GeneRic Autonomic Signaling Protocol (GRASP)
Universität Bremen TZI
Postfach 330440
Bremen
D-28359
Germany
cabo@tzi.org
School of Computer Science
University of Auckland
PB 92019
Auckland
1142
New Zealand
brian.e.carpenter@gmail.com
Huawei Technologies Co., Ltd
No.156 Beiqing Road
Q14, Huawei Campus
Hai-Dian District
Beijing
100095
China
leo.liubing@huawei.com
Operations and Management
ANIMA
autonomic networking
autonomous operation
self-management
This document specifies the GeneRic Autonomic Signaling Protocol (GRASP), which
enables autonomic nodes and Autonomic Service Agents to dynamically discover peers,
to synchronize state with each other, and to negotiate parameter settings with each
other. GRASP depends on an external security environment that is described
elsewhere. The technical objectives and parameters for specific application scenarios
are to be described in separate documents. Appendices briefly discuss requirements
for the protocol and existing protocols with comparable features.
Introduction
The success of the Internet has made IP-based networks bigger and
more complicated. Large-scale ISP and enterprise networks have become more and more
problematic for human-based management. Also, operational costs are growing quickly.
Consequently, there are increased requirements for autonomic behavior in the networks.
General aspects of Autonomic Networks are discussed in
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
. The reader should consult this document
to understand how various autonomic components fit together.
In order to achieve autonomy, devices that embody Autonomic Service Agents
(ASAs, )
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 limitation on the types of parameters and resources concerned,
which can 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 discovery, synchronization, or negotiation is referred to as a technical
objective, i.e., a configurable parameter or set of parameters
(defined more precisely in ).
Negotiation is an iterative process, requiring multiple message exchanges forming
a closed loop between the negotiating entities. In fact, these entities are
ASAs, normally but not necessarily in different network devices.
State synchronization, when needed,
can be regarded as a special case of negotiation without iteration.
Both negotiation and synchronization must logically follow discovery.
More details of the requirements are found in .
describes a behavior model for a protocol
intended to support discovery, synchronization, and negotiation. The
design of GeneRic Autonomic Signaling Protocol (GRASP) in
is 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 on the
local link, but it also supports diversion to peers on other links.
There is no assumption of any particular form of network topology.
When a device starts up with no preconfiguration,
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 in a large, 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 as part of a decision process among distributed
devices or between networks, it must run in a secure and strongly authenticated
environment.
In realistic deployments, not all devices will
support GRASP. Therefore, some Autonomic Service Agents will directly
manage a group of non-autonomic nodes, and other non-autonomic nodes
will be managed traditionally. Such mixed scenarios
are not discussed in this specification.
Protocol Overview
Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be interpreted as
described in BCP 14
when, and only when, they appear in all capitals, as shown here.
This document uses terminology defined in .
The following additional terms are used throughout this document:
- 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 ASAs interact iteratively to agree on parameter
settings that best satisfy the objectives of both ASAs.
- State Synchronization:
- A process by which ASAs interact to receive the current state of parameter
values stored in other ASAs. 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 data structure whose main contents are a name
and a value. The value consists of a single configurable parameter or a set of
parameters of some kind. The exact format of an objective is defined in . An objective occurs in three contexts:
discovery, negotiation, and synchronization. Normally, a given objective will
not occur in negotiation and synchronization contexts simultaneously.
- One ASA may support multiple independent objectives.
-
The parameter(s) in the value of a given objective apply to a specific
service or function or action. They 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. Each node is expected to contain one or more
ASAs which may each manage subsidiary non-autonomic nodes.
-
- Discovery Objective:
- an objective in the process of discovery. Its value may be undefined.
- Synchronization Objective:
- an objective whose specific technical content needs to be synchronized
among two or more ASAs. Thus, each ASA will maintain its own copy of the
objective.
- Negotiation Objective:
- an objective whose specific technical content needs to be decided in
coordination with another ASA. Again, each ASA will maintain its own copy of
the objective.
- A detailed discussion of objectives, including their format, is found in
.
- Discovery Initiator:
- An ASA that 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. It sends a Discovery Response, as described later.
- Synchronization Initiator:
- An ASA that starts synchronization by sending a request message referring
to a specific synchronization objective.
- Synchronization Responder:
- A peer ASA that responds with the value of a synchronization objective.
- Negotiation Initiator:
- An ASA that 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.
- GRASP Instance:
-
This refers to an instantiation of a GRASP protocol engine, likely
including multiple threads or processes as well as dynamic data structures
such as a discovery cache, running in a given security environment on a single
device.
- GRASP Core:
-
This refers to the code and shared data structures of a GRASP instance,
which will communicate with individual ASAs via a suitable Application
Programming Interface (API).
- Interface or GRASP Interface:
-
Unless otherwise stated, this refers to a network interface, which might
be physical or virtual, that a specific instance of GRASP is currently
using. A device might have other interfaces that are not used by GRASP and
which are outside the scope of the Autonomic Network.
High-Level Deployment Model
A GRASP implementation will be part of the Autonomic Networking Infrastructure (ANI)
in an autonomic node, which must also provide an appropriate security environment.
In accordance with , this SHOULD be the
Autonomic Control Plane (ACP) .
As a result, all autonomic nodes in the ACP are able to trust each other.
It is expected that GRASP will access the ACP by using a typical socket programming interface,
and the ACP will make available only network interfaces within the Autonomic Network.
If there is no ACP, the considerations described in apply.
There will also be one or more Autonomic Service Agents (ASAs). In the minimal case
of a single-purpose device, these components might be fully integrated with GRASP
and the ACP. A more common model is expected to be a multipurpose device capable of containing
several ASAs, such as a router or large switch. In this case it is expected that the ACP, GRASP and the ASAs will
be implemented as separate processes, which are able to support
asynchronous and simultaneous operations, for example by multithreading.
In some scenarios, a limited negotiation model might be deployed based on a limited
trust relationship such as that between two administrative domains. ASAs might then
exchange limited information and negotiate some particular configurations.
GRASP is explicitly designed to operate within a single addressing realm.
Its discovery and flooding mechanisms do not support autonomic operations that
cross any form of address translator or upper-layer proxy.
A suitable 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.
Details of the API are out of scope for the present document.
For further details of possible deployment models, see
.
An instance of GRASP must be aware of the network interfaces it will use, and of the
appropriate global-scope
and link-local addresses. In the presence of the ACP, such information will be available from
the adjacency table discussed in .
In other cases, GRASP must determine such information for itself. Details depend on the
device and operating system. In the rest of this document, the terms 'interfaces'
or 'GRASP interfaces'
refers only to the set of network interfaces that a specific instance
of GRASP is currently using.
Because GRASP needs to work with very high reliability, especially during bootstrapping
and during fault conditions, it is essential that every implementation continues to
operate in adverse conditions. For example, discovery failures, or any kind of socket
exception at any time, must not cause irrecoverable failures in GRASP itself, and must
return suitable error codes through the API so that ASAs can also recover.
GRASP must not depend upon nonvolatile data storage. All runtime error
conditions, and events such as address renumbering, network interface failures,
and CPU sleep/wake cycles, must be handled in such a way that GRASP will still
operate correctly and securely afterwards ().
An autonomic node will normally run a single instance of GRASP, which is used by multiple ASAs.
Possible exceptions are mentioned below.
High-Level Design
This section describes the behavior model and general design of
GRASP, supporting discovery, synchronization, and negotiation, to
act as a platform for different technical objectives.
- A generic platform:
- The protocol design is generic and independent of the synchronization or
negotiation contents. The technical contents will vary according to the
various technical objectives and the different pairs of counterparts.
