Understanding CNI

What is CNI?

CNI is a Cloud Native Computing Foundation (CNCF) project that defines:

Core Purpose:

• Network Configuration: Standardized way to configure container networking
• Runtime Independence: Works with any container runtime that supports CNI
• Plugin Architecture: Extensible plugin system for different network implementations
• Simple Interface: Simple JSON-based configuration format

Key Characteristics:

• Lightweight: Minimal overhead and simple implementation
• Extensible: Plugin-based architecture for different network types
• Runtime Agnostic: Works with any CNI-compatible container runtime
• Kubernetes Native: Native integration with Kubernetes networking

CNI Architecture

CNI follows a simple, plugin-based architecture:

Core Components:

• CNI Specification: Standard interface definition
• CNI Plugins: Network implementation plugins
• Container Runtime: Container runtime that invokes CNI
• Network Configuration: JSON configuration files

Plugin Types:

• Main Plugins: Primary network configuration (bridge, host-device, etc.)
• IPAM Plugins: IP address management (host-local, dhcp, etc.)
• Meta Plugins: Additional functionality (portmap, tuning, etc.)

How CNI Works

CNI Execution Flow

CNI follows a standardized execution process:

1. Container Creation:

• Container runtime creates container namespace
• Runtime invokes CNI with ADD command
• CNI plugin configures network interface
• Container gets network connectivity

2. Container Deletion:

• Container runtime stops container
• Runtime invokes CNI with DEL command
• CNI plugin cleans up network configuration
• Network resources are released

3. Network Operations:

• ADD: Configure network for container
• DEL: Remove network configuration
• CHECK: Verify network configuration
• VERSION: Get plugin version information

CNI Configuration

JSON-based configuration for network setup:

Basic Configuration:

{
  "cniVersion": "0.4.0",
  "name": "mynet",
  "type": "bridge",
  "bridge": "cni0",
  "ipam": {
    "type": "host-local",
    "subnet": "10.244.0.0/16"
  }
}

Configuration Elements:

• cniVersion: CNI specification version
• name: Network name identifier
• type: CNI plugin type
• bridge: Network bridge name
• ipam: IP address management configuration

Popular CNI Plugins

1. Bridge Plugin

Simple bridge-based networking:

Features:

• Layer 2 Bridging: Creates virtual bridge for containers
• IP Assignment: Assigns IP addresses to containers
• Host Connectivity: Enables host-to-container communication
• Simple Configuration: Easy to configure and understand

Use Cases:

• Development Environments: Simple container networking
• Single-Host Deployments: Containers on single host
• Learning and Testing: Understanding container networking
• Basic Connectivity: Simple container-to-container communication

2. Calico

High-performance networking and security:

Features:

• BGP Routing: Border Gateway Protocol for routing
• Network Policies: Fine-grained network security policies
• Cross-Subnet: Cross-subnet container communication
• High Performance: Optimized for performance and scalability

Use Cases:

• Production Kubernetes: Enterprise Kubernetes deployments
• Multi-Cluster: Cross-cluster networking
• Security-Focused: Environments requiring network policies
• Large Scale: High-performance, large-scale deployments

3. Flannel

Simple overlay networking:

Features:

• Overlay Network: Virtual network overlay
• Multiple Backends: VXLAN, host-gw, UDP backends
• Simple Configuration: Easy to configure and deploy
• Kubernetes Integration: Native Kubernetes integration

Use Cases:

• Kubernetes Default: Default networking for many Kubernetes distributions
• Simple Overlays: Basic overlay networking requirements
• Development: Development and testing environments
• Small to Medium Scale: Small to medium-scale deployments

4. Weave Net

Simple and resilient networking:

Features:

• Mesh Networking: Peer-to-peer mesh network
• Automatic Discovery: Automatic peer discovery
• Encryption: Built-in encryption for traffic
• Fault Tolerance: Resilient to network failures

Use Cases:

• Distributed Systems: Distributed container deployments
• Security Requirements: Environments requiring encrypted traffic
• Fault Tolerance: Systems requiring high availability
• Simple Deployment: Easy deployment and management

5. Cilium

eBPF-based networking and security:

Features:

• eBPF Technology: Uses eBPF for networking and security
• Layer 7 Policies: Application-layer security policies
• Observability: Deep observability and monitoring
• High Performance: High-performance networking

Use Cases:

• Advanced Security: Environments requiring advanced security
• Observability: Systems requiring deep observability
• Performance: High-performance networking requirements
• Modern Architectures: Cloud-native and microservices architectures

