Resilient Ethernet Protocol (REP)

Resilient Ethernet Protocol (REP) is a protocol used to replace the Spanning Tree Protocol (STP) in some specific Layer 2 network designs. REP is available in the IE-2000 and IE-3400 series switches.

REP Elements

• Segments
• REP uses the concept of a segment. A segment ID is configured on switches' interfaces belonging to the same segment.
• Two edge ports are configured where the REP segment ends. They are not to connect with each other.
• One port is blocking in a segment, called the alternate port.
• Other ports are transit ports.
• REP Port Roles
• REP ports are either failed, open, or alternate.
• All regular segment ports start out as failed ports.
• After adjacencies have been determined, ports move to the Alternate state.
• After negotiations on the Alternate port are done, the remaining ports move to the Open state while one port stays in the Alternate state.
• When a failure occurs on a link, all ports move to the Failed state.
• When the Alternate port receives the notification, it is moved to the Open state.
• REP Link Status Layer (LSL)
• Establishing connectivity with a unique neighbor.
• Periodically checking the integrity of the connection with the neighbor.
• Sending and receiving messages for higher-layer state machines.
• Acknowledging data received from the neighbor.
• Limiting rates of Protocol Data Units (PDUs).
• Hardware Flood Layer (HFL)
• HFL is the REP module that facilitates rapid convergence after link failures.
• HFL sends multicast PDUs to a special MAC address (0100.0ccc.ccce) on the REP administrative VLAN instead of sending PDUs to the BPDU MAC address like LSL.
• REP Operation
• When a port is line protocol up, REP sends out an LSL Hello Message and starts an election or a re-election for port roles of all ports in the segment.
• Upon receiving an LSL, REP sends an acknowledgment to indicate the port is functional.
• When a port is line protocol down, the port becomes a failed port