- Multiple instances:
-
Normally, a single main instance of the GRASP protocol engine will exist
in an autonomic node, and each ASA will run as an independent asynchronous
process. However, scenarios where multiple instances of GRASP run in a single
node, perhaps with different security properties, are possible (). In this case, each instance
MUST listen independently for GRASP link-local multicasts, and
all instances MUST be woken by each such multicast in order
for discovery and flooding to work correctly.
- Security infrastructure:
- As noted above, the protocol itself has no built-in security
functionality and relies on a separate secure infrastructure.
- 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, allowing a
rapid mode of operation described in . These processes can also be performed independently when
appropriate.
-
Thus, for some objectives, especially those concerned with application-layer
services, another discovery mechanism such as DNS-based Service Discovery
MAY be used. The
choice is left to the designers of individual ASAs.
- A uniform pattern for technical objectives:
-
The synchronization and negotiation objectives are defined according to a
uniform pattern. The values that they contain could be carried either in a
simple binary format or in a complex object format. The basic protocol design
uses the Concise Binary Object Representation (CBOR) , which is readily extensible for unknown, future
requirements.
- A flexible model for synchronization:
-
GRASP supports synchronization between two nodes, which could be used
repeatedly 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 the Distributed Node Consensus Protocol (DNCP) is considered
more appropriate. GRASP can coexist with DNCP.
- A simple initiator/responder model for negotiation:
-
Multiparty negotiations are very complicated to model and cannot readily
be guaranteed to converge. GRASP uses a simple bilateral model and can support
multiparty negotiations by indirect steps.
- Organizing of synchronization or negotiation content:
-
The technical content transmitted by GRASP will be organized according to
the relevant function or service. The objectives for different functions or
services are kept separate because they may be negotiated or synchronized
with different counterparts or have different response times. Thus a normal
arrangement is a single ASA managing a small set of closely related
objectives, with a version of that ASA in each relevant autonomic
node. Further discussion of this aspect is out of scope for the current
document.
- Requests and responses in negotiation procedures:
-
The initiator can negotiate a specific negotiation objective with relevant
counterpart ASAs. It can request relevant information from a counterpart so
that it can coordinate its local configuration. It can request the counterpart
to make a matching configuration. It can request simulation or forecast
results by sending some dry-run conditions.
Beyond the traditional yes/no answer, the responder can reply with a suggested
alternative value for the objective concerned. This would start a
bidirectional negotiation ending in a compromise between the two ASAs.
- Convergence of negotiation procedures:
-
To enable convergence when a responder suggests a new value or condition
in a negotiation step reply, it should be as close as possible to the original
request or previous suggestion. The suggested value of later negotiation steps
should be chosen between the suggested values from the previous two
steps. GRASP provides mechanisms to guarantee convergence (or failure) in a
small number of steps, namely a timeout and a maximum number of iterations.
- Extensibility:
-
GRASP intentionally does not have a version number, and it can be extended by
adding new message types and options. The Invalid message (M_INVALID) will be
used to signal that an implementation does not recognize a message or option
sent by another implementation. In normal use, new semantics will be added by
defining new synchronization or negotiation objectives.
Quick Operating Overview
An instance of GRASP is expected to run as a separate core module,
providing an API (such as ) to interface to
various ASAs.
These ASAs may operate without special privilege, unless they need it for
other reasons (such as configuring IP addresses or manipulating routing
tables).
The GRASP mechanisms used by the ASA are built around GRASP objectives
defined as data structures
containing administrative information such as the objective's unique
name and its current value. The format and size of the value is
not restricted by the protocol, except that it must be possible to
serialize it for transmission in CBOR, which is no
restriction at all in practice.
GRASP provides the following mechanisms:
- A discovery mechanism (M_DISCOVERY, M_RESPONSE) by which an ASA can
discover other ASAs supporting a given objective.
-
A negotiation request mechanism (M_REQ_NEG) by which an ASA can start
negotiation of an objective with a counterpart ASA. Once a negotiation has
started, the process is symmetrical, and there is a negotiation step message
(M_NEGOTIATE) for each ASA to use in turn. Two other functions support negotiating
steps (M_WAIT, M_END).
-
A synchronization mechanism (M_REQ_SYN) by which an ASA can request the
current value of an objective from a counterpart ASA. With this,
there is a corresponding response function (M_SYNCH) for an ASA that
wishes to respond to synchronization requests.
-
A flood mechanism (M_FLOOD) by which an ASA can cause the current value of
an objective to be flooded throughout the Autonomic Network so that any ASA can
receive it. One application of this is to act as an announcement, avoiding the need for
discovery of a widely applicable objective.
Some example messages and simple message flows are provided in .
GRASP Basic Properties and Mechanisms
Required External Security Mechanism
GRASP does not specify transport security because it is meant to
be adapted to different environments. Every solution adopting GRASP
MUST specify a security and transport substrate used by GRASP in
that solution.
The substrate MUST enforce sending and receiving GRASP messages
only between members of a mutually trusted group running GRASP. Each
group member is an instance of GRASP. The group members are nodes of
a connected graph. The group and graph are created by the security
and transport substrate and are called the GRASP domain. The substrate
must support unicast messages between any group members and
(link-local) multicast messages between adjacent group members. It
must deny messages between group members and non-group members. With
this model, security is provided by enforcing group membership, but
any member of the trusted group can attack the entire network until
revoked.
Substrates MUST use cryptographic member authentication and
message integrity for GRASP messages. This can be end to end or
hop by hop across the domain. The security and transport substrate
MUST provide mechanisms to remove untrusted members from the
group.
If the substrate does not mandate and enforce GRASP message
encryption, then any service using GRASP in such a solution MUST
provide protection and encryption for message elements whose
exposure could constitute an attack vector.
The security and transport substrate for GRASP in the ANI is the
ACP. Unless otherwise noted, we assume this security and transport
substrate in the remainder of this document. The ACP does mandate
the use of encryption; therefore, GRASP in the ANI can rely on GRASP
messages being encrypted. The GRASP domain is the ACP: all nodes in
an autonomic domain connected by encrypted virtual links formed by
the ACP. The ACP uses hop-by-hop security
(authentication and encryption) of messages. Removal of nodes relies on
standard PKI certificate revocation or expiry of sufficiently short-lived
certificates. Refer to
for more details.
As mentioned in , some GRASP operations might be
performed across an administrative domain boundary by mutual agreement, without the
benefit of an ACP. Such operations
MUST be confined to a separate instance of GRASP with its own copy of all GRASP
data structures running across a separate GRASP domain with a security and transport substrate.
In the most simple case, each point-to-point interdomain GRASP peering could be a
separate domain, and the security and transport substrate could be built using transport or network-layer
security protocols. This is subject to future specifications.
An exception to the requirements for the security and transport substrate exists
for highly constrained subsets of GRASP meant to support the establishment of a security and transport substrate,
described in the following section.
Discovery Unsolicited Link-Local (DULL) GRASP
Some services may need to use insecure GRASP discovery, response,
and flood messages without being able to use preexisting security
associations, for example, as part of discovery for establishing
security associations such as a security substrate for GRASP.
Such operations being intrinsically insecure, they need to be confined to link-local
use to minimize the risk of malicious actions. Possible examples
include discovery of candidate ACP neighbors
, discovery of bootstrap
proxies , or perhaps
initialization services in networks using GRASP without being fully autonomic
(e.g., no ACP).
Such usage MUST be limited to link-local operations on a single interface and MUST be confined
to a separate insecure instance of GRASP with its own copy of all GRASP
data structures. This instance is nicknamed DULL -- Discovery Unsolicited Link-Local.
The detailed rules for the DULL instance of GRASP are as follows:
- An initiator MAY send Discovery or Flood Synchronization link-local
multicast messages that MUST have a loop count of 1, to prevent
off-link operations.
Other unsolicited GRASP message types MUST NOT be sent.
- A responder MUST silently discard any message whose loop count is not 1.
