were received from Michael Behringer, Jeferson
Campos Nobre, Laurent Ciavaglia, Zongpeng Du, Yu Fu, Joel Halpern,
Zhenbin Li, Dimitri Papadimitriou, Pierre Peloso, Reshad Rahman,
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. References
8.1. Normative References
[I-D.greevenbosch-appsawg-cbor-cddl]
Vigano, C. and H. Birkholz, "CBOR data definition language
(CDDL): a notational convention to express CBOR data
structures", draft-greevenbosch-appsawg-cbor-cddl-07 (work
in progress), October 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>.
[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005,
<http://www.rfc-editor.org/info/rfc4086>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
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[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, DOI 10.17487/RFC5280, May 2008,
<http://www.rfc-editor.org/info/rfc5280>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <http://www.rfc-editor.org/info/rfc7049>.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC7217, April 2014,
<http://www.rfc-editor.org/info/rfc7217>.
8.2. Informative References
[I-D.behringer-anima-reference-model]
Behringer, M., Carpenter, B., Eckert, T., Ciavaglia, L.,
Liu, B., Jeff, J., and J. Strassner, "A Reference Model
for Autonomic Networking", draft-behringer-anima-
reference-model-04 (work in progress), October 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-02 (work in progress),
October 2015.
[I-D.ietf-anima-autonomic-control-plane]
Behringer, M., Bjarnason, S., BL, B., and T. Eckert, "An
Autonomic Control Plane", draft-ietf-anima-autonomic-
control-plane-01 (work in progress), October 2015.
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[I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Behringer, M., and S.
Bjarnason, "Bootstrapping Key Infrastructures", draft-
ietf-anima-bootstrapping-keyinfra-01 (work in progress),
October 2015.
[I-D.ietf-homenet-dncp]
Stenberg, M. and S. Barth, "Distributed Node Consensus
Protocol", draft-ietf-homenet-dncp-12 (work in progress),
November 2015.
[I-D.ietf-homenet-hncp]
Stenberg, M., Barth, S., and P. Pfister, "Home Networking
Control Protocol", draft-ietf-homenet-hncp-10 (work in
progress), November 2015.
[I-D.ietf-netconf-restconf]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", draft-ietf-netconf-restconf-09 (work in
progress), December 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-06 (work in progress), July 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, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
September 1997, <http://www.rfc-editor.org/info/rfc2205>.
[RFC2608] Guttman, E., Perkins, C., Veizades, J., and M. Day,
"Service Location Protocol, Version 2", RFC 2608,
DOI 10.17487/RFC2608, June 1999,
<http://www.rfc-editor.org/info/rfc2608>.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
DOI 10.17487/RFC2629, June 1999,
<http://www.rfc-editor.org/info/rfc2629>.
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[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, DOI 10.17487/RFC2865, June 2000,
<http://www.rfc-editor.org/info/rfc2865>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<http://www.rfc-editor.org/info/rfc3209>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <http://www.rfc-editor.org/info/rfc3315>.
[RFC3416] Presuhn, R., Ed., "Version 2 of the Protocol Operations
for the Simple Network Management Protocol (SNMP)",
STD 62, RFC 3416, DOI 10.17487/RFC3416, December 2002,
<http://www.rfc-editor.org/info/rfc3416>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<http://www.rfc-editor.org/info/rfc4861>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC5971] Schulzrinne, H. and R. Hancock, "GIST: General Internet
Signalling Transport", RFC 5971, DOI 10.17487/RFC5971,
October 2010, <http://www.rfc-editor.org/info/rfc5971>.
[RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko,
"The Trickle Algorithm", RFC 6206, DOI 10.17487/RFC6206,
March 2011, <http://www.rfc-editor.org/info/rfc6206>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<http://www.rfc-editor.org/info/rfc6241>.
[RFC6733] Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
Ed., "Diameter Base Protocol", RFC 6733,
DOI 10.17487/RFC6733, October 2012,
<http://www.rfc-editor.org/info/rfc6733>.
