Device Level Ring
Device Level Ring (DLR) is a Layer 2 protocol that enables redundancy in a ring topology, providing fast network fault detection and reconfiguration for industrial networks. DLR is an EtherNet/IP™ protocol that is defined by the Open DeviceNet® Vendors’ Association (ODVA).
DLR network includes at least one node configured to be a ring supervisor, and any number of normal ring nodes. All DLR ring nodes are required to have at least two Ethernet ports and incorporate embedded switch technology. Non-DLR multiport devices—switches or end devices—may be present in the ring, subject to certain implementation constraints. (No MAC table filtering is one example.) Non-DLR devices also affect the worst-case ring recovery time.
The DLR protocol supports a simple, single-ring topology. However, a network installation may use more than one DLR-based ring, so long as each ring is isolated so that DLR protocol messages from one ring are not present on another ring.
DLR supports redundant gateways for connecting with network infrastructure outside of the DLR network. The DLR redundant gateway feature provides mechanisms for automatically or manually selecting an active gateway. It also provides for automatic switchover to a backup gateway in the event of a connection failure.
A DLR ring can operate on access or trunk interfaces. A DLR ring configured with access ports can connect switches or end nodes. A DLR ring with trunk interfaces serves as an infrastructure that connects DLR-capable switches and devices in multiple VLANs. All the interfaces on the ring should have the same VLAN membership.