- A responder MUST silently discard any message referring to a GRASP objective that is
not directly part of a service that requires this insecure mode.
- A responder MUST NOT relay any multicast messages.
- A Discovery Response MUST indicate a link-local address.
- A Discovery Response MUST NOT include a Divert option.
- A node MUST silently discard any message whose source address is not link-local.
To minimize traffic possibly observed by third parties,
GRASP traffic SHOULD be minimized by using only Flood Synchronization
to announce objectives and their associated locators, rather than by using Discovery
and Discovery Response messages. Further details are out of scope for this document.
Transport Layer Usage
All GRASP messages, after they are serialized as a CBOR byte string, are transmitted
as such directly over the transport protocol in use. The transport protocol(s) for a GRASP
domain are specified by the security and transport substrate as introduced in .
GRASP discovery and flooding messages are designed for GRASP domain-wide flooding
through hop-by-hop link-local multicast forwarding between adjacent GRASP nodes. The
GRASP security and transport substrate needs to specify how these link-local multicasts
are transported. This can be unreliable transport (UDP) but it SHOULD be reliable
transport (e.g., TCP).
If the substrate specifies an unreliable transport such as UDP for discovery and flooding messages,
then it MUST NOT use IP fragmentation because of its loss characteristic, especially
in multi-hop flooding. GRASP MUST then enforce at the user API level a limit to the size
of discovery and flooding messages, so that no fragmentation can occur. For IPv6 transport, this
means that the size of those messages' IPv6 packets must be at most 1280 bytes (unless there is a known
larger minimum link MTU across the whole GRASP domain).
All other GRASP messages are unicast between group members of the GRASP domain. These
MUST use a reliable transport protocol because GRASP itself does not provide for error detection,
retransmission, or flow control. Unless otherwise specified by the security and transport
substrate, TCP MUST be used.
The security and transport substrate for GRASP in the ANI is the ACP. Unless otherwise noted,
we assume this security and transport substrate in the remainder of this document when describing
GRASP's message transport. In the ACP, TCP is used for GRASP unicast messages. GRASP discovery and
flooding messages also use TCP: these link-local messages are forwarded by replicating them to
all adjacent GRASP nodes on the link via TCP connections to those adjacent GRASP nodes. Because
of this, GRASP in the ANI has no limitations on the size of discovery and flooding messages with
respect to fragmentation issues. While the ACP is being built using a DULL instance of GRASP,
native UDP multicast is used to discover ACP/GRASP neighbors on links.
For link-local UDP multicast, GRASP listens to the well-known
GRASP Listen Port (). Transport connections for discovery
and flooding on relay nodes must terminate in GRASP instances (e.g., GRASP ASAs) so
that link-local multicast, hop-by-hop flooding of M_DISCOVERY and M_FLOOD messages and hop-by-hop forwarding
of M_RESPONSE responses and caching of those responses along the path work correctly.
Unicast transport connections used for synchronization and negotiation can terminate
directly in ASAs that implement objectives; therefore, this traffic does not need to
pass through GRASP instances. For this, the ASA listens on its own dynamically assigned ports,
which are communicated to its peers during discovery. Alternatively, the GRASP instance
can also terminate the unicast transport connections and pass the traffic from/to the
ASA if that is preferable in some implementations (e.g., to better decouple ASAs from
network connections).
Discovery Mechanism and Procedures
Separated Discovery and Negotiation Mechanisms
Although discovery and negotiation or synchronization are defined
together in GRASP, they are separate mechanisms. The discovery
process could run independently from the negotiation or synchronization
process. Upon receiving a Discovery message (),
the
recipient node should return a Discovery Response message in which it either
indicates itself as a discovery responder or diverts the
initiator towards another more suitable ASA. However, this
response may be delayed if the recipient needs to relay
the Discovery message onward, as described in .
The discovery action (M_DISCOVERY) will normally be followed by
a negotiation (M_REQ_NEG) or synchronization (M_REQ_SYN) 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 responding to that objective as a negotiation counterpart, as a
synchronization responder, or as source for flooding. For example, an ASA might perform
discovery even if it only wishes to act as a synchronization initiator or negotiation initiator.
Such an ASA does not itself need to respond to Discovery messages.
It is also 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 Overview
A complete discovery process will start with a multicast Discovery message (M_DISCOVERY) on the
local link. On-link neighbors supporting the discovery objective will
respond directly with Discovery Response (M_RESPONSE) messages. A neighbor with multiple interfaces may respond
with a cached Discovery Response. If it has no cached response, it will relay the
Discovery message on its other GRASP interfaces.
If a node receiving the relayed Discovery message
supports the discovery objective, it will respond to the relayed Discovery message.
If it has a cached response, it will respond with that.
If not, it will repeat the discovery process, which thereby becomes iterative.
The loop count and timeout will ensure that the process ends. Further details
are given in .
A Discovery message MAY be sent unicast to a peer node,
which SHOULD then proceed exactly as if the message had been multicast,
except that when TCP is used, the response will be
on the same socket as the query. However,
this mode does not guarantee successful discovery in the general case.
Discovery Procedures
Discovery starts as an on-link operation. The Divert option
can tell the discovery initiator to contact an off-link
ASA for that discovery objective. If the security and transport substrate
of the GRASP domain (see ) uses UDP link-local multicast,
then the discovery initiator sends these to the ALL_GRASP_NEIGHBORS link-local
multicast address (), and all GRASP nodes need
to listen to this address to act as discovery responders.
Because this port
is unique in a device, this is a function of the GRASP instance
and not of an individual ASA. As a result, each ASA will need to
register the objectives that it supports with the local GRASP instance.
If an ASA in a neighbor device supports the requested discovery objective,
the device SHOULD respond to the link-local multicast with a unicast Discovery Response
message () with locator option(s) () unless it is
temporarily unavailable. 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. However, it SHOULD NOT respond
with a cached response on an interface if it learned that information from
the same interface because the peer in question will answer directly if still
operational.
If a device has no information about the requested discovery objective
and is not acting as a discovery relay (see ), it MUST silently
discard the Discovery message.
The discovery initiator MUST set a reasonable timeout on the
discovery process. A suggested value is 100 milliseconds multiplied by the loop count
embedded in the objective.
If no Discovery Response is received within the timeout,
the Discovery message MAY be repeated with a newly generated
Session ID (). An exponential backoff SHOULD be used
for subsequent repetitions to limit the load during busy periods. The
details of the backoff algorithm will depend on the use case for the
objective concerned but MUST be consistent with the recommendations
in for low data-volume multicast.
Frequent repetition might be symptomatic of a denial-of-service attack.
After a GRASP device successfully discovers a locator for a discovery responder
supporting a specific objective, it SHOULD cache this information, including the interface
index via which it was discovered. This cache record MAY be used for future
negotiation or synchronization, and the locator SHOULD be passed on when appropriate
as a Divert option to another discovery initiator.
The cache mechanism MUST include a lifetime for each entry. The
lifetime is derived from a time-to-live (ttl) parameter in each
Discovery Response message.
Cached entries MUST be ignored or deleted after their lifetime expires.
In some environments, unplanned address renumbering might occur.
In such cases, the lifetime SHOULD be short compared to
the typical address lifetime. The discovery mechanism
needs to track the node's current address to ensure that Discovery
Responses always indicate the correct address.
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.
Discovery Relaying
A GRASP instance with multiple link-layer interfaces (typically
running in a router) MUST support discovery on all
GRASP interfaces. We refer to this as a 'relaying instance'.
DULL instances () are
always single-interface instances and therefore MUST NOT perform discovery relaying.
If a relaying instance 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 reissuing a new Discovery
message as a link-local multicast on its other GRASP
interfaces.
