A Generic Autonomic Signaling Protocol (GRASP)Universität Bremen TZIPostfach 330440D-28359 BremenGermanycabo@tzi.orgDepartment of Computer ScienceUniversity of AucklandPB 92019Auckland1142New Zealandbrian.e.carpenter@gmail.comHuawei Technologies Co., LtdQ14, Huawei CampusNo.156 Beiqing RoadHai-Dian District, Beijing100095P.R. Chinaleo.liubing@huawei.comThis 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.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
and . 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
.
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 ).Following this Introduction, 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.
describes a behavior model for a protocol
intended to support discovery, synchronization and negotiation. The
design of GeneRic Autonomic Signaling Protocol (GRASP) in
of this document is mainly based on this behavior model. The relevant capabilities
of various existing protocols are reviewed in .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.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
or interfaces for coordination between ASAs are out of scope
for the present document.D1. ASAs may be designed to manage anything, as required in
. A basic requirement
is therefore that the protocol can 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.D7. The discovery process should be flexible enough to allow for
special cases, such as the following:
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.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 .
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.
Depending on the type of network involved, discovery of other
central functions might be needed, such as
the Network Operations
Center (NOC) .
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
. D9. There must be a mechanism for handling stale discovery results.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,
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:
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. 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.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. Management logging, monitoring, alerts and tools for intervention are required.
However, these can only be features of individual ASAs.
Another document discusses how
such agents may be linked into conventional OAM systems via an 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. 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. In particular, it should be possible for ASAs
to be implemented independently of each other as user space programs rather than as kernel
code. The classes of device in which the protocol
might run is discussed in .
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. 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
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 key words.This document uses terminology defined in .The following additional terms are used throughout this document:
Autonomic Device: identical to Autonomic Node.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. 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.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. 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 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. Discovery Initiator: an ASA that spontaneously starts discovery
by sending a discovery message referring to a specific discovery
objective.Discovery Responder: a peer that either contains an ASA supporting the discovery objective
indicated by the discovery initiator, or caches the locator(s) of the ASA(s) supporting
the objective. The locator(s) are indicated in a Discovery Response,
which is normally sent by the protocol kernel, as described later.Synchronization Initiator: an ASA that spontaneously starts synchronization
by sending a request message referring to a specific synchronization
objective.Synchronization Responder: a peer ASA which responds with the
value of a synchronization objective.Negotiation Initiator: an ASA that spontaneously starts
negotiation by sending a request message referring to a specific
negotiation objective.Negotiation Counterpart: a peer with which the Negotiation
Initiator negotiates a specific negotiation objective.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.A generic platform
The protocol is designed as a generic platform, which
is independent from the synchronization or negotiation contents. It takes
care of the general intercommunication between
counterparts. The technical contents will vary according to the
various technical objectives and the different pairs of
counterparts.The protocol is expected to form part of an Autonomic Networking Infrastructure
. 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.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.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 .
For some objectives, especially those concerned with application layer
services, another discovery mechanism such as the future DNS Service
Discovery or
Service Location Protocol
MAY be used. The choice is left to the designers of individual
ASAs.
A uniform pattern for technical contents
The synchronization and negotiation contents are defined
according to a uniform pattern. They could be carried either in simple
binary format or in payloads described by a
flexible language. The basic protocol design uses the Concise
Binary Object Representation (CBOR) .
The format is extensible for unknown future requirements. 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
is
considered more appropriate. GRASP can coexist with DNCP.
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.
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.Self-aware network deviceEvery 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 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.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.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.
Failed negotiationThere 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.The protocol SHOULD run within a secure Autonomic Control Plane (ACP)
. 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
is RECOMMENDED for this purpose, based on a local Public Key Infrastructure (PKI)
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 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 , 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., , 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 limited to the strictly necessary minimum.
A full analysis of the initialisation process is out of scope for the
present document. 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 link-local multicast, the GRASP protocol listens to the GRASP Listen Port
(). This port is also used to listen for unicast discovery responses.
