How do you implement loop-free alternate paths with EAPS or ERPS?

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Loop detection and protection are essential for preventing network instability and congestion caused by broadcast storms, multiple frame copies, and MAC address table corruption. In a LAN switching environment, you can use different methods to avoid or mitigate loops, such as Spanning Tree Protocol (STP), Rapid Spanning Tree Protocol (RSTP), or Multiple Spanning Tree Protocol (MSTP). However, these protocols have some limitations, such as slow convergence, high CPU utilization, and complex configuration. Alternatively, you can use Ethernet Automatic Protection Switching (EAPS) or Ethernet Ring Protection Switching (ERPS) to implement loop-free alternate paths in your network. In this article, you will learn how to do that and what are the benefits and drawbacks of each method.

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Brent Addis

I secure your networks and infrastructure using a Zero Trust architecture methodology. | Trust Nothing | PCNSE |…

1 What is EAPS?

EAPS is a proprietary protocol developed by Extreme Networks that provides fast and simple loop protection for Layer 2 networks. EAPS works by creating one or more logical rings of switches, where one link is designated as the control link and the other links are the data links. The control link is blocked by default to prevent loops, and only used to exchange EAPS messages between the master and the slave nodes. The master node monitors the status of the data links and sends EAPS messages to the slave node to unblock or block the control link as needed. If a data link fails, the master node detects the failure and instructs the slave node to unblock the control link, thus creating an alternate path for traffic. The recovery time is typically less than 50 milliseconds.

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Brent Addis

I secure your networks and infrastructure using a Zero Trust architecture methodology. | Trust Nothing | PCNSE | Extreme Blackbelt #491
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Having used EAPS myself inside of a variety of organisations I can confirm it's ease of use, and that yes, bring up an alternate path is less than 50 milliseconds (During scheduled failover we generally don't lose traffic at all). I've run EAPS in many situations over the past 15 years, covering a single building, up to an EAPS ring around the length of the north island on NZ, covering roughly 800km's as the crow flies. Failover was always seamless, and during Cyclone Gabrielle fell over to the western ring flawlessly when the primary fibre provider was ripped up.

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2 What is ERPS?

ERPS is a standardized protocol defined by ITU-T G.8032 that provides loop protection and fast recovery for Ethernet ring topologies. ERPS works by creating a ring of switches, where one link is designated as the ring protection link (RPL) and the other links are the ring links. The RPL is blocked by default to prevent loops, and only used to exchange ERPS messages between the nodes. Each node has a role of either ring port or RPL owner, depending on its position in the ring. The RPL owner is responsible for monitoring the status of the ring links and sending ERPS messages to the other nodes to unblock or block the RPL as needed. If a ring link fails, the RPL owner detects the failure and sends an ERPS message to unblock the RPL, thus creating an alternate path for traffic. The recovery time is typically less than 50 milliseconds.

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3 How to configure EAPS?

In order to configure EAPS, each switch in the ring needs to undergo the following steps: creating an EAPS domain and assigning a domain ID, defining the control VLAN and the protected VLANs, configuring the master node and the control port, configuring the transit node and the data ports, and enabling EAPS on the domain. For example, to configure EAPS on switch A as the master node, you can use commands such as “create eaps eaps1”, “configure eaps eaps1 domain 1”, “configure eaps eaps1 mode master”, “configure eaps eaps1 control-vlan control”, “configure eaps eaps1 protected-vlan vlan10”, “configure eaps eaps1 add port 1:1 control”, “configure eaps eaps1 add port 1:2 data”, and “enable eaps”.

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4 How to configure ERPS?

To configure ERPS, you need to perform the following steps on each switch in the ring: create an ERPS instance and assign an instance ID, define the RPL owner, the RPL port, and the ring ports, configure the control VLAN and the protected VLANs, and enable ERPS on the instance. For example, to configure ERPS on switch A as the RPL owner, you can use the commands listed in the code block. It is important to note that this process must be repeated for each switch in the ring in order to ensure successful ERPS configuration.

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5 What are the advantages and disadvantages of EAPS and ERPS?

EAPS and ERPS both provide fast and reliable loop protection and recovery for Ethernet rings, but they have distinct advantages and disadvantages. For example, EAPS is vendor-specific, while ERPS is vendor-neutral, meaning EAPS only works with Extreme Networks switches while ERPS works with any switch that supports the standard. Additionally, EAPS uses a master-slave model, while ERPS uses a distributed model. This means EAPS relies on a single master node to control the loop protection, while ERPS relies on a consensus among all nodes. Furthermore, EAPS blocks the control link while ERPS blocks the RPL. This means that EAPS uses one less link for data traffic and may have less bandwidth utilization than ERPS, which uses one more link for control traffic and may have more latency and jitter.

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Brent Addis

I secure your networks and infrastructure using a Zero Trust architecture methodology. | Trust Nothing | PCNSE | Extreme Blackbelt #491
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I can agree with this. Also I have always found EAPS far easier to configure with a smaller required config. EAPS will also allow you to use CFM (Cable Fault Management). This means that even if a link appears to be okay from a packets getting to the other end perspective, if there is packetloss and/or jitter, it can force a failover. I've found with ERPS when using differing vendors things don't always match up exactly depending on how closely the vendor followed the RFC.

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6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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Brent Addis

I secure your networks and infrastructure using a Zero Trust architecture methodology. | Trust Nothing | PCNSE | Extreme Blackbelt #491
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Consider a single vendor solution if possible, even if choosing ERPS. ERPS is designed to work across multiple vendors, but it's not always a clean solution. My own recommendation would be Extreme and EAPS due to ease of use and the fact CFM is available as an option.

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How do you implement loop-free alternate paths with EAPS or ERPS?

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1 What is EAPS?

2 What is ERPS?

3 How to configure EAPS?

4 How to configure ERPS?

5 What are the advantages and disadvantages of EAPS and ERPS?

6 Here’s what else to consider

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