The relayed Discovery message MUST have the
same Session ID and 'initiator' field as the incoming message (see ). The IP
address in the 'initiator' field is only used to disambiguate the
Session ID and is never used to address Response packets.
Response packets are sent back to the relaying instance, not the
original initiator.
The M_DISCOVERY message does not encode the transport address
of the originator or relay. Response packets must therefore be
sent to the transport-layer address of the connection on which the
M_DISCOVERY message was received. If the M_DISCOVERY was relayed
via a reliable hop-by-hop transport connection, the response is
simply sent back via the same connection.
If the M_DISCOVERY was relayed via link-local (e.g., UDP)
multicast, the response is sent back via a reliable hop-by-hop
transport connection with the same port number as the source port
of the link-local multicast. Therefore, if link-local multicast is
used and M_RESPONSE messages are required (which is the case in
almost all GRASP instances except for the limited use of DULL
instances in the ANI), GRASP needs to be able to bind to one port
number on UDP from which to originate the link-local multicast
M_DISCOVERY messages and the same port number on the reliable
hop-by-hop transport (e.g., TCP by default) to be able to respond to
transport connections from responders that want to send M_RESPONSE
messages back. Note that this port does not need to be the
GRASP_LISTEN_PORT.
The relaying instance 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. For example, the rate limit
could be set to a small multiple of the observed rate of Discovery
messages during normal operation. The relaying instance
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 that carries a given cached Session ID and initiator
address more than once. These precautions avoid discovery loops
and mitigate potential overload.
Since the relay device is unaware of the timeout set by the original
initiator, it SHOULD set a suitable timeout for the relayed Discovery message.
A suggested value is 100 milliseconds multiplied by the remaining loop count.
The discovery results received by the relaying instance MUST in turn be
sent as a Discovery Response message to the Discovery message that caused
the relay action.
Rapid Mode (Discovery with Negotiation or Synchronization)
A Discovery message MAY include an
objective option. This allows a rapid mode of negotiation
() or
synchronization ().
Rapid mode is currently limited to a single objective
for simplicity of design and implementation. A possible future extension
is to allow multiple objectives in rapid mode for greater efficiency.
Negotiation Procedures
A negotiation initiator opens a transport connection to a
counterpart ASA using the address, protocol, and port obtained during discovery.
It then sends a negotiation request (using M_REQ_NEG) to the counterpart,
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 a dry run and a live
configuration change, will be defined separately for each type of negotiation
objective. Any state associated with a dry-run operation,
such as temporarily reserving a resource for subsequent use in a live
run, is entirely a matter for the designer of the ASA concerned.
Each negotiation session as a whole is subject to a timeout
(default GRASP_DEF_TIMEOUT milliseconds, ),
initialized when the request is sent (see ).
If no reply message of any kind is received within the timeout,
the negotiation request MAY be repeated with a newly generated
Session ID (). An exponential backoff SHOULD be used
for subsequent repetitions. The
details of the backoff algorithm will depend on the use case for the
objective concerned.
If the counterpart can immediately apply the requested
configuration, it will give an immediate positive (O_ACCEPT) answer using the Negotiation End (M_END) message.
This will end the negotiation phase immediately. Otherwise, it will
negotiate (using M_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
bidirectional negotiation using the Negotiate (M_NEGOTIATE) message to reach a compromise between the two ASAs.
The negotiation procedure is ended when one of the negotiation
peers sends a Negotiation End (M_END) message, which contains an Accept (O_ACCEPT)
or Decline (O_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. When the procedure
ends for whatever reason, the transport connection SHOULD be closed.
A transport session failure is treated as a negotiation failure.
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 multithreaded mode or its logical equivalent. Certain negotiation
objectives may have restrictions on multithreading, 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
(, M_WAIT).
Rapid Mode (Discovery/Negotiation Linkage)
A Discovery message MAY include a Negotiation
Objective option. In this case, it is as if the initiator sent the sequence
M_DISCOVERY immediately followed by M_REQ_NEG.
This has implications for the construction of the GRASP core, as it must carefully
pass the contents of the Negotiation Objective option to the ASA so that it
may evaluate the objective directly. When a Negotiation Objective option is
present, the ASA replies with an M_NEGOTIATE message (or M_END with O_ACCEPT if it is
immediately satisfied with the proposal) rather than with an M_RESPONSE.
However, if the recipient node does not support rapid mode, discovery will
continue normally.
It is possible that a Discovery Response will arrive from a responder that
does not support rapid mode before such a Negotiation message arrives.
In this case, rapid mode will not occur.
This rapid mode could reduce the interactions between
nodes so that a higher efficiency could be achieved. However, a network in which some
nodes support rapid mode and others do not will have complex timing-dependent behaviors.
Therefore, the rapid negotiation function SHOULD be disabled by default.
Synchronization and Flooding Procedures
Unicast Synchronization
A synchronization initiator opens a transport connection to a
counterpart ASA using the address, protocol, and port obtained during discovery.
It then sends a Request Synchronization message (M_REQ_SYN, ) to the
counterpart, including a specific synchronization objective.
The counterpart responds with a Synchronization message (M_SYNCH, )
containing the current value of the requested synchronization
objective. No further messages are needed, and the transport
connection SHOULD be closed. A transport session failure is treated
as a synchronization failure.
If no reply message of any kind is received within a given 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. The
details of the backoff algorithm will depend on the use case for the
objective concerned.
Flooding
In the case just described, the message exchange is unicast and
concerns only one synchronization objective. For large groups of nodes
requiring the same data, synchronization flooding is available. For this,
a flooding initiator MAY send an unsolicited Flood Synchronization message () containing
one or more Synchronization Objective option(s), if and only if the specification
of those objectives permits it. This is sent as a multicast message to the
ALL_GRASP_NEIGHBORS multicast address ().
Receiving flood multicasts is a function of the GRASP core,
as in the case of discovery multicasts ().
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 GRASP interfaces. If it receives a multicast
Flood Synchronization message on a given interface, it MUST relay
it by reissuing a Flood Synchronization message as a link-local multicast
on its other GRASP 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.
Link-layer flooding is supported by GRASP by setting the loop count to 1
and sending with a link-local source address. Floods with link-local source addresses
and a loop count other than 1 are invalid, and such messages MUST be discarded.
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.
For example, the rate limit could be set to a small multiple of the observed
rate of flood messages during normal operation.
The relaying device MUST cache the Session ID value and initiator address of each relayed
Flood Synchronization message for a time not less than twice GRASP_DEF_TIMEOUT milliseconds.
To prevent loops, it MUST NOT relay a Flood Synchronization message
that 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,
or new nodes that join the network, or nodes that rejoin the network
after a fault. An ASA that initiates a flood SHOULD repeat the flood
at a suitable frequency, which MUST be consistent with the recommendations
in for low data-volume multicast.
The ASA SHOULD also act as a synchronization responder for
the objective(s) concerned. Thus nodes that require an objective subject to
flooding can either wait for the next flood or 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 or equivalent strong
security in place. However, because
of the security weakness of link-local multicast (),
synchronization objectives that are flooded SHOULD NOT contain unencrypted private
information and SHOULD be validated by the recipient ASA.
Rapid Mode (Discovery/Synchronization Linkage)
A Discovery message MAY include a Synchronization
Objective option. In this case, the Discovery message also acts
as a Request Synchronization message to indicate to the discovery responder
that it could directly reply to the discovery initiator with
a Synchronization message () with synchronization data for rapid processing,
if the discovery target supports the corresponding synchronization
objective. The design implications are similar to those discussed in .
It is possible that a Discovery Response will arrive from a responder that
does not support rapid mode before such a Synchronization message arrives.
In this case, rapid mode will not occur.
This rapid mode could reduce the interactions between
nodes so that a higher efficiency could be achieved. However, a network in which some
nodes support rapid mode and others do not will have complex timing-dependent behaviors.