CNI in Kubernetes

Kubernetes CNI Integration

Kubernetes uses CNI for pod networking:

Integration Points:

• kubelet: Invokes CNI plugins for pod networking
• CNI Configuration: Stored in /etc/cni/net.d/
• Plugin Binaries: Located in /opt/cni/bin/
• Network Policies: Kubernetes network policies work with CNI

Kubernetes Requirements:

• Pod-to-Pod Communication: All pods can communicate with each other
• Pod-to-Service Communication: Pods can reach Kubernetes services
• Host-to-Pod Communication: Host can reach pods
• External Communication: Pods can reach external resources

CNI Configuration in Kubernetes

Kubernetes CNI configuration:

Configuration Location:

• Default: /etc/cni/net.d/
• Configuration Files: JSON configuration files
• Plugin Binaries: /opt/cni/bin/
• Network Name: Usually “cbr0” or custom name

Configuration Example:

{
  "cniVersion": "0.4.0",
  "name": "kubernetes",
  "type": "bridge",
  "bridge": "cbr0",
  "ipam": {
    "type": "host-local",
    "subnet": "10.244.0.0/16"
  }
}

CNI Best Practices

1. Plugin Selection

Choose the right CNI plugin for your environment:

Selection Criteria:

• Performance Requirements: Network performance needs
• Security Requirements: Security and policy requirements
• Scale: Number of pods and nodes
• Complexity: Operational complexity tolerance
• Integration: Integration with existing infrastructure

Recommendations:

• Development: Bridge plugin for simple development
• Production: Calico or Cilium for production environments
• Security: Cilium for advanced security requirements
• Performance: Calico for high-performance requirements

2. Network Planning

Plan your network architecture:

Network Design:

• Subnet Planning: Plan IP address ranges and subnets
• Pod CIDR: Define pod network CIDR
• Service CIDR: Define service network CIDR
• Node CIDR: Define node network CIDR

Considerations:

• IP Address Space: Ensure sufficient IP addresses
• Network Overlap: Avoid network address conflicts
• Routing: Plan routing between networks
• Security: Consider network security requirements

3. Configuration Management

Manage CNI configuration effectively:

Configuration Management:

• Version Control: Store configurations in version control
• Templates: Use configuration templates
• Validation: Validate configurations before deployment
• Documentation: Document configuration decisions

Operational Practices:

• Backup: Backup CNI configurations
• Testing: Test configurations in non-production
• Rollback: Plan for configuration rollback
• Monitoring: Monitor CNI plugin health

4. Troubleshooting

Effective CNI troubleshooting:

Common Issues:

• Network Connectivity: Pod-to-pod communication issues
• IP Address Conflicts: Duplicate IP addresses
• Plugin Failures: CNI plugin failures
• Configuration Errors: Invalid configuration files

Troubleshooting Steps:

• Check Plugin Status: Verify CNI plugin is running
• Validate Configuration: Check configuration syntax
• Network Connectivity: Test network connectivity
• Logs: Review CNI and kubelet logs

CNI and Service Mesh

Service Mesh Integration

CNI works with service mesh technologies:

Istio Integration:

• CNI Compatibility: Istio works with any CNI plugin
• Traffic Management: Service mesh handles traffic management
• Security: Service mesh provides additional security
• Observability: Enhanced observability capabilities

Benefits:

• Layered Security: CNI + service mesh security
• Traffic Control: Fine-grained traffic control
• Observability: Comprehensive network observability
• Policy Enforcement: Multi-layer policy enforcement

Tetrate Service Bridge

Enterprise service mesh with CNI:

TSB Features:

• Multi-Cluster: Multi-cluster service mesh management
• CNI Agnostic: Works with any CNI plugin
• Enterprise Security: Enterprise-grade security features
• Centralized Management: Centralized service mesh management

Integration Benefits:

• Unified Management: Unified management of networking and service mesh
• Enterprise Features: Enterprise-grade features and support
• Compliance: Compliance and security certifications
• Professional Support: Professional support and services

Related Resources

• What Is Kubernetes? - Understanding Kubernetes basics
• What Is a Service Mesh? - Service mesh fundamentals
• Kubernetes Networking - Kubernetes networking concepts
• Container Networking - Container networking fundamentals
• Tetrate Service Bridge - Enterprise service mesh platform

Learn More

For organizations working with CNI and container networking:

• CNI Specification - Official CNI specification
• CNCF CNI Project - CNCF CNI project information
• Tetrate Networking Assessment - Evaluate your networking setup
• Service Mesh Implementation - Professional implementation services
• Container Networking Training - Container networking training