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[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<http://www.rfc-editor.org/info/rfc6762>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<http://www.rfc-editor.org/info/rfc6763>.
[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
DOI 10.17487/RFC6887, April 2013,
<http://www.rfc-editor.org/info/rfc6887>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<http://www.rfc-editor.org/info/rfc7228>.
[RFC7558] Lynn, K., Cheshire, S., Blanchet, M., and D. Migault,
"Requirements for Scalable DNS-Based Service Discovery
(DNS-SD) / Multicast DNS (mDNS) Extensions", RFC 7558,
DOI 10.17487/RFC7558, July 2015,
<http://www.rfc-editor.org/info/rfc7558>.
[RFC7575] Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
Networking: Definitions and Design Goals", RFC 7575,
DOI 10.17487/RFC7575, June 2015,
<http://www.rfc-editor.org/info/rfc7575>.
[RFC7576] Jiang, S., Carpenter, B., and M. Behringer, "General Gap
Analysis for Autonomic Networking", RFC 7576,
DOI 10.17487/RFC7576, June 2015,
<http://www.rfc-editor.org/info/rfc7576>.
Appendix A. Open Issues
o 7. Cross-check against other ANIMA WG documents for consistency
and gaps.
o 43. Rapid mode synchronization and negotiation is currently
limited to a single objective for simplicity of design and
implementation. A future consideration is to allow multiple
objectives in rapid mode for greater efficiency.
o 48. Should the Appendix "Capability Analysis of Current
Protocols" be deleted before RFC publication?
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Appendix B. Closed Issues [RFC Editor: Please remove]
o 1. UDP vs TCP: For now, this specification suggests UDP and TCP
as message transport mechanisms. This is not clarified yet. UDP
is good for short conversations, is necessary for multicast
discovery, and generally fits the discovery and divert scenarios
well. However, it will cause problems with large messages. TCP
is good for stable and long sessions, with a little bit of time
consumption during the session establishment stage. If messages
exceed a reasonable MTU, a TCP mode will be required in any case.
This question may be affected by the security discussion.
RESOLVED by specifying UDP for short message and TCP for longer
one.
o 2. DTLS or TLS vs built-in security mechanism. For now, this
specification has chosen a PKI based built-in security mechanism
based on asymmetric cryptography. However, (D)TLS might be chosen
as security solution to avoid duplication of effort. It also
allows essentially similar security for short messages over UDP
and longer ones over TCP. The implementation trade-offs are
different. The current approach requires expensive asymmetric
cryptographic calculations for every message. (D)TLS has startup
overheads but cheaper crypto per message. DTLS is less mature
than TLS.
RESOLVED by specifying external security (ACP or (D)TLS).
o The following open issues applied only if the original security
model was retained:
* 2.1. For replay protection, GRASP currently requires every
participant to have an NTP-synchronized clock. Is this OK for
low-end devices, and how does it work during device
bootstrapping? We could take the Timestamp out of signature
option, to become an independent and OPTIONAL (or RECOMMENDED)
option.
* 2.2. The Signature Option states that this option could be any
place in a message. Wouldn't it be better to specify a
position (such as the end)? That would be much simpler to
implement.
RESOLVED by changing security model.
o 3. DoS Attack Protection needs work.
RESOLVED by adding text.
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o 4. Should we consider preferring a text-based approach to
discovery (after the initial discovery needed for bootstrapping)?
This could be a complementary mechanism for multicast based
discovery, especially for a very large autonomic network.
Centralized registration could be automatically deployed
incrementally. At the very first stage, the repository could be
empty; then it could be filled in by the objectives discovered by
different devices (for example using Dynamic DNS Update). The
more records are stored in the repository, the less the multicast-
based discovery is needed. However, if we adopt such a mechanism,
there would be challenges: stateful solution, and security.
RESOLVED for now by adding optional use of DNS-SD by ASAs.
Subsequently removed by editors as irrelevant to GRASP istelf.
o 5. Need to expand description of the minimum requirements for the
specification of an individual discovery, synchronization or
negotiation objective.
RESOLVED for now by extra wording.