Therefore, the rapid synchronization function SHOULD be configured off by default
and MAY be configured on or off by Intent.
GRASP Constants
- ALL_GRASP_NEIGHBORS
- A link-local scope multicast address used by a GRASP-enabled device to
discover GRASP-enabled neighbor (i.e., on-link) devices. All devices that
support GRASP are members of this multicast group.
- IPv6 multicast address: ff02::13
- IPv4 multicast address: 224.0.0.119
- GRASP_LISTEN_PORT (7017)
- A well-known UDP user port that every GRASP-enabled network device
MUST listen to for link-local multicasts when UDP is used for
M_DISCOVERY or M_FLOOD messages in the GRASP instance. This user port
MAY also be used to listen for TCP or UDP unicast messages in a
simple implementation of GRASP ().
- GRASP_DEF_TIMEOUT (60000 milliseconds)
- The default timeout used to determine that an operation 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.
- GRASP_DEF_MAX_SIZE (2048)
- The default maximum message size in bytes.
Session Identifier (Session ID)
This is an up to 32-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 pseudorandom number generator (PRNG) using a locally
generated seed that is unlikely to be used by any other device in the same
network. The PRNG SHOULD be cryptographically strong .
When allocating a new Session ID, GRASP MUST
check that the value is not already in use and SHOULD check that it has not been
used recently by consulting a cache of current and recent sessions. In the unlikely
event of a clash, GRASP MUST generate a new value.
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.
In the highly unlikely event of two peers opening sessions with the same
Session ID value, this tag will allow the two sessions to be distinguished.
Multicast GRASP messages and their responses, which may be relayed between links,
therefore include a field that carries the initiator's global IP address.
There is a highly unlikely race condition in which two peers start simultaneous negotiation
sessions with each other using the same Session ID value. Depending on various
implementation choices, this might lead to the two sessions being confused.
See for details of how to avoid this.
GRASP Messages
Message Overview
This section defines the GRASP message format and message types.
Message types not listed here are reserved for future use.
The messages currently defined are:
- Discovery and Discovery Response (M_DISCOVERY, M_RESPONSE).
- Request Negotiation, Negotiation, Confirm Waiting, and Negotiation End (M_REQ_NEG, M_NEGOTIATE, M_WAIT, M_END).
- Request Synchronization, Synchronization, and Flood Synchronization (M_REQ_SYN, M_SYNCH, M_FLOOD).
- No Operation and Invalid (M_NOOP, M_INVALID).
GRASP Message Format
GRASP messages share an identical header format and a
variable format area for options. GRASP message headers and options
are transmitted in Concise Binary Object Representation (CBOR)
. In this specification, they are described
using Concise 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 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 .
If an unrecognized MESSAGE_TYPE is received in a unicast message,
an Invalid message () MAY be returned. Otherwise, the message
MAY be logged and MUST be discarded. If an unrecognized MESSAGE_TYPE is received
in a multicast message, it MAY be logged and MUST be silently discarded.
Message Size
GRASP nodes MUST be able to receive unicast messages of at least GRASP_DEF_MAX_SIZE bytes. GRASP nodes
MUST NOT send unicast messages longer than GRASP_DEF_MAX_SIZE bytes unless a longer size is explicitly
allowed for the objective concerned. For example, GRASP negotiation itself could be used
to agree on a longer message size.
The message parser used by GRASP should be configured to know about the GRASP_DEF_MAX_SIZE, or
any larger negotiated message size, so that it may defend against overly long messages.
The maximum size of multicast messages (M_DISCOVERY and M_FLOOD) depends on the link-layer
technology or the link-adaptation layer in use.
Discovery Message
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 all Discovery
messages via UDP to port GRASP_LISTEN_PORT at the link-local
ALL_GRASP_NEIGHBORS multicast address on each link-layer interface in use by GRASP.
It then listens for unicast TCP responses on a given port and stores the discovery
results, including responding discovery objectives and
corresponding unicast locators.
The listening port used for TCP MUST be the same port as used for sending the
Discovery UDP multicast, on a given interface. In an implementation with a
single GRASP instance in a node, this MAY be GRASP_LISTEN_PORT. To support
multiple instances in the same node, the GRASP discovery mechanism in each
instance needs to find, for each interface, a dynamic port that it can bind to
for both sending UDP link-local multicast and listening for TCP before
initiating any discovery.
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 that is highly likely to be
unique for this purpose, for example, using . Determination
of a node's globally unique IP address is implementation dependent.
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). If the discovery initiator
requires only on-link responses, the loop count MUST be set to 1.
- 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 initiator 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).
As mentioned in , a Discovery message MAY be sent unicast to a peer node,
which SHOULD then proceed exactly as if the message had been multicast.
Discovery Response Message
In fragmentary CDDL, a Discovery Response message follows the pattern:
A node that 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 MUST contain a time-to-live (ttl) for the validity of the response, given
as a positive integer value in milliseconds. Zero implies a value significantly
greater than GRASP_DEF_TIMEOUT milliseconds (). A suggested
value is ten times that amount.
- 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 used to send the Discovery message (as explained in ).
In the case of a relayed Discovery message, the Discovery Response
is thus sent to the relay, not the original initiator.
In all cases, the transport session SHOULD be closed after sending the Discovery Response.
A transport session failure is treated as no response.
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 that indicate the locator(s) of the discovery objective.
More details on the processing of Discovery Responses are given in
.
Request Messages
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 of the negotiation or
synchronization counterpart, using the appropriate protocol and port numbers
(selected from the discovery result). If the discovery result is an FQDN,
it will be resolved first.
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. The default is 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.
Similarly, when an initiator sends a Request Synchronization, it SHOULD initialize
a synchronization timer. The default is GRASP_DEF_TIMEOUT milliseconds.
The initiator will consider that synchronization has failed
if there is no response before 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.
This is to avoid unnecessary timeouts if, for example, an ASA exits prematurely
but the GRASP core is listening on its behalf.
To avoid the highly unlikely race condition in which two nodes simultaneously request
sessions with each other using the same Session ID (),
a node MUST verify that the received Session ID is not already locally active
when it receives a Request message. In case of a clash,
it MUST discard the Request message, in which case the initiator will detect a timeout.
Negotiation Message
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.
Negotiation End Message
In fragmentary CDDL, a Negotiation End message follows the
pattern:
A negotiation counterpart sends a Negotiation End message to close
the negotiation. It MUST contain either an Accept option or
a Decline option, defined in and . It could be sent either by the requesting node
or the responding node.
Confirm Waiting Message
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, when the initiator's timer expires, the initiator MUST treat
the negotiation procedure as failed.
Synchronization Message
In fragmentary CDDL, a Synchronization message follows the pattern:
A node that 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.
Flood Synchronization Message
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 port GRASP_LISTEN_PORT at
the link-local ALL_GRASP_NEIGHBORS multicast address, in accordance
with the rules in .
-
The initiator address is provided, as described for Discovery messages (),
only to disambiguate the Session ID.
-
The message MUST contain a time-to-live (ttl) for the validity of the contents, given
as a positive integer value in milliseconds. There is no default;
zero indicates an indefinite lifetime.
-
The synchronization data are 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).
-
Each objective option MAY be followed by a locator option () associated with
the flooded objective. In its absence, an empty option MUST be included
to indicate a null locator.
A node that receives a Flood Synchronization message
MUST cache the received objectives for use by local
ASAs. Each cached objective MUST be tagged with the
locator option sent with it, or with a null tag if an empty locator
option was sent. If a subsequent Flood Synchronization message
carries an objective with the same name and the same tag, the
corresponding cached copy of the objective MUST be
overwritten. If a subsequent Flood Synchronization message carrying
an objective with same name arrives with a different tag, a new
cached entry MUST be created.
