| Network Working Group | B. Carpenter |
| Internet-Draft | Univ. of Auckland |
| Intended status: Standards Track | B. Liu |
| Expires: August 23, 2015 | Huawei Technologies Co., Ltd |
| February 19, 2015 |
A Generic Discovery and Negotiation Protocol for Autonomic Networking
draft-carpenter-anima-gdn-protocol-02
This document establishes requirements for a protocol that enables intelligent devices to dynamically discover peer devices, to synchronize state with them, and to negotiate parameter settings mutually with them. The document then defines a general protocol for discovery, synchronization and negotiation, while the technical objectives for specific scenarios are to be described in separate documents. An Appendix briefly discusses existing protocols with comparable features.
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The success of the Internet has made IP-based networks bigger and more complicated. Large-scale ISP and enterprise networks have become more and more problematic for human based management. Also, operational costs are growing quickly. Consequently, there are increased requirements for autonomic behavior in the networks. General aspects of autonomic networks are discussed in [I-D.irtf-nmrg-autonomic-network-definitions] and [I-D.irtf-nmrg-an-gap-analysis]. In order to fulfil autonomy, devices that embody autonomic service agents need to be able to discover each other, to synchronize state with each other, and to negotiate parameters and resources directly with each other. There is no restriction on the type of parameters and resources concerned, which include very basic information needed for addressing and routing, as well as anything else that might be configured in a conventional network.
Following this Introduction, Section 2 describes the requirements for network device discovery, synchronization and negotiation. Negotiation is an iterative process, requiring multiple message exchanges forming a closed loop between the negotiating devices. State synchronization, when needed, can be regarded as a special case of negotiation, without iteration. Section 3.2 describes a behavior model for a protocol intended to support discovery, synchronization and negotiation. The design of Generic Discovery and Negotiation Protocol (GDNP) in Section 3 of this document is mainly based on this behavior model. The relevant capabilities of various existing protocols are reviewed in Appendix A.
The proposed discovery mechanism is oriented towards synchronization and negotiation objectives. It is based on a neighbor discovery process, but also supports diversion to off-link peers. Although many negotiations will occur between horizontally distributed peers, many target scenarios are hierarchical networks, which is the predominant structure of current large-scale networks. However, when a device starts up with no pre-configuration, it has no knowledge of a hierarchical superior. The protocol itself is capable of being used in a small and/or flat network structure such as a small office or home network as well as a professionally managed network. Therefore, the discovery mechanism needs to be able to allow a device to bootstrap itself without making any prior assumptions about network structure.
Because GDNP can be used to perform a decision process among distributed devices or between networks, it adopts a tight certificate-based security mechanism, which needs a Public Key Infrastructure (PKI) [RFC5280] system. The PKI may be managed by an operator or be autonomic, as discussed in [I-D.pritikin-anima-bootstrapping-keyinfra].
It is understood that in realistic deployments, not all devices will support GDNP. It is expected that some autonomic service agents will manage a group of non-autonomic nodes, and that other non-autonomic nodes will be managed traditionally. Such mixed scenarios are not discussed in this specification.
This section discusses the requirements for discovery, negotiation and synchronization capabilities.
In an autonomic network we must assume that when a device starts up it has no information about any peer devices, the network structure, or what specific role it must play. In some cases, when a new application session starts up within a device, the device may again lack information about relevant peer devices. It might be necessary to set up resources on multiple other devices, coordinated and matched to each other so that there is no wasted resource. Security settings might also need updating to allow for the new device or user. Therefore a basic requirement is that there must be a mechanism by which a device can separately discover peer devices for each of the technical objectives that it needs to manage. Some objectives may only be significant on the local link, but others may be significant across the routed network and require off-link operations. Thus, the relevant peer devices might be immediate neighbors on the same layer 2 link or they might be more distant and only accessible via layer 3. The mechanism must therefore support both on-link discovery and off-link discovery of peers that support specific technical objectives.
The relevant peer devices may be different for different technical objectives. Therefore discovery needs to be repeated as often as necessary to find peers capable of acting as counterparts for each objective that a discovery initiator needs to handle. In many scenarios, the discovery process may be followed by a synchronization or negotiation process. Therefore, a discovery objective may be associated with one or more synchronization or negotiation objectives.
When a device first starts up, it has no knowledge of the network structure. Therefore the discovery process must be able to support any network scenario, assuming only that the device concerned is bootstrapped from factory condition.
In some networks, as mentioned above, there will be some hierarchical structure, at least for certain synchronization or negotiation objectives. A special case of discovery is that each device must be able to discover its hierarchical superior for each such objective that it is capable of handling. This is part of the more general requirement to discover off-link devices.
