Device Level Ring (DLR) Phase 3 Redundant Gateway

In March 2020, Rockwell Automation released what is referenced as Phase 3 of Device Level Ring (DLR) architectures. Phase 3 bring the capability of Redundant Gateway to a DLR ring.

With Redundant Gateways, multiple communication paths between a DLR ring and the surrounding network infrastructure are possible. Redundant Gateway IES require, at minimum, two physical ports to connect to the DLR network and one or more uplink ports for connection to the surrounding network infrastructure.

According to the ODVA specifications, gateway switchover times can range from 14 ms to 6.1 seconds, depending on the uplink network resiliency protocol chosen.

Redundant Gateway Operation

The primary gateway is the only device that will forward DLR traffic between its DLR ring port, uplink, and IACS end device ports. Backup gateways do not directly link DLR ring ports with the uplink and IACS end device ports and must therefore forward all traffic from directly connected end devices to the surrounding network infrastructure and back to the DLR ring via the primary gateway uplink(s). In the event of an uplink failure, end devices on a backup gateway will lose their connection to ring traffic. It is for this reason that IACS end devices should not be connected to a DLR gateway.


DLR features added in phases

Let’s review the previous DLR phase releases by Rockwell Automation, as well as what’s being planned for the next phase:

  • Phase 1 released in 2018 brought the ability to create a switch level ring.
  • Phase 2 released in 2019 brought the capability to mix switches and devices in a device level ring.
  • Phase 3 now released in 2020 brings redundant gateway capability to a device level ring.
  • Phase 4, planned for 2021, will bring VLAN trunking,

For a deeper dive into Device Level Ring (DLR) operation and architectures, see our previous blog post: https://blog.reynoldsonline.com/device-level-ring/


DLR Phase 3 Reference Architectures

In the Deploying Device Level Ring within a Converged Plantwide Ethernet Architecture Design and Implementation Guide published by Cisco and Rockwell Automation, reference architectures are documented. These reference architectures were fully tested and validated by Rockwell Automation, and their results are published in the document. Below are the four reference architectures for DLR with Redundant Gateway that were validated.

Reference the Design Implementation Guide for complete results and recommendations.

Switch-Level DLR with Redundant Gateway (24 Switches)

For the best performance for IACS applications when communicating to and from outside the DLR, it is recommended to implement the unicast connection type and to use Flex Links or EtherChannel Layer 2 resiliency protocols for the uplinks in redundant star topology. Multicast traffic should be kept local to the DLR ring and limited from traversing the uplinks.


Single Mixed Device/Switch-Level DLR (100 Mbps) with Redundant Gateway

For the best performance for IACS applications when communicating to and from outside the DLR, it is recommended to implement unicast connection type and to use Flex Links or EtherChannel Layer 2 resiliency protocols for the uplinks in redundant star topology. Multicast traffic should be kept local to the DLR ring and limited from traversing the uplinks.


Multiple Mixed Device/Switch-Level DLR with Redundant Gateway at Mixed Ring Speeds (Single VLAN)

For the best performance for IACS applications when communicating to and from outside the DLR, it is recommended to implement unicast connection type and to use Flex Links for Layer 2 resiliency protocol for the uplinks in redundant star topology. Multicast traffic should be kept local to the DLR ring and limited from traversing the uplinks.


Multiple Mixed Device/Switch-Level DLR with Redundant Gateway at Mixed Ring Speeds (Multiple VLAN)

To get the best performance of IACS applications when communicating to and from outside the DLR, it is recommended to implement a unicast connection type and to use EtherChannel for Layer 2 resiliency protocols for the uplinks in redundant star topology. Multicast traffic should be kept local to the DLR ring and limited from traversing the uplinks.


CPwE Reference Architectures

Looking for more information? The chart below provides links to the various CPwE reference architecture white papers and design implementation guides published by Cisco and Rockwell Automation.

TopicDesign GuideWhitepaper
Design Considerations for Securing IACS Networks (CIP Security)N/AENET-WP031A-EN-P
Converged Plantwide Ethernet – Baseline DocumentENET-TD001E-EN-PN/A
Deploying 802.11 Wireless LAN Technology within a Converged Plantwide Ethernet ArchitectureENET-TD006A-EN-PENET-WP034A-EN-P
Deploying Identity and Mobility Services within a Converged Plantwide Ethernet ArchitectureENET-TD008B-EN-PENET-WP037C-EN-P
Securely Traversing IACS Data Across the Industrial Demilitarized Zone (IDMZ)ENET-TD009B-EN-PENET-WP038B-EN-P
Deploying Network Address Translation within a Converged Plantwide Ethernet ArchitectureENET-TD007A-EN-PENET-WP036A-EN-P
Migrating Legacy IACS Networks to a Converged Plantwide Ethernet ArchitectureENET-TD011A-EN-PENET-WP040A-EN-P
Deploying A Resilient Converged Plantwide Ethernet ArchitectureENET-TD010B-EN-PENET-WP039D-EN-P
Deploying Industrial Firewalls within a Converged Plantwide Ethernet ArchitectureENET-TD002A-EN-PENET-WP011B-EN-P
Deploying Device Level Ring within a Converged Plantwide Ethernet ArchitectureENET-TD015C-EN-PENET-WP016D-EN-P
OEM Networking within a Converged Plantwide Ethernet ArchitectureENET-TD018A-EN-PENET-WP018A-EN-P
Cloud Connectivity to a Converged Plantwide Ethernet ArchitectureENET-TD017A-EN-PENET-WP019B-EN-P
Deploying Industrial Data Center within a Converged Plantwide Ethernet ArchitectureENET-TD014A-EN-PENET-WP013A-EN-P
Deploying Scalable Time Distribution within a Converged Plantwide Ethernet ArchitectureENET-TD016A-EN-PENET-WP017B-EN-P
Deploying Network Security within a Converged Plantwide Ethernet ArchitectureENET-TD019A-EN-PENET-WP023B-EN-P
Deploying Parallel Redundancy Protocol within a Converged Plantwide Ethernet ArchitectureENET-TD021A-EN-PENET-WP041A-EN-P

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