Port 698: OLSR — Where mesh networks find their way

Port 698 carries OLSR (Optimized Link State Routing Protocol), the routing protocol designed for mobile ad-hoc networks and wireless mesh networks. When devices need to find routes without any central router or authority, OLSR on port 698 is how they discover who can reach whom.

What OLSR does

OLSR solves a fundamental problem: how do you route packets in a network where there's no fixed infrastructure? No central router. No predetermined paths. Just a collection of wireless devices that need to find ways to reach each other.

Traditional routing protocols assume stable infrastructure. OLSR assumes chaos—devices joining and leaving, connections appearing and disappearing, the network topology constantly shifting. And it handles this by having every node continuously announce what it knows about the network.

The key insight: multipoint relays

Here's the problem with mesh networks: if every node forwards every routing message, the network drowns in overhead. Classic flooding means exponential message growth. In a 100-node network, a single announcement could trigger thousands of retransmissions.

OLSR's innovation is multipoint relays (MPRs). Instead of every node forwarding broadcasts, each node selects a minimal set of neighbors to act as relays. These MPR nodes are chosen strategically—they're positioned to reach all two-hop neighbors with minimal redundancy.

The result: routing updates flood the network, but with a fraction of the messages. You get complete topology information without drowning in broadcasts. It's routing by consensus, optimized for wireless.

How it works

OLSR operates through two types of messages, both sent via UDP on port 698:

HELLO messages — Each node broadcasts HELLO packets to discover its immediate neighbors and measure link quality. These messages stay local—they're never forwarded. They answer: "Who can I reach directly?"

Topology Control (TC) messages — Nodes selected as MPRs broadcast TC messages containing their routing table information. These messages are forwarded by other MPRs, flooding the network efficiently. They answer: "Who can everyone else reach?"

From these messages, each node builds a complete topology map of the network. It knows not just its neighbors, but the entire graph of who connects to whom. Then it runs Dijkstra's shortest-path algorithm to compute routes to every destination.

The topology map updates continuously. As nodes move, as links fail, as new devices join—the HELLO and TC messages adapt, and routes recalculate automatically.

The history

RFC 3626, published in October 2003, defined OLSR as an experimental protocol.¹ The work came from Project Hipercom at INRIA (the French National Institute for Research in Computer Science and Automation), with Thomas Clausen and Philippe Jacquet as editors.

The protocol emerged from research into mobile ad-hoc networks (MANETs)—scenarios where wireless devices form networks without infrastructure. Military communications. Disaster relief. Sensor networks. Any situation where you can't rely on fixed routers and predetermined topology.

But the real-world deployment that proved OLSR's viability came from an unexpected place: community wireless networks.

Freifunk and the mesh revolution

In Germany, the Freifunk initiative (German for "free radio") built city-scale mesh networks using OLSR. The idea was simple: anyone could set up a wireless router running Freifunk firmware, and it would automatically mesh with neighboring routers. No central planning. No ISP required. Just neighbors sharing connectivity.

By 2026, Freifunk counts about 400 local communities with over 41,000 access points across Germany.² Cities like Munich, Berlin, and Hamburg have networks spanning thousands of nodes. And it works—ordinary people running ordinary routers, forming Internet infrastructure through pure cooperation.

The protocol spread beyond Germany. The OLPC (One Laptop Per Child) project in Afghanistan used Freifunk for mesh deployments, distributing digital books and educational media.³ In Ghana, mesh networks bridge the digital divide in villages. In Vietnam, they provide Internet at FOSS conferences. Wherever infrastructure is absent or unreliable, OLSR-based meshes fill the gap.

Why mesh networks matter

Port 698 represents a different model of networking. Not hierarchical—peer-to-peer. Not centrally controlled—self-organizing. Not reliant on infrastructure—resilient by design.

When a hurricane destroys cell towers, mesh networks can form from whatever devices survived. When authoritarian regimes shut down the Internet, mesh networks can route around the censorship. When communities can't afford or access traditional ISPs, mesh networks let them build their own infrastructure.

OLSR makes this possible by solving the routing problem elegantly. It gives every node enough information to make intelligent routing decisions, while keeping overhead manageable. It's the mathematical foundation beneath the social movement of community wireless.

Security considerations

OLSR has no built-in security. Any node can inject routing messages. Any device can claim to be an MPR. Any packet on port 698 is trusted by default.

This is by design—OLSR assumes a cooperative network. In community meshes, participants trust each other. In military or disaster scenarios, the network is physically isolated. Authentication and encryption would add overhead and complexity that many deployments don't need.

But it means OLSR is vulnerable in adversarial environments:

• Route injection attacks — Malicious nodes can advertise false routes, attracting traffic
• Denial of service — Flooding the network with fake topology messages can overwhelm legitimate routing
• Eavesdropping — All routing traffic is plaintext, exposing network topology

If you're deploying OLSR in an untrusted environment, you need additional security layers. Encrypted tunnels between nodes. Authentication of routing messages. Network segmentation. OLSR itself won't protect you—it's optimized for efficiency, not security.

Checking for OLSR traffic

To see if OLSR is running on your system:

# Check what's listening on port 698
sudo lsof -i :698
sudo netstat -tulpn | grep :698

# On Linux, check for the olsrd daemon
ps aux | grep olsrd

# Capture OLSR packets
sudo tcpdump -i any udp port 698 -v

If you see traffic on port 698 and you're not intentionally running a mesh network, investigate. It could be legitimate mesh networking software, or it could be something unexpected.

Related ports

• Port 520 — RIP (Routing Information Protocol), the simpler distance-vector routing protocol
• Port 179 — BGP (Border Gateway Protocol), how the Internet's backbone routers exchange routes
• Port 89 — OSPF, the link-state protocol OLSR was inspired by