During initialisation, a device must be able to establish mutual trust with the rest of the network and join the PKI. Although this must inevitably start with a discovery action, it is a special case precisely because trust is not yet established. This topic is the subject of [I-D.pritikin-anima-bootstrapping-keyinfra]. In addition, depending on the type of network involved, discovery of other central functions might be needed, such as the Network Operations Center (NOC) [I-D.eckert-anima-stable-connectivity].
We start by considering routing protocols, the closest approximation to autonomic networking in widespread use. Routing protocols use a largely autonomic model based on distributed devices that communicate repeatedly with each other. However, routing is mainly based on one-way information synchronization (in either direction), rather than on bi-directional negotiation. The focus is reachability, so current routing protocols only consider simple link status, i.e., up or down. More information, such as latency, congestion, capacity, and particularly unused capacity, would be helpful to get better path selection and utilization rate. Also, autonomic networks need to be able to manage many more dimensions, such as security settings, power saving, load balancing, etc. A basic requirement for the protocol is therefore the ability to represent, discover, synchronize and negotiate almost any kind of network parameter.
Human intervention in complex situations is costly and error-prone. Therefore, synchronization or negotiation of parameters without human intervention is desirable whenever the coordination of multiple devices can improve overall network performance. It follows that a requirement for the protocol is to be capable of running in any device that would otherwise need human intervention.
Human intervention in large networks is often replaced by use of a top-down network management system (NMS). It therefore follows that a requirement for the protocol is to be capable of running in any device that would otherwise be managed by an NMS, and that it can co-exist with an NMS.
Since the goal is to minimize human intervention, it is necessary that the network can in effect "think ahead" before changing its parameters. In other words there must be a possibility of forecasting the effect of a change by a "dry run" mechanism before actually installing the change. This will be an application of the protocol rather than a feature of the protocol itself.
Status information and traffic metrics need to be shared between nodes for dynamic adjustment of resources and for monitoring purposes. While this might be achieved by existing protocols when they are available, the new protocol needs to be able to support parameter exchange, including mutual synchronization, even when no negotiation as such is required.
Recovery from faults and identification of faulty devices should be as automatic as possible. However, the protocol's role is limited to the ability to handle discovery, synchronization and negotiation at any time, in case an autonomic service agent detects an anomaly such as a negotiation counterpart failing.
Management logging, monitoring, alerts and tools for intervention are required. However, these can only be features of individual autonomic service agents. Another document [I-D.eckert-anima-stable-connectivity] discusses how such agents may be linked into conventional OAM systems via an Autonomic Control Plane [I-D.behringer-anima-autonomic-control-plane].
The protocol needs to be able to deal with a wide variety of technical objectives, covering any type of network parameter. Therefore the protocol will need either an explicit information model describing its messages, or at least a flexible and extensible message format. One design consideration is whether to adopt an existing information model or to design a new one. Another consideration is whether it should be able to carry some or all of the message formats used by existing configuration protocols.
To be a generic platform, the protocol payload format should be independent of the transport protocol or IP version. In particular, it should be able to run over IPv6 or IPv4. However, some functions, such as multicasting or broadcasting on a link, might need to be IP version dependent. In case of doubt, IPv6 should be preferred.
The protocol must be able to access off-link counterparts via routable addresses, i.e., must not be restricted to link-local operation.
The negotiation process must be guaranteed to terminate (with success or failure) and if necessary it must contain tie-breaking rules for each technical objective that requires them. While this must be defined specifically for each use case, the protocol should have some general mechanisms in support of loop and deadlock prevention.
Dependencies: In order to decide a configuration on a given device, the device may need information from neighbors. This can be established through the negotiation procedure, or through synchronization if that is sufficient. However, a given item in a neighbor may depend on other information from its own neighbors, which may need another negotiation or synchronization procedure to obtain or decide. Therefore, there are potential dependencies among negotiation or synchronization procedures. Thus, there need to be clear boundaries and convergence mechanisms for these negotiation dependencies. Also some mechanisms are needed to avoid loop dependencies.
Policy constraints: There must be provision for general policy intent rules to be applied by all devices in the network (e.g., security rules, prefix length, resource sharing rules). However, policy intent distribution might not use the negotiation protocol itself.
Management monitoring, alerts and intervention: Devices should be able to report to a monitoring system. Some events must be able to generate operator alerts and some provision for emergency intervention must be possible (e.g. to freeze synchronization or negotiation in a mis-behaving device). These features may not use the negotiation protocol itself.
The protocol needs to be fully secure against forged messages and man-in-the middle attacks, and as secure as reasonably possible against denial of service attacks. It needs to be capable of encryption in order to resist unwanted monitoring, although this capability may not be required in all deployments.
