B.A.T.M.A.N. (Routing Protocol)

B.A.T.M.A.N. (Better Approach To Mobile Ad-hoc Reseau pour mineurs) is a routing protocol for multi-hop wireless mesh networks, developed by the German Freifunk community to replace the older OLSR protocol. It is the routing engine that lets community and off-grid meshes self-organize without any central coordinator — a core building block for sovereign, infrastructure-free networks where nodes join, move, and leave constantly.

The core idea: no node needs the map

Classic link-state protocols like OLSR have every node flood link information until each one can compute a full topology graph — expensive in airtime and CPU, and fragile on lossy radio links where the "map" is stale the moment it is drawn. B.A.T.M.A.N. inverts this. Each node periodically broadcasts small originator messages (OGMs); neighbors rebroadcast them, and every node simply records which neighbor delivered another node's OGMs most reliably. That neighbor becomes the best next hop toward that destination. No node ever holds the whole map — routing knowledge is spread across the mesh, one hop at a time — yet the collective effect is loop-free, self-healing paths that adapt as radio conditions shift.

Why it suits real-world radio

Counting received OGMs is, in effect, a continuous measurement of link quality: a flaky link drops messages and quietly loses its status as best next hop, without any explicit failure detection. This statistical approach keeps per-node processing and control traffic low, which is exactly what cheap, low-power hardware can afford. Freifunk's community networks — thousands of rooftop nodes run by volunteers — are the proving ground: the protocol was engineered around lossy, asymmetric, constantly changing links because that is what the community actually had.

batman-adv: the mesh as one big switch

The original implementation was a userspace daemon routing at Layer 3. Its successor, batman-adv (B.A.T.M.A.N. Advanced), moved into the mainline Linux kernel and operates at OSI Layer 2, forwarding Ethernet frames rather than IP packets. To everything above it, the entire mesh looks like one big virtual switch: DHCP, IPv6, mDNS, and ordinary applications work transparently across multiple radio hops with zero application-level awareness. Being a kernel module, it runs efficiently on low-end routers and single-board computers — the class of hardware a homestead mesh is actually built from.

Where it fits in a sovereign network

B.A.T.M.A.N. solves one specific layer of the problem: picking paths through a cloud of Wi-Fi-class radios. It complements, rather than competes with, the other pieces of an off-grid stack. Long-range, low-bandwidth links such as LoRa and Meshtastic cover kilometres at kilobits; batman-adv covers neighbourhoods at megabits; overlay stacks such as Reticulum can ride across all of them, stitching mixed media into one addressable network. A practical build might mesh a property's buildings with batman-adv on commodity Wi-Fi routers, bridge to town over a point-to-point link, and fall back to LoRa for telemetry when the fast links fail. Every layer of that network answers to its operators and nobody else — which is the entire point.

B.A.T.M.A.N. optimizes for resilience and simplicity, not raw throughput: every mesh hop roughly halves usable bandwidth on a single radio, and Layer 2 flooding of broadcast traffic sets practical limits on how large one mesh segment should grow before it needs routing or gateway boundaries. The protocol also deliberately trusts its participants — it measures link quality, not honesty — so on a mesh that strangers can join, security has to come from the layers above, whether that is WPA on the radio links, VPN tunnels, or an end-to-end encrypted overlay. None of this diminishes the achievement: batman-adv turned a pile of commodity routers into self-healing neighbourhood infrastructure that has run community networks for well over a decade, maintained in the open, owned by the people who deploy it. That is the standard sovereign networking should be measured against.