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, based
on a conceptual API. However, the authors have not yet decided
whether to have a separate document or have it in the protocol
document.
RESOLVED: recommend a separate document.
o 8. Consideration of ADNCP proposal.
RESOLVED by adding optional use of DNCP for flooding-type
synchronization.
o 9. Clarify how a GDNP instance knows whether it is running inside
the ACP. (Sheng)
RESOLVED by improved text.
o 10. Clarify how a non-ACP GDNP instance initiates (D)TLS.
(Sheng)
RESOLVED by improved text and declaring DTLS out of scope for this
draft.
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o 11. Clarify how UDP/TCP choice is made. (Sheng) [Like DNS? -
Brian]
RESOLVED by improved text.
o 12. Justify that IP address within ACP or (D)TLS environment is
sufficient to prove AN identity; or explain how Device Identity
Option is used. (Sheng)
RESOLVED for now: we assume that all ASAs in a device are trusted
as soon as the device is trusted, so they share credentials. In
that case the Device Identity Option is useless. This needs to be
reviewed later.
o 13. Emphasise that negotiation/synchronization are independent
from discovery, although the rapid discovery mode includes the
first step of a negotiation/synchronization. (Sheng)
RESOLVED by improved text.
o 14. Do we need an unsolicited flooding mechanism for discovery
(for discovery results that everyone needs), to reduce scaling
impact of flooding discovery messages? (Toerless)
RESOLVED: Yes, added to requirements and solution.
o 15. Do we need flag bits in Objective Options to distinguish
distinguish Synchronization and Negotiation "Request" or rapid
mode "Discovery" messages? (Bing)
RESOLVED: yes, work on the API showed that these flags are
essential.
o 16. (Related to issue 14). Should we revive the "unsolicited
Response" for flooding synchronisation data? This has to be done
carefully due to the well-known issues with flooding, but it could
be useful, e.g. for Intent distribution, where DNCP doesn't seem
applicable.
RESOLVED: Yes, see #14.
o 17. Ensure that the discovery mechanism is completely proof
against loops and protected against duplicate responses.
RESOLVED: Added loop count mechanism.
o 18. Discuss the handling of multiple valid discovery responses.
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RESOLVED: Stated that the choice must be available to the ASA but
GRASP implementation should pick a default.
o 19. Should we use a text-oriented format such as JSON/CBOR
instead of native binary TLV format?
RESOLVED: Yes, changed to CBOR.
o 20. Is the Divert option needed? If a discovery response
provides a valid IP address or FQDN, the recipient doesn't gain
any extra knowledge from the Divert. On the other hand, the
presence of Divert informs the receiver that the target is off-
link, which might be useful sometimes.
RESOLVED: Decided to keep Divert option.
o 21. Rename the protocol as GRASP (GeneRic Autonomic Signaling
Protocol)?
RESOLVED: Yes, name changed.
o 22. Does discovery mechanism scale robustly as needed? Need hop
limit on relaying?
RESOLVED: Added hop limit.
o 23. Need more details on TTL for caching discovery responses.
RESOLVED: Done.
o 24. Do we need "fast withdrawal" of discovery responses?
RESOLVED: This doesn't seem necessary. If an ASA exits or stops
supporting a given objective, peers will fail to start future
sessions and will simply repeat discovery.
o 25. Does GDNP discovery meet the needs of multi-hop DNS-SD?
RESOLVED: Decided not to consider this further as a GRASP protocol
issue. GRASP objectives could embed DNS-SD formats if needed.
o 26. Add a URL type to the locator options (for security bootstrap
etc.)
RESOLVED: Done, later renamed as URI.
o 27. Security of Flood multicasts (Section 3.3.5.1).
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RESOLVED: added text.
o 28. Does ACP support secure link-local multicast?
RESOLVED by new text in the Security Considerations.
o 29. PEN is used to distinguish vendor options. Would it be
better to use a domain name? Anything unique will do.
RESOLVED: Simplified this by removing PEN field and changing
naming rules for objectives.
o 30. Does response to discovery require randomized delays to
mitigate amplification attacks?
