Flannel¶

Simple, lightweight overlay network for Kubernetes — the "it just works" CNI.

Overview¶

Flannel is the simplest CNI plugin for Kubernetes, providing basic L3 networking via VXLAN overlay. It is designed to be easy to install and configure with minimal operational overhead. Flannel is the default CNI in K3s and is widely used in development, testing, and small production clusters. It does not implement network policies — you must pair it with Calico or another policy engine for that.

Key Facts¶

Attribute	Detail
Repository	github.com/flannel-io/flannel
Stars	~9k+ ⭐
Latest Version	v0.28.2 (March 2026)
Language	Go
License	Apache 2.0
Governance	Community (flannel-io)

Evaluation¶

Pros	Cons
Simplest CNI to install and operate	No network policy support
Default in K3s	VXLAN overlay adds latency
WireGuard backend for encryption	No L7 visibility
Minimal resource footprint	No service mesh integration
Extremely stable and battle-tested	No observability features
host-gw mode for bare-metal speed	Not recommended for large production

Architecture¶

flowchart TB
    subgraph Node1["Node 1"]
        Pod1["Pod A\n10.244.0.2"]
        Flannel1["flanneld\n(DaemonSet)"]
        VTEP1["VXLAN VTEP\n(flannel.1)"]
    end

    subgraph Node2["Node 2"]
        Pod2["Pod B\n10.244.1.2"]
        Flannel2["flanneld"]
        VTEP2["VXLAN VTEP\n(flannel.1)"]
    end

    ETCD_F["etcd / K8s API\n(subnet lease store)"]

    Pod1 -->|"encapsulated\nin VXLAN"| VTEP1
    VTEP1 -->|"UDP 8472"| VTEP2
    VTEP2 --> Pod2
    Flannel1 -->|"lease"| ETCD_F
    Flannel2 -->|"lease"| ETCD_F

    style Node1 fill:#2e7d32,color:#fff
    style Node2 fill:#2e7d32,color:#fff

Backends¶

Backend	Performance	Requirement	Encryption
VXLAN	Good (encapsulation overhead)	Any network	No
host-gw	Best (direct routing)	Same L2 network	No
WireGuard	Good	Kernel WireGuard module	Yes
UDP	Worst (userspace)	Fallback only	No