In Kubernetes, networking holds immense significance as it enables seamless communication among various components and facilitates uninterrupted data flow. To allow pods within a Kubernetes cluster to engage with other pods and cluster services, each of them requires an exclusive IP address. Consequently, networking solutions in Kubernetes encompass more than mere interconnecting machines and devices. They establish the groundwork for service identification, load distribution, and upholding the overall system's cohesion.

Through this blog, we aim to explore the intricacies and subtleties surrounding three widely used Kubernetes networking plugins: Calico, Flannel, and Cilium. We will analyze each plugin, emphasizing their prominent attributes, configurations, deployment considerations, performance traits, scalability, and recommended methodologies. Ultimately, this article aims to present a comparative assessment of, and essential factors to consider, when choosing the appropriate Container Network Interface (CNI) for your Kubernetes cluster, specifically within the framework of the Civo platform.

What are Kubernetes networking plugins?

Kubernetes networking plugins, also known as CNIs (Container Network Interfaces), enable these networking capabilities for clusters. They are responsible for the allocation of IP addresses to pods and setting up routes on each node for traffic forwarding. CNIs like Calico, Flannel, and Cilium offer distinct approaches to solve networking-related challenges in Kubernetes. They provide different features, performance characteristics, and operational complexities, making each uniquely suited to specific use cases and scenarios.

Cilium networking plugin

Cilium logo

Cilium is a powerful open-source networking plugin that provides secure network connectivity between application services deployed in Linux container management platforms like Kubernetes. It leverages eBPF (extended Berkeley Packet Filter), a revolutionary technology in the Linux kernel, to provide advanced networking features, load balancing, and network security.

Explore more about Cilium through these resources:

Key features and capabilities

Cilium is rich in features that cover networking, load balancing, and security. It provides native support for Kubernetes Network Policies and additionally introduces CiliumNetworkPolicies, extending the capabilities of Kubernetes' built-in network policies.

One of Cilium's standout features is its ability to understand and filter network traffic for many popular application protocols such as HTTP, gRPC, and Kafka. This means you can write network policies that understand application-level concepts, significantly improving the granularity and effectiveness of your security posture.

Moreover, thanks to eBPF, Cilium can also provide visibility into the network, application protocol metadata, and security.

Best practices for using Cilium

Due to the advanced capabilities of Cilium, it may not be the first choice for all Kubernetes clusters. If you decide to test out Cilium, it is important to consider how to use it safely. Here are some of the best practices and helpful tips for using Cilium in the most secure manner:

Implement comprehensive network policies Leverage Cilium's advanced network policy capabilities to define and enforce fine-grained security controls. Use CiliumNetworkPolicies to create policies that understand application-level protocols and concepts. Regularly review and update network policies to adapt to evolving security needs.
Carefully plan and configure eBPF features Cilium's feature set, powered by eBPF, provides advanced networking and security capabilities. Plan and configure these features carefully, considering your specific requirements and the impact on performance and security. Enable and disable features as needed, and thoroughly test your configuration before deploying it to production.
Monitor and analyze network traffic Take advantage of Cilium's observability features to gain visibility into your network traffic. Utilize Cilium's integration with the Hubble observability platform to monitor and analyze network flows, application-level metrics, and security events. Regularly review and analyze the collected data to identify any anomalies or potential security threats.
Secure eBPF and kernel components Since Cilium heavily relies on eBPF and interacts with the Linux kernel, ensure proper security measures for these components. Keep the Linux kernel updated with the latest security patches and updates. Implement appropriate access controls, isolation mechanisms, and security configurations to protect eBPF programs and the underlying kernel.
Engaging with the Cilium community Stay updated with the latest developments, releases, and security advisories from the Cilium community, as the project is in rapid development. Engage with the community through their Slack channel, GitHub, or social media channels to gain insights, share experiences, and seek assistance.

Calico networking plugin

Calico logo

Calico is another open-source networking interface and network security solution for workloads running on hosts ranging from physical machines to containers. Calico aims to be both approachable and scalable, providing the Kubernetes flat networking model assigning each pod its own IP address, meaning traffic within a cluster does not require NAT (Network Address Translation).

Key features and capabilities

Calico aims to provide rich networking options as well as integrate security features. By focusing on providing a purely Internet Protocol (IP) solution, Calico delivers reliable and high-performance networking within Kubernetes.

Similar to Cilium, one of Calico's most attractive features is its support for network policies. These Kubernetes network policies provide granular controls for administrators to manage network communication, allowing them to specify which pods can communicate with each other and other network endpoints.

