Cisco Industrial Ring Redundancy: REP vs MRP vs PRP vs HSR vs DLR

Cisco industrial switches support five ring and redundancy protocols, and they fall into two groups. REP (Cisco-proprietary) and MRP (IEC 62439-2, the PROFINET standard) recover a ring in milliseconds to sub-second. PRP and HSR (both IEC 62439-3) deliver zero-loss redundancy — PRP over two parallel networks, HSR within a ring. DLR (defined by ODVA for EtherNet/IP) recovers a ring in under 3 ms. REP and MRP run across the Cisco IE lineup; PRP, HSR, and DLR require an IE3400 or IE9300.

This guide is for engineers choosing a redundancy protocol for an industrial network: how each one works, the recovery time it actually delivers, the fieldbus ecosystem it belongs to, and — the part most comparisons skip — which Cisco IE switch you have to buy to run it.

Industrial Ring Redundancy Protocols Compared

The table below summarizes the five protocols on the attributes that decide a design: the standard behind them, the topology they use, worst-case recovery time, the automation ecosystem they pair with, and the Cisco Catalyst IE switches that support them.

Protocol	Standard	Topology	Recovery time	Ecosystem	Cisco IE support
REP	Cisco proprietary	Ring / segment	~50 ms to sub-second by media; REP Fast ≤50 ms	Cisco networks	IE3100, IE3200, IE3300, IE3400, IE9300
MRP	IEC 62439-2	Ring	500 / 200 / 30 ms (≤50 nodes); 10 ms (≤14); default 200 ms	PROFINET	IE3100, IE3200, IE3300, IE3400
PRP	IEC 62439-3	Parallel (two LANs)	Zero (bumpless)	IEC 61850, utilities	IE3400, IE9300
HSR	IEC 62439-3	Ring	Zero (seamless)	IEC 61850, utilities	IE3400, IE9300
DLR	ODVA (EtherNet/IP)	Ring	< 3 ms (≤50 nodes)	EtherNet/IP	IE3400

Two patterns drive every decision that follows. First, recovery time splits the field: PRP, HSR, and DLR are built for near-zero loss, while REP and MRP manage a fast but measurable reconvergence. Second, ecosystem usually picks the protocol for you — PROFINET lines use MRP, EtherNet/IP lines use DLR, and IEC 61850 substations use PRP or HSR.

Ring vs Parallel Redundancy: Why PRP Is Not a Ring

Four of these five protocols are true ring protocols — REP, MRP, HSR, and DLR all run on a closed loop of switches and recover when a link in the ring breaks. PRP is the exception. PRP does not use a ring at all: it duplicates every frame across two completely independent parallel networks, LAN A and LAN B, and the receiver takes whichever copy arrives first. Calling it “ring redundancy” is loose shorthand; mechanically it is parallel redundancy.

That distinction matters because it changes how loss is handled. A ring protocol always has a moment of reconvergence after a break — even if it is under 3 ms with DLR — because traffic has to be redirected around the failure. PRP and HSR avoid that moment entirely by sending two live copies at once, so a single failure costs zero frames. The trade-off is infrastructure: HSR gets its zero loss inside one ring, while PRP needs two full parallel networks and dual-attached end devices (or a RedBox to attach single-interface gear). Group the five as zero-loss (PRP, HSR, DLR) versus managed-recovery (REP, MRP), and the rest of the choice gets simple.

What Is REP, Cisco’s Resilient Ethernet Protocol?

REP is Cisco’s proprietary alternative to Spanning Tree Protocol for ring and segment topologies. Instead of STP’s slower tree reconvergence, REP defines a segment of switches with one blocked port that opens the instant a link fails, giving faster and more predictable recovery on a Cisco ring. It is the default choice when the whole ring is Cisco and you want simple, fast Layer 2 resiliency without a fieldbus-specific protocol.

REP’s recovery depends on the media. On Fast Ethernet, link-down detection is about 10 ms and convergence is roughly 50 ms; on fiber Gigabit it is in the tens to low hundreds of milliseconds; on copper Gigabit it can run to 500–750 ms because of the slower link-down detection on RJ-45. REP Fast, the enhanced mode, brings convergence to within 50 ms when neighboring switches also run REP Fast. Because REP is Cisco-proprietary, every node in the ring must be a Cisco switch — it does not interoperate with third-party industrial gear, which is the main reason to choose an open standard instead.

