Flannel review
A free, focused CNI for straightforward Kubernetes cluster networking.
Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
Flannel is open-source infrastructure software for container networking, designed primarily for Kubernetes clusters. It runs a flanneld agent on each host, allocates per-host subnets, manages leases, and provides Layer 3 IPv4 connectivity between nodes. Its Kubernetes CNI plugin can also work with Docker, making it a practical fit for teams that want straightforward cluster networking without a hosted service or paid plan structure.
The main technical choice is the transport backend. Flannel supports VXLAN, host-gw, WireGuard, and IPsec, so operators can select an approach that matches their cluster network and encryption requirements. Configuration can use the Kubernetes API or etcd, and the project includes Helm integration guidance. Dual-stack IPv4 and IPv6 support is available for selected backends rather than across every option, so backend selection matters for clusters that require both protocols.
Flannel keeps its core scope focused: subnet allocation, node-to-node transport, and Kubernetes CNI integration. Network policy support is available through the Kubernetes SIGs network policy controller deployed alongside Flannel, rather than through native enforcement in the flanneld binary. That makes Flannel a sensible choice for teams prioritizing a simple networking layer and flexible backend options. Teams that need policy enforcement as a central, native capability should consider a policy-focused CNI instead.
Flannel pros and cons
- Where it wins
- Free and open-source with no paid tier structure
- VXLAN, host-gw, WireGuard, and IPsec backend options
- Kubernetes CNI with subnet and lease management
- Where it doesn't
- Network policy enforcement uses a separate controller
- Dual-stack support applies only to selected backends
- Feature scope is narrower than policy-focused CNIs
Flannel fact sheet, pricing and score →
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