Configuring ERP ERP Overview
OmniSwitch AOS Release 8 Network Configuration Guide December 2017 page 11-5
ERP Basic Operation
ERP operates over standard Ethernet interfaces that are physically connected in a ring topology. It uses an
Automatic Protection Switching (APS) protocol to coordinate protection and recovery switching
mechanisms over the Ethernet ring.
In an Ethernet ring, each node is connected to two adjacent nodes using two independent links called ring
links. A ring link is bound by two adjacent nodes on ports called ring ports. The ring nodes support
standard FDB (Filtering database) MAC learning, forwarding, flush behavior, and port blocking and
unblocking mechanisms.
The Ethernet ring has a designated Ring Protection Link (RPL), which is blocked under normal conditions
in order to avoid forming a loop in the ring. When a link or port failure is detected, a Signal Failure (SF)
message is sent on the ring to inform other ring nodes of the failure condition. At this point the ring is
operating in protection mode. When this mode is invoked, the RPL is unblocked forming a new traffic
pattern on the ring, (for example, traffic is accommodated on the RPL but blocked on the failed link). The
node responsible for blocking and unblocking the RPL is called the RPL Owner.
ERP Ring Modes
A ring operates in one of two modes: idle (normal operation; all links up and RPL is blocked) and
protection (protection switching activated; a ring failure has triggered the RPL into a forwarding state).
The following illustration shows an example of an ERP ring operating in the idle mode; all ring nodes are
up and the RPL is blocked:
Normal Mode
If a link or node failure occurs in the ring shown in the above illustration, the ring transitions as follows
into the protection mode:
• Nodes adjacent to the failure detect and report the failure using the R-APS (SF) message.
• The R-APS (SF) message triggers the RPL owner to unblock the RPL.
• All nodes in the ring flush all the dynamic MAC addresses learned on their ring ports.
The ring is now operating in the protection mode, as shown below:
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