Port 854: DLEP — When radios need to talk to routers

What Runs on Port 854

Port 854 is assigned to DLEP (Dynamic Link Exchange Protocol) for both TCP and UDP.¹ DLEP creates a communication channel between routers and modems—especially tactical radios—so the radio can report changing link characteristics in real time.

When a router relies on a modem or radio to send packets over a wireless link, it needs to know: What's the current data rate? What's the latency? Is the remote node still reachable? DLEP provides those answers as conditions change.

The Problem DLEP Solves

Here's the challenge: You're routing packets through a mobile network. A soldier with a tactical radio walks behind a building. Signal quality drops from excellent to terrible in seconds.

Without DLEP, the router only finds out the link degraded when packets start failing. It infers the problem through timeouts and retransmissions. That takes time—time you don't have in a tactical environment where every second of connectivity matters.

With DLEP, the radio immediately tells the router: "The link just dropped to 100 Kbps and latency spiked to 500ms." The router can make better decisions instantly—reroute traffic, adjust quality-of-service policies, or buffer data until conditions improve.

How DLEP Works

DLEP operates as a bidirectional, event-driven protocol.² The modem or radio maintains a session with the router on port 854 and sends updates whenever link characteristics change:

• Data rate changes — "We just went from 10 Mbps to 1 Mbps"
• Latency updates — "Round-trip time increased to 300ms"
• Link status — "The remote node disappeared" or "Connection restored"

This isn't polling. The radio pushes updates as events occur. When a remote node is lost, DLEP notifies the router immediately, dramatically shortening network reconvergence time compared to waiting for routing protocols to detect the failure.

History and Context

DLEP was developed to address a specific problem in military tactical networks: routers and radios from different manufacturers needed a standard way to communicate link information.³

Tactical wireless networks are characterized by mobility and unpredictable transmission channels—what researchers call DIL (Disconnected, Intermittent, and Limited) environments. Soldiers move. Vehicles drive behind hills. Signal quality fluctuates constantly.

The core DLEP specification was published as RFC 8175 in June 2017.² Since then, multiple extensions have been developed for specific capabilities: multi-hop forwarding (RFC 8629), latency range reporting (RFC 8757), flow control (RFC 9893), and more.

DLEP emerged as part of broader Radio-to-Router Interface (R2RI) standardization efforts, giving heterogeneous tactical networks a common language for link state information.

Who Uses DLEP

DLEP is primarily deployed in:

• Military tactical radio systems — DoD radio systems use DLEP to expose link metrics to routing layers
• Mobile networks with dynamic topologies — Any environment where link quality changes rapidly
• Disaster recovery communications — First responder networks with mobile nodes and variable connectivity

The protocol was developed with military applications in mind but applies to any scenario where routers need real-time awareness of changing wireless link conditions.

Security Considerations

DLEP operates between a router and a directly connected modem or radio—typically a trusted local connection. The protocol itself doesn't mandate encryption, but implementations should secure the channel when operating over untrusted networks.

The risk: If an attacker can inject false DLEP messages, they could trick the router into believing link conditions have degraded (causing unnecessary rerouting) or improved (causing packet loss when the router over-commits to a weak link).

RFC 8175 recommends authentication and encryption for DLEP sessions, especially in tactical environments where adversaries may attempt to disrupt communications.

Why This Port Matters

Port 854 represents a recognition that inference isn't fast enough.

Traditional routing protocols infer link quality from packet loss, delays, and acknowledgment patterns. But the modem already knows the signal strength dropped. The radio already knows the remote node vanished. DLEP gives them a voice.

In tactical networks, this matters. The difference between a router learning about link degradation in 50 milliseconds versus 5 seconds can determine whether a message gets through or a connection fails.

Related Ports

• Port 520 — RIP (Routing Information Protocol), an early dynamic routing protocol
• Port 179 — BGP (Border Gateway Protocol), which routes based on policy and path information
• Port 646 — LDP (Label Distribution Protocol), used in MPLS networks

DLEP doesn't replace routing protocols—it enhances them by providing accurate, timely link state information that routing decisions depend on.