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.
The following terms are used throughout this document:
This section describes a behavior model and some considerations for designing a generic discovery, synchronization and negotiation protocol, which can act as a platform for different technical objectives.
NOTE: This protocol is described here in a stand-alone fashion as a proof of concept. An elementary version has been prototyped by Huawei and the Beijing University of Posts and Telecommunications. However, this is not yet a definitive proposal for IETF adoption. In particular, adaptation and extension of one of the protocols discussed in Appendix A might be an option. Also, the security model outlined below would in practice be part of a general security mechanism in an autonomic control plane [I-D.behringer-anima-autonomic-control-plane]. This whole specification is subject to change as a result.
A certificate-based security mechanism provides security properties for GDNP:
The authority of the GDNP message sender depends on a Public Key Infrastructure (PKI) system with a Certification Authority (CA), which should normally be run by the network operator. In the case of a network with no operator, such as a small office or home network, the PKI itself needs to be established by an autonomic process, which is out of scope for this specification.
A Request message MUST carry a Certificate option, defined in Section 3.8.6. The first Negotiation Message, responding to a Request message, SHOULD also carry a Certificate option. Using these messages, recipients build their certificate stores, indexed by the Device Certificate Tags included in every GDNP message. This process is described in more detail below.
Every message MUST carry a signature option (Section 3.8.7).
For now, the authors do not think packet size is a problem. In this GDNP specification, there SHOULD NOT be multiple certificates in a single message. The current most used public keys are 1024/2048 bits; some may reach 4096. With overhead included, a single certificate is less than 500 bytes. Messages are expected to be far shorter than the normal packet MTU within a modern network.
Hash functions are used to provide message integrity checks. In order to provide a means of addressing problems that may emerge in the future with existing hash algorithms, as recommended in [RFC4270], a mechanism for negotiating the use of more secure hashes in the future is provided.
In addition to hash algorithm agility, a mechanism for signature algorithm agility is also provided.
The support for algorithm agility in this document is mainly a unilateral notification mechanism from sender to recipient. If the recipient does not support the algorithm used by the sender, it cannot authenticate the message. Senders in a single administrative domain are not required to upgrade to a new algorithm simultaneously.
So far, the algorithm agility is supported by one-way notification, rather than negotiation mode. As defined in Section 3.8.7, the sender notifies the recipient what hash/signature algorithms it uses. If the responder doesn't know a new algorithm used by the sender, the negotiation request would fail. In order to establish a negotiation session, the sender MAY fall back to an older, less preferred algorithm. Certificates and network policy intent SHOULD limit the choice of algorithms.
When receiving a GDNP message, a recipient MUST discard the GDNP message if the Signature option is absent, or the Certificate option is in a Request Message.
For the Request message and the Response message with a Certification Option, the recipient MUST first check the authority of this sender following the rules defined in [RFC5280]. After successful authority validation, an implementation MUST add the sender's certification into the local trust certificate record indexed by the associated Device Certificate Tag (Section 3.5).
The recipient MUST now authenticate the sender by verifying the Signature and checking a timestamp, as specified in Section 3.3.2.3. The order of two procedures is left as an implementation decision. It is RECOMMENDED to check timestamp first, because signature verification is much more computationally expensive.
The signature field verification MUST show that the signature has been calculated as specified in Section 3.8.7. The public key used for signature validation is obtained from the certificate either carried by the message or found from a local trust certificate record by searching the message-carried Device Certificate Tag.
Only the messages that get through both the signature verifications and timestamp check are accepted and continue to be handled for their contained GDNP options. Messages that do not pass the above tests MUST be discarded as insecure messages.
Recipients SHOULD be configured with an allowed timestamp Delta value, a "fuzz factor" for comparisons, and an allowed clock drift parameter. The recommended default value for the allowed Delta is 300 seconds (5 minutes); for fuzz factor 1 second; and for clock drift, 0.01 second.
The timestamp is defined in the Signature Option, Section 3.8.7. To facilitate timestamp checking, each recipient SHOULD store the following information for each sender:
An accepted GDNP message is any successfully verified (for both timestamp check and signature verification) GDNP message from the given peer. It initiates the update of the above variables. Recipients MUST then check the Timestamp field as follows:
An implementation MAY use some mechanism such as a timestamp cache to strengthen resistance to replay attacks. When there is a very large number of nodes on the same link, or when a cache filling attack is in progress, it is possible that the cache holding the most recent timestamp per sender will become full. In this case, the node MUST remove some entries from the cache or refuse some new requested entries. The specific policy as to which entries are preferred over others is left as an implementation decision.
