| Internet Engineering Task Force | S. Jiang |
| Internet-Draft | Y. Yin |
| Intended status: Informational | Huawei Technologies Co., Ltd |
| Expires: July 22, 2014 | B. E. Carpenter |
| Univ. of Auckland | |
| January 18, 2014 |
Network Configuration Negotiation Problem Statement and Requirements
draft-jiang-config-negotiation-ps-02
This document describes a problem statement and general requirements for distributed autonomous configuration of multiple aspects of networks, in particular carrier networks. The basic model is that network elements need to negotiate configuration settings with each other to meet overall goals. The document describes a generic negotiation behavior model. The document also reviews whether existing management and configuration protocols may be suitable for autonomic networks.
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The success of IP and the Internet has made the network model very complicated, and networks have become larger and larger. The network of a large ISP typically contains more than a hundred thousand network devices which play many roles. The initial setup configuration, dynamic management and maintenance, troubleshooting and recovery of these devices have become a huge outlay for network operators. Particularly, these devices are managed by many different staff requiring very detailed training and skills. The coordination of these staff is also difficult and often inefficient. There are therefore increased requirements for autonomy in the networks. [I-D.boucadair-network-automation-requirements] is one of the attempts to describe such requirements. It listed a "requirement for a protocol to convey configuration information towards the managed entities". However, this document is going further by requiring a configuration negotiation protocol rather than only unidirectional provisioning.
Autonomic operation means network devices could decide configurations by themselves [refer to forthcoming NMRG drafts]. There are already many existing internal implementations or algorithms for a network device to decide or compute its configuration according to its own status, often referred to as device intelligence. In one particular area, routing protocols, distributed autonomous configuration is a well established mechanism. The question is how to extend autonomy to cover all kinds of configuration, not just routing tables.
However, in order to make right or good decisions, the network devices need to know more information than just routes from the relevant or neighbor devices. There are dependencies between such information and configurations. Currently, most of these configurations currently require centralised manual coordination. The basic model for this document is that in an autonomous network, devices will need to negotiate directly with one another to provide this coordination.
Today, there is no generic negotiation protocol that can be used to control decision processes among distributed devices or between networks. Proprietary network management systems are widely used but tend to be hierarchical systems ultimately relying on a console operator and a central database. An autonomous system needs to be less hierarchical and with less dependence on an operator. This requires network elements to negotiate directly with each other, with an absolute minimum or zero configuration data at the installation stage.
This document analyzes the requirements for a generic negotiation protocol and the application scenarios, then gives considerations for detailed technical requirements for designing such a protocol. Some existing protocols are also reviewed as part of the analysis. A protocol behavior model, which may be used to define such a negotiation protocol, is also described.
Routing protocols are a typical autonomic model based on distributed devices. But routing is mainly one-way information announcement (in both directions), rather than bi-directional negotiation. Its only focus is reachability. The future networks need to be able to manage many more dimensions of the network, such as power saving, load balancing, etc. The current routing protocols only show simple link status, as up or down. More information, such as latency, congestion, capacity, and particularly available throughput, is very helpful to get better path selection and utilization rate.
A negotiation model with no human intervention is needed when the coordination of multiple devices can provide better overall network performance.
A negotiation model provides a possibility for forecasting. A "dry run" becomes possible before the concrete configuration takes place.
Another area is tunnel management, with automatic setup, maintenance, and removal. A related area is ad hoc routes, without encapsulation, to handle specific traffic flows (which might be regarded as a form of software defined networking).
Negotiation of security mechanisms, for example to determine the strongest possible protection for a given link, is another example.
When a new user or device comes online, it might be necessary to set up resources on multiple relevant devices, coordinated and matched to each other so that there is no wasted resource. Security settings might also be needed to allow for the new user/device.
Status information and traffic metrics need to be shared between nodes for dynamic adjustment of resources.
Troubleshooting should be as autonomous as possible. Although it is far from trivial, there is a need to detect the "real" breakdown amongst many alerts, and then take action to reconfigure the relevant devices. Again, routing protocols have done this for many years, but in an autonomous network it is not just routing that needs to reconfigure itself after a failure.
The typical scenario is that there is a new access gateway, which could be a wireless base station, WiFi hot spot, Data Center switch, VPN site switch, enterprise CE, home gateway, etc. When it is plugged into the network, bi-direction configuration/control is needed. The upstream network needs to configure the device, its delegated prefix(es), DNS server, etc. For this direction, DHCP might be suitable and sufficient. However, there is another direction: the connection of downstream devices also needs to trigger the upstream devices, for example the provider edge, to create a corresponding configuration, by setting up a new tunnel, service, authentication, etc.