For unicast transport sessions used for synchronization and negotiation, the ASA
concerned listens on its own dynamically assigned port, which is communicated to its peers
during discovery. Separated discovery and negotiation mechanismsAlthough 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 ()
message, the
recipient node should return a response message in which it either
indicates itself as a discovery responder or diverts the
initiator towards another more suitable ASA.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.The initiator of a discovery action for a given objective need not
be capable of supporting that objective for negotiation or as a source
for synchronization or flooding. In other words an ASA might perform
discovery because it only wishes to receive synchronization data.It is entirely possible to use GRASP discovery without any 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.Discovery ProceduresDiscovery 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 link-local
multicast address (). Every network
device that supports GRASP always listens to a well-known
UDP port to capture the discovery messages. Because this port
is unique in a device, this is a function of the GRASP kernel
and not of an individual ASA. As a result, each ASA will need to
register the objectives that it supports with the GRASP kernel.If an ASA in a neighbor device supports the requested discovery objective,
the device MAY respond to the link-local multicast with a unicast Discovery Response
message () 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, ),
the Discovery message MAY be repeated, with a newly generated
Session ID (). 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 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 as a link-local multicast on its other
interfaces. The relayed discovery message MUST have the same Session ID as the incoming
discovery message and MUST be tagged with the IP address of its original initiator.
Since the relay device is unaware of the timeout set by the original
initiator it SHOULD set a timeout at least equal to GRASP_DEF_TIMEOUT milliseconds.The relaying device 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 and initiator address of each relayed
Discovery message until any Discovery Responses have arrived or
the discovery process has timed out.
To prevent loops, it MUST NOT relay a Discovery message
which carries a given cached Session ID and initiator address more than once.
These precautions avoid discovery loops and mitigate potential overload.The discovery results received by the relaying device MUST in turn be
sent as a Discovery Response message to the Discovery message that caused
the relay action.This relayed discovery mechanism, with caching of the results,
should be sufficient to support most network bootstrapping scenarios.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.
Rapid Mode (Discovery/Negotiation binding)A Discovery message MAY include a Negotiation
Objective option. This allows a rapid mode of negotiation
described in . A similar mechanism
is defined for synchronization in .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, ),
the negotiation request MAY be repeated, with a newly generated
Session ID (). 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
().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.A synchronization initiator sends a synchronization request to a
counterpart, including a specific synchronization objective.
The counterpart responds with a Synchronization message ()
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, ),
the synchronization request MAY be repeated, with a newly generated
Session ID (). An exponential backoff SHOULD be used
for subsequent repetitions.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 ().Every network device that supports GRASP always listens to a well-known
UDP port to capture flooding messages. Because this port is unique in a device,
this is a function of the GRASP kernel.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).
Also, 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 .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 the same Session ID as the incoming
message and MUST be tagged with the IP address of its original initiator. The relaying device MUST decrement the loop count within the first 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 and initiator address of each relayed
Flood Synchronization message for a finite time not less than twice GRASP_DEF_TIMEOUT milliseconds.
To prevent loops, it MUST NOT relay a Flood Synchronization message
which carries a given cached Session ID and initiator address more than once.
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 . 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 (),
synchronization objectives that are flooded SHOULD NOT contain unencrypted sensitive
information and SHOULD be validated by the recipient ASA.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 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.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 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. A well defined
Application Programming Interface (API) will be needed
between GRASP and the ASAs. In some implementations, ASAs would run in user
space with a GRASP library providing the API, and this library would in turn
communicate via system calls with core GRASP functions running in kernel mode.
For further details of possible deployment models, see
.
ALL_GRASP_NEIGHBORA 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: TBD1IPv4 multicast address: TBD2GRASP_LISTEN_PORT (TBD3)A UDP and TCP port that
every GRASP-enabled network device always listens to.GRASP_DEF_TIMEOUT (60000 milliseconds)The default timeout used to
determine that a discovery etc. has failed to complete.GRASP_DEF_LOOPCT (6)The default loop count used to
determine that a negotiation has failed to complete, and to avoid looping messages.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.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 .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 and their responses, which may be relayed between links,
therefore include a field that carries the initiator's global IP address.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.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)
. In this specification, they are described
using CBOR data definition language (CDDL)
.
Fragmentary CDDL is used to describe each item in this section. A complete and normative
CDDL specification of GRASP is given in , including constants such
as message types.