Best practices for using Calico

To begin using Calico, you should take into account some of these best practices and helpful tips to ensure you are using it correctly:

Secure network policies Leverage Calico's network policy capabilities to enforce granular controls over network communication. Define and enforce policies that restrict network traffic between Pods based on specific criteria, such as IP addresses, ports, or labels. Regularly review and update network policies to align with your security requirements.
Proper configuration of BGP peering If you choose to use BGP peering with Calico, ensure that the BGP configuration is correctly set up. Follow best practices for BGP peering, including proper authentication, routing filters, and peering with trusted and authorized entities only. Regularly monitor and maintain the BGP peering configuration to ensure its integrity and security.
Regular updates and patches Keep your Calico deployment updated with the latest releases, patches, and security updates. Stay informed about the Calico community's announcements and security advisories to address any vulnerabilities or issues promptly. Regularly test and validate updates in a non-production environment before applying them to production clusters.
Secure Calico node components Pay attention to the security of the underlying infrastructure and nodes running Calico. Implement best practices for securing the host operating system, container runtime, and Kubernetes components. Follow industry-standard security guidelines, such as using secure communication protocols, enabling appropriate access controls, and regularly scanning for vulnerabilities.
Secure Calico's etcd Backend If you choose to use Calico's etcd backend, ensure proper security measures are in place to protect the etcd cluster. Apply access controls, encryption, and authentication mechanisms to safeguard the integrity and confidentiality of the etcd data. Regularly monitor and audit etcd for any security issues.

Flannel networking plugin

flannel logo

Flannel is an open-source, approachable, and easy-to-use networking plugin designed to meet Kubernetes networking requirements. It aims to provide a robust yet straightforward network fabric for pods, emphasizing ease of use and compatibility.

Key features and capabilities

As with other container network interfaces, Flannel creates a virtual network within Kubernetes clusters, where each pod is assigned a unique IP address. It employs a network overlay mechanism to ensure accurate routing of traffic across hosts.

Significantly, Flannel is designed to be compatible with diverse backends such as VXLAN and host-gateway, among others. This flexibility allows Flannel to adapt to various network environments and configurations. However, it is important to highlight that, unlike the two CNIs discussed above, Flannel does not directly support Kubernetes Network Policies, which can be crucial for security-centric contexts.

Best practices for using Flannel

When using Flannel, try to incorporate these best practices and tips for using it safely:

Secure the underlying network infrastructure Implement network segmentation, access controls, and monitoring. Follow industry best practices for network security, such as firewall rules, intrusion detection systems, and regular security audits.
Use additional security layers Given that Flannel doesn't inherently support Kubernetes Network Policies, use additional security layers to enforce network policies and access controls. Implement network-level firewalls, security groups, or leverage other, Kubernetes-specific, security solutions.
Regularly update and patch Flannel Stay updated with the latest releases and security patches for Flannel. Monitor the Flannel community's announcements and security advisories to promptly address any vulnerabilities or issues. Test updates in a non-production environment before rolling them out to production clusters.
Properly configure backends Depending on your environment, choose the appropriate backend for Flannel (e.g., VXLAN). Ensure that the backend configuration aligns with your network requirements and follows best practices for security and performance. Regularly review and update the backend configuration as needed.
Monitor and audit Flannel Implement monitoring and logging mechanisms to track network activity and detect any anomalies or potential security breaches. Regularly review the logs and audit network traffic to identify any suspicious patterns or unauthorized access attempts.

Comparison of Kubernetes networking plugins

While Calico, Flannel, and Cilium are all great Kubernetes networking plugins, it is essential to select the appropriate one for your individual needs as they do have different points of focus. In this section, we will take a look at how these plugins differ, allowing you to make an informed decision on areas such as security, configuration, and performance.

Configuration and deployment considerations

To begin with, it is important to look at the configuration and deployment considerations for each option. The ease, complexity, flexibility, and scalability of deployment vary across Calico, Flannel, and Cilium. The table shown below looks into how these considerations play out for each of these solutions:

Calico Deploying Calico in a Kubernetes cluster involves applying the appropriate Calico manifest for your specific deployment. You can choose between multiple options, including Calico with its own etcd (recommended for large-scale deployments), Calico with Kubernetes API datastore (a simpler option), or Calico in policy-only mode (to manage network policies only and have another networking solution act as the CNI).

In terms of configuration, Calico provides flexibility with options to configure BGP (Border Gateway Protocol) peering, IP pools, and network policies to meet your networking requirements.
Flannel Flannel's configuration is primarily handled by a configuration file that dictates the networking details, including the subnet allocation. Deploying Flannel is typically a process wherein a Flannel manifest is applied to the Kubernetes cluster, which sets up the Flannel daemonset on each node.
Cilium Cilium's deployment in a Kubernetes cluster can be achieved using Helm or YAML files. While the process is straightforward, the configuration can be complex due to its extensive feature set.

It's crucial to carefully consider your network requirements and thoroughly plan your configuration before deploying Cilium. This includes factors like enabling and disabling various protocol visibility features, configuring network policies, and setting up Cilium's Hubble observability platform if needed.