Furthermore, after the communication between gateway and provider has been established, the devices would like to optimize their configurations interactively according to dynamic link status or performance measurements, power consumption, etc. For dynamic management and maintenance, there are many other network events that downstream network devices may need to report to upstream network devices and then initiate some configuration change on these upstream devices. Currently, these kinds of synchronizing operations require the involvement of human operators.
Similar requirements can also appear between other types of downstream and upstream network devices.
Within a large network, in many segments, there are network devices that are in equivalent positions. They have a peer rather than hierarchical relationship. There may be many horizontal traffic flows or tunnels between them. In order to make these connections efficient, their configurations (for example, quality of service parameters) have to match each other. Any change of a device's configuration may require synchronizing with its peer network devices.
However, in many cases the peer network devices may not be able to make the exact changes as requested. Instead, another slightly different change may be the best choice for optimal performance. In order to decide on this best choice, multiple rounds of information exchange between peers may be necessary. This should be done without requiring the involvement of human operators. To provide this ability, a mechanism for network devices to be able to negotiate with each other is needed.
A network may announce some information about its internal capabilities to connected peer networks, so that the peer networks can react accordingly. BGP routing information is a simple example.
Beyond reachability, more information may enable better coordination among networks. Examples include traffic engineering among multiple connections between two networks, particularly when these connections are geographically distributed; dynamic capacity adjustment to match changing traffic from a peer network; dynamic establishment and adjustment of differentiated service classes to support Service Level Agreements; and so on.
In distributed routers, many data such as status indicators or traffic measurements are dynamically changing. These may be the triggers for subsequent negotiation. For example, assume there are two routers A and B sharing traffic load. Router A may request the traffic situation of router B, then start negotiation, such as requesting router B to handle all the traffic so that router A can enter power-saving mode. Another example is that a device may request its neighbor to send a forecast or dry-run result based on a given potential configuration change. Then, the initiating router can evaluate whether the potential configuration change would meet its original target.
Even with autonomous negotiation, some initial configuration data cannot be avoided in some devices. A design goal is to reduce this to an absolute minimum. This information may have to be pre-configured on the device before it has been deployed physically, and is typically static. A preliminary list of unavoidable configuration data is:
Ideally, everything else (topology, link capacity, address prefixes, shared resources, customer authentication and authority, etc.) will be discovered or negotiated autonomously according to general policy for various negotiated objective.
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 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 Configure 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 yet exclude extended RSVP or GIST as a negotiation protocol.
It is worth noting that some of the above protocols have either an explicit information model describing their messages, or at least a flexible and extensible message format. A negotiation protocol will require such capabilities. One design consideration is whether to adopt an existing information model or to design a new one. Another consideration is whether to be able to carry some or all of the message formats used by the above protocols.
This section describes a behavior model and some considerations for designing a generic negotiation protocol, which would act as a platform for different negotiation objectives.
This document does not include a detailed threat analysis for autonomous configuration, but it is obvious that a successful attack on autonomic nodes would be extremely harmful, as such nodes might end up with a completely undesirable configuration. A concrete protocol proposal will therefore require a threat analysis, and some form of strong authentication and, if possible, built-in protection against denial of service attacks.
Separation of network devices and user devices may become very helpful in this kind of scenario.
Also, security configuration itself should become autonomic whenever possible. However, in the security area at least, operator override of autonomic configuration must be possible for emergency use.
As noted earlier, 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 autonomous device should be capable of proving its identity and authenticating its messages. One approach would be to use a private/public key pair and sufficiently strong cryptography. Each device would generate its own private key, which is never exported from the device. The device identity and public key would be recorded in a network-wide database. The alternative of using symmetric keys (shared secrets) is less attractive, since it creates a risk of key leakage as well as a key management problem when devices are installed or removed.
Generally speaking, no personal information is expected to be involved in the negotiation protocol, so there should be no direct impact on personal privacy. Nevertheless, traffic flow paths, VPNs, etc. may be negotiated, which could be of interest for traffic analysis. Also, carriers generally want to conceal details of their network topology and traffic density from outsiders. Therefore, since insider attacks cannot be prevented in a large carrier network, the security mechanism for the negotiation protocol needs to provide message confidentiality.
This draft does not request any IANA action.
The authors want to thank Zhenbin Li, Bing Liu for valuable comments.
This document was produced using the xml2rfc tool [RFC2629].
draft-jiang-negotiation-config-ps-02, text improvements, added extra existing protocols, 2014-01-19.
draft-jiang-negotiation-config-ps-01, add more requirements, and add more considerations for behavior model, 2013-10-11.
draft-jiang-negotiation-config-ps-00, original version, 2013-06-29.