MRP: Media Redundancy Protocol for PROFINET Rings

MRP is the open ring-redundancy standard defined in IEC 62439-2, and it is the protocol PROFINET networks use. One switch acts as the Media Redundancy Manager (MRM) that controls the ring and blocks one port; the rest act as Media Redundancy Clients (MRC). If a link fails, the manager reopens the blocked port to restore the loop. Because it is an open standard, MRP interoperates with conformant PROFINET devices from other vendors, which is why Siemens-based lines standardize on it.

MRP’s recovery time is configurable by ring size. IEC 62439-2 specifies worst-case recovery of 500 ms, 200 ms, or 30 ms for rings of up to 50 switches, and 10 ms for rings of up to 14 switches; Cisco IE switches default to 200 ms for a ring of up to 50 nodes. For most PROFINET cells the 200 ms profile is adequate, but motion and fast-process applications that need the 30 ms or 10 ms profiles must respect the node-count limits that come with them.

PRP Explained: Zero-Loss Over Two Parallel Networks

PRP, defined in IEC 62439-3, delivers seamless redundancy by sending every frame twice over two independent LANs at the same time. A doubly-attached node (DANP) transmits identical copies on LAN A and LAN B; the receiver accepts the first copy and discards the duplicate. Because both networks carry live traffic continuously, a failure of one entire LAN causes zero recovery time and zero lost frames — there is nothing to reconverge. Single-interface devices attach through a RedBox (redundancy box) that does the duplication on their behalf.

This bumpless behavior is why PRP is a staple of IEC 61850 substation automation and other hard-real-time utility networks, where even a few milliseconds of loss is unacceptable. The cost is that you build and maintain two separate networks rather than one ring, and end devices (or RedBoxes) must be dual-attached. On Cisco, PRP is an FPGA-based feature: the IE3400 supports a single PRP instance on a fixed set of ports (Gi1/1–Gi1/4), and the IE9300 aggregation series supports it on specific models.

How Does HSR Differ From PRP?

HSR is the ring-topology member of the same IEC 62439-3 family, and it solves the same zero-loss problem with less infrastructure. Where PRP needs two parallel networks, HSR puts the redundancy inside a single ring: each node sends every frame in both directions around the loop — one copy clockwise, one counter-clockwise — and the destination keeps the first to arrive. The result is the same seamless, zero-frame-loss recovery as PRP, but in one ring instead of two LANs.

The practical choice between them comes down to topology and end devices. HSR suits a ring of HSR-aware nodes and avoids building a second network, while PRP suits a flat plant where devices already have two interfaces or sit behind RedBoxes, and where the two-LAN design is acceptable. PRP and HSR are also commonly bridged at the boundary of an IEC 61850 network. On Cisco, HSR — like PRP — depends on the FPGA, so it runs on the IE3400 and IE9300, not on the IE3200 or IE3300.

DLR: Device Level Ring for EtherNet/IP

DLR is the ring-redundancy protocol for EtherNet/IP, defined by ODVA, and it is what Rockwell/Allen-Bradley automation networks use at the device level. A DLR ring has a ring supervisor that monitors the loop and blocks one path; when a link fails, the supervisor reconverges the ring extremely fast. DLR recovers in under 3 ms for rings of up to 50 nodes, which puts it close to the zero-loss protocols while keeping the simplicity of a single ring of EtherNet/IP devices.

On Cisco, the IE3400 can act as a DLR ring supervisor, backup supervisor, or a regular beacon-based ring node, helping the connected devices recover from a ring fault within 3 ms. The IE3400’s FPGA redundancy profile supports two DLR rings on the base system and up to three rings when an expansion module is added. As with PRP and HSR, DLR is an FPGA feature, so it is an IE3400 capability — not something the IE3200 or IE3300 can run.

Choosing a Ring Redundancy Protocol by Fieldbus and Recovery

For most networks the automation ecosystem makes the decision before recovery time does. Choose MRP for PROFINET lines and DLR for EtherNet/IP lines — those are the native ring protocols for each fieldbus, and matching the protocol to the controller ecosystem keeps device interoperability and engineering tools straightforward. Choose PRP or HSR when you need true zero-loss redundancy, typically IEC 61850 substations and utility automation: PRP when devices are dual-attached across two networks, HSR when you want zero loss inside a single ring. Choose REP when the ring is all-Cisco and you want fast, simple Layer 2 resiliency without a fieldbus-specific protocol.