A negotiation initiator sends a negotiation request to a counterpart device, including a specific negotiation objective. It may request the negotiation counterpart to make a specific configuration. Alternatively, it may request a certain simulation or forecast result by sending a dry run configuration. The details, including the distinction between dry run and an actual configuration change, will be defined separately for each type of negotiation objective.
If the counterpart can immediately apply the requested configuration, it will give an immediate positive (accept) answer. This will end the negotiation phase immediately. Otherwise, it will negotiate. It will reply with a proposed alternative configuration that it can apply (typically, a configuration that uses fewer resources than requested by the negotiation initiator). This will start a bi-directional negotiation to reach a compromise between the two network devices.
The negotiation procedure is ended when one of the negotiation peers sends a Negotiation Ending message, which contains an accept or decline option and does not need a response from the negotiation peer. Negotiation may also end in failure (equivalent to a decline) if a timeout is exceeded or a loop count is exceeded.
A negotiation procedure concerns one objective and one counterpart. Both the initiator and the counterpart may take part in simultaneous negotiations with various other devices, or in simultaneous negotiations about different objectives. Thus, GDNP is expected to be used in a multi-threaded mode. Certain negotiation objectives may have restrictions on multi-threading, for example to avoid over-allocating resources.
Rapid Mode (Discovery/Negotiation linkage)
A synchronization initiator sends a synchronization request to a counterpart device, including a specific synchronization objective. The counterpart responds with a Response message containing the current value of the requested synchronization objective. No further messages are needed. If no Response message is received, the synchronization request MAY be repeated after a suitable timeout.
In the case just described, the message exchange is unicast and concerns only one synchronization objective. In the following two cases, multiple synchronization objectives may be combined.
A synchronization responder MAY send an unsolicited Response message containing one or more Synchronization Objective option(s), if and only if the specification of those objectives permits it. This MAY be sent as a multicast message to the ALL_GDNP_NEIGHBOR multicast address (Section 3.4). In this case a suitable mechanism is needed to avoid excessive multicast traffic. This mechanism MUST be defined as part of the specification of the synchronization objective(s) concerned. It might be a simple rate limit or a more complex mechanism such as the Trickle algorithm [RFC6206].
Rapid Mode (Discovery/Synchronization linkage)
A GDNP-enabled Device MUST generate a stable public/private key pair before it participates in GDNP. There MUST NOT be any way of accessing the private key via the network or an operator interface. The device then uses the public key as its identifier, which is cryptographic in nature. It is a GDNP unique identifier for a GDNP participant.
It then gets a certificate for this public key, signed by a Certificate Authority that is trusted by other network devices. The Certificate Authority SHOULD be managed within the local administrative domain, to avoid needing to trust a third party. The signed certificate would be used for authentication of the message sender. In a managed network, this certification process could be performed at a central location before the device is physically installed at its intended location. In an unmanaged network, this process must be autonomic, including the bootstrap phase.
A 128-bit Device Certifcate Tag, which is generated by taking a cryptographic hash over the device certificate, is a short presentation for GDNP messages. It is the index key to find the device certificate in a recipient's local trusted certificate record.
The tag value is formed by taking a SHA-1 hash algorithm [RFC3174] over the corresponding device certificate and taking the leftmost 128 bits of the hash result.
A 24-bit opaque value used to distinguish multiple sessions between the same two devices. A new Session ID MUST be generated for every new Discovery or Request message, and for every unsolicited Response message. All follow-up messages in the same discovery, synchronization or negotiation procedure, which is initiated by the request message, MUST carry the same Session ID.
The Session ID SHOULD have a very low collision rate locally. It is RECOMMENDED to be generated by a pseudo-random algorithm using a seed which is unlikely to be used by any other device in the same network [RFC4086].
This document defines the following GDNP message format and types. Message types not listed here are reserved for future use. The numeric encoding for each message type is shown in parentheses.
All GDNP messages share an identical fixed format header and a variable format area for options. Every Message carries the Device Certificate Tag of its sender and a Session ID. Options are presented serially in the options field, with no padding between the options. Options are byte-aligned.
The following diagram illustrates the format of GDNP messages:
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MESSAGE_TYPE | Session ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Device Certificate Tag | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options (variable length) | . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
DISCOVERY (MESSAGE_TYPE = 1):
A discovery initiator sends a DISCOVERY message to initiate a discovery process.
The discovery initiator sends the DISCOVERY messages to the link-local ALL_GDNP_NEIGHBOR multicast address for discovery, and stores the discovery results (including responding discovery objectives and corresponding unicast addresses or FQDNs).
