Network Working Group C. Bormann
Internet-Draft Universität Bremen TZI
Intended status: Standards Track B. Carpenter, Ed.
Expires: January 3, 2018 Univ. of Auckland
B. Liu, Ed.
Huawei Technologies Co., Ltd
July 2, 2017

A Generic Autonomic Signaling Protocol (GRASP)


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.

Status of This Memo

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Table of Contents

1. Introduction

The success of the Internet has made IP-based networks bigger and more complicated. Large-scale ISP and enterprise networks have become more and more problematic for human based management. Also, operational costs are growing quickly. Consequently, there are increased requirements for autonomic behavior in the networks. General aspects of autonomic networks are discussed in [RFC7575] and [RFC7576].

One approach is to largely decentralize the logic of network management by migrating it into network elements. A reference model for autonomic networking on this basis is given in [I-D.ietf-anima-reference-model]. The reader should consult this document to understand how various autonomic components fit together. In order to fulfill autonomy, devices that embody Autonomic Service Agents (ASAs, [RFC7575]) 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 Section 2.1).

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 Appendix E. Section 2.3 describes a behavior model for a protocol intended to support discovery, synchronization and negotiation. The design of GeneRic Autonomic Signaling Protocol (GRASP) in Section 2 of this document is based on this behavior model. The relevant capabilities of various existing protocols are reviewed in Appendix F.

The proposed discovery mechanism is oriented towards synchronization and negotiation objectives. It is based on a neighbor discovery process on the local link, but 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 pre-configuration, it has no knowledge of the topology. The protocol itself is capable of being used in a small and/or flat network structure such as a small office or home network as well as 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.

2. GRASP Protocol Overview

2.1. Terminology

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

This document uses terminology defined in [RFC7575].

The following additional terms are used throughout this document:

2.2. 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 [I-D.ietf-anima-reference-model], this SHOULD be the Autonomic Control Plane (ACP) [I-D.ietf-anima-autonomic-control-plane]. 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 Section 2.5.1 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 multi-purpose 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 multi-threading.

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 [I-D.ietf-anima-reference-model].

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 [I-D.ietf-anima-reference-model]. 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 non-volatile data storage. All run time 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 (Section 2.5.1) afterwards.

An autonomic node will normally run a single instance of GRASP, used by multiple ASAs. Possible exceptions are mentioned below.

2.3. 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.

2.4. Quick Operating Overview

An instance of GRASP is expected to run as a separate core module, providing an API (such as [I-D.liu-anima-grasp-api]) 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:

Some example messages and simple message flows are provided in Appendix D.

2.5. GRASP Protocol Basic Properties and Mechanisms

2.5.1. 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 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 is created by the security substrate and 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. 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 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 substrate for GRASP in the ANI is the ACP. Unless otherwise noted, we assume this security substrate in the remainder of this document. The ACP does mandate the use of encryption; therefore GRASP in the ANI can rely on GRASP message 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/encryption) of messages. Removal of nodes relies on standard PKI certificate revocation or expiry of sufficiently short lived certificates. Refer to [I-D.ietf-anima-autonomic-control-plane] for more details.

As mentioned in Section 2.3, 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 substrate. In the most simple case, each point-to-point interdomain GRASP peering could be a separate domain and the security 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 substrate exists for highly constrained subsets of GRASP meant to support the establishment of a security substrate, described in the following section.

2.5.2. Discovery Unsolicited Link-Local (DULL) GRASP

Some services may need to use insecure GRASP discovery, response and flood messages without being able to use pre-existing 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 [I-D.ietf-anima-autonomic-control-plane], discovery of bootstrap proxies [I-D.ietf-anima-bootstrapping-keyinfra] 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:

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 Response. Further details are out of scope for this document

2.5.3. 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, which itself runs within the security environment discussed in the previous section.

GRASP discovery and flooding messages are designed for use over link-local multicast UDP. They MUST NOT be fragmented, and therefore MUST NOT exceed the link MTU size. An implementation should report any attempt to send a longer message as a run-time error.

All other GRASP messages are unicast and could in principle run over any transport protocol. An implementation MUST support use of TCP. It MAY support use of another transport protocol but the details are out of scope for this specification. However, GRASP itself does not provide for error detection or retransmission of its unicast messages, so an unreliable transport protocol MUST NOT be used.

For considerations when running without an ACP, see Section 2.5.1.

For link-local multicast, the GRASP protocol listens to the well-known GRASP Listen Port (Section 2.6). For unicast transport sessions used for discovery responses, synchronization and negotiation, the ASA concerned normally listens on its own dynamically assigned ports, which are communicated to its peers during discovery. However, a minimal implementation MAY use the GRASP Listen Port for this purpose.

2.5.4. 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 (Section 2.8.4) message, the recipient node should return a response message in which it either indicates itself as a discovery responder or diverts the initiator towards another more suitable ASA. However, this response may be delayed if the recipient needs to relay the discovery onwards, as described below.

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 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 (of M_DISCOVERY) on the local link. On-link neighbors supporting the discovery objective will respond directly (with M_RESPONSE). A neighbor with multiple interfaces may respond with a cached discovery response. If it has no cached response, it will relay the discovery on its other GRASP interfaces. If a node receiving the relayed discovery supports the discovery objective, it will respond to the relayed discovery. If it has a cached response, it will respond with that. If not, it will repeat the discovery process, which thereby becomes iterative. The loop count and timeout will ensure that the process ends. Further details are given below.

A Discovery message MAY be sent unicast (via UDP or TCP) 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. A Discovery message is sent by a discovery initiator via UDP to the ALL_GRASP_NEIGHBORS link-local multicast address (Section 2.6). Every network device that supports GRASP always listens to a well-known UDP port to capture the discovery messages. Because this port is unique in a device, this is a function of the GRASP 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 (Section 2.8.5) 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, on a link that supports link-local multicast, it SHOULD NOT respond with a cached response on an interface if it learnt 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 below) 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 (Section 2.7). 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 [RFC8085] 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 [RFC3493] 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'.

Constrained Instances (Section 2.5.2) 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 re-issuing a new Discovery message as a link-local multicast on its other GRASP interfaces.

The relayed discovery message MUST have the same Session ID as the incoming discovery message and MUST be tagged with the IP address of its original initiator (see Section 2.8.4). Note that this initiator address is only used to allow for disambiguation of the Session ID and is never used to address Response packets, which are sent to the relaying instance, not the original initiator.

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 which 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. 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 (Section or synchronization (Section 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.

2.5.5. 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, Section 2.6), initialised when the request is sent (see Section 2.8.6). If no reply message of any kind is received within the timeout, the negotiation request MAY be repeated, with a newly generated Session ID (Section 2.7). 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 M_END). 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 bi-directional negotiation (using M_NEGOTIATE) to reach a compromise between the two ASAs.

