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You may have heard the term Crosswork Network Controller, or CNC, and quite likely in conjunction with Segment Routing. You are probably asking yourself: why I should care about CNC or, for that matter, Segment Routing? What can they do for me? What is CNC, and why all the buzz? These are the questions we will answer in this article.  

What is Segment Routing?

CNC is a Segment Routing software-defined networking (SDN) controller for transport networks. So, what, why should I care? To answer this question, we must first describe what Segment Routing (SR) is and why it has gained so much traction lately. 

Segment Routing replaces traditional MPLS (Multiprotocol Label Switching), often referred to as SR-MPLS, which dramatically simplifies MPLS by eliminating protocols and reducing complexity, making it easier to monitor and manage your network leveraging existing hardware. This results in reduced operational costs and greater user satisfaction. It also offers features like topology-independent fast reroute and traffic engineering (SR-TE). 

Fast reroute provides sub-50ms fast reroute for any topology. That translates to fewer outages, shorter downtimes and ultimately better end-user experience. SR-TE can steer traffic along any desired path in the network, enabling the network operator to use disjoint paths or constrain traffic to a low-latency forwarding path. Doing so provides end-to-end application service level agreements (SLAs) that enhance user experience, especially for voice, video and real-time applications.  

Check out our segment routing articles to better understand SR's functionality, features and advantages.  

What is CNC?

CNC is a Segment Routing SDN controller for transport networks that provides a GUI (graphical user interface) dashboard to create and manage transport and VPN (virtual private network) services. It supports advanced segment routing policies like low latency, disjointedness, path constraints and bandwidth awareness. It does this by creating transport paths with these parameters and binding the VPN services to the transport paths all in a single platform. In addition, CNC facilities proactive network monitoring and visualization along with closed-loop network automation. The Crosswork solution combines the capabilities of products including Crosswork Network Controller, Crosswork Network Automation, Crosswork Optimization Engine, NSO and SR PCE. These products are all part of the CNC installation and perform unique functions. 

Why CNC? 

Now, let's look at the advantages of CNC and how those translate into an improved network solution resulting in an enhanced user experience. CNC provides a single pane of glass to manage and deploy the transport and layered L3 and L2 VPN services in conjunction with SR-TE, resulting in a simpler operation model with a lower cost of ownership. The true power of CNC comes from the flexibility of SR-TE to provision transport paths beyond the traditional IGP (interior gateway protocol) shortest path. CNC, in conjunction with segment routing, allows an operator to provision end-to-end services with SLAs based on several criteria unique to SR-TE. With SR-TE, CNC can create low-latency paths, which delay-sensitive real-time applications can use. This improves user experience, especially when the default high bandwidth path is congested. 

CNC can instruct SR-TE to provide a constraint-based high bandwidth, low-latency, or explicit path that avoids certain links in the network. This is often done to reduce the cost of transporting traffic over tariff-based links or avoid congested links. These paths are built to be used only by specific endpoints or applications. This is accomplished with the SR-TE feature Automated Steering. Automated Steering allows traffic destined to defined network destinations to be marked or colored via BGP so that they can be steered into a predefined SR-TE policy providing a defined SLA.

Local congestion mitigation (LCM) and bandwidth on demand (BWoD) features unique to a bandwidth broker like CNC allow us to take SR-TE to the next level. LCM and BWoD provide controller-based enhancements to SR-TE. LCM is an interval-based solution that relies on CNC to proactively search for congestion across network links and suggest recommendations to redirect some of the traffic over alternate paths dynamically. This alleviates network bottlenecks and can reduce costs by eliminating the need to provision additional links for increased bandwidth. BWoD relies on SNMP (simple network management protocol) polling to measure interface congestion and deliver policies that meet defined bandwidth requirements. 

Ultimately this leads to a congestion-free path that is available for real-time and delay-sensitive traffic. This translates to fewer dropped packets improving the user experience and guaranteeing bandwidth for high-priority data flows. A further discussion on LCM and BWoD is available in the article Cisco CNC and SR-TE, Better Together

CNC takes automation and network optimization to the next level by delivering service orchestration, service path computation, network optimization, network device management and deployment, and automatic remediation and anomaly detection. By combining device management with transport and SR policy provisioning, the operational process is simplified and unified, resulting in an overall lower cost of ownership. Furthermore, Crosswork Network Controller offers network optimization controls via SNMP data gathering and telemetry data streamed from network devices directly to CNC, which is next to impossible even with an experienced and skilled network operations staff.  

At the heart of the Cisco Crosswork Network Suite of products is the Crosswork Optimization Engine, or COE. Crosswork Optimization Engine provides a network topology map that allows for real-time visualization of devices along with link utilization and SR-TE policy provisioning in conjunction with L2 and L3 Service provisioning. Combining all these features into a single platform reduces operational simplicity. The user interface allows the operator to easily create and modify or remove SR-MPLS policies and preview the policy before deployment. COE can continuously track SR-MPLS policies with dynamic path computation to honor SLA objectives set forth by end-user objectives.  


CNC is a powerful tool for automating and provisioning transport networks that also functions as a bandwidth broker. It enhances the already robust SR-TE model by providing local congestion mitigation and bandwidth on demand services. The utilization of CNC for these use cases enhances SR-TE making it far more flexible and attractive and reducing operational costs and complexity.

Please contact us today with any questions or details on SR-TE and CNC.

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