What is DLR?
DLR stands for Device Level Ring and is a redundancy protocol designed for fast network recovery at the device level. It is specifically developed for use within Ethernet/IP networks in industrial automation.
DLR provides fast failover (<3 ms) when a cable or device fails, without using external switches or STP-like mechanisms.
🧠 How does DLR work?
- Industrial devices (such as Drives, IO modules, HMIs) are connected to one another in a ring topology
- One device acts as the Ring Supervisor, the others as Ring Nodes
- The supervisor periodically sends beacon messages in both directions
- If beacons are missing on one path, a fault is detected and the ring is healed
- DLR uses Layer 2 Ethernet — fast, without dependence on IP or RSTP
DLR is standardised within the ODVA EtherNet/IP ecosystem and ideal for machine builders and OEM environments.
🏭 Use of DLR in industrial networks
- Local network redundancy in production machines and modular installations
- Building rings with field equipment only (no expensive switches required)
- Fast communication between PLC, Drives, IO and HMI within a skid or line
- Standard in Rockwell Automation systems (Allen-Bradley CompactLogix, ControlLogix)
- Often combined with VLAN or QoS for data segmentation and prioritisation
DLR is used in systems where millisecond recovery is critical but infrastructure must remain compact.
🔍 DLR vs. MRP vs. RSTP
| Protocol | Recovery time | Topology | Managed by | Usage |
|---|---|---|---|---|
| DLR | <3 ms | Ring between devices | Ring Supervisor | EtherNet/IP, Rockwell |
| MRP | <200 ms | Ring with switches | Switch with MRP | Widespread in industrial networks |
| RSTP | 1–10 s | Flexible (mesh/tree) | Switches | Basic redundancy in IT/OT |
🔐 Security considerations
- DLR works without IP addresses → harder to monitor with traditional tools
- Use Port Security and physical security against unauthorised access
- Deploy SIEM or network monitoring with DLR-aware components
- Confine DLR to specific VLAN zones for segmentation
- Only trusted devices should act as Ring Supervisor
A tampered or misconfigured DLR device can disrupt the ring or block recovery.
📌 In summary
DLR is an ultra-fast redundancy protocol for device rings within Ethernet/IP networks that delivers availability with minimal cost and infrastructure. It is particularly useful for compact, modular and time-critical applications in industry.