The negotiation procedure is ended when one of the negotiation peers sends a Negotiation Ending (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 multi-threaded mode or its logical equivalent. Certain negotiation objectives may have restrictions on multi-threading, for example to avoid over-allocating resources.

Some configuration actions, for example wavelength switching in optical networks, might take considerable time to execute. The ASA concerned needs to allow for this by design, but GRASP does allow for a peer to insert latency in a negotiation process if necessary (Section 2.8.9, 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.

2.5.6. 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 synchronization request (using M_REQ_SYN) to the counterpart, including a specific synchronization objective. The counterpart responds with a Synchronization message (M_SYNCH, Section 2.8.10) 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, Section 2.6), the synchronization request MAY be repeated, with a newly generated Session ID (Section 2.7). 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 (Section 2.6).

Receiving flood multicasts is a function of the GRASP core, as in the case of discovery multicasts (Section

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 [RFC6206].

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 re-issuing 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 which carries a given cached Session ID and initiator address more than once. These precautions avoid synchronization loops and mitigate potential overload.

Note that this mechanism is unreliable in the case of sleeping nodes, 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 [RFC8085] 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 Section 2.5.1. 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 (Section 4), 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 Section 2.8.10 with synchronization data for rapid processing, if the discovery target supports the corresponding synchronization objective. The design implications are similar to those discussed in Section

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.

2.6. GRASP Constants

2.7. 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 pseudo-random number generator (PRNG) using a locally generated seed which is unlikely to be used by any other device in the same network. The PRNG SHOULD be cryptographically strong [RFC4086]. 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 Section 2.8.6 for details of how to avoid this.

2.8. GRASP Messages

2.8.1. Message Overview

This section defines the GRASP message format and message types. Message types not listed here are reserved for future use.

The messages currently defined are:

2.8.2. GRASP Message Format

GRASP messages share an identical header format and a variable format area for options. GRASP message headers and options are transmitted in Concise Binary Object Representation (CBOR) [RFC7049]. In this specification, they are described using CBOR data definition language (CDDL) [I-D.greevenbosch-appsawg-cbor-cddl]. Fragmentary CDDL is used to describe each item in this section. A complete and normative CDDL specification of GRASP is given in Section 5, including constants such as message types.

Every GRASP message, except the No Operation message, carries a Session ID (Section 2.7). Options are then presented serially in the options field.

In fragmentary CDDL, every GRASP message follows the pattern:

  grasp-message = (message .within message-structure) / noop-message

  message-structure = [MESSAGE_TYPE, session-id, ?initiator,

  MESSAGE_TYPE = 1..255
  session-id = 0..4294967295 ;up to 32 bits
  grasp-option = any

The MESSAGE_TYPE indicates the type of the message and thus defines the expected options. Any options received that are not consistent with the MESSAGE_TYPE SHOULD be silently discarded.

The No Operation (noop) message is described in Section 2.8.13.

The various MESSAGE_TYPE values are defined in Section 5.

All other message elements are described below and formally defined in Section 5.

If an unrecognized MESSAGE_TYPE is received in a unicast message, an Invalid message (Section 2.8.12) 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.

2.8.3. 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 link adaptation layer in use.

2.8.4. Discovery Message

In fragmentary CDDL, a Discovery message follows the pattern:

  discovery-message = [M_DISCOVERY, session-id, initiator, objective]

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 for this purpose that is highly likely to be unique, for example using [RFC7217]. Determination of a node's globally unique IP address is implementation-dependent.

A Discovery message MUST include exactly one of the following:

As mentioned in Section, a Discovery message MAY be sent unicast to a peer node, which SHOULD then proceed exactly as if the message had been multicast.

2.8.5. Discovery Response Message

In fragmentary CDDL, a Discovery Response message follows the pattern:

  response-message = [M_RESPONSE, session-id, initiator, ttl,
                     (+locator-option // divert-option), ?objective)]
  ttl = 0..4294967295 ; in milliseconds

A node which receives a Discovery message SHOULD send a Discovery Response message if and only if it can respond to the discovery. Section 2.8.4). In the case of a relayed Discovery message, the Discovery Response is thus sent to the relay, not the original initiator.

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 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 (Section 2.9.5) to indicate its own location. A sequence of multiple kinds of locator options (e.g. IP address option and FQDN option) is also valid.

If the responding node itself does not support the discovery objective, but it knows the locator of the discovery objective, then it SHOULD respond to the discovery message with a divert option (Section 2.9.2) embedding a locator option or a combination of multiple kinds of locator options which indicate the locator(s) of the discovery objective.

More details on the processing of Discovery Responses are given in Section 2.5.4.

2.8.6. Request Messages

In fragmentary CDDL, Request Negotiation and Request Synchronization messages follow the patterns:

request-negotiation-message = [M_REQ_NEG, session-id, objective]

request-synchronization-message = [M_REQ_SYN, session-id, objective]


A negotiation or synchronization requesting node sends the appropriate Request message to the unicast address 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 (Section 2.8.9), 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 (Section 2.7), when a node receives a Request message, it MUST verify that the received Session ID is not already locally active. In case of a clash, it MUST discard the Request message, in which case the initiator will detect a timeout.

2.8.7. Negotiation Message

In fragmentary CDDL, a Negotiation message follows the pattern:

  negotiate-message = [M_NEGOTIATE, session-id, objective]

A negotiation counterpart sends a Negotiation message in response to a Request Negotiation message, a Negotiation message, or a Discovery message in Rapid Mode. A negotiation process MAY include multiple steps.

The Negotiation message MUST include the relevant Negotiation Objective option, with its value updated according to progress in the negotiation. The sender MUST decrement the loop count by 1. If the loop count becomes zero the message MUST NOT be sent. In this case the negotiation session has failed and will time out.

2.8.8. Negotiation End Message

In fragmentary CDDL, a Negotiation End message follows the pattern:

  end-message = [M_END, session-id, accept-option / decline-option]

A negotiation counterpart sends an Negotiation End message to close the negotiation. It MUST contain either an accept or a decline option, defined in Section 2.9.3 and Section 2.9.4. It could be sent either by the requesting node or the responding node.

2.8.9. Confirm Waiting Message

In fragmentary CDDL, a Confirm Waiting message follows the pattern:

  wait-message = [M_WAIT, session-id, waiting-time]
  waiting-time = 0..4294967295 ; in milliseconds

A responding node sends a Confirm Waiting message to ask the requesting node to wait for a further negotiation response. It might be that the local process needs more time or that the negotiation depends on another triggered negotiation. This message MUST NOT include any other options. When received, the waiting time value overwrites and restarts the current negotiation timer (Section 2.8.6).

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.

2.8.10. Synchronization Message

In fragmentary CDDL, a Synchronization message follows the pattern:

  synch-message = [M_SYNCH, session-id, objective]

A node which receives a Request Synchronization, or a Discovery message in Rapid Mode, sends back a unicast Synchronization message with the synchronization data, in the form of a GRASP Option for the specific synchronization objective present in the Request Synchronization.