Note: the purpose of this mechanism is to allow the recipient of
flooded values to distinguish between different senders of the same
objective, and if necessary communicate with them using the locator,
protocol, and port included in the locator option. Many objectives
will not need this mechanism, so they will be flooded with a null
locator.
Cached entries MUST be ignored or deleted after
their lifetime expires.
Invalid Message
In fragmentary CDDL, an Invalid message follows the pattern:
This message MAY be sent by an implementation in
response to an incoming unicast message that it considers
invalid. The Session ID value MUST be copied from the
incoming message. The content SHOULD be diagnostic
information such as a partial copy of the invalid message up to the
maximum message size. An M_INVALID message MAY be
silently ignored by a recipient. However, it could be used in
support of extensibility, since it indicates that the remote node
does not support a new or obsolete message or option.
An M_INVALID message MUST NOT be sent in response to an M_INVALID message.
No Operation Message
In fragmentary CDDL, a No Operation message follows the pattern:
This message MAY be sent by an implementation that for practical reasons needs to
initialize a socket. It MUST be silently ignored by a recipient.
GRASP Options
This section defines the GRASP options for the negotiation
and synchronization protocol signaling. Additional
options may be defined in the future.
Format of GRASP Options
GRASP options SHOULD be CBOR arrays that MUST start with an unsigned
integer identifying the specific option type carried in this option.
These option types are formally defined in .
GRASP options may be defined to include encapsulated GRASP options.
Divert Option
The Divert option is used to redirect a GRASP request to another
node, which may be more appropriate for the intended negotiation or synchronization. It
may redirect to an entity that is known as a specific negotiation or synchronization
counterpart (on-link or off-link) or a default gateway. The Divert
option MUST only be encapsulated in Discovery Response messages.
If found elsewhere, it SHOULD be silently ignored.
A discovery initiator MAY ignore a Divert option if it only requires direct
Discovery Responses.
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.
Accept Option
The Accept option is used to indicate to the negotiation counterpart
that the proposed negotiation content is accepted.
The Accept option MUST only be encapsulated in Negotiation End
messages. If found elsewhere, it SHOULD be silently ignored.
In fragmentary CDDL, the Accept option follows the pattern:
Decline Option
The Decline option is used to indicate to the negotiation
counterpart the proposed negotiation content is declined and to 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 might be scenarios where an ASA wants
to decline the proposed value and restart the negotiation process.
In this case, it is an implementation choice whether to send a Decline
option or to continue with a Negotiation message, with an objective
option that contains a null value or one that contains a new
value that might achieve convergence.
Locator Options
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
option, and Locator URI 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 Locator URI option,
this information can be encoded in the URI itself.
Note: It is assumed that all locators used in locator options are in scope throughout
the GRASP domain. As stated in ,
GRASP is not intended to work across disjoint addressing
or naming realms.
Locator IPv6 Address Option
In fragmentary CDDL, the Locator 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. However, during initialization, a link-local address
MAY be used for specific objectives only (). In this case, the
corresponding Discovery Response message MUST be
sent via the interface to which the link-local address
applies.
Note 2: A link-local IPv6 address MUST NOT be
used when this option is included in a Divert option.
Note 3: The IPPROTO values are taken from the existing IANA
Protocol Numbers registry in order to specify TCP or UDP. If GRASP
requires future values that are not in that registry, a new
registry for values outside the range 0..255 will be needed.
Locator IPv4 Address Option
In fragmentary CDDL, the Locator 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.
Locator FQDN Option
In fragmentary CDDL, the Locator FQDN option follows the pattern:
The content of this option is the FQDN
of the target followed by the protocol number and port number to
be used.
Note 1: Any FQDN that 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.
Locator URI Option
In fragmentary CDDL, the Locator URI option follows the pattern:
The content of this option is the URI of the target
followed by the protocol number and port number to be used (or by null values if not required)
.
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. Therefore, its use is not further
described in this specification.
Objective Options
Format of Objective Options
An objective option is used to identify objectives for
the purposes of discovery, negotiation, or synchronization.
All objectives MUST be in the following format,
described in fragmentary CDDL:
All objectives are identified by a unique name that is a UTF-8
string , to be compared
byte by byte.
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 FQDN 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.
GRASP treats the objective name as an opaque string. For example, "EX1", "32473:EX1",
"example.com:EX1", "example.org:EX1", and "user@example.org:EX1" are five different objectives.
The 'objective-flags' field is described in .
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
. It is placed in the objective rather than in the GRASP
message format because, as far as the ASA is concerned, it is a property of the
objective itself.
The 'objective-value' field expresses the actual value of a negotiation
or synchronization objective. Its format is defined in the
specification of the objective and may be a simple value
or a data structure of any kind, as long as it can be represented in CBOR.
It is optional only in a Discovery or Discovery Response message.
Objective Flags
An objective may be relevant for discovery only, for discovery and negotiation, or
for discovery and synchronization. This is expressed in the objective by logical flag bits:
These bits are independent and may be combined appropriately, e.g., (F_DISC and F_SYNCH) or
(F_DISC and F_NEG) or (F_DISC and F_NEG and F_NEG_DRY).
Note that for a given negotiation session, an objective must be used either for negotiation or for
dry-run negotiation. Mixing the two modes in a single negotiation is not possible.
General Considerations for Objective Options
As mentioned above, objective options MUST be assigned a unique name.
As long as privately defined objective options obey the rules above, this document
does not restrict their choice of name, but the entity or person concerned SHOULD publish the names in use.
Names are expressed as UTF-8 strings for convenience in designing objective options for
localized use. For generic usage, names expressed in the ASCII subset of UTF-8 are RECOMMENDED.
Designers planning to use non-ASCII names are strongly advised to consult
or its successor
to understand the complexities involved. Since GRASP compares names byte by byte,
all issues of Unicode profiling and canonicalization MUST be specified in the design of the
objective option.
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 and/or 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 'value' field SHOULD be set to the 'null' value defined
by CBOR.
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.
The design of an objective interacts in various ways with the design of the ASAs
that will use it. ASA design considerations are discussed in
.
Organizing of Objective Options
Generic objective options MUST be specified in documents
available to the public and SHOULD be designed to use either
the negotiation or the synchronization mechanism described above.
As noted earlier, one negotiation objective is handled by each
GRASP negotiation thread. Therefore, a negotiation objective, which is
based on a specific function or action, SHOULD be organized as a single
GRASP option. It is NOT RECOMMENDED to organize multiple negotiation
objectives into a single option nor to split a single function
or action into multiple negotiation objectives.
It is important to understand that GRASP negotiation does not
support transactional integrity. If transactional integrity is needed for
a specific objective, this must be ensured by the ASA. For example, an ASA
might need to ensure that it only participates in one negotiation thread
at the same time. Such an ASA would need to stop listening for incoming
negotiation requests before generating an outgoing negotiation request.
A synchronization objective SHOULD be organized as a single GRASP option.
Some objectives will support more than one operational mode.
An example is a negotiation objective with both a dry-run mode
(where the negotiation is to determine whether the other end can, in fact,
make the requested change without problems) and a live mode, as explained
in . The semantics of such
modes will be defined in the specification of the objectives. These
objectives SHOULD include flags indicating the
applicable mode(s).
An issue requiring particular attention is that GRASP itself is
not a transactionally safe protocol. Any state associated with a dry-run operation,
such as temporarily reserving a resource for subsequent use in a live
run, is entirely a matter for the designer of the ASA concerned.
As indicated in , an objective's value may
include multiple parameters. Parameters
might be categorized into two classes: the obligatory ones presented as
fixed fields and the optional ones presented in
some other form of data structure embedded in CBOR. The format might be
inherited from an existing management or configuration protocol, with
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, YANG, etc. GRASP itself is agnostic on
these questions. The only restriction is that the format can be mapped
into CBOR.
