Software-Defined Networking (SDN)-based IPsec Flow Protection

Software-Defined Networking (SDN) is an architecture that enables users to directly program, orchestrate, control and manage network resources through software. SDN paradigm relocates the control of network resources to a dedicated network element, namely SDN controller. The SDN controller manages and configures the distributed network resources and provides an abstracted view of the network resources to the SDN applications. The SDN application can customize and automate the operations (including management) of the abstracted network resources in a programmable manner via this interface . Typically, traditional IPsec VPN concentrators and, in general, gateways supporting IKE/IPsec, are configured manually. This makes the IPsec security association (SA) management difficult and generates a lack of flexibility, specially if the number of security policies and SAs to handle is high. With the grow of SDN-based scenarios where network resources are deployed in an autonomous manner, a mechanism to manage IPsec SAs according to the SDN architecture becomes more relevant. Thus, the SDN-based service described in this document will autonomously deal with IPsec-based data protection also in such as an autonomous manner. First, this document exposes the requirements to support the protection of data flows using IPsec . We consider two cases: 1) Where the network resource implements the IKE protocol, the IPsec Security Policy Database (SPD) and the Security Association Database (SAD), and the SDN controller is in charge of provisioning with required information both IKE and the SPD in the network resource; 2) Where the SDN controller handles the IPsec SPD and takes the role of an Internet Key Exchange (IKE) entity in the IPsec architecture. In this sense, it will provision the required parameters to create valid entries in the Security Association Database (SAD), which we assumed to be in the data plane. Therefore, the data plane will have only support for IPsec while SPD and IKE functionality is moved to the control plane. In both cases, to carry out this provisioning, an interface/protocol will be required between the SDN controller and the data plane to send: the policies to be applied in the SPD and the credentials for the IKE negotiation (case 1); or the required IPsec SA parameters such as keys, cryptographic algorithms, IP addresses, IPsec protocol (AH or ESP), IPsec protocol mode (tunnel or transport), lifetime of the SA, etc (case 2). An example for case 1 using NETFCONF/YANG can be found in . A YANG model for IPsec can be found in . Second, this document considers two scenarios to manage autonomously IPsec SAs: gateway-to-gateway and host-to-gateway . The gateway-to-gateway scenario shows how flow protection services are useful when data is to be protected across gateways in the network. More precisely, the use case described in depicts how these services could be used to protect IP traffic among various geographically distributed networks under the domain of the same SDN controller. A variant of this scenario is also covered in , where the network devices are under different SDN controllers. The host-to-gateway scenario described in covers the case where one end user belonging to a network wants to access securely its network from another external network. In such a case, an IPsec SA needs to be established between the end user's host and the gateway. In this document, we describe how the SDN controller can still configure automatically the IPsec SA in the gateway but after an IKE negotiation.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119. When these words appear in lower case, they have their natural language meaning.

This document uses the terminology described in , , , , , , and . In addition, the following terms are defined below: Software-Defined Networking: A set of techniques enabling to directly program, orchestrate, control, and manage network resources, which facilitates the design, delivery and operation of network services in a dynamic and scalable manner . Flow / Data Flow: Set of network packets sharing a set of characteristics, for example IP dst/src values or QoS parameters. Network Resources: Network devices that can perform packet forwarding in a network system. The network resources include network switch, router, gateway, VPN concentrators, and similar devices. This document makes no difference if these network devices are physical or virtual. Flow Protection Policy: The set of rules defining the conditions under which a data flow MUST be protected, and the rules that MUST be applied to the specific flow. IKE: Protocol to establish IPsec Security Associations (SAs). It requires information about the required authentication method (i.e. preshared keys), DH groups, modes and algorithms for IKE phase 1, etc. SPD: IPsec Security Policy Database. It includes information about IPsec policies direction (in, out), local and remote addresses, inbound and outboud SAs, etc. SAD: IPsec Security Associations Database. It includes information about IPsec security associations, such as SPI, destination addresses, authentication and encryption algorithms and keys.

Flow-based data protection: SDN-based flow protection services based on IPsec to allow the protection of specific data flows based on defined security policies. Bootstrapping security associations: SDN-based flow protection allow the centralized bootstrapping of IKE credentials (case 1) and IPsec key material for AH and ESP (case 2) to eventually protect specific data flows among network resources and end users.

In this case, the SDN controller is in charge of controlling and applying SPD entries in the network resource. It also has to derive and deliver IKE credentials (for example a pre-shared key) to the network resource for the IKE authentication. With these policies and credentials, the IKE implementation runs to build the IPsec SAs. The application (administrator) will send the IPsec requirements and end points information, and the SDN controller will translate those requirements into SPD Policies that will be installed in the network resource. With that information, the network resources can just run IKE to establish the IPsec SA. shows the different layers and corresponding functionality. Advantages: It is simple since network resources typically have and IKE/IPsec implementations. Disadvantages: 1) IKE implementations needs to renegotiate IPsec SAs upon SPD entries changes without restarting IKE daemon. 2) Data plane more complex.

SDN-based IPsec flow protection services provide dynamic and flexible network resource management to protect data flows among network resources and end users. In order to support this capability in case 1, the following requirements are to be met: The network resource MUST implement IKE, IPsec, SPD and the SADs. It MUST provide an (southbound) interface to configure SPD policies and IKE credentials. A southbound protocol MUST support sending these SPD Policies and IKE Credentials to the network resource. It requires an (northbound) application interface in the SDN controller allowing the management of IPsec Policies. In scenarios where multiple controllers are implicated, SDN-based flow protection service may require a mechanism to discover which SDN controller is controlling a specific network resource.

This section describes the referenced architecture to support SDN- based IPsec flow protection where the SDN controller owns the SPD and the IKE implementation.

As shown in , applications for flow protection run on the top of the SDN controller . When an administrator enforces flow protection policies through an application interface, the SDN controller inserts the corresponding flow protection policies into its Security Policy Database (SPD) to meet such flow protection policies in an autonomous manner. According to these policies, when the controller decides that a flow MUST be protected by means of IPsec, it inserts a new flow entry into the corresponding network resources' flow tables, along with an entry in the Security Associations Database (SAD) including all IPsec parameters needed to protect the flow (keys, ESP or AH, transport or tunnel, ...). This enforcement MAY be triggered by the network resource when it does not know how to handle the IP packet. Basically, it forwards the IP packet to the controller so that it can take a decision based on the SPD. This allow network resources to protect data flows based in rules dynamically enforced by the SDN controller. Advantages: 1) There is clear separation of data plane (IPsec protection per flow) and control plane (IKE and SPD policies). Hence, it allows less complex data planes. 2) IKE does not need to be run in gateway-to-gateway scenario with a single controller (see ). Disadvantages: 1) The overload of IKE negotiation is shifted to the SDN controller. 2) IPSec SPD and SAD management need to be decoupled, changing the traditional paradigm defined in IPsec where SPD and SAD are placed in the network resource

In order to support this capability in case 2, the following requirements are to be met: It requires the provision of flow entries in network resources. Flow entries may need to include fields such as AH or ESP parameters, tunnel or transport mode and crypto material to process an IP packet with IPsec (in the end, the Security Association Database (SADs) is managed by the network resource). In the same way a southbound protocol MUST support sending this information to the network resource. Network resources MUST be capable to protect data flows with IPsec, such as the capability to forward data through an IPsec tunnel. It requires an (northbound) application interface in the SDN controller allowing the management of IPsec policies. In scenarios where multiple controllers are implicated, SDN-based flow protection service may require a mechanism to discover which SDN controller is managing a specific network resource.

According to a Network Security Function (NSF) is a function that ensures "integrity, confidentiality and availability of network communications" among other aspects. As such, the network resource we describe in this document can be considered as a NSF with IPsec support. Additionally, the SDN controller can be considered as a Security controller. In a framework for Interface to Network Security Functions is described. Three possible interfaces are described: Client Facing (service layer) Interface; NSF Facing (capability) Interface and Vendor Facing Interface. and describe the mapping with our use case. In the right side of the figure each entity follows the same terminology than .

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Security Interface | IKE Credential and SPD Policies Distribution| Controller +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NSF Facing (capability) Interface +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Control Support | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Network | IKEv2 | IPsec(SPD) | Security +-------------------------------------------- + Function (NSF) | IPsec (SAD) Data Protection and Forwarding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]>

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Security Interface | IKEv2 | IPsec (SPD) | Controller +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Key Derivation and Distribution | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NSF Facing (capability) Interface +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Control Support | Network +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Security | IPsec (SAD) Data Protection and Forwarding | Function (NSF) +---------------------------------------------+ ]]> NOTE: We believe these use cases can be considered as additional uses cases to the work proposed in though we have found some differences between the mapping to I2NSF we show in this document and that reference. That is something that we will have to analyze in the future.

This section explains three use cases as examples for the SDN-based IPsec Flow Protection Service.

Enterprise A has a headquarter office (HQ) and several branch offices (BO) interconnected through an Internet connection provided by an Internet Service Provicer (ISP). This ISP has deployed a SDN-based architecture to provide connectivity to all its clients, including HQ and BOs, so the HQ is provided with a gateway that acts as a router between Internet and each BO's internal network. Now, Enterprise A requires that all traffic between the HQ and BOs MUST be protected, for example, with confidentiality and integrity. The Entrepise A's administrator has to configure flow protection policies in the ISP's SDN controller, determining that all traffic among Enterprise A's HQ (HQ A) and each BO MUST be protected. Let us assume, for example, with an IPsec ESP tunnel. On the one hand, in case 1, these policies are translated into IPsec SPD entries and the SDN controller enforces these entries in the network resources.

| Translate |--->| South. Prot. | | Protect. Pol. |IPsec Policies| | | | | +--------------+ +--------------+ | | | | | | | | | +--------------------------|-----|-------+ | | | (3) | |--------------------------+ +---| From V V To HQ A +------------------+ +------------------+ BO ------>| GW1 |=============>| GW2 |-------> |IKE/IPsec(SPD/SAD)| |IKE/IPsec(SPD/SAD)| +------------------+ (4) +------------------+ ]]> describes the data and control communication planes in case 1, when a data packet is sent from HQ A with destination BO : The administrator establishes a general Flow Protection Policies. The SDN controller translates into IPsec Policies entries. The SDN Controller looks for the network resources involved (GW1 and GW2) and inserts the IPsec SPD entries in both GW1 and GW2 IPsec SPDs and keys and configuration information related with IKE. All packets belonging to the flow that matches the IPsec SDP inserted by the SDN controller triggers the IKE negotiation in GW1 and GW2 by using the enforced configuration keys and parameters. On the other hand, in case 2, these Flow Protection Policies defined by the administrator are translated into IPsec SPD entries and inserted into the SDN controller that represents the IPsec SPD.

| IPSec |------>| South. Prot. | | | | | (SPD) | | | | | | +-------+ (2) +----------------+ | | | | | | | | | | | (1) | +------------------- | --- | ------------+ | | | | | (3) | | |--------------------+ +---| From | V V To HQ A +----------+ +----------+ BO ------->| GW1 |==================>| GW2 |-------> |IPsec(SAD)| |IPsec(SAD)| +----------+ (4) +----------+ ]]> Assuming that configuration step has happened (0), describes the data and control communication planes in case 2, when a data packet is sent from HQ A with destination BO : When the data packet arrives for first time to the gateway in HQ A (GW1), it sends the packet to the SDN Controller. The SDN Controller looks for security policies in its SPD table and decides that the flow MUST be protected, for example, with IPsec ESP in tunnel mode. The SDN controller derives keys for the IPsec tunnel and enforces them, along with other information required, such as IPsec mode (ESP or AH), into both gateways' IPsec Security Association Database (SAD). All packets belonging to the flow are tunneled between GW1 and GW2 by using the enforced configuration keys and parameters. No need to run IKE between GW1 and GW2. In general (for case 1 and case2), this system presents various advantages to the ISP: (i) it allows to create a security association among two network resources, with only the application of specific security policies at the application layer. Thus, the ISP can manage all security associations in a centralized point and with an abstracted view of the network; (ii) All new resources deployed after the application of the new policies will not need to be manually configured, thus allowing its deployment in an automated manner.

Two organizations, Enterprise A and Enterprise B, have its headquarters interconnected through an Internet connection provided by different ISPs, called ISP_A and ISP_B. They have deployed a SDN-based architecture to provide Internet connectivity to all its clients, so Enterprise A's headquarters is provisioned with a gateway deployed by ISP_A and Enterprise B's headquarters is provisioned with a gateway deployed by ISP_B. Now, these organizations require that all traffic among its headquarters to be protected with confidentiality and integrity, so the ISPs have to configure Flow Protection Policies in their SDN Controllers. Those policies are translated into flow protection policy rules into the SDN Controller's of each ISP, so all traffic exchanged among these headquarters will be protected, for example, by means of an IPsec ESP tunnel.

| SDN | Protect. ---> Controller | (2) | Controller | (1) | | | | +-------------+ +-------------+ | | | (3) (3) | From V V To HQ A +------------------+ +------------------+ BO ------>| GW1 |=============>| GW2 |-------> |IKE/IPsec(SPD/SAD)| |IKE/IPsec(SPD/SAD)| +------------------+ (4) +------------------+ ]]> On the one hand, case 1, describes the data and control plane communications required when a data packet is sent from Enterprise A's HQ (HQ A) to destination Enterprise B's HQ (HQ B): The administrator establishes a general Flow Protection Policies, which the SDN controller translates into IPsec Policies. The ISP_A's SDN Controller realizes that traffic between GW1 and GW2 MUST be protected. Nevertheless, the controller notices that GW2 is under the control of another SDN controller, so it starts negotiations with the other controller to agree on the IPsec SPD policies and IKE credentials for their respective gateway NOTE: This may require extensions in the East/West interface. Then, both SDN controllers enforce the IKE credentials and related parameters and the IPsec SPD Policies entries in their respective gateways. All packets belonging to the flow that matches the IPsec SDP inserted by the SDN controller triggers the IKE negotiation GW1 and GW2 by using the enforced configuration keys and parameters.

Prot. | SDN |<=================>| SDN | Pol.(0)| Controller | (2) | Controller | |IKE/IPsec(SPD)| |IKE/IPsec(SPD)| +--------------+ +--------------+ A | | (1) | | (3) (3) | From | V V To HQ A +-----------+ (4) +-----------+ HQ B --------->| GW1 |====================>| GW2 |-------> |IPsec (SAD)| |IPsec (SAD)| +-----------+ +-----------+ ]]> On the other hand, case 2, describes the data and control plane communications required when a data packet is sent from Enterprise A's HQ (HQ A) to destination Enterprise B's HQ (HQ B): When the data packet arrives for first time to the gateway in Enterprise A's headquarters (GW1), it sends the packet to its SDN Controller. The ISP_A's SDN Controller looks for security policies in its SPD table and decides that the flow between GW1 and GW2 MUST be protected, for example, with IPsec ESP in tunnel mode. Nevertheless, the controller notices that GW2 is under the control of another SDN controller, so it starts negotiations with the other controller in order to generate key material. This could be performed by running IKEv2 (NOTE:more discussion is required). Once the controllers have generated shared key material, both enforce these keys into their respective gateways' Security Association Databases (SAD) along with the IPsec mode and other parameters that may be required. Therefore, all packets belonging to the flow are protected between GW1 and GW2 by using the enforced configuration keys and parameters. In general (case 1 and case 2), this system presents various advantages to both ISPs: (i) it allows to create a security association among two network resources across ISPs, from each ISP point of view, only the application of specific Flow Protection Policies at the application layer is needed, so they can manage all security associations in a centralized point and with an abstracted view of the network; (ii) All new resources deployed after the application of the new policies will not need to be manually configured, thus allowing its deployment in an automated manner.

Alice is a member of Enterprise A who needs to connect to the HQ's internal network. Enterprise A has deployed a IPsec-based VPN concentrator in its HQ to allow members of the organization, like Alice, to connect to the HQ's internal network in a secure manner. Traditionally, VPN concentrators are built as appliances, configured manually to authenticate and establish secure associations with incoming users, for example, by running IKEv2 to establish an IPsec tunnel. With the SDN-base management of IPsec protection service we can automate these configuration. In case 1, as we can see in , the administrator configures a Flow Protection Policy in the SDN controller (1). The SDN controller translates that into IPsec Policies and installs those SPD entries and IKE credentials in the corresponding gateway (VPN concentrator) (2). With those policies and IKE credentials, end user and gateway can negotiate IKE.

| Translate |--->| South. Prot. | | Protect. Pol. |IPsec Policies| | | | | +--------------+ +--------------+ | | | | | (2) | | +--------------------------|-------------+ |-------+ V +----------+ +-------------------+ | End user | | Gateway | To | (Alice) | | (VPN conc.) | HQ | IKE/IPsec|====================>| IKE/IPsec(SPD/SAD)|-------> +----------+ (3) +-------------------+ ]]> In case 2, the role of running IKEv2 now resides in the SDN control plane (i.e. the SDN controller), as we can see in . Here, the gateway forwards IKE packets to the controller. Therefore, the IKEv2 negotiation is performed by the end user and the SDN controller (1), being this fact completely transparent for the end user. Once the IKEv2 negotiation has been successfully completed, new key material is available in the end user and in the SDN controller. This key material, along with other parameters like the IPsec mode, are to be provisioned into the gateway's SAD (2). Now the end user and the gateway share key material, thus being able to establish an IPsec tunnel to protect all traffic among them (3). In general, this feature allows the configuration of network resources such as VPN concentrators as a service, so these could be deployed and disposed as required by policies, such as network load, in an autonomous manner.

| South. Prot.| | | |IPsec(SPD)| | | | | +---------- +-------------+ | | A | | | | | | +------ | ----------- | -----------+ | | (1) | |----- (2) | V +----------+ (1) +---|-----------+ | |<------------------------| | | End user | | Gateway | To | (Alice) | | (VPN conc.) | HQ | IKE/IPsec|====================>| IPsec(SAD) |-------> +----------+ (3) +---------------+ ]]>

TBD.

Authors want to thank Carlos J. Bernardos and Alejandro Perez-Mendez for their valuable comments.