2.8.11. Flood Synchronization Message

In fragmentary CDDL, a Flood Synchronization message follows the pattern:

  flood-message = [M_FLOOD, session-id, initiator, ttl,
                  +[objective, (locator-option / [])]]
  ttl = 0..4294967295 ; in milliseconds

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 Section 2.5.6.

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 carrying an objective with 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.

2.8.12. Invalid Message

In fragmentary CDDL, an Invalid message follows the pattern:

  invalid-message = [M_INVALID, session-id, ?any]

This message MAY be sent by an implementation in response to an incoming unicast message that it considers invalid. The session-id 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.

2.8.13. No Operation Message

In fragmentary CDDL, a No Operation message follows the pattern:

  noop-message = [M_NOOP]

This message MAY be sent by an implementation that for practical reasons needs to initialize a socket. It MUST be silently ignored by a recipient.

2.9. GRASP Options

This section defines the GRASP options for the negotiation and synchronization protocol signaling. Additional options may be defined in the future.

2.9.1. Format of GRASP Options

GRASP options are CBOR objects that MUST start with an unsigned integer identifying the specific option type carried in this option. These option types are formally defined in Section 5. Apart from that the only format requirement is that each option MUST be a well-formed CBOR object. In general a CBOR array format is RECOMMENDED to limit overhead.

GRASP options may be defined to include encapsulated GRASP options.

2.9.2. Divert Option

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

A discovery initiator MAY ignore a Divert option if it only requires direct discovery responses.

In fragmentary CDDL, the Divert option follows the pattern:

  divert-option = [O_DIVERT, +locator-option]

The embedded Locator Option(s) (Section 2.9.5) point to diverted destination target(s) in response to a Discovery message.

2.9.3. Accept Option

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

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

In fragmentary CDDL, the Accept option follows the pattern:

  accept-option = [O_ACCEPT]

2.9.4. Decline Option

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

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

In fragmentary CDDL, the Decline option follows the pattern:

  decline-option = [O_DECLINE, ?reason]
  reason = text  ;optional UTF-8 error message

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 Negotiate message, with an objective option that contains a null value, or one that contains a new value that might achieve convergence.

2.9.5. 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 (Fully Qualified Domain Name) Option and URI (Uniform Resource Identifier) Option.

Since ASAs will normally run as independent user programs, locator options need to indicate the network layer locator plus the transport protocol and port number for reaching the target. For this reason, the Locator Options for IP addresses and FQDNs include this information explicitly. In the case of the URI Option, this information can be encoded in the URI itself.

Note: It is assumed that all locators used in locator options are in scope throughout the GRASP domain. As stated in Section 2.2, GRASP is not intended to work across disjoint addressing or naming realms. Locator IPv6 address option

In fragmentary CDDL, the IPv6 address option follows the pattern:

  ipv6-locator-option = [O_IPv6_LOCATOR, ipv6-address,
                         transport-proto, port-number]
  ipv6-address = bytes .size 16

  transport-proto = IPPROTO_TCP / IPPROTO_UDP
  port-number = 0..65535

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 (Section 2.5.2). 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 IPv4 address option follows the pattern:

  ipv4-locator-option = [O_IPv4_LOCATOR, ipv4-address,
                         transport-proto, port-number]
  ipv4-address = bytes .size 4

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 FQDN option follows the pattern:

  fqdn-locator-option = [O_FQDN_LOCATOR, text,
                         transport-proto, port-number]

The content of this option is the Fully Qualified Domain Name of the target followed by the protocol number and port number to be used.

Note 1: Any FQDN which might not be valid throughout the network in question, such as a Multicast DNS name [RFC6762], MUST NOT be used when this option is used within the Divert option.

Note 2: Normal GRASP operations are not expected to use this option. It is intended for special purposes such as discovering external services. Locator URI option

In fragmentary CDDL, the URI option follows the pattern:

  uri-locator = [O_URI_LOCATOR, text,
                 transport-proto / null, port-number / null]

The content of this option is the Uniform Resource Identifier of the target followed by the protocol number and port number to be used (or by null values if not required) [RFC3986].

Note 1: Any URI which might not be valid throughout the network in question, such as one based on a Multicast DNS name [RFC6762], MUST NOT be used when this option is used within the Divert option.

Note 2: Normal GRASP operations are not expected to use this option. It is intended for special purposes such as discovering external services. Therefore its use is not further described in this specification.

2.10. Objective Options

2.10.1. Format of Objective Options

An objective option is used to identify objectives for the purposes of discovery, negotiation or synchronization. All objectives MUST be in the following format, described in fragmentary CDDL:

  objective = [objective-name, objective-flags, loop-count, ?objective-value]
  objective-name = text
  objective-value = any 
  loop-count = 0..255

All objectives are identified by a unique name which is a UTF-8 string [RFC3629], to be compared byte by byte.

The names of generic objectives MUST NOT include a colon (":") and MUST be registered with IANA (Section 6).

The names of privately defined objectives MUST include at least one colon (":"). The string preceding the last colon in the name MUST be globally unique and in some way identify the entity or person defining the objective. The following three methods MAY be used to create such a globally unique string:

  1. The unique string is a decimal number representing a registered 32 bit Private Enterprise Number (PEN) [RFC5612] that uniquely identifies the enterprise defining the objective.
  2. The unique string is a fully qualified domain name that uniquely identifies the entity or person defining the objective.
  3. The unique string is an email address that uniquely identifies the entity or person defining the objective.

The GRASP protocol treats the objective name as an opaque string. For example, "EX1", "32473:EX1", "", " and "" would be five different objectives.

The 'objective-flags' field is described below.

The 'loop-count' field is used for terminating negotiation as described in Section 2.8.7. It is also used for terminating discovery as described in Section 2.5.4, and for terminating flooding as described in Section 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 is to express the actual value of a negotiation or synchronization objective. Its format is defined in the specification of the objective and may be a simple value or a data structure of any kind, as long as it can be represented in CBOR. It is optional because it is optional in a Discovery or Discovery Response message.

2.10.2. Objective flags

An objective may be relevant for discovery only, for discovery and negotiation, or for discovery and synchronization. This is expressed in the objective by logical flag bits:

  objective-flags = uint .bits objective-flag
  objective-flag = &(
  F_DISC: 0    ; valid for discovery
  F_NEG: 1     ; valid for negotiation
  F_SYNCH: 2   ; valid for synchronization
  F_NEG_DRY: 3 ; negotiation is dry-run

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 either used for negotiation, or for dry-run negotiation. Mixing the two modes in a single negotiation is not possible.

2.10.3. General Considerations for Objective Options

As mentioned above, Objective Options MUST be assigned a unique name. As long as privately defined Objective Options obey the rules above, this document does not restrict their choice of name, but the entity or person concerned SHOULD publish the names in use.