A DISCOVERY message MUST include exactly one of the following:
RESPONSE (MESSAGE_TYPE = 2):
A node which receives a DISCOVERY message sends a Response message to respond to a discovery. It MUST contain the same Session ID as the DISCOVERY message. It MAY include a copy of the discovery objective from the DISCOVERY message.
If the responding node supports the discovery objective of the discovery, it MUST include at least one kind of locator option (Section 3.8.8) to indicate its own location. A combination of multiple kinds of locator options (e.g. IP address option + FQDN option) is also valid.
If the responding node itself does not support the discovery objective, but it knows the locator of the discovery objective, then it SHOULD respond to the discovery message with a divert option (Section 3.8.2) embedding a locator option or a combination of multiple kinds of locator options which indicate the locator(s) of the discovery objective.
A node which receives a synchronization request sends a Response message with the synchronization data. A node MAY send an unsolicited Response Message with synchronization data and this MAY be sent to the link-local ALL_GDNP_NEIGHBOR multicast address, in accordance with the rules in Section 3.3.4.
If the response contains synchronization data, this will be in the form of GDNP Option(s) for the specific synchronization objective(s).
REQUEST (MESSAGE_TYPE = 3):
A negotiation or synchronization requesting node sends the REQUEST message to the unicast address (directly stored or resolved from the FQDN) of the negotiation or synchronization counterpart (selected from the discovery results).
A request message MUST include the relevant objective option, with the requested value in the case of negotiation.
When an initiator sends a REQUEST message, it MUST initialize a negotiation timer for the new negotiation thread with the value GDNP_DEF_TIMEOUT milliseconds. Unless this timeout is modified by a CONFIRM-WAITING message (Section 3.7.7), the initiator will consider that the negotiation has failed when the timer expires.
When an initiator sends a REQUEST message, it MUST initialize the loop count of the objective option with a value defined in the specification of the option or, if no such value is specified, with GDNP_DEF_LOOPCT.
NEGOTIATION (MESSAGE_TYPE = 4):
A negotiation counterpart sends a NEGOTIATION message in response to a REQUEST message, a NEGOTIATION message, or a DISCOVERY message in Rapid Mode. A negotiation process MAY include multiple steps.
The NEGOTIATION message MUST include the relevant Negotiation Objective option, with its value updated according to progress in the negotiation. The sender MUST decrement the loop count by 1. If the loop count becomes zero both parties will consider that the negotiation has failed.
NEGOTIATION-ENDING (MESSAGE_TYPE = 5):
A negotiation counterpart sends an NEGOTIATION-ENDING message to close the negotiation. It MUST contain one, but only one of accept/decline option, defined in Section 3.8.3 and Section 3.8.4. It could be sent either by the requesting node or the responding node.
CONFIRM-WAITING (MESSAGE_TYPE = 6):
A responding node sends a CONFIRM-WAITING message to indicate the requesting node to wait for a further negotiation response. It might be that the local process needs more time or that the negotiation depends on another triggered negotiation. This message MUST NOT include any other options than the Waiting Time Option (Section 3.8.5).
This section defines the GDNP general option for the negotiation and synchronization protocol signalling. Option types 10~63 are reserved for GDNP general options defined in the future.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | option-code | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | option-data | | (option-len octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
GDNP options are scoped by using encapsulation. If an option contains other options, the outer Option-len includes the total size of the encapsulated options, and the latter apply only to the outer option.
The divert option is used to redirect a GDNP request to another node, which may be more appropriate for the intended negotiation or synchronization. It may redirect to an entity that is known as a specific negotiation or synchronization counterpart (on-link or off-link) or a default gateway. The divert option MUST only be encapsulated in Response messages. If found elsewhere, it SHOULD be silently ignored.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_DIVERT | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Locator Option(s) of Diversion Device(s) | . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The accept option is used to indicate to the negotiation counterpart that the proposed negotiation content is accepted.
The accept option MUST only be encapsulated in Negotiation-ending messages. If found elsewhere, it SHOULD be silently ignored.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_ACCEPT | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The decline option is used to indicate to the negotiation counterpart the proposed negotiation content is declined and end the negotiation process.
The decline option MUST only be encapsulated in Negotiation-ending messages. If found elsewhere, it SHOULD be silently ignored.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_DECLINE | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Notes: there are scenarios where a negotiation counterpart wants to decline the proposed negotiation content and continue the negotiation process. For these scenarios, the negotiation counterpart SHOULD use a Negotiate message, with either an objective option that contains at least one data field with all bits set to 1 to indicate a meaningless initial value, or a specific objective option that provides further conditions for convergence.
