Requirements for Client-Facing Interface to Security Controller

Programming security policies in a network has been a fairly complex task that often requires very deep knowledge of developers' specific devices. This has been the biggest challenge for both service providers and enterprises, henceforth named as security administrator in this document. The challenge is amplified due to virtualization because security appliances come in both physical and virtual forms and are supplied by a variety of developers who have their own proprietary interfaces to manage and implement the security policies on their devices. Even if a security administrator deploys a single developer solution with a set of one or more security functions across its entire network, it is difficult to manage security policies due to the complexity of network security features available in the developer devices, and the difficulty in mapping the user intent to developer-specific configurations. The security administrator may use asset of developer-specific APIs or a developer-provided management system that gives some abstraction in the form of GUI to help provision and manage security policies. However, the single developer approach is highly restrictive in today's network for the following reasons: The security administrator cannot rely on a single developer because one developer may not be able keep up to date with the customer security needs or specific deployment models. A large organization may have a presence across different sites and regions; which means, it is not possible to have a complete solution from a single developer due to technical, regulatory or business reasons. If and when the security administrator migrates from one developer to another, it is almost impossible to migrate security policies from one management system to another without complex manual work. Security administrators are implementing various security functions in virtual forms or physical forms to attain the flexibility, elasticity, performance, and operational efficiency they require. Practically, that often requires different sources (developers and open source) that provide the best of breed for any such security function. The security administrator might choose various devices or network services (such as routers, switches, firewall devices, and overlay-networks) as enforcement points for security policies for any reason (such as network design simplicity, cost, most-effective place, scale and performance). In order to ease the deployment of security policies across different developers and devices, the Interface to Network Security Functions (I2NSF) working group in the IETF is defining a client-facing interface from the security controller to clients [I-D. ietf-i2nsf-framework] [I-D. ietf-i2nsf-terminology]. The easiness of deployment should be agnostic to type of device, be it physical or virtual, or type of the policy, be it dynamic or static. Using these interfaces, a user can write any application (e.g. GUI portal, template engine, etc.) to control the implementation of security policies on security functional elements, but this is completely out of scope for the I2NSF working group. This document captures the requirements for the client-facing interface that can be easily used by security administrators without knowledge of specific security devices or features. We refer to this as "user-intent" based interfaces. To further clarify, in the scope of this document, the "user-intent" here does not mean some free-from natural language input or an abstract intent such as "I want my traffic secure" or "I don't want DDoS attacks in my network"; rather the user-intent here means that policies are described using client-oriented expressions such as application names, application groups, device groups, user groups etc. with a vocabulary of verbs (e.g., drop, tap, throttle), prepositions, conjunctions, conditionals, adjectives, and nouns instead of using standard n-tuples from the packet header.

Business Support System Command Line Interface Configuration Management Database Used interchangeably with Service Provider Security Controller or management system throughout this document Create, Retrieve, Update, Delete Firewall Graphical User Interface Intrusion Detection System Intrusion Protection System Lightweight Directory Access Protocol Network Security Function, defined by Operation Support System Role Based Access Control Security Information and Event Management Universal Resource Locator Refers to NSF being instantiated on Virtual Machines

The "Client-Facing Interface" ensures that a security administrator can deploy any device from any developer and still be able to use same consistent interface. In essence, these interfaces provide a management framework to manage security administrator's security policies. Henceforth in this document, we use "security policy management interface" interchangeably when we refer to the client-facing interface.

Traditionally, security policies have been expressed using proprietary interfaces. These interfaces are defined by a developer either based on CLI or a GUI system; but more often these interfaces are built using developer specific networking construct such IP address, protocol and application constructs with L4-L7 information. This requires security operators to translate their oragnzational business objectives into actionable security policies on security device using developers policy constructs. But, this alone is not sufficient to render policies in the network as operator also need to identify the device where the policy need to be applied in a complex network environment with multiple policy enforcement points. The User-intent based framework defines constructs such as user-group, application-group, device-group and location group. The security operator would use these constructs to express a security policy instead of proprietary constructs. The policy defined in such a manner is referred to user-intent based policies in this draft. The idea is to enable security operator to use constructs they knows best in expressing security policies; which simplify their tasks and help in avoiding human errors in complex security provisioing.

The basic rules in defining the client-facing interfaces are as following: Agnostic of network topology and NSF location in the network. Agnostic to the features and capabilities supported in NSFs. Agnostic to the resources available in NSFs or resources available for various features/capabilities. Agnostic to the network function type, be it stateful firewall, IDP, IDS, Router, Switch. Declarative/Descriptive model instead of Imperative/Prescriptive model - What security policies need to enforce (declarative) instead of how they would be actually implemented (imperative). Agnostic of developer, implementation and form-factor (physical, virtual). Agnostic to how NSF is implemented and its hosting environment. Agnostic to how NSF becomes operational - Network connectivity and other hosting requirements Agnostic to NSF control plane implementation (if there is one) E.g., cluster of NSF active as one unified service for scale and/ or resilience. Agnostic to NSF data plane implementation i.e. Encapsulation, Service function chains.

This document does not describe requirements for NSF-facing interface; they are expected to be defined in a separate draft. This draft does not mandate a specific deployment model but rather shows how client interfaces remain the same and interact with the overall security framework from security administrator's perspective. Traditionally, medium and larger operators deploy management systems to manage their statically-defined security policies. This approach may not be suitable nor sufficient for modern automated and dynamic data centers that are largely virtualized and rely on various management systems and controllers to dynamically implement security policies over any types of resources. There are two different deployment models in which the client-facing interface referred to in this document could be implemented. These models have no direct impact on the client-facing interface, but illustrate the overall security policy and management framework and where the various processing functions reside. These models are: Management without an explicit management system for control of devices and NSFs. In this deployment, the security controller acts as a NSF policy management system that takes information passed over the client security policy interface and translates into data on the I2NSF southbound interface. The I2NSF interfaces are implemented by security device/function developers. This would usually be done by having an I2NSF agent embedded in the security device or NSF. This deployment model is shown in .

RESTful API SUPA or I2NSF Policy Management ^ Client-facing | Security Policy Interface | (Independent of individual | NSFs, devices,and developers)| | ------------------------------ | | | Security Controller | | | ------------------------------ | ^ Southbound Security | I2NSF | Capability Interface | NSF-facing | (Specific to NSFs) | Interface | .............................. | | v | ------------- ------------- | I2NSF Agent | | I2NSF Agent | |-------------| |-------------| | |---| | | NSF | | NSF | NSFs | | | | (virtual -------------\ /------------- and | \ / | physical) | X | | / \ | -------------/ \------------- | I2NSF Agent | | I2NSF Agent | |-------------| |-------------| | |---| | | NSF | | NSF | | | | | ------------- ------------- Management with an explicit management system for control of devices and NSFs. This model is similar to the model above except that security controller interacts with a dedicated management system which could either proxy I2NSF southbound interfaces or could provide a layer where security devices or NSFs do not support an I2NSF agent to process I2NSF southbound interfaces. This deployment model is shown in .

RESTful API SUPA or I2NSF Policy Management ^ Client-facing | Security Policy Interface | (Independent of individual | NSFs,devices,and developers) | | ------------------------------ | | | Security Controller | | | ------------------------------ | ^ Southbound Security | I2NSF | Capability Interface | NSF-facing | (Specific to NSFs) | Interface | .............................. | | v | ------------------------------ | | | I2NSF Proxy Agent / | | Management System | | | ------------------------------ | ^ | Proprietary | | Functional | | Interface | .............................. | | v | ------------- ------------- | |---| | | NSF | | NSF | NSFs | | | | (virtual -------------\ /------------- and | \ / | physical) | X | | / \ | -------------/ \------------- | |---| | | NSF | | NSF | | | | | ------------- ------------- Although the deployment models discussed here don't necessarily affect the client security policy interface, they do give an overall context for defining a security policy interface based on abstraction.

As stated in the guiding principles for defining I2NSF client-facing interface, the security policies and the client-facing interface shall be defined from a user/client perspective and abstracted away from the type of NSF, NSF specific implementation, controller implementation, NSF topology, NSF interfaces, controller southbound interfaces. Thus, the security policy definition shall be declarative, expressing the user/client intent, and driven by how security administrators view security policies from the definition, communication and deployment perspective. The security controller's implementation is outside the scope of this document and the I2NSF working group. At a high level, the requirements for the client-facing interface in order to express and build security policies are as follows: Multi-Tenancy Authentication and Authorization Role-Based Access Control (RBAC) Protection from Attacks Protection from Misconfiguration Policy Lifecycle Management Dynamic Policy Endpoint Groups Policy Rules Policy Actions Generic Policy Model Policy Conflict Resolution Backward Compatibility Third-Party Integration Telemetry Data The above constructs are by no means a complete list and may not be sufficient for all use-cases and all operators, but should be a good start for a wide variety of use-cases in both Service Provider networks and Enterprise networks.

A security administrator that uses security policies may have internal tenants and would like to have a framework wherein each tenant manages its own security policies to provide isolation across different tenants. An operator may be a cloud service provider with multi-tenant deployments where each tenant is a different organization and must allow complete isolation across different tenants. It should be noted that tenants in turn can have their own tenants, so a recursive relation exists. For instance, a tenant in a cloud service provider may have multiple departments or organizations that need to manage their own security rules. Some key concepts are listed below and used throughout the document hereafter: An entity that owns and manages the security Policies applied on itself. A user authorized to manage the security policies for a Policy-Tenant. A user within a Policy-Tenant who is authorized to access certain resources of that tenant according to the security policies of the Policy-Tenant. A collection of Policy-Users. This group identifies a set of users based on a policy tag or on static information. The tag to identify the user is dynamically derived from systems such as Active Directory or LDAP. For example, an operator may have different user-groups, such as HR-users, Finance-users, Engineering-users, to classify a set of users in each department.

Security administrators MUST authenticate to and be authorized by security controller before they are able to issue control commands and any policy data exchange commences. There must be methods defined for Policy-Administrator be authenticated and authorized to use the security controller. There are several authentication methods available such as OAuth, XAuth and X.509 certificate based. The authentication scheme between Policy-Administrator and security controller may also be mutual instead of one-way. Any specific method may be determined based on organizational and deployment needs and outside the scope of I2NSF. In addition, there must be a method to authorize the Policy-Administrator for performing certain action. It should be noted that, depending on the deployment model, Policy-Administrator authentication and authorization to perform actions communicated to the controller could be performed as part of a portal or another system prior to communication the action to the controller.

Policy-Authorization-Role represents a role assigned to a Policy-User or Policy-User Group that determines whether the user or the user-group has read-write access, read-only access, or no access for certain resources. A User or a User-Group can be mapped to a Policy-Authorization- Role using an internal or external identity provider or mapped statically.

There Must be protections from attacks, malicious or otherwise, from clients or a client impersonator. Potential attacks could come from a botnet or a host or hosts infected with virus or some unauthorized entity. It is recommended that security controller use adedicated IP interface for client-facing communications and those communications should be carried over an isolated out-of-band network. In addition, it is recommended that traffic between clients and security controllers be encrypted. Furthermore, some straightforward traffic/session control mechanisms (i.e., Rate-limit, ACL, White/Black list) can be employed on the security controller to defend against DDoS flooding attacks.

There Must be protections from mis-configured clients, unintentional or otherwise. System and policy validations should be implemented. Validation may be based on a set of default parameters or custom tuned thresholds such as # of policy changes submitted; # of objects requested in given time interval, etc.

In order to provide more sophisticated security framework, there should be a mechanism to express that a policy becomes dynamically active/enforced or inactive based on either security administrator intervention or an event. One example of dynamic policy management is when the security administrator pre-configures all the security policies, but the policies get activated/enforced or deactivated based on dynamic threats faced by the security administrator. Basically, a threat event may activate certain inactive policies, and once a new event indicates that the threat has gone away, the policies become inactive again. There are four models for dynamically activating policies: o The policy may be dynamically activated by the I2NSF client or associated management entity, and dynamically communicated over the I2NSF client-facing interface to the controller to program I2NSF functions using the I2NSF NSF-facing interface o The policy may be pulled dynamically by the controller upon detecting an event over the I2NSF monitoring interface o The policy may be statically pushed to the controller and dynamically programmed on the NSFs upon potentially detecting another event o The policy can be programmed in the N2SFs functions, and activated/deactivated upon policy attributes, like time or admin enforced. The client-facing interface should support the following policy attributes for policy enforcement: The policy, once configured, remains active/enforced until removed by the security administrator. The policy configuration specifies the time profile that determines when policy is activated/enforced. Otherwise, it is de-activated. The policy configuration specifies the event profile that determines when policy is activated/enforced. It also specifies the duration attribute of that policy once activated based on event. For instance, if the policy is activated upon detecting an application flow, the policy could be de-activated when the corresponding session is closed or the flow becomes inactive for certain time. A policy could be a composite policy, that is composed of many rules, and subject to updates and modification. For policy maintenance purposes, enforcement, and auditability, it becomes important to name and version the policies. Thus, the policy definition SHALL support policy naming and versioning. In addition, the i2NSF client-facing interface SHALL support the activation, deactivation, programmability, and deletion of policies based on name and version. In addition, it Should support reporting on the state of policies by name and version. For instance, a client may probe the controller about the current policies enforced for a tenant and/or a sub-tenant (organization) for auditability or verification purposes.

When the security administrator configures a security policy, the intention is to apply this policy to certain subsets of the network. The subsets may be identified based on criteria such as users, devices, and applications. We refer to such a subset of the network as a "Policy Endpoint Group". One of the biggest challenges for a security administrator is how to make sure that security policies remain effective while constant changes are happening to the "Policy Endpoint Group" for various reasons (e.g., organizational changes). If the policy is created based on static information such as user names, application, or network subnets, then every time that this static information changes policies would need to be updated. For example, if a policy is created that allows access to an application only from the group of Human Resource users (the HR-users group), then each time the HR- users group changes, the policy needs to be updated. Changes to policy could be highly taxing to the security administrator for various operational reasons. The policy management framework must allow "Policy Endpoint Group" to be dynamic in nature so that changes to the group (HR-users in our example) automatically result in updates to its content. We call these dynamic Policy Endpoint Groups "Meta-data Driven Groups". The meta-data is a tag associated with endpoint information such as users, applications, and devices. The mapping from meta-data to dynamic content could come either from standards-based or proprietary tools. The security controller could use any available mechanisms to derive this mapping and to make automatic updates to the policy content if the mapping information changes. The system SHOULD allow for multiple, or sets of tags to be applied to a single network object. The client-facing policy interface must support endpoint groups for user-intent based policy management. The following meta-data driven groups MAY be used for configuring security polices: This group identifies a set of users based on a tag or on static information. The tag to identify user is dynamically derived from systems such as Active Directory or LDAP. For example, an operator may have different user-groups, such as HR-users, Finance-users, Engineering-users, to classify a set of users in each department. This group identifies a set of devices based on a tag or on static information. The tag to identify device is dynamically derived from systems such as configuration mannagement database (CMDB). For example, a security administrator may want to classify all machines running one operating system into one group and machines running another operating system into another group. This group identifies a set of applications based on a tag or on static information. The tag to identify application is dynamically derived from systems such as CMDB. For example, a security administrator may want to classify all applications running in the Legal department into one group and all applications running under a specific operating system into another group. In some cases, the application can semantically associated with a VM or a device. However, in other cases, the application may need to be associated with a set of identifiers (e.g., transport numbers, signature in the application packet payload) that identify the application in the corresponding packets. The mapping of application names/tags to signatures in the associated application packets should be defined and communicated to the NSF. The client-facing Interface shall support the communication of this information. This group identifies a set of location tags. Tag may correspond 1:1 to location. The tag to identify location is either statically defined or dynamically derived from systems such as CMDB. For example, a security administrator may want to classify all sites/locations in a geographic region as one group.

The security policy rules can be as simple as specifying a match for the user or application specified through "Policy Endpoint Group" and take one of the "Policy Actions" or more complicated rules that specify how two different "Policy Endpoint Groups" interact with each other. The client-facing interface must support mechanisms to allow the following rule matches. Policy Endpoint Groups: The rule must allow a way to match either a single or a member of a list of "Policy Endpoint Groups". There must be a way to express a match between two "Policy Endpoint Groups" so that a policy can be effective for communication between two groups. The rule must allow a way to express whether the security administrator wants to match the "Policy Endpoint Group" as the source or destination. The default should be to match both directions if the direction rule is not specified in the policy. The rule should allow the security administrator to express a match for threats that come either in the form of feeds (such as botnet feeds, GeoIP feeds, URL feeds, or feeds from a SIEM) or speciality security appliances. Threats could be identified by Tags/names in policy rules. The tag is a label of one or more event types that may be detected by a threat detection system. The threat could be from malware and this requires a way to match for virus signatures or file hashes.

The security administrator must be able to configure a variety of actions within a security policy. Typically, security policy specifies a simple action of "deny" or "permit" if a particular condition is matched. Although this may be enough for most of the simple policies, the I2NSF client-facing interface must also provide a more comprehensive set of actions so that the interface can be used effectively across various security functions. Policy action MUST be extensible so that additional policy action specifications can easily be added. The following list of actions SHALL be supported: This action means continue processing the next rule or allow the packet to pass if this is the last rule. This is often a default action. This action means stop further packet processing and drop the packet. This action means stop further packet processing, drop the packet, and drop connection (for example, by sending a TCP reset). This action means create a log entry whenever a rule is matched. This action means that whenever a new connection is established it should be authenticated. This action may be relevant for event driven policy where certain events would activate a configured policy that quarantines or redirects certain packets or flows. The redirect action must specify whether the packet is to be tunneled and in that case specify the tunnel or encapsulation method and destination identifier. This action creates a Netflow record; Need to define Netflow server or local file and version of Netflow. This action counts the packets that meet the rule condition. This action encrypts the packets on an identified flow. The flow could be over an Ipsec tunnel, or TLS session for instance. This action decrypts the packets on an identified flow. The flow could be over an Ipsec tunnel, or TLS session for instance. This action defines shaping a flow or a group of flows that match the rule condition to a designated traffic profile. This action defines traffic that matches the rule condition by a designated DSCP value and/or VLAN 802.1p Tag value. Instantiate a NSF with predefined profile. A NSF can be any of FW, LB, IPS, IDS, honeypot, or VPN, etc. This action optimize packet delivery using a set of predefined packet optimization methods. This action load balance connections based on predefined LB schemes or profiles. The policy actions should support combination of terminating actions and non-terminating actions. For example, Syslog and then Permit; Count and then Redirect. Policy actions SHALL support any L2, L3, L4-L7 policy actions.

Client-facing interface SHALL provide a generic metadata model that defines once and then be used by appropriate model elements any times, regardless of where they are located in the class hierarchy, as necessary. Client-facing interface SHALL provide a generic context model that enables the context of an entity, and its surrounding environment, to be measured, calculated, and/or inferred. Client-facing interface SHALL provide a generic policy model that enables context-aware policy rules to be defined to change the configuration and monitoring of resources and services as context changes.

Client-facing interface SHALL be able to detect policy "conflicts", and SHALL specify methods on how to resolve these "conflicts" For example: two clients issues conflicting set of security policies to be applied to the same Policy Endpoint Group.

It MUST be possible to add new capabilities to client-facing interface in a backward compatible fashion.

The security policies in the security administrator's network may require the use of specialty devices such as honeypots, behavioral analytics, or SIEM in the network, and may also involve threat feeds, virus signatures, and malicious file hashes as part of comprehensive security policies. The client-facing interface must allow the security administrator to configure these threat sources and any other information to provide integration and fold this into policy management.

One of the most important aspect of security is to have visibility into the networks. As threats become more sophisticated, the security administrator must be able to gather different types of telemetry data from various devices in the network. The collected data could simply be logged or sent to security analysis engines for behavioral analysis, policy violations, and for threat detection. The client-facing interface MUST allow the security administrator to collect various kinds of data from NSFs. The data source could be syslog, flow records, policy violation records, and other available data. Detailed client-facing interface telemetry data should be available between clients and security controllers. Clients should be able to subscribe and receive these telemetry data. client should be able to receive notifications when a policy is dynamically updated.

The client-facing interface must support a version number for each RESTful API. This is very important because the client application and the controller application will most likely come from different developers. Even if the developer is same, it is hard to imagine that two different applications would be released in lock step. Without API versioning, it is hard to debug and figure out issues if application breaks. Although API versioning does not guarantee that applications will always work, it helps in debugging if the problem is caused by an API mismatch.

Abstraction and standardization of the client-facing interface is of tremendous value to security administrators as it gives them the flexibility of deploying any developers' NSF without needing to redefine their policies or change the client interface. However this might also look like as an obstacle to innovation. If an NSF developer comes up with new feature or functionality that can't be expressed through the currently defined client-facing interface, there must be a way to extend existing APIs or to create a new API that is relevant for that NSF developer only.

The APIs for client interface must be derived from the YANG based data model. The YANG data model for client interface must capture all the requirements as defined in this document to express a security policy. The interface between a client and controller must be reliable to ensure robust policy enforcement. One such transport mechanism is RESTCONF that uses HTTP operations to provide necessary CRUD operations for YANG data objects, but any other mechanism can be used.

The client-facing interface must allow the security administrator to collect various alarms and events from the NSF in the network. The events and alarms may be either related to security policy enforcement or NSF operation. The events and alarms could also be used as a input to the security policy for autonomous handling.

The client-facing interface must allow the security administrator to pass any additional metadata that a user may want to provide for a security policy e.g. certain security policy needs to be applied only on linux machine or windows machine or that a security policy must be applied on the device with Trusted Platform Module chip.

The client-facing interface must allow the security administrator the ability to test the security policies before the policies are actually applied e.g. a user may want to verify if a policy creates potential conflicts with the existing policies or whether a certain policy can be implemented. The test interface provides such capabilities without actually applying the policies.

This document requires no IANA actions. RFC Editor: Please remove this section before publication.

The editors would like to thank Adrian Farrel for helpful discussions and advice.