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 [RFC7564] or its successor to understand the complexities involved. Since the GRASP protocol 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/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 [I-D.carpenter-anima-asa-guidelines].

2.10.4. Organizing of Objective Options

Generic objective options MUST be specified in documents available to the public and SHOULD be designed to use either the negotiation or the synchronization mechanism described above.

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

It is important to understand that GRASP negotiation does not support transactional integrity. If transactional integrity is needed for a specific objective, this must be ensured by the ASA. For example, an ASA might need to ensure that it only participates in one negotiation thread at the same time. Such an ASA would need to stop listening for incoming negotiation requests before generating an outgoing negotiation request.

A synchronization objective SHOULD be organized as a single GRASP option.

Some objectives will support more than one operational mode. An example is a negotiation objective with both a "dry run" mode (where the negotiation is to find out whether the other end can in fact make the requested change without problems) and a "live" mode, as explained in Section 2.5.5. 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 Section 2.1, 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. The GRASP protocol 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 Section 2.3, it is acceptable for an ASA to use an alternative method of discovery.

Normally, a GRASP objective will refer to specific technical parameters as explained in Section 2.1. However, it is acceptable to define an abstract objective for the purpose of managing or coordinating ASAs. It is also acceptable to define a special-purpose objective for purposes such as trust bootstrapping or formation of the ACP.

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 revert to best-effort service). This MUST be specified for individual negotiation objectives.

2.10.5. Experimental and Example Objective Options

The names "EX0" through "EX9" have been reserved for experimental options. Multiple names have been assigned because a single experiment may use multiple options simultaneously. These experimental options are highly likely to have different meanings when used for different experiments. Therefore, they SHOULD NOT be used without an explicit human decision and MUST NOT be used in unmanaged networks such as home networks.

These names are also RECOMMENDED for use in documentation examples.

3. Implementation Status [RFC Editor: please remove]

Two prototype implementations of GRASP have been made.

3.1. BUPT C++ Implementation

3.2. Python Implementation

4. 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 Section 2.5.1, GRASP MUST run within a secure environment such as the Autonomic Control Plane [I-D.ietf-anima-autonomic-control-plane], except for the constrained instances described in Section 2.5.2.

- 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 Autonomic Control Plane [I-D.ietf-anima-autonomic-control-plane], 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 (Section 2.5.1), the Session ID (Section 2.7) will act as a nonce to provide limited protection against third parties injecting responses. A full analysis of the secure bootstrap process is in [I-D.ietf-anima-bootstrapping-keyinfra].

- Authorization and Roles

The GRASP protocol 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 Section 2.5.1 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 clear and with no authentication. They are only sent on interfaces within the autonomic network (see Section 2.1 and Section 2.5.1). 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 (Section 2.5.1), and an untrusted forger will not be able to receive responses. In the case of Flood Synchronization, an on-link eavesdropper will be able to receive the flooded objectives but there is no response message to consider. Some precautions for Flood Synchronization messages are suggested in Section

- 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 Section 2.5.4. However, malicious code installed inside the Autonomic Control Plane could always launch DoS attacks consisting of spurious discovery messages, or of 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 succesfully enrolled [I-D.ietf-anima-bootstrapping-keyinfra] 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 Section 2.5.2.

- Security of discovered locators

When GRASP discovery returns an IP address, it MUST be that of a node within the secure environment (Section 2.5.1). If it returns an FQDN or a URI, the ASA that receives it MUST NOT assume that the target of the locator is within the secure environment.

5. CDDL Specification of GRASP

grasp-message = (message .within message-structure) / noop-message

message-structure = [MESSAGE_TYPE, session-id, ?initiator,

session-id = 0..4294967295 ;up to 32 bits
grasp-option = any

message /= discovery-message
discovery-message = [M_DISCOVERY, session-id, initiator, objective]

message /= response-message ;response to Discovery
response-message = [M_RESPONSE, session-id, initiator, ttl,
                   (+locator-option // divert-option), ?objective]

message /= synch-message ;response to Synchronization request
synch-message = [M_SYNCH, session-id, objective] 

message /= flood-message
flood-message = [M_FLOOD, session-id, initiator, ttl,
                +[objective, (locator-option / [])]]

message /= request-negotiation-message
request-negotiation-message = [M_REQ_NEG, session-id, objective]

message /= request-synchronization-message
request-synchronization-message = [M_REQ_SYN, session-id, objective]

message /= negotiation-message
negotiation-message = [M_NEGOTIATE, session-id, objective]

message /= end-message
end-message = [M_END, session-id, accept-option / decline-option ]

message /= wait-message
wait-message = [M_WAIT, session-id, waiting-time]

message /= invalid-message
invalid-message = [M_INVALID, session-id, ?any]

noop-message = [M_NOOP]

divert-option = [O_DIVERT, +locator-option]

accept-option = [O_ACCEPT]

decline-option = [O_DECLINE, ?reason]
reason = text  ;optional UTF-8 error message

waiting-time = 0..4294967295 ; in milliseconds
ttl = 0..4294967295 ; in milliseconds

locator-option /= [O_IPv4_LOCATOR, ipv4-address,
                   transport-proto, port-number]
ipv4-address = bytes .size 4

locator-option /= [O_IPv6_LOCATOR, ipv6-address,
                   transport-proto, port-number]
ipv6-address = bytes .size 16

locator-option /= [O_FQDN_LOCATOR, text, transport-proto, port-number]

locator-option /= [O_URI_LOCATOR, text,
                   transport-proto / null, port-number / null]

transport-proto = IPPROTO_TCP / IPPROTO_UDP
port-number = 0..65535

initiator = ipv4-address / ipv6-address

objective-flags = uint .bits objective-flag

objective-flag = &(
  F_DISC: 0    ; valid for discovery
  F_NEG: 1     ; valid for negotiation
  F_SYNCH: 2   ; valid for synchronization
  F_NEG_DRY: 3 ; negotiation is dry-run

objective = [objective-name, objective-flags, loop-count, ?objective-value]

objective-name = text ;see section "Format of Objective Options"

objective-value = any 

loop-count = 0..255

; Constants for message types and option types

M_NOOP = 0
M_END = 6
M_WAIT = 7

O_DIVERT = 100
O_ACCEPT = 101
O_IPv6_LOCATOR = 103
O_IPv4_LOCATOR = 104

6. IANA Considerations

This document defines the GeneRic Autonomic Signaling Protocol (GRASP).

Section 2.6 explains the following link-local multicast addresses, which IANA is requested to assign for use by GRASP:

ALL_GRASP_NEIGHBORS multicast address
(IPv6): (TBD1). Assigned in the IPv6 Link-Local Scope Multicast Addresses registry.
ALL_GRASP_NEIGHBORS multicast address
(IPv4): (TBD2). Assigned in the IPv4 Multicast Local Network Control Block.