Every GRASP message, except the No Operation message, carries a Session ID ().
Options are then presented serially in the options field.In fragmentary CDDL, every GRASP message follows the pattern: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 .The various MESSAGE_TYPE values are defined in .All other message elements are described below and formally defined in .In fragmentary CDDL, a Discovery message follows the pattern:
A discovery initiator sends a Discovery message
to initiate a discovery process for a particular objective option.
The discovery initiator sends the Discovery
messages via UDP to port GRASP_LISTEN_PORT at the link-local
ALL_GRASP_NEIGHBOR multicast address. It then listens for unicast
TCP responses on the same port, and stores the discovery
results (including responding discovery objectives and
corresponding unicast locators).
The 'initiator' field in the message is a globally unique IP address of the
initiator, for the sole purpose of disambiguating the Session ID
in other nodes. If for some reason the initiator does not
have a globally unique IP address, it MUST use a link-local
address for this purpose that is highly likely to be
unique, for example using .
A Discovery message MUST include exactly one of the following:
a discovery objective option ().
Its loop count MUST be set to a suitable value to prevent discovery
loops (default value is GRASP_DEF_LOOPCT).
a negotiation objective option (). 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
().
a synchronization objective option ().
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).In fragmentary CDDL, a Discovery Response message follows the pattern:
A node which receives a Discovery message SHOULD send a
Discovery Response message if and only if it can respond to the discovery.
It MUST contain the same Session ID and initiator as the Discovery message.
It MAY include a copy of the discovery objective from
the Discovery message. It is sent to the sender of the Discovery message via TCP
at the port GRASP_LISTEN_PORT.
If the responding node supports the discovery objective
of the discovery, it MUST include at least one kind of
locator option () 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 () embedding a locator
option or a combination of multiple kinds of locator
options which indicate the locator(s) of the discovery
objective.
In fragmentary CDDL, Request Negotiation and Request Synchronization messages follow the patterns:
A negotiation or synchronization requesting node
sends the appropriate Request message to the unicast address (directly
stored or resolved from an FQDN or URI) of the negotiation or
synchronization counterpart, using the appropriate protocol and port numbers
(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 (),
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.In fragmentary CDDL, a Negotiation message follows the pattern: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.In fragmentary CDDL, a Negotiation End message follows the pattern:
A negotiation counterpart sends an Negotiation End
message to close the negotiation. It MUST contain
either an accept or a decline option,
defined in and .
It could be sent either by the
requesting node or the responding node.In fragmentary CDDL, a Confirm Waiting message follows the pattern:
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
().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.In fragmentary CDDL, a Synchronization message follows the pattern: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.In fragmentary CDDL, a Flood Synchronization message follows the pattern:
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 .
The initiator address is provided as described for Discovery messages.
The synchronization data will be in the form of GRASP Option(s) for specific
synchronization 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.In fragmentary CDDL, a No Operation message follows the pattern:
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.This section defines the GRASP options for the negotiation
and synchronization protocol signaling. Additional
options may be defined in the future.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 . 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
requirementThe 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:The embedded Locator Option(s) ()
point to diverted destination target(s) in response to a Discovery message. 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: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: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.These locator options are used to present reachability information for an ASA,
a device or an interface. They are Locator IPv6 Address
Option, Locator IPv4 Address Option, Locator FQDN (Fully
Qualified Domain Name) Option and URI (Uniform Resource Identifier) Option.Since ASAs will normally run as independent user programs, locator options need
to indicate the network layer locator plus the transport protocol and port number for
reaching the target. For this reason, the Locator Options for IP addresses
and FQDNs include this information explicitly. In the case of the URI Option,
this information can be encoded in the URI itself.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. In fragmentary CDDL, the IPv6 address option follows the pattern:The content of this option is a binary IPv6 address followed by the protocol number and port number to be used.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.In fragmentary CDDL, the IPv4 address option follows the pattern:The content of this option is a binary IPv4 address followed by the protocol number and port number to be used.Note: If an operator has internal network address translation for IPv4,
this option MUST NOT be used within the Divert option.In fragmentary CDDL, the FQDN option follows the pattern:The content of this option is the Fully Qualified Domain Name of the target followed by the protocol number and port number to be used.