RESOLVED: WG feedback is that it's unnecessary.
o 31. We have specified repeats for failed discovery etc. Is that
sufficient to deal with sleeping nodes?
RESOLVED: WG feedback is that it's unnecessary to say more.
o 32. We have one-to-one synchronization and flooding
synchronization. Do we also need selective flooding to a subset
of nodes?
RESOLVED: This will be discussed as a protocol extension in a
separate draft (draft-liu-anima-grasp-distribution).
o 33. Clarify if/when discovery needs to be repeated.
RESOLVED: Done.
o 34. Clarify what is mandatory for running in ACP, expand
discussion of security boundary when running with no ACP - might
rely on the local PKI infrastructure.
RESOLVED: Done.
o 35. State that role-based authorization of ASAs is out of scope
for GRASP. GRASP doesn't recognize/handle any "roles".
RESOLVED: Done.
o 36. Reconsider CBOR definition for PEN syntax. ( objective-name
= text / [pen, text] ; pen = uint )
RESOLVED: See issue 29.
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o 37. Are URI locators really needed?
RESOLVED: Yes, e.g. for security bootstrap discovery, but added
note that addresses are the normal case (same for FQDN locators).
o 38. Is Session ID sufficient to identify relayed responses?
Isn't the originator's address needed too?
RESOLVED: Yes, this is needed for multicast messages and their
responses.
o 39. Clarify that a node will contain one GRASP instance
supporting multiple ASAs.
RESOLVED: Done.
o 40. Add a "reason" code to the DECLINE option?
RESOLVED: Done.
o 41. What happens if an ASA cannot conveniently use one of the
GRASP mechanisms? Do we (a) add a message type to GRASP, or (b)
simply pass the discovery results to the ASA so that it can open
its own socket?
RESOLVED: Both would be possible, but (b) is preferred.
o 42. Do we need a feature whereby an ASA can bypass the ACP and
use the data plane for efficiency/throughput? This would require
discovery to return non-ACP addresses and would evade ACP
security.
RESOLVED: This is considered out of scope for GRASP, but a comment
has been added in security considerations.
o 44. In requirement T9, the words that encryption "may not be
required in all deployments" were removed. Is that OK?.
RESOLVED: No objections.
o 45. Device Identity Option is unused. Can we remove it
completely?.
RESOLVED: No objections. Done.
o 46. The 'initiator' field in DISCOVER, RESPONSE and FLOOD
messages is intended to assist in loop prevention. However, we
also have the loop count for that. Also, if we create a new
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Session ID each time a DISCOVER or FLOOD is relayed, that ID can
be disambiguated by recipients. It would be simpler to remove the
initiator from the messages, making parsing more uniform. Is that
OK?
RESOLVED: Yes. Done.
o 47. REQUEST is a dual purpose message (request negotiation or
request synchronization). Would it be better to split this into
two different messages (and adjust various message names
accordingly)?
RESOLVED: Yes. Done.
Appendix C. Change log [RFC Editor: Please remove]
draft-ietf-anima-grasp-03, 2016-02-24:
Protocol change: Removed initiator field from certain messages and
adjusted relaying requirement to simplify loop detection. Also
clarified narrative explanation of discovery relaying.
Protocol change: Split Request message into two (Request Negotiation
and Request Synchronization) and updated other message names for
clarity.
Protocol change: Dropped unused Device ID option.
Further clarified text on transport layer usage.
New text about multicast insecurity in Security Considerations.
Various other clarifications and editorial fixes, including moving
some material to Appendix.
draft-ietf-anima-grasp-02, 2016-01-13:
Resolved numerous issues according to WG discussions.
Renumbered requirements, added D9.
Protocol change: only allow one objective in rapid mode.
Protocol change: added optional error string to DECLINE option.
Protocol change: removed statement that seemed to say that a Request
not preceded by a Discovery should cause a Discovery response. That
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made no sense, because there is no way the initiator would know where
to send the Request.