Section 2.6 explains the following User Port, which IANA is requested to assign for use by GRASP for both UDP and TCP:

Service Name: Generic Autonomic Signaling Protocol (GRASP)
Transport Protocols: UDP, TCP
Description: See Section 2.6
Reference: RFC XXXX (this document)

The IANA is requested to create a GRASP Parameter Registry including two registry tables. These are the GRASP Messages and Options Table and the GRASP Objective Names Table.

GRASP Messages and Options Table. The values in this table are names paired with decimal integers. Future values MUST be assigned using the Standards Action policy defined by [RFC8126]. The following initial values are assigned by this document:

M_NOOP = 0
M_END = 6
M_WAIT = 7

O_DIVERT = 100
O_ACCEPT = 101
O_IPv6_LOCATOR = 103
O_IPv4_LOCATOR = 104

GRASP Objective Names Table. The values in this table are UTF-8 strings which MUST NOT include a colon (":"), according to Section 2.10.1. Future values MUST be assigned using the Specification Required policy defined by [RFC8126].

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 Section 2.10.3 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:


7. Acknowledgements

A major contribution to the original version of this document was made by Sheng Jiang and significant contributions were made by Toerless Eckert. Significant early review inputs were received from Joel Halpern, Barry Leiba, Charles E. Perkins, and Michael Richardson. William Atwood provided important assistance in debugging a prototype implementation.

Valuable comments were received from Michael Behringer, Jeferson Campos Nobre, Laurent Ciavaglia, Zongpeng Du, Yu Fu, Joel Jaeggli, Zhenbin Li, Dimitri Papadimitriou, Pierre Peloso, Reshad Rahman, Markus Stenberg, Martin Stiemerling, Rene Struik, Martin Thomson, Dacheng Zhang, and participants in the NMRG research group, the ANIMA working group, and the IESG.

8. References

8.1. Normative References

[I-D.greevenbosch-appsawg-cbor-cddl] Birkholz, H., Vigano, C. and C. Bormann, "CBOR data definition language (CDDL): a notational convention to express CBOR data structures", Internet-Draft draft-greevenbosch-appsawg-cbor-cddl-10, March 2017.
[I-D.ietf-anima-autonomic-control-plane] Behringer, M., Eckert, T. and S. Bjarnason, "An Autonomic Control Plane", Internet-Draft draft-ietf-anima-autonomic-control-plane-06, March 2017.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 2003.
[RFC3986] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005.
[RFC4086] Eastlake 3rd, D., Schiller, J. and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, DOI 10.17487/RFC4086, June 2005.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, October 2013.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque Interface Identifiers with IPv6 Stateless Address Autoconfiguration (SLAAC)", RFC 7217, DOI 10.17487/RFC7217, April 2014.
[RFC8085] Eggert, L., Fairhurst, G. and G. Shepherd, "UDP Usage Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, March 2017.

8.2. Informative References

[I-D.carpenter-anima-asa-guidelines] Carpenter, B. and S. Jiang, "Guidelines for Autonomic Service Agents", Internet-Draft draft-carpenter-anima-asa-guidelines-01, January 2017.
[I-D.chaparadza-intarea-igcp] Behringer, M., Chaparadza, R., Petre, R., Li, X. and H. Mahkonen, "IP based Generic Control Protocol (IGCP)", Internet-Draft draft-chaparadza-intarea-igcp-00, July 2011.
[I-D.ietf-anima-bootstrapping-keyinfra] Pritikin, M., Richardson, M., Behringer, M., Bjarnason, S. and K. Watsen, "Bootstrapping Remote Secure Key Infrastructures (BRSKI)", Internet-Draft draft-ietf-anima-bootstrapping-keyinfra-06, May 2017.
[I-D.ietf-anima-reference-model] Behringer, M., Carpenter, B., Eckert, T., Ciavaglia, L., Pierre, P., Liu, B., Nobre, J. and J. Strassner, "A Reference Model for Autonomic Networking", Internet-Draft draft-ietf-anima-reference-model-03, March 2017.
[I-D.ietf-anima-stable-connectivity] Eckert, T. and M. Behringer, "Using Autonomic Control Plane for Stable Connectivity of Network OAM", Internet-Draft draft-ietf-anima-stable-connectivity-02, February 2017.
[I-D.liu-anima-grasp-api] Carpenter, B., Liu, B., Wang, W. and X. Gong, "Generic Autonomic Signaling Protocol Application Program Interface (GRASP API)", Internet-Draft draft-liu-anima-grasp-api-04, June 2017.
[I-D.stenberg-anima-adncp] Stenberg, M., "Autonomic Distributed Node Consensus Protocol", Internet-Draft draft-stenberg-anima-adncp-00, March 2015.
[RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S. and S. Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification", RFC 2205, DOI 10.17487/RFC2205, September 1997.
[RFC2334] Luciani, J., Armitage, G., Halpern, J. and N. Doraswamy, "Server Cache Synchronization Protocol (SCSP)", RFC 2334, DOI 10.17487/RFC2334, April 1998.
[RFC2608] Guttman, E., Perkins, C., Veizades, J. and M. Day, "Service Location Protocol, Version 2", RFC 2608, DOI 10.17487/RFC2608, June 1999.
[RFC2865] Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, DOI 10.17487/RFC2865, June 2000.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 2003.
[RFC3416] Presuhn, R., "Version 2 of the Protocol Operations for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3416, DOI 10.17487/RFC3416, December 2002.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J. and W. Stevens, "Basic Socket Interface Extensions for IPv6", RFC 3493, DOI 10.17487/RFC3493, February 2003.
[RFC4861] Narten, T., Nordmark, E., Simpson, W. and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, September 2007.
[RFC5612] Eronen, P. and D. Harrington, "Enterprise Number for Documentation Use", RFC 5612, DOI 10.17487/RFC5612, August 2009.
[RFC5971] Schulzrinne, H. and R. Hancock, "GIST: General Internet Signalling Transport", RFC 5971, DOI 10.17487/RFC5971, October 2010.
[RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O. and J. Ko, "The Trickle Algorithm", RFC 6206, DOI 10.17487/RFC6206, March 2011.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011.
[RFC6733] Fajardo, V., Arkko, J., Loughney, J. and G. Zorn, "Diameter Base Protocol", RFC 6733, DOI 10.17487/RFC6733, October 2012.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, DOI 10.17487/RFC6762, February 2013.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013.
[RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R. and P. Selkirk, "Port Control Protocol (PCP)", RFC 6887, DOI 10.17487/RFC6887, April 2013.
[RFC7558] Lynn, K., Cheshire, S., Blanchet, M. and D. Migault, "Requirements for Scalable DNS-Based Service Discovery (DNS-SD) / Multicast DNS (mDNS) Extensions", RFC 7558, DOI 10.17487/RFC7558, July 2015.
[RFC7564] Saint-Andre, P. and M. Blanchet, "PRECIS Framework: Preparation, Enforcement, and Comparison of Internationalized Strings in Application Protocols", RFC 7564, DOI 10.17487/RFC7564, May 2015.
[RFC7575] Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A., Carpenter, B., Jiang, S. and L. Ciavaglia, "Autonomic Networking: Definitions and Design Goals", RFC 7575, DOI 10.17487/RFC7575, June 2015.
[RFC7576] Jiang, S., Carpenter, B. and M. Behringer, "General Gap Analysis for Autonomic Networking", RFC 7576, DOI 10.17487/RFC7576, June 2015.
[RFC7787] Stenberg, M. and S. Barth, "Distributed Node Consensus Protocol", RFC 7787, DOI 10.17487/RFC7787, April 2016.
[RFC7788] Stenberg, M., Barth, S. and P. Pfister, "Home Networking Control Protocol", RFC 7788, DOI 10.17487/RFC7788, April 2016.
[RFC8040] Bierman, A., Bjorklund, M. and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017.
[RFC8126] Cotton, M., Leiba, B. and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017.