Note 1: Any FQDN which might not be valid throughout the network in question,
such as a Multicast DNS name , 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.In fragmentary CDDL, the URI option follows the pattern:The content of this option is the Uniform Resource Identifier of the target
.
Note 1: Any URI which might not be valid throughout the network in question,
such as one based on a Multicast DNS name , 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.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: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 ().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:
The unique string is a decimal number representing a registered 32 bit Private Enterprise
Number (PEN) that uniquely identifies the enterprise
defining the objective.The unique string is a fully qualified domain name that uniquely identifies the entity or person
defining the objective.The unique string is an email address that uniquely identifies the entity or person
defining the objective.
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
. It is also used for terminating discovery as
described in , and for terminating flooding as described in
.
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.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: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 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. 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).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 , 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 . 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.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.Two prototype implementations of GRASP have been made.Name: BaseNegotiator.cpp, msg.cpp, Client.cpp, Server.cppDescription: C++ implementation of GRASP kernel and APIMaturity: Prototype code, interoperable between Ubuntu.Coverage: Corresponds to draft-carpenter-anima-gdn-protocol-03. Since it was implemented
based on the old version draft, the most significant limitations comparing to current protocol design
include:
Not support CBORNot support FloodingNot support loop avoidanceonly coded for IPv6, any IPv4 is accidentalLicensing: Huawei License.Experience: https://github.com/liubingpang/IETF-Anima-Signaling-Protocol/blob/master/README.mdContact: https://github.com/liubingpang/IETF-Anima-Signaling-ProtocolName: graspyDescription: Python 3 implementation of GRASP kernel and API.Maturity: Prototype code, interoperable between Windows 7 and Debian.Coverage: Corresponds to draft-ietf-anima-grasp-05. Limitations include:
insecure: uses a dummy ACP module and does not implement TLSonly coded for IPv6, any IPv4 is accidentalFQDN and URI locators incompletely supportedno code for rapid moderelay code is lazy (no rate control)all unicast transactions use TCP (no unicast UDP)optional Objective option in Response messages not implementedworkarounds for defects in Python socket module and Windows socket peculiaritiesLicensing: Simplified BSDExperience: https://www.cs.auckland.ac.nz/~brian/graspy/graspy.pdfContact: https://www.cs.auckland.ac.nz/~brian/graspy/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. - AuthenticationA 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 (),
the Session ID () 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 RolesThe 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 confidentialityGenerally 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
requires either an ACP or the use of TLS.- Link-local multicast securityGRASP 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 attackers. In the case of Discovery, the Discovery Responses
are unicast and will therefore be protected (), 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 .- DoS Attack ProtectionGRASP 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 . Additionally,
it is of great importance that firewalls prevent any GRASP messages
from entering the domain from an untrusted source. - Security during bootstrap and discoveryA 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
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 locatorsWhen GRASP discovery returns an IP address, it MUST be that of a node
within the secure environment (). 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.This document defines the General Discovery and Negotiation
Protocol (GRASP). explains the following link-local multicast
addresses, which IANA is requested to assign for use by GRASP:(IPv6): (TBD1).
Assigned in the IPv6 Link-Local Scope Multicast Addresses registry.(IPv4): (TBD2).
Assigned in the IPv4 Multicast Local Network Control Block.
explains the following UDP and TCP port,
which IANA is requested to assign for use by GRASP:(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 . The following initial values are assigned by this document: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 .
The following initial values are assigned by this document: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,
Toerless Eckert,
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.7. Cross-check against other ANIMA WG documents for consistency and gaps.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. 48. Should the Appendix "Capability Analysis of Current Protocols" be deleted before RFC publication?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.
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).
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.3. DoS Attack Protection needs work.
RESOLVED by adding text.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.
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.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.8. Consideration of ADNCP proposal.
RESOLVED by adding optional use of DNCP for flooding-type synchronization.9. Clarify how a GDNP instance knows whether it is running inside the ACP. (Sheng)
RESOLVED by improved text.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.
11. Clarify how UDP/TCP choice is made. (Sheng) [Like DNS? - Brian]
RESOLVED by improved text.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.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. 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. 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. 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.