Recovery time is the tie-breaker when ecosystem does not decide. If you cannot lose a single frame, only PRP and HSR (zero loss) or DLR (under 3 ms) qualify. If a short, bounded reconvergence is acceptable, MRP (down to 10–30 ms on small rings) and REP (≤50 ms with REP Fast) are simpler to deploy. Avoid REP when any node is non-Cisco — it is proprietary and will not interoperate — and avoid assuming a basic switch can run the zero-loss protocols, because that is a hardware question, covered next.

Which Cisco IE Switch Supports Each Protocol?

This is where protocol choice becomes a purchasing decision, because the five protocols do not run on the same hardware. Managed-ring redundancy is available across the rugged lineup, but the zero-loss and EtherNet/IP protocols depend on the IE3400’s FPGA and the IE9300 platform.

REP and MRP: Supported Across the IE Lineup

REP runs on the IE3100, IE3200, IE3300, IE3400, and IE9300, and MRP runs on the IE3100, IE3200, IE3300, and IE3400 (including the IE3400 Heavy Duty). If your design only needs a managed Cisco ring (REP) or a PROFINET ring (MRP), a Catalyst IE3300 rugged switch is enough, and the choice between models comes down to ports, modularity, and power rather than the protocol. For a model-by-model look at the two most common edge platforms, see our Cisco IE3300 and IE3400 comparison.

PRP, HSR, and DLR: IE3400 and IE9300 Only

PRP, HSR, and DLR are FPGA-based features. The IE3200 and IE3300 do not support them — a Network Advantage license does not change that, because the capability is in the IE3400’s hardware, not the license tier. For zero-loss or EtherNet/IP ring redundancy you need a Catalyst IE3400 rugged switch at the edge (PRP on Gi1/1–Gi1/4, HSR, or DLR supervisor with sub-3 ms recovery), or a Catalyst IE9300 aggregation switch for PRP and HSR at the distribution layer. Sizing a substation or EtherNet/IP design around these protocols is exactly the kind of BOM question to confirm before ordering.

Frequently Asked Questions

What is the difference between PRP and HSR?

Both are defined in IEC 62439-3 and both give zero-loss, seamless redundancy by sending duplicate frames. The difference is topology: PRP duplicates traffic across two independent parallel networks (LAN A and LAN B), while HSR sends both copies around a single ring in opposite directions. PRP needs two full networks and dual-attached devices; HSR achieves the same zero loss inside one ring.

Which industrial redundancy protocol has the fastest recovery?

PRP and HSR are the fastest because they have no recovery time at all — both paths are always live, so a single failure loses zero frames. DLR recovers in under 3 ms. MRP can reach 10–30 ms on small rings, and REP runs from about 50 ms to several hundred milliseconds depending on the media, with REP Fast within 50 ms.

Should I use MRP or DLR?

Match the protocol to your fieldbus. Use MRP on PROFINET networks and DLR on EtherNet/IP networks — each is the native ring protocol for that ecosystem, so it interoperates with the controllers and devices already on the line. Mixing the two on the same ring is not how either is designed to run.

Does the Cisco IE3300 support PRP or HSR?

No. PRP, HSR, and DLR depend on the IE3400’s FPGA, so the IE3200 and IE3300 cannot run them, even with a Network Advantage license. The IE3300 does support REP and MRP. For PRP, HSR, or DLR you need an IE3400 or, at the aggregation layer, an IE9300.

Do these protocols work with non-Cisco devices?

MRP, PRP, HSR, and DLR are open standards (IEC 62439-2, IEC 62439-3, and ODVA EtherNet/IP), so they interoperate with conformant devices from other vendors. REP is Cisco-proprietary and works only between Cisco switches, so a REP ring must be all-Cisco.

Final Buying Note

The protocol usually picks itself from your fieldbus and your loss tolerance — MRP for PROFINET, DLR for EtherNet/IP, PRP or HSR for zero-loss IEC 61850, REP for an all-Cisco ring. The hardware is the part to get right before you order: REP and MRP run across the IE3100–IE3400 range, but PRP, HSR, and DLR require an IE3400 at the edge or an IE9300 in aggregation. Layer23-Switch can confirm the right platform, port placement, and licensing for your redundancy design and quote brand-new original Cisco units with warranty and RMA.