Appendix A. Open Issues [RFC Editor: This section should be empty. Please remove]

Appendix B. Closed Issues [RFC Editor: Please remove]

Appendix C. Change log [RFC Editor: Please remove]

draft-ietf-anima-grasp-14, 2017-07-02:

Updates following additional IESG comments:

Updated 2.5.1 and 2.5.2 based on IESG security feedback (specify dependency against security substrate).

Strengthened requirement for reliable transport protocol.

draft-ietf-anima-grasp-13, 2017-06-06:

Updates following additional IESG comments:

Removed all mention of TLS, including SONN, since it was under-specified.

Clarified other text about trust and security model.

Banned Rapid Mode when multicast is insecure.

Explained use of M_INVALID to support extensibility

Corrected details on discovery cache TTL and discovery timeout.

Improved description of multicast UDP w.r.t. RFC8085.

Clarified when transport connections are opened or closed.

Noted that IPPROTO values come from the Protocol Numbers registry

Protocol change: Added protocol and port numbers to URI locator.

Removed inaccurate text about routing protocols

Moved Requirements section to an Appendix.

Other editorial and technical clarifications.

draft-ietf-anima-grasp-12, 2017-05-19:

Updates following IESG comments:

Clarified that GRASP runs in a single addressing realm

Improved wording about FQDN resolution, clarified that URI usage is out of scope.

Clarified description of negotiation timeout.

Noted that 'dry run' semantics are ASA-dependent

Made the ACP a normative reference

Clarified that LL multicasts are limited to GRASP interfaces

Unicast UDP moved out of scope

Editorial clarifications

draft-ietf-anima-grasp-11, 2017-03-30:

Updates following IETF 98 discussion:

Encryption changed to a MUST implement.

Pointed to guidance on UTF-8 names.

draft-ietf-anima-grasp-10, 2017-03-10:

Updates following IETF Last call:

Protocol change: Specify that an objective with no initial value should have its value field set to CBOR 'null'.

Protocol change: Specify behavior on receiving unrecognized message type.

Noted that UTF-8 names are matched byte-for-byte.

Added brief guidance for Expert Reviewer of new generic objectives.

Numerous editorial improvements and clarifications and minor text rearrangements, none intended to change the meaning.

draft-ietf-anima-grasp-09, 2016-12-15:

Protocol change: Add F_NEG_DRY flag to specify a "dry run" objective.

Protocol change: Change M_FLOOD syntax to associate a locator with each objective.

Concentrated mentions of TLS in one section, with all details out of scope.

Clarified text around constrained instances of GRASP.

Strengthened text restricting LL addresses in locator options.

Clarified description of rapid mode processsing.

Specified that cached discovery results should not be returned on the same interface where they were learned.

Shortened text in "High Level Design Choices"

Dropped the word 'kernel' to avoid confusion with o/s kernel mode.

Editorial improvements and clarifications.

draft-ietf-anima-grasp-08, 2016-10-30:

Protocol change: Added M_INVALID message.

Protocol change: Increased Session ID space to 32 bits.

Enhanced rules to avoid Session ID clashes.

Corrected and completed description of timeouts for Request messages.

Improved wording about exponential backoff and DoS.

Clarified that discovery relaying is not done by limited security instances.

Corrected and expanded explanation of port used for Discovery Response.

Noted that Discovery message could be sent unicast in special cases.

Added paragraph on extensibility.

Specified default maximum message size.

Added Appendix for sample messages.

Added short protocol overview.

Editorial fixes, including minor re-ordering for readability.

draft-ietf-anima-grasp-07, 2016-09-13:

Protocol change: Added TTL field to Flood message (issue 51).

Protocol change: Added Locator option to Flood message (issue 51).

Protocol change: Added TTL field to Discovery Response message (corrollary to issue 51).

Clarified details of rapid mode (issues 43 and 50).

Description of inter-domain GRASP instance added (issue 49).

Description of limited security GRASP instances added (issue 52).

Strengthened advice to use TCP rather than UDP.

Updated IANA considerations and text about well-known port usage (issue 53).

Amended text about ASA authorization and roles to allow for overlapping ASAs.

Added text recommending that Flood should be repeated periodically.

Editorial fixes.

draft-ietf-anima-grasp-06, 2016-06-27:

Added text on discovery cache timeouts.

Noted that ASAs that are only initiators do not need to respond to discovery message.

Added text on unexpected address changes.

Added text on robust implementation.

Clarifications and editorial fixes for numerous review comments

Added open issues for some review comments.

draft-ietf-anima-grasp-05, 2016-05-13:

Noted in requirement T1 that it should be possible to implement ASAs independently as user space programs.

Protocol change: Added protocol number and port to discovery response. Updated protocol description, CDDL and IANA considerations accordingly.

Clarified that discovery and flood multicasts are handled by the GRASP core, not directly by ASAs.

Clarified that a node may discover an objective without supporting it for synchronization or negotiation.

Added Implementation Status section.

Added reference to SCSP.

Editorial fixes.

draft-ietf-anima-grasp-04, 2016-03-11:

Protocol change: Restored initiator field in certain messages and adjusted relaying rules to provide complete loop detection.

Updated IANA Considerations.

draft-ietf-anima-grasp-03, 2016-02-24:

Protocol change: Removed initiator field from certain messages and adjusted relaying requirement to simplify loop detection. Also clarified narrative explanation of discovery relaying.

Protocol change: Split Request message into two (Request Negotiation and Request Synchronization) and updated other message names for clarity.

Protocol change: Dropped unused Device ID option.

Further clarified text on transport layer usage.

New text about multicast insecurity in Security Considerations.

Various other clarifications and editorial fixes, including moving some material to Appendix.

draft-ietf-anima-grasp-02, 2016-01-13:

Resolved numerous issues according to WG discussions.

Renumbered requirements, added D9.

Protocol change: only allow one objective in rapid mode.

Protocol change: added optional error string to DECLINE option.