17. Ensure that the discovery mechanism is completely proof against loops
and protected against duplicate responses.
RESOLVED: Added loop count mechanism.
18. Discuss the handling of multiple valid discovery responses.
RESOLVED: Stated that the choice must be available to the ASA
but GRASP implementation should pick a default. 19. Should we use a text-oriented format such as JSON/CBOR instead of
native binary TLV format?
RESOLVED: Yes, changed to CBOR. 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. 21. Rename the protocol as GRASP (GeneRic Autonomic Signaling Protocol)?
RESOLVED: Yes, name changed.22. Does discovery mechanism scale robustly as needed? Need hop limit on relaying?
RESOLVED: Added hop limit.23. Need more details on TTL for caching discovery responses.
RESOLVED: Done.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. 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.26. Add a URL type to the locator options (for security bootstrap etc.)
RESOLVED: Done, later renamed as URI. 27. Security of Flood multicasts ().
RESOLVED: added text.28. Does ACP support secure link-local multicast?
RESOLVED by new text in the Security Considerations.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.30. Does response to discovery require randomized delays to mitigate amplification attacks?
RESOLVED: WG feedback is that it's unnecessary.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.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).33. Clarify if/when discovery needs to be repeated.
RESOLVED: Done.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.35. State that role-based authorization of ASAs is out of scope for GRASP.
GRASP doesn't recognize/handle any "roles".
RESOLVED: Done.36. Reconsider CBOR definition for PEN syntax.
( objective-name = text / [pen, text] ; pen = uint )
RESOLVED: See issue 29.37. 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).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.39. Clarify that a node will contain one GRASP instance supporting multiple ASAs.
RESOLVED: Done.40. Add a "reason" code to the DECLINE option?
RESOLVED: Done.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.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. 44. In requirement T9, the words that encryption "may not be required in all deployments"
were removed. Is that OK?.
RESOLVED: No objections.45. Device Identity Option is unused. Can we remove it completely?.
RESOLVED: No objections. Done.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
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.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.draft-ietf-anima-grasp-05, 2016-05-13:
Noted in requirement T1 that it should be possible to implement ASAs independently as user space programs.
Protocol change: Added protocol number and port to discovery response. Updated protocol description, CDDL and IANA considerations accordingly.
Clarified that discovery and flood multicasts are handled by the GRASP kernel, not directly by ASAs.
Clarified that a node may discover an objective without supporting it for synchronization or negotiation.
Added Implementation Status section.
Added reference to SCSP.
Editorial fixes.
draft-ietf-anima-grasp-04, 2016-03-11:
Protocol change: Restored initiator field in certain messages and adjusted relaying rules
to provide complete loop detection.
Updated IANA Considerations.
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 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.
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 improvementsdraft-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,
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.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)
provides service discovery for managed networks,
but requires configuration of its own servers. DNS-SD
combined with mDNS provides service discovery for
small networks with a single link layer.
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.Simple Network Management Protocol (SNMP) uses
a command/response model not well suited for peer negotiation. Network Configuration
Protocol (NETCONF) 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)
, Neighbor Discovery (ND) ,
Port Control Protocol (PCP) , Remote Authentication
Dial In User Service (RADIUS) , Diameter ,
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)
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 .
A more generic design is General Internet
Signalling Transport (GIST) , 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
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)
. This is defined as a generic form
of state synchronization protocol, with a proposed usage profile being the
Home Networking Control Protocol (HNCP)
for configuring Homenet routers. A specific application of DNCP for autonomic
networking was proposed in .
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 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:
Every participating node has a unique node identifier.DNCP messages are encoded as a sequence of TLV objects, sent over
unicast UDP or TCP, with or without (D)TLS security.Multicast is used only for discovery of DNCP neighbors
when lower security is acceptable.Synchronization of state is maintained by a flooding process using the Trickle algorithm.
There is no bilateral synchronization or negotiation capability.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.The Server Cache Synchronization Protocol (SCSP) also describes
a method for cache synchronization and cache replication among a group of nodes.A proposal was made some years ago for an IP based Generic Control Protocol
(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 . Also, we have not identified a path
by which one of the existing protocols could be extended to meet the
requirements.