The waiting time option is used to indicate that the negotiation counterpart needs to wait for a further negotiation response, since the processing might need more time than usual or it might depend on another triggered negotiation.
The waiting time option MUST only be encapsulated in Confirm-waiting messages. If found elsewhere, it SHOULD be silently ignored. When received, its value overwrites the negotiation timer (Section 3.7.4).
The counterpart SHOULD send a Negotiation, Negotiation-Ending or another Confirm-waiting message before the negotiation timer expires. If not, the initiator MUST abandon or restart the negotiation procedure, to avoid an indefinite wait.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_WAITING | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Time | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Certificate option carries the certificate of the sender. The format of the Certificate option is as follows:
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION Certificate | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Certificate (variable length) . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Signature option allows public key-based signatures to be attached to a GDNP message. The Signature option is REQUIRED in every GDNP message and could be any place within the GDNP message. It protects the entire GDNP header and options. A TimeStamp has been integrated in the Signature Option for anti-replay protection. The format of the Signature option is described as follows:
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_SIGNATURE | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | HA-id | SA-id | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Timestamp (64-bit) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Signature (variable length) . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
These locator options are used to present a device's or interface's reachability information. They are Locator IPv4 Address Option, Locator IPv6 Address Option and Locator FQDN (Fully Qualified Domain Name) Option.
Note that it is assumed that all locators are in scope throughout the GDNP domain. GDNP is not intended to work across disjoint addressing or naming realms.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_LOCATOR_IPV4ADDR | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4-Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note: If an operator has internal network address translation for IPv4, this option MUST NOT be used within the Divert option.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_LOCATOR_IPV6ADDR | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | IPv6-Address | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note: A link-local IPv6 address MUST NOT be used when this option is used within the Divert option.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_FQDN | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Fully Qualified Domain Name | | (variable length) | . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note: Any FQDN which might not be valid throughout the network in question, such as a Multicast DNS name [RFC6762], MUST NOT be used when this option is used within the Divert option.
An objective option is used to identify objectives for the purposes of discovery, negotiation or synchronization. All objectives must follow a common format as follows:
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_XXX | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | loop-count | flags | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ value | . (variable length) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Objective Options MUST be assigned an option type greater than 64 in the GDNP option table.
An Objective Option that contains no additional fields, i.e., has a length of 4 octets, is a discovery objective and MUST only be used in Discovery and Response messages.
The Negotiation Objective Options contain negotiation objectives, which are various according to different functions/services. They MUST be carried by Discovery, Request or Negotiation Messages only. The negotiation initiator MUST set the initial "loop-count" to a value specified in the specification of the objective or, if no such value is specified, to GDNP_DEF_LOOPCT.
For most scenarios, there should be initial values in the negotiation requests. Consequently, the Negotiation Objective options MUST always be completely presented in a Request message, or in a Discovery message in rapid mode. If there is no initial value, the bits in the value field SHOULD all be set to 1 to indicate a meaningless value, unless this is inappropriate for the specific negotiation objective.
Synchronization Objective Options are similar, but MUST be carried by Discovery, Request or Response messages only. They include value fields only in Response messages.
As noted earlier, one negotiation objective is handled by each GDNP negotiation thread. Therefore, a negotiation objective, which is based on a specific function or action, SHOULD be organized as a single GDNP option. It is NOT RECOMMENDED to organize multiple negotiation objectives into a single option, nor to split a single function or action into multiple negotiation objectives.
A synchronization objective SHOULD also be organized as a single GDNP option.
Some objectives will support more than one operational mode. An example is a negotiation objective with both a "dry run" mode (where the negotiation is to find out whether the other end can in fact make the requested change without problems) and a "live" mode. Such modes will be defined in the specification of such an objective. These objectives SHOULD include a "flags" octet, with bits indicating the applicable mode(s).
An objective may have multiple parameters. Parameters can be categorized into two classes: the obligatory ones presented as fixed fields; and the optional ones presented in TLV sub-options or some other form of data structure. The format might be inherited from an existing management or configuration protocol, the objective option acting as a carrier for that format. The data structure might be defined in a formal language, but that is a matter for the specifications of individual objectives. There are many candidates, according to the context, such as ABNF, RBNF, XML Schema, possibly YANG, etc. The GDNP protocol itself is agnostic on these questions.
It is NOT RECOMMENDED to split parameters in a single objective into multiple options, unless they have different response periods. An exception scenario may also be described by split objectives.
Option codes 128~159 have been reserved for vendor specific options. Multiple option codes have been assigned because a single vendor might use multiple options simultaneously. These vendor specific options are highly likely to have different meanings when used by different vendors. Therefore, they SHOULD NOT be used without an explicit human decision and SHOULD NOT be used in unmanaged networks such as home networks.
There is one general requirement that applies to all vendor specific options. They MUST start with a field that uniquely identifies the enterprise that defines the option, in the form of a registered 32 bit Private Enterprise Number (PEN) [I-D.liang-iana-pen]. There is no default value for this field. Note that it is not used during discovery. It MUST be verified during negotiation or synchronization.
In the case of a vendor-specific objective, the loop count and flags, if present, follow the PEN.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_vendor | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PEN | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | loop-count | flags | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ value | . (variable length) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option code 176~191 have been reserved for experimental options. Multiple option codes have been assigned because a single experiment may use multiple options simultaneously. These experimental options are highly likely to have different meanings when used for different experiments. Therefore, they SHOULD NOT be used without an explicit human decision and SHOULD NOT be used in unmanaged networks such as home networks.
These option codes are also RECOMMENDED for use in documentation examples.
There are various design questions that are worthy of more work in the near future, as listed below (statically numbered for reference purposes):
It is obvious that a successful attack on negotiation-enabled nodes would be extremely harmful, as such nodes might end up with a completely undesirable configuration that would also adversely affect their peers. GDNP nodes and messages therefore require full protection.
- Authentication
- Privacy and confidentiality
- DoS Attack Protection
- Security during bootstrap and discovery
Section 3.4 defines the following multicast addresses, which have been assigned by IANA for use by GDNP:
Section 3.4 defines the following UDP and TCP port, which has been assigned by IANA for use by GDNP:
This document defined a new General Discovery and Negotiation Protocol. The IANA is requested to create a new GDNP registry. The IANA is also requested to add two new registry tables to the newly-created GDNP registry. The two tables are the GDNP Messages table and GDNP Options table.
Initial values for these registries are given below. Future assignments are to be made through Standards Action or Specification Required [RFC5226]. Assignments for each registry consist of a type code value, a name and a document where the usage is defined.
GDNP Messages table. The values in this table are 16-bit unsigned integers. The following initial values are assigned in Section 3.7 in this document:
Type | Name | RFCs
---------+-----------------------------+------------
0 |Reserved | this document
1 |Discovery | this document
2 |Response | this document
3 |Request Message | this document
4 |Negotiation Message | this document
5 |Negotiation-end Message | this document
6 |Confirm-waiting Message | this document
GDNP Options table. The values in this table are 16-bit unsigned integers. The following initial values are assigned in Section 3.8 and Section 3.9.1 in this document:
Type | Name | RFCs
---------+-----------------------------+------------
0 |Reserved | this document
1 |Divert Option | this document
2 |Accept Option | this document
3 |Decline Option | this document
4 |Waiting Time Option | this document
5 |Certificate Option | this document
6 |Signature Option | this document
7 |Device IPv4 Address Option | this document
8 |Device IPv6 Address Option | this document
9 |Device FQDN Option | this document
10~63 |Reserved for future GDNP |
|General Options |
64~127 |Reserved for future GDNP |
|Objective Options |
128~159 |Vendor Specific Options | this document
160~175 |Reserved for future use |
176~191 |Experimental Options | this document
192~65535|Reserved for future use |
The IANA is also requested to create two new registry tables in the GDNP Parameters registry. The two tables are the Hash Algorithm for GDNP table and the Signature Algorithm for GDNP table.
Initial values for these registries are given below. Future assignments are to be made through Standards Action or Specification Required [RFC5226]. Assignments for each registry consist of a name, a value and a document where the algorithm is defined.
Hash Algorithm for GDNP. The values in this table are 16-bit unsigned integers. The following initial values are assigned for Hash Algorithm for GDNP in this document:
Name | Value | RFCs
---------------------+-----------+------------
Reserved | 0x0000 | this document
SHA-1 | 0x0001 | this document
SHA-256 | 0x0002 | this document
Signature Algorithm for GDNP. The values in this table are 16-bit unsigned integers. The following initial values are assigned for Signature Algorithm for GDNP in this document:
Name | Value | RFCs
---------------------+-----------+------------
Reserved | 0x0000 | this document
RSASSA-PKCS1-v1_5 | 0x0001 | this document
A major contribution to the original version of this document was made by Sheng Jiang.
Valuable comments were received from Michael Behringer, Zongpeng Du, Yu Fu, Zhenbin Li, Dimitri Papadimitriou, Michael Richardson, Markus Stenberg, Rene Struik, Dacheng Zhang, and other participants in the NMRG research group and the ANIMA working group.