Protocol change: removed statement that seemed to say that a Request not preceded by a Discovery should cause a Discovery response. That made no sense, because there is no way the initiator would know where to send the Request.

Protocol change: Removed PEN option from vendor objectives, changed naming rule accordingly.

Protocol change: Added FLOOD message to simplify coding.

Protocol change: Added SYNCH message to simplify coding.

Protocol change: Added initiator id to DISCOVER, RESPONSE and FLOOD messages. But also allowed the relay process for DISCOVER and FLOOD to regenerate a Session ID.

Protocol change: Require that discovered addresses must be global (except during bootstrap).

Protocol change: Receiver of REQUEST message must close socket if no ASA is listening for the objective.

Protocol change: Simplified Waiting message.

Protocol change: Added No Operation message.

Renamed URL locator type as URI locator type.

Updated CDDL definition.

Various other clarifications and editorial fixes.

draft-ietf-anima-grasp-01, 2015-10-09:

Updated requirements after list discussion.

Changed from TLV to CBOR format - many detailed changes, added co-author.

Tightened up loop count and timeouts for various cases.

Noted that GRASP does not provide transactional integrity.

Various other clarifications and editorial fixes.

draft-ietf-anima-grasp-00, 2015-08-14:

File name and protocol name changed following WG adoption.

Added URL locator type.

draft-carpenter-anima-gdn-protocol-04, 2015-06-21:

Tuned wording around hierarchical structure.

Changed "device" to "ASA" in many places.

Reformulated requirements to be clear that the ASA is the main customer for signaling.

Added requirement for flooding unsolicited synch, and added it to protocol spec. Recognized DNCP as alternative for flooding synch data.

Requirements clarified, expanded and rearranged following design team discussion.

Clarified that GDNP discovery must not be a prerequisite for GDNP negotiation or synchronization (resolved issue 13).

Specified flag bits for objective options (resolved issue 15).

Clarified usage of ACP vs TLS/DTLS and TCP vs UDP (resolved issues 9,10,11).

Updated DNCP description from latest DNCP draft.

Editorial improvements.

draft-carpenter-anima-gdn-protocol-03, 2015-04-20:

Removed intrinsic security, required external security

Format changes to allow DNCP co-existence

Recognized DNS-SD as alternative discovery method.

Editorial improvements

draft-carpenter-anima-gdn-protocol-02, 2015-02-19:

Tuned requirements to clarify scope,

Clarified relationship between types of objective,

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

Improved description of objective options,

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

Allow multiple discovery objectives in one response,

Provided for missing or multiple discovery responses,

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

Minor editorial and technical corrections and clarifications,

Reorganized future work list.

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

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

Appendix D. Example Message Formats

For readers unfamiliar with CBOR, this appendix shows a number of example GRASP messages conforming to the CDDL syntax given in Section 5. Each message is shown three times in the following formats:

  1. CBOR diagnostic notation.
  2. Similar, but showing the names of the constants. (Details of the flag bit encoding are omitted.)
  3. Hexadecimal version of the CBOR wire format.

Long lines are split for display purposes only.

D.1. Discovery Example

The initiator (2001:db8:f000:baaa:28cc:dc4c:9703:6781) multicasts a discovery message looking for objective EX1:

[1, 13948744, h'20010db8f000baaa28ccdc4c97036781', ["EX1", 5, 2, 0]]
[M_DISCOVERY, 13948744, h'20010db8f000baaa28ccdc4c97036781',
              ["EX1", F_SYNCH_bits, 2, 0]]

A peer (2001:0db8:f000:baaa:f000:baaa:f000:baaa) responds with a locator:

[2, 13948744, h'20010db8f000baaa28ccdc4c97036781', 60000,
              [103, h'20010db8f000baaaf000baaaf000baaa', 6, 49443]] 
[M_RESPONSE, 13948744, h'20010db8f000baaa28ccdc4c97036781', 60000,
              [O_IPv6_LOCATOR, h'20010db8f000baaaf000baaaf000baaa',
               IPPROTO_TCP, 49443]]

D.2. Flood Example

The initiator multicasts a flood message. The single objective has a null locator. There is no response:

[9, 3504974, h'20010db8f000baaa28ccdc4c97036781', 10000,  
             [["EX1", 5, 2, ["Example 1 value=", 100]],[] ] ] 
[M_FLOOD, 3504974, h'20010db8f000baaa28ccdc4c97036781', 10000,
             [["EX1", F_SYNCH_bits, 2, ["Example 1 value=", 100]],[] ] ]

D.3. Synchronization Example

Following successful discovery of objective EX2, the initiator unicasts a request:

[4, 4038926, ["EX2", 5, 5, 0]] 
[M_REQ_SYN, 4038926, ["EX2", F_SYNCH_bits, 5, 0]] 

The peer responds with a value:

[8, 4038926, ["EX2", 5, 5, ["Example 2 value=", 200]]] 
[M_SYNCH, 4038926, ["EX2", F_SYNCH_bits, 5, ["Example 2 value=", 200]]] 

D.4. Simple Negotiation Example

Following successful discovery of objective EX3, the initiator unicasts a request:

[3, 802813, ["EX3", 3, 6, ["NZD", 47]]] 
[M_REQ_NEG, 802813, ["EX3", F_NEG_bits, 6, ["NZD", 47]]] 

The peer responds with immediate acceptance. Note that no objective is needed, because the initiator's request was accepted without change:

[6, 802813, [101]] 
[M_END , 802813, [O_ACCEPT]]

D.5. Complete Negotiation Example

Again the initiator unicasts a request:

[3, 13767778, ["EX3", 3, 6, ["NZD", 410]]] 
[M_REQ_NEG, 13767778, ["EX3", F_NEG_bits, 6, ["NZD", 410]]]

The responder starts to negotiate (making an offer):

[5, 13767778, ["EX3", 3, 6, ["NZD", 80]]] 
[M_NEGOTIATE, 13767778, ["EX3", F_NEG_bits, 6, ["NZD", 80]]] 

The initiator continues to negotiate (reducing its request, and note that the loop count is decremented):

[5, 13767778, ["EX3", 3, 5, ["NZD", 307]]] 
[M_NEGOTIATE, 13767778, ["EX3", F_NEG_bits, 5, ["NZD", 307]]] 

The responder asks for more time:

[7, 13767778, 34965] 
[M_WAIT, 13767778, 34965] 

The responder continues to negotiate (increasing its offer):

[5, 13767778, ["EX3", 3, 4, ["NZD", 120]]] 
[M_NEGOTIATE, 13767778, ["EX3", F_NEG_bits, 4, ["NZD", 120]]]

The initiator continues to negotiate (reducing its request):

[5, 13767778, ["EX3", 3, 3, ["NZD", 246]]] 
[M_NEGOTIATE, 13767778, ["EX3", F_NEG_bits, 3, ["NZD", 246]]]

The responder refuses to negotiate further:

[6, 13767778, [102, "Insufficient funds"]] 
[M_END , 13767778, [O_DECLINE, "Insufficient funds"]] 

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.