Protocol change: Removed PEN option from vendor objectives, changed
naming rule accordingly.
Protocol change: Added FLOOD message to simplify coding.
Protocol change: Added SYNCH message to simplify coding.
Protocol change: Added initiator id to DISCOVER, RESPONSE and FLOOD
messages. But also allowed the relay process for DISCOVER and FLOOD
to regenerate a Session ID.
Protocol change: Require that discovered addresses must be global
(except during bootstrap).
Protocol change: Receiver of REQUEST message must close socket if no
ASA is listening for the objective.
Protocol change: Simplified Waiting message.
Protocol change: Added No Operation message.
Renamed URL locator type as URI locator type.
Updated CDDL definition.
Various other clarifications and editorial fixes.
draft-ietf-anima-grasp-01, 2015-10-09:
Updated requirements after list discussion.
Changed from TLV to CBOR format - many detailed changes, added co-
author.
Tightened up loop count and timeouts for various cases.
Noted that GRASP does not provide transactional integrity.
Various other clarifications and editorial fixes.
draft-ietf-anima-grasp-00, 2015-08-14:
File name and protocol name changed following WG adoption.
Added URL locator type.
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draft-carpenter-anima-gdn-protocol-04, 2015-06-21:
Tuned wording around hierarchical structure.
Changed "device" to "ASA" in many places.
Reformulated requirements to be clear that the ASA is the main
customer for signaling.
Added requirement for flooding unsolicited synch, and added it to
protocol spec. Recognized DNCP as alternative for flooding synch
data.
Requirements clarified, expanded and rearranged following design team
discussion.
Clarified that GDNP discovery must not be a prerequisite for GDNP
negotiation or synchronization (resolved issue 13).
Specified flag bits for objective options (resolved issue 15).
Clarified usage of ACP vs TLS/DTLS and TCP vs UDP (resolved issues
9,10,11).
Updated DNCP description from latest DNCP draft.
Editorial improvements.
draft-carpenter-anima-gdn-protocol-03, 2015-04-20:
Removed intrinsic security, required external security
Format changes to allow DNCP co-existence
Recognized DNS-SD as alternative discovery method.
Editorial improvements
draft-carpenter-anima-gdn-protocol-02, 2015-02-19:
Tuned requirements to clarify scope,
Clarified relationship between types of objective,
Clarified that objectives may be simple values or complex data
structures,
Improved description of objective options,
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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-gdn-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-gdn-protocol-00, combination of draft-jiang-
config-negotiation-ps-03 and draft-jiang-config-negotiation-protocol-
02, 2014-10-08.
Appendix D. 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. [RFC7558] aims to extend
this to larger autonomous networks but this is not yet standardized.
However, both SLP and DNS-SD appear to target primarily application
layer services, not the layer 2 and 3 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.
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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 some signaling 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 signaling across many hops rather than at device-to-device
signaling. 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.
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].
DNCP "is designed to provide a way for each participating node to
publish a set of TLV (Type-Length-Value) tuples, and to provide a
shared and common view about the data published... DNCP is most
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suitable for data that changes only infrequently... If constant rapid
state changes are needed, the preferable choice is to use an
additional point-to-point channel..."
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.
DNCP does not meet the needs of a general negotiation protocol,
because it is designed specifically for flooding synchronization.
Also, in its HNCP profile it is limited to link-local messages and to
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. Many of the protocols assume that they are working in a
traditional top-down or north-south scenario, rather than a fluid
peer-to-peer scenario. Most of them are specialized in one way or
another. As a result, we have not identified a combination of
existing protocols that meets the requirements in Section 2. Also,
we have not identified a path by which one of the existing protocols
could be extended to meet the requirements.
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Authors' Addresses
Carsten Bormann
Universitaet Bremen TZI
Postfach 330440
D-28359 Bremen
Germany
Email: cabo@tzi.org
Brian Carpenter (editor)
Department of Computer Science
University of Auckland
PB 92019
Auckland 1142
New Zealand
Email: brian.e.carpenter@gmail.com
Bing Liu (editor)
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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