Ideal use cases for each plugin

By examining the strengths and areas of specialization for the three plugins, we can better assess where and why Calico, Flannel, or Cilium might be the right fit for particular environments. The table below explores how features of each plugin can address distinct requirements, whether it be network scalability, security, or simplicity.

Calico Calico excels in environments that require high availability and scalability. Its rich feature set makes Calico an excellent choice for large clusters where maintaining performance at scale is critical.

Furthermore, the policy-driven network security offered by Calico makes it suitable for use cases with rigorous security requirements. It can help enforce strict network segmentation and access controls, which is particularly useful for multi-tenant environments or applications dealing with sensitive data.
Flannel Flannel is an excellent choice for straightforward Kubernetes networking requirements where approachability and ease of use are paramount. Its compatibility with various backends makes it adaptable to different environments. In situations where advanced networking features are not required and there is less emphasis on network policies, Flannel can be a robust and efficient solution.
Cilium Cilium shines in environments with critical security, scalability, and visibility. Its ability to understand application protocols makes it a top choice for securing modern microservice architectures where traditional network-layer controls are not enough.

In addition, its support for eBPF makes it excellent for providing observability into your network traffic. These capabilities are valuable in complex deployments where understanding and debugging the interaction between services can be challenging.

Performance characteristics and scalability

Performance is a critical aspect to consider when selecting a networking plugin. In the below section, you will find a comparison between the three plugins and an outline of their performance characteristics and scalability:

Calico Calico's direct IP-to-IP routing provides high performance and low latency, making it an excellent choice for high-performance requirements.
Flannel Flannel's performance is generally satisfactory for many use cases, although the overlay network may add some overhead that could slightly increase latency compared to Calico.
Cilium Cilium, powered by eBPF, offers high-performance networking and scales well with increased traffic, but this high performance must be considered in line with its complexity.

Network architecture and design differences

The architectural differences between Calico, Flannel, and Cilium reflect their diverse strengths and use cases. The below table outlines a comparison between the three plugins and their network architecture and design differences:

Calico Calico uses a pure IP networking fabric and offers a flat networking model that eliminates the need for an overlay network. This approach provides high performance and scalability.
Flannel Flannel employs an overlay network. Its relative simplicity and support for different backends make it versatile and easy to use, although it may lack the advanced security features inherent to the other two solutions explored here.
Cilium Cilium leverages eBPF to provide a robust networking solution that incorporates application-level visibility and control. This makes it a compelling choice for complex microservice-based applications.

Security features and policies

If security is an important element for you to consider as part of your project requirements, the table below will help you identify which of the three plugins has specific security features and policies:

Calico Calico's network policy enforcement allows administrators to control traffic flow in their cluster, providing robust security measures.
Flannel Flannel, unfortunately, does not natively support network policies, making it a less attractive option for environments with stringent security requirements. However, other cloud-native projects can be used to mitigate the CNI natively lacking this policy control.
Cilium Cilium goes a step further by understanding application-level protocols and providing application-aware network security, setting it apart in scenarios where advanced network security is a priority.

What to consider when selecting a networking plugin

Selecting the right networking plugin for your Kubernetes environment requires a careful evaluation of various factors:

  • Performance: If your use case requires high-performance networking, you might prefer Calico or Cilium, both of which offer performance advantages due to their respective network architectures.
  • Security: If network security is a critical concern, particularly at the application layer, Cilium's support for application-aware network policies may tilt the scales in its favor. Calico also provides strong network policy capabilities.
  • Simplicity: If simplicity is a priority, Flannel's straightforward approach and easy-to-understand design could make it a strong contender.
  • Observability: If deep visibility into your networking is needed, Cilium's extensive observability capabilities would be beneficial.
  • Scalability: For large-scale deployments, you may want to consider the scalability features of Calico and Cilium, which offer efficient networking even as cluster sizes increase.


The Kubernetes networking landscape has projects that fulfill various requirements. We have explored the characteristics and features of three popular networking plugins: Calico, Flannel, and Cilium. We've seen that Calico offers a blend of simplicity, high performance, and network security features. Flannel, with its uncomplicated approach, shines in scenarios where getting up and running is paramount. Cilium, with its eBPF-powered network architecture, provides advanced networking and security features and excels in offering deep network visibility.

Ultimately, the choice between Calico, Flannel, and Cilium depends on your unique use case, technical requirements, and the specifics of your Kubernetes environment. Each plugin has its strengths and scenarios where it shines.

The selection of an optimal networking plugin holds immense significance, as it can profoundly shape the outcome of your Kubernetes experience. Therefore we encourage you to dedicate time and effort to explore diverse alternatives and assess their compatibility with your specific needs.