Appendix E. 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 the GRASP signaling protocol. Furthermore, requirements for ASAs themselves, such as the processing of Intent [RFC7575], are out of scope for the present document.

E.1. Requirements for Discovery

D1. ASAs may be designed to manage any type of configurable device or software, as required in Appendix E.2. A basic requirement is therefore that the protocol can represent and discover any kind of technical objective (as defined in Section 2.1) among arbitrary subsets of participating nodes.

In an autonomic network we must assume that when a device starts up it has no information about any peer devices, the network structure, or what specific role it must play. The ASA(s) inside the device are in the same situation. In some cases, when a new application session starts up within a device, the device or ASA may again lack information about relevant peers. 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:

D2. 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.

D3. When an ASA starts up, it must require no configured location information about any peers in order to discover them.

D4. If an ASA supports multiple technical objectives, relevant peers may be different for different discovery objectives, so discovery needs to be 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.

D5. 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.

D6. Some objectives may only be significant on the local link, but others may be significant across the routed network and require off-link operations. Thus, the relevant peers might be immediate neighbors on the same layer 2 link, or they might be more distant and only accessible via layer 3. The mechanism must therefore provide both on-link and off-link discovery of ASAs supporting specific technical objectives.

D7. The discovery process should be flexible enough to allow for special cases, such as the following:

D8. The discovery process must not generate excessive traffic and must take account of sleeping nodes.

D9. There must be a mechanism for handling stale discovery results.

E.2. Requirements for Synchronization and Negotiation Capability

Autonomic networks need to be able to manage many different types of parameter 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.

SN1. 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.

SN2. 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.

SN3. Synchronization must be possible for groups of nodes ranging from small to very large.

SN4. To avoid "reinventing the wheel", the protocol should be able to encapsulate the data formats used by existing configuration protocols (such as NETCONF/YANG) in cases where that is convenient.

SN5. Human intervention in complex situations is costly and error-prone. Therefore, synchronization or negotiation of parameters without human intervention is desirable whenever the coordination of multiple devices can improve overall network performance. It 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 [I-D.ietf-anima-reference-model].

SN6. Human intervention in large networks is often replaced by use of a top-down network management system (NMS). It therefore follows that the protocol, as part of the Autonomic Networking Infrastructure, should be capable of running in any device that would otherwise be managed by an NMS, and that it can co-exist with an NMS, and with protocols such as SNMP and NETCONF.

SN7. Specific autonomic features are expected to be implemented by individual ASAs, but the protocol must be general enough to allow them. Some examples follow:

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 [I-D.ietf-anima-stable-connectivity] discusses how such agents may be linked into conventional OAM systems via an Autonomic Control Plane [I-D.ietf-anima-autonomic-control-plane].

SN8. The protocol will be able to deal with a wide variety of technical objectives, covering any type of network parameter. Therefore the protocol will need 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.

E.3. Specific Technical Requirements

T1. It should be convenient for ASA designers to define new technical objectives and for programmers to express them, without excessive impact on run-time efficiency and footprint. 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 [I-D.ietf-anima-reference-model].

T2. The protocol should be easily extensible in case the initially defined discovery, synchronization and negotiation mechanisms prove to be insufficient.

T3. To be a generic platform, the protocol payload format should be independent of the transport protocol or IP version. In particular, it should be able to run over IPv6 or IPv4. However, some functions, such as multicasting on a link, might need to be IP version dependent. By default, IPv6 should be preferred.

T4. The protocol must be able to access off-link counterparts via routable addresses, i.e., must not be restricted to link-local operation.

T5. It must also be possible for an external discovery mechanism to be used, if appropriate for a given technical objective. In other words, GRASP discovery must not be a prerequisite for GRASP negotiation or synchronization.

T6. The protocol must be capable of distinguishing multiple simultaneous operations with one or more peers, especially when wait states occur.

T7. 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.

T8. Management monitoring, alerts and intervention: Devices should be able to report to a monitoring system. Some events must be able to generate operator alerts and some provision for emergency intervention must be possible (e.g. to freeze synchronization or negotiation in a mis-behaving device). These features might not use the signaling protocol itself, but its design should not exclude such use.

T9. 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.

Appendix F. Capability Analysis of Current Protocols

This appendix discusses various existing protocols with properties related to the requirements described in Appendix E. The purpose is to evaluate whether any existing protocol, or a simple combination of existing protocols, can meet those requirements.

Numerous protocols include some form of discovery, but these all appear to be very specific in their applicability. Service Location Protocol (SLP) [RFC2608] provides service discovery for managed networks, but requires configuration of its own servers. DNS-SD [RFC6763] combined with mDNS [RFC6762] provides service discovery for small networks with a single link layer. [RFC7558] aims to extend this to larger autonomous networks but this is not yet standardized. However, both SLP and DNS-SD appear to target primarily application layer services, not the layer 2 and 3 objectives relevant to basic network configuration. Both SLP and DNS-SD are text-based protocols.

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

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

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

RESTCONF [RFC8040] is a protocol intended to convey NETCONF information expressed in the YANG language via HTTP, including the ability to transit HTML intermediaries. While this is a powerful approach in the context of centralised configuration of a complex network, it is not well adapted to efficient interactive negotiation between peer devices, especially simple ones that might not include YANG processing already.

The Distributed Node Consensus Protocol (DNCP) [RFC7787] is defined as a generic form of state synchronization protocol, with a proposed usage profile being the Home Networking Control Protocol (HNCP) [RFC7788] for configuring Homenet routers. A specific application of DNCP for autonomic networking was proposed in [I-D.stenberg-anima-adncp].

DNCP "is designed to provide a way for each participating node to publish a set of TLV (Type-Length-Value) tuples, and to provide a shared and common view about the data published... DNCP is most 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:

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) [RFC2334] 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) [I-D.chaparadza-intarea-igcp]. This was aimed at information exchange and negotiation but not directly at peer discovery. However, it has many points in common with the present work.

None of the above solutions appears to completely meet the needs of generic discovery, state synchronization and negotiation in a single solution. Many of the protocols assume that they are working in a traditional top-down or north-south scenario, rather than a fluid peer-to-peer scenario. Most of them are specialized in one way or another. As a result, we have not identified a combination of existing protocols that meets the requirements in Appendix E. Also, we have not identified a path by which one of the existing protocols could be extended to meet the requirements.

Authors' Addresses

Carsten Bormann Universität Bremen TZI Postfach 330440 D-28359 Bremen, Germany EMail:
Brian Carpenter (editor) Department of Computer Science University of Auckland PB 92019 Auckland, 1142 New Zealand EMail:
Bing Liu (editor) Huawei Technologies Co., Ltd Q14, Huawei Campus No.156 Beiqing Road Hai-Dian District, Beijing, 100095 P.R. China EMail: