How to secure your SDN controller

Managing networks has become increasingly complex, and as the number of IoT devices continues to proliferate, managing networks faces even greater challenges. This complexity makes it difficult to reconfigure traditional networks in a timely manner to respond to malicious events or fix configuration errors.

Software Defined Networking (SDN) helps network engineers flexibly and dynamically change the behavior of the network at the node level, which is usually not available in traditional networks. SDN uses virtualization to simplify the management of network resources and provides a solution for increasing capacity without significantly increasing costs.

As network control shifts from hardware to software, the result is that multiple devices are merged into a single controller, allowing network engineers to control the entire network, but this model has obvious security risks that must be addressed.

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Advantages of SDN

SDN makes it easier to integrate services such as real-time HD video conferencing and cloud applications into an enterprise environment, and application developers or testers can isolate and run workloads without worrying about virtual tenants in the production network. This can speed up problem resolution and reduce the time required for testing before deployment.

SDN brings the advantage of greater visibility and control through a centralized dashboard. The controller can determine the best route, congestion, link health and priority for each application's traffic flow to track in real time, while the ability to route specific application traffic through different paths or multiple paths provides redundancy.

For example, if an enterprise’s application is hosted by two separate cloud service providers, the traffic of a specific user can be routed to the cloud service provider with lower average latency, which can enable the enterprise to provide a better user experience.

Another advantage of SDN is that there is no need to worry about vendor lock-in. The goal of SDN is to use open standards. Enterprises can easily use products from multiple vendors, which helps reduce costs. By aggregating multiple computing, storage, and processing functions on low-cost commercial servers, capital expenditures can be significantly reduced. This virtualization can automate a large amount of manual network configuration and improve its traceability.

Security is also a major advantage of using SDN for enterprises, which means that enterprises can expand their defense capabilities from simply blocking specific attacks to actively modifying them to adapt to new threats. SDN controllers can centrally push global security policy updates through the network, and virtual switches can filter data packets at the edge of the network and redirect suspicious traffic to other security devices for further analysis.

Security issues of SDN

An important issue regarding SDN security is that virtualizing every aspect of the network infrastructure amplifies the impact of an attack. The SDN controller is often a prime target for attackers because it is the central point for network decision making and, as such, becomes the center of attack.

An attacker could try to gain full control of your network by breaking into the controller or posing as a control network. Once the central controller is compromised, the attacker can take full control of your network. This is an extreme scenario, but as the use of SDN continues to grow, this attack scenario is very likely to become a reality.

Some new types of denial of service attacks attempt to exploit potential scaling limitations of SDN infrastructure by looking for specific automated processes that use large amounts of CPU. SDN can be very vulnerable due to the separation of the control and data planes, and a disruption in the communication link between the two planes could allow attackers to find a vulnerability.

Due to the programmability of SDN controllers, engineers can safely apply security policies on the controller's northbound interface, opening up new ways to implement security policies on the network. Of course, the programmable northbound interface is also a potential vulnerability.

Additionally, applications installed on the controller could reconfigure the network, and attackers could trick network engineers into installing an application that has been compromised and could take the network completely by surprise.

How to secure your SDN controller

Access control to SDN controllers is very important to prevent unauthorized activities. Role-based access policies should be used and reviewed consistently. Any unauthorized attempts should alert security personnel, and configuration changes must be audited regularly.

It is important to use a high availability controller architecture to prevent distributed denial of service (DDoS) attacks. Having high availability in the design will allow you to test updates or changes in the production environment as well as provide the option of failover if the update does not work properly.

Northbound communications should be encrypted via TLS or SSH, and any northbound applications should be securely coded. Any attack or compromise of these applications could impact the security and operation of the controller. Additionally, avoid using default passwords for these applications and ensure that the application has some form of authentication in place when communicating with the controller.

For southbound communication, it is important to authenticate endpoints using TLS, and control protocol traffic should be isolated from the main data flow, preferably over an out-of-band network.

Security factors must be considered when designing an SDN solution. The controller is the core of SDN, and it is critical to protect the controller and the applications that communicate with it, as well as the traffic between the controller and the applications.