This document was produced using the xml2rfc tool [RFC2629].
draft-carpenter-anima-discovery-negotiation-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-discovery-negotiation-protocol-01, restructured the logical flow of the document, updated to describe synchronization completely, add unsolicited responses, numerous corrections and clarifications, expanded future work list, 2015-01-06.
draft-carpenter-anima-discovery-negotiation-protocol-00, combination of draft-jiang-config-negotiation-ps-03 and draft-jiang-config-negotiation-protocol-02, 2014-10-08.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC3174] | Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1 (SHA1)", RFC 3174, September 2001. |
| [RFC4086] | Eastlake, D., Schiller, J. and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, June 2005. |
| [RFC5280] | Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R. and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, May 2008. |
| [RFC6206] | Levis, P., Clausen, T., Hui, J., Gnawali, O. and J. Ko, "The Trickle Algorithm", RFC 6206, March 2011. |
This appendix discusses various existing protocols with properties related to the above negotiation and synchronisation requirements. The purpose is to evaluate whether any existing protocol, or a simple combination of existing protocols, can meet those requirements.
Numerous protocols include some form of discovery, but these all appear to be very specific in their applicability. Service Location Protocol (SLP) [RFC2608] provides service discovery for managed networks, but requires configuration of its own servers. DNS-SD [RFC6763] combined with mDNS [RFC6762] provides service discovery for small networks with a single link layer. [I-D.ietf-dnssd-requirements] aims to extend this to larger autonomous networks. However, both SLP and DNS-SD appear to target primarily application layer services, not the layer 2 and 3 objectives relevant to basic network configuration.
Routing protocols are mainly one-way information announcements. The receiver makes independent decisions based on the received information and there is no direct feedback information to the announcing peer. This remains true even though the protocol is used in both directions between peer routers; there is state synchronization, but no negotiation, and each peer runs its route calculations independently.
Simple Network Management Protocol (SNMP) [RFC3416] uses a command/response model not well suited for peer negotiation. Network Configuration Protocol (NETCONF) [RFC6241] uses an RPC model that does allow positive or negative responses from the target system, but this is still not adequate for negotiation.
There are various existing protocols that have elementary negotiation abilities, such as Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [RFC3315], Neighbor Discovery (ND) [RFC4861], Port Control Protocol (PCP) [RFC6887], Remote Authentication Dial In User Service (RADIUS) [RFC2865], Diameter [RFC6733], etc. Most of them are configuration or management protocols. However, they either provide only a simple request/response model in a master/slave context or very limited negotiation abilities.
There are also signalling protocols with an element of negotiation. For example Resource ReSerVation Protocol (RSVP) [RFC2205] was designed for negotiating quality of service parameters along the path of a unicast or multicast flow. RSVP is a very specialised protocol aimed at end-to-end flows. However, it has some flexibility, having been extended for MPLS label distribution [RFC3209]. A more generic design is General Internet Signalling Transport (GIST) [RFC5971], but it is complex, tries to solve many problems, and is also aimed at per-flow signalling across many hops rather than at device-to-device signalling. However, we cannot completely exclude extended RSVP or GIST as a synchronization and negotiation protocol. They do not appear to be directly useable for peer discovery.
We now consider two protocols that are works in progress at the time of this writing. Firstly, RESTCONF [I-D.ietf-netconf-restconf] is a protocol intended to convey NETCONF information expressed in the YANG language via HTTP, including the ability to transit HTML intermediaries. While this is a powerful approach in the context of centralised configuration of a complex network, it is not well adapted to efficient interactive negotiation between peer devices, especially simple ones that are unlikely to include YANG processing already.
Secondly, we consider Distributed Node Consensus Protocol (DNCP) [I-D.ietf-homenet-dncp]. This is defined as a generic form of state synchronization protocol, with a proposed usage profile being the Home Networking Control Protocol (HNCP) [I-D.ietf-homenet-hncp] for configuring Homenet routers.
Specific features of DNCP include:
Clearly DNCP does not meet the needs of a general negotiation protocol, especially in its HNCP profile due to the limitation to link-local messages and its strict dependency on IPv6. However, at the minimum it is a very interesting test case for this style of interaction between devices without needing a central authority.
A proposal was made some years ago for an IP based Generic Control Protocol (IGCP) [I-D.chaparadza-intarea-igcp]. This was aimed at information exchange and negotiation but not directly at peer discovery. However, it has many points in common with the present work.
None of the above solutions appears to completely meet the needs of generic discovery, state synchronization and negotiation in a single solution. Neither is there an obvious combination of protocols that does so. Therefore, this document proposes the design of a protocol that does meet those needs. However, this proposal needs to be compared with alternatives such as extension and adaptation of GIST or DNCP, or combination with IGCP.