It is NOT RECOMMENDED to mix parameters that have significantly
different response-time characteristics in a single objective. Separate
objectives are more suitable for such a scenario.
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.
To guarantee convergence, a limited number of rounds or a timeout is needed
for each negotiation objective.
Therefore, the definition of each negotiation objective SHOULD clearly specify
this, for example, a default loop count and timeout,
so that the negotiation can always be terminated properly. If not,
the GRASP defaults will apply.
There must be a well-defined procedure for concluding that a negotiation cannot
succeed, and if so, deciding what happens next (e.g., deadlock
resolution, tie-breaking, or reversion to best-effort
service). This MUST be specified for individual negotiation objectives.
Experimental and Example Objective Options
The names "EX0" through "EX9" have been reserved for experimental options.
Multiple names have been assigned because a single experiment
may use multiple options simultaneously. These experimental options
are highly likely to have different meanings when used for different
experiments. Therefore, they SHOULD NOT be used without an explicit
human decision and MUST NOT be used in unmanaged networks such as
home networks.
These names are also RECOMMENDED for use in documentation
examples.
Security Considerations
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.
As explained in , GRASP MUST run within a secure
environment such as the ACP
,
except for the constrained instances described in .
- Authentication
- A cryptographically authenticated identity for each device is
needed in an Autonomic Network. It is not safe to assume that a
large network is physically secured against interference or that all
personnel are trustworthy. Each autonomic 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 must be deployed in an existing secure environment,
the protocol itself specifies nothing concerning the trust anchor and
certification authority. For example, in the ACP
, all nodes can
trust each other and the ASAs installed in them.
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 the injecting of responses by third parties.
A full analysis of the secure bootstrap process is in
.
- Authorization and roles
- GRASP is agnostic about the roles and capabilities of individual
ASAs and about which objectives a particular ASA is authorized to support. An implementation
might support precautions such as allowing only one ASA in a given node to modify
a given objective, but this may not be appropriate in all cases. For example,
it might be operationally useful to allow an old and a new version of the same
ASA to run simultaneously during an overlap period. These questions are out
of scope for the present specification.
- Privacy and confidentiality
- GRASP is intended for network-management purposes involving
network elements, not end hosts. Therefore, no personal information
is expected to be involved in the signaling protocol, so there should be no direct
impact on personal privacy. Nevertheless, applications that do
convey personal information cannot be excluded. Also, traffic flow paths, VPNs,
etc., could be negotiated, which could be of interest for traffic
analysis. 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 an alternative security mechanism.
- Link-local multicast security
- GRASP has no reasonable alternative to using link-local
multicast for Discovery or Flood Synchronization messages, and these
messages are sent in the clear and with no authentication. They are only
sent on interfaces within the Autonomic Network (see and ). They are, however, 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 protection
- GRASP discovery partly relies on insecure link-local multicast. Since
routers participating in GRASP sometimes relay Discovery messages from one link
to another, this could be a vector for denial-of-service attacks. Some
mitigations are specified in . However, malicious
code installed inside the ACP could always launch
DoS attacks consisting of either spurious Discovery messages or spurious
Discovery Responses. It is important that firewalls prevent any GRASP messages
from entering the domain from an unknown source.
- Security during bootstrap and discovery
- A node cannot trust GRASP traffic from other nodes until the security
environment (such as the ACP) has identified the trust anchor and can authenticate traffic
by validating certificates for other nodes. Also, until it has successfully enrolled
, a node 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. Secure synchronization and negotiation
will be impossible until enrollment is complete. Further details
are given in .
- Security of discovered locators
- When 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.
CDDL Specification of GRASP
IANA Considerations
This document defines the GeneRic Autonomic Signaling Protocol (GRASP).
explains the following link-local multicast
addresses that IANA has assigned for use by GRASP.
Assigned in the "Link-Local Scope Multicast Addresses" subregistry
of the "IPv6 Multicast Address Space Registry":
- Address(es):
- ff02::13
- Description:
- ALL_GRASP_NEIGHBORS
- Reference:
- RFC 8990
Assigned in the "Local Network Control Block (224.0.0.0 - 224.0.0.255 (224.0.0/24))"
subregistry of the "IPv4 Multicast Address Space Registry":
- Address(es):
- 224.0.0.119
- Description:
- ALL_GRASP_NEIGHBORS
- Reference:
- RFC 8990
explains the following User Port (GRASP_LISTEN_PORT),
which IANA has assigned for use by GRASP for both UDP and TCP:
- Service Name:
- grasp
- Port Number:
- 7017
- Transport Protocol:
- udp, tcp
- Description
- GeneRic Autonomic Signaling Protocol
- Assignee:
- IESG <iesg@ietf.org>
- Contact:
- IETF Chair <chair@ietf.org>
- Reference:
- RFC 8990
The IANA has created the "GeneRic Autonomic Signaling Protocol (GRASP) Parameters" registry,
which includes two subregistries: "GRASP Messages and Options" and
"GRASP Objective Names".
The values in the "GRASP Messages and Options" subregistry 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:
Initial Values of the "GRASP Messages and Options" Subregistry
Value | Message/Option |
0 |
M_NOOP |
1 |
M_DISCOVERY |
2 |
M_RESPONSE |
3 |
M_REQ_NEG |
4 |
M_REQ_SYN |
5 |
M_NEGOTIATE |
6 |
M_END |
7 |
M_WAIT |
8 |
M_SYNCH |
9 |
M_FLOOD |
99 |
M_INVALID |
100 |
O_DIVERT |
101 |
O_ACCEPT |
102 |
O_DECLINE |
103 |
O_IPv6_LOCATOR |
104 |
O_IPv4_LOCATOR |
105 |
O_FQDN_LOCATOR |
106 |
O_URI_LOCATOR |
The values in the "GRASP Objective Names" subregistry are UTF-8
strings that MUST NOT include a colon (":"), according
to . Future values
MUST be assigned using the Specification Required policy
defined by .
To assist expert review of a new objective, the specification should
include a precise description of the format of the new objective, with
sufficient explanation of its semantics to allow independent
implementations. See for
more details. If the new objective is similar in name or purpose to a
previously registered objective, the specification should explain why a
new objective is justified.
The following initial values are assigned by this document:
Initial Values of the "GRASP Objective Names" Subregistry
Objective Name | Reference |
EX0 |
RFC 8990 |
EX1 |
RFC 8990 |
EX2 |
RFC 8990 |
EX3 |
RFC 8990 |
EX4 |
RFC 8990 |
EX5 |
RFC 8990 |
EX6 |
RFC 8990 |
EX7 |
RFC 8990 |
EX8 |
RFC 8990 |
EX9 |
RFC 8990 |
References
Normative References
An Autonomic Control Plane (ACP)
Informative References
GeneRic Autonomic Signaling Protocol Application Program Interface (GRASP API)
A Reference Model for Autonomic Networking
Bootstrapping Remote Secure Key Infrastructure (BRSKI)
Example Message Formats
For readers unfamiliar with CBOR, this appendix shows a number of example GRASP
messages conforming to the CDDL syntax given in .
Each message is shown three times in the following formats:
- CBOR diagnostic notation.
- Similar, but showing the names of the constants. (Details of the flag bit encoding are omitted.)
- Hexadecimal version of the CBOR wire format.
Long lines are split for display purposes only.
Discovery Example
The initiator (2001:db8:f000:baaa:28cc:dc4c:9703:6781) multicasts a Discovery message
looking for objective EX1:
A peer (2001:0db8:f000:baaa:f000:baaa:f000:baaa) responds with a locator:
Flood Example
The initiator multicasts a Flood Synchronization message. The single objective has a null locator. There is no response:
Synchronization Example
Following successful discovery of objective EX2, the initiator unicasts a Request Synchronization message:
The peer responds with a value:
Simple Negotiation Example
Following successful discovery of objective EX3, the initiator unicasts a Request Negotiation message:
The peer responds with immediate acceptance. Note that no objective is needed
because the initiator's request was accepted without change:
Complete Negotiation Example
Again the initiator unicasts a Request Negotiation message:
The responder starts to negotiate (making an offer):
The initiator continues to negotiate (reducing its request, and note that the loop count is decremented):
The responder asks for more time:
The responder continues to negotiate (increasing its offer):
The initiator continues to negotiate (reducing its request):
The responder refuses to negotiate further:
This negotiation has failed. If either side had sent
[M_END, 13767778, [O_ACCEPT]] it would have succeeded, converging
on the objective value in the preceding M_NEGOTIATE. Note that apart
from the initial M_REQ_NEG, the process is symmetrical.
Requirement Analysis of Discovery, Synchronization, and Negotiation
This section discusses the requirements for discovery, negotiation,
and synchronization capabilities. The primary user of the protocol is an Autonomic Service
Agent (ASA), so the requirements are mainly expressed as the features needed by an ASA.
A single physical device might contain several ASAs, and a single ASA might manage
several technical objectives. If a technical objective is managed by several ASAs,
any necessary coordination is outside the scope of GRASP.
Furthermore, requirements for ASAs themselves, such as the processing of Intent
, are out of scope for the present document.
Requirements for Discovery
-
ASAs may be designed to manage any type of configurable device or software,
as required in . A basic requirement
is therefore that the protocol can represent and discover any
kind of technical objective (as defined in )
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 the 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 within a device, the device or ASA may again lack
information about relevant peers. For example, 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:
- When an ASA first starts up, it may have 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.
- When an ASA starts up, it must require no configured location information about any
peers in order to discover them.
- If an ASA supports multiple technical objectives, relevant peers may be different
for different discovery objectives, so discovery needs to be performed separately 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.
- Following discovery, an ASA will normally perform negotiation
or synchronization for the corresponding objectives. The design
should allow for this by conveniently linking discovery to negotiation
and synchronization. It may provide an optional mechanism to
combine discovery and negotiation/synchronization in a single protocol exchange.
- 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.
-
The discovery process should be flexible enough to allow for
special cases, such as the following:
- During initialization, a device must be able to establish mutual trust
with autonomic nodes elsewhere in the network and participate in 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.
This does not preclude the device having multiple credentials.
-
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 initialization,
as well as discovery during ongoing operation.
- The discovery process must not generate excessive traffic and
must take account of sleeping nodes.
- There must be a mechanism for handling stale discovery results.
Requirements for Synchronization and Negotiation Capability
Autonomic Networks need to be able to manage many
different types of parameters and consider many dimensions,
such as latency, load, unused or limited resources,
conflicting resource requests,
security settings, power saving, load balancing, etc.
Status information and resource 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.
- A basic requirement for the protocol is therefore the
ability to represent, discover, synchronize, and negotiate almost any
kind of network parameter among selected subsets of participating nodes.
- Negotiation is an iterative request/response process that must be guaranteed to terminate
(with success or failure). While tie-breaking rules 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.
- Synchronization must be possible for groups of nodes ranging from small to very large.
- To avoid "reinventing the wheel", the protocol should be able to encapsulate the
data formats used by existing configuration protocols (such as Network Configuration Protocol (NETCONF) and YANG)
in cases where that is convenient.
- Human intervention in complex situations is costly and error prone.
Therefore, synchronization or negotiation of parameters without human
intervention is desirable whenever the coordination of multiple devices can improve
overall network performance. It follows that the protocol's resource requirements
must be small enough to fit in any device that would otherwise need human intervention.
The issue of running in constrained nodes
is discussed in .
- 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, should
be capable of running in any device that would otherwise be managed by
an NMS, and that it can coexist with an NMS and with protocols
such as SNMP and NETCONF.
- Specific autonomic features are expected to be implemented by individual ASAs,
but the protocol must be general enough to allow them. Some examples follow:
- Dependencies and conflicts: In order to
decide upon a configuration for 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 or uncontrolled growth in a tree of dependencies.
It is the ASA designer's responsibility
to avoid or detect looping dependencies or excessive growth of dependency trees.
The protocol's role is limited to bilateral signaling between ASAs
and the avoidance of loops during bilateral signaling.
- Recovery from faults and identification of faulty devices should be
as automatic as possible. The protocol's role is limited to discovery, synchronization, and
negotiation. These processes can occur at any time, and an ASA may
need to repeat any of these steps when the ASA detects an event
such as a negotiation counterpart failing.
- Since a major goal is to minimize human intervention, it is necessary that the
network can in effect "think ahead" before changing its parameters. One aspect
of this is an ASA that relies on a knowledge base to predict network behavior.
This is out of scope for the signaling protocol. However, another aspect is
forecasting the effect of a change by a "dry run" negotiation before actually
installing the change. Signaling a dry run is therefore a desirable feature
of the protocol.
Note that management logging, monitoring, alerts, and tools for intervention are required.
However, these can only be features of individual ASAs, not of the protocol itself.
Another document discusses how
such agents may be linked into conventional Operations, Administration, and Maintenance (OAM) systems via an Autonomic Control Plane
.
- 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 a flexible and easily extensible format for
describing objectives. At a later stage, it may be desirable to adopt an explicit
information model. One consideration is whether to adopt an existing
information model or to design a new one.
Specific Technical Requirements
- It should be convenient for ASA designers to define new technical objectives
and for programmers to express them, without excessive impact on
runtime efficiency and footprint. In particular, it should be convenient for ASAs
to be implemented independently of each other as user-space programs rather than as kernel
code, where such a programming model is possible. The classes of device in which the protocol
might run is discussed in .
- The protocol should be easily extensible in case the initially defined discovery,
synchronization, and negotiation mechanisms prove to be insufficient.
- 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. By default, IPv6 should
be preferred.
- The protocol must be able to access off-link counterparts via routable addresses,
i.e., must not be restricted to link-local operation.
- 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 protocol must be capable of distinguishing multiple simultaneous
operations with one or more peers, especially when wait states occur.
- Intent: Although the distribution of Intent is out of scope
for this document, the protocol must not by design exclude its
use for Intent distribution.
- 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 misbehaving device). These features
might not use the signaling protocol itself, but its design should not exclude such use.
- Because this protocol may directly cause changes to device configurations
and have significant impacts on a running network, all protocol exchanges need 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. There must also
be an encryption mechanism 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.
Capability Analysis of Current Protocols
This appendix discusses various existing protocols with properties
related to the requirements described in . 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 it requires configuration of its own servers. DNS-Based Service Discovery (DNS-SD)
combined with Multicast DNS (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.
Simple Network Management Protocol (SNMP) uses
a command/response model not well suited for peer negotiation.
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
specialized protocol aimed at end-to-end flows.
A more generic design is General Internet
Signalling Transport (GIST) ; however, it
tries to solve many problems, making it complex, 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 usable for peer discovery.
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 centralized configuration of a
complex network, it is not well adapted to efficient interactive
negotiation between peer devices, especially simple ones that might
not include YANG processing already.
The Distributed Node Consensus Protocol (DNCP)
is defined as a generic form
of a 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 .
According to :
DNCP is designed to provide a way for each participating node to
publish a set of TLV (Type-Length-Value) tuples (at most 64 KB) 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 and 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.
Acknowledgments
A major contribution to the original draft version of this document was
made by ,
and significant contributions were made by .
Significant early review inputs were received from
, ,
, and .
provided important assistance in
debugging a prototype implementation.
Valuable comments were received from
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
and participants in the Network Management Research Group,
the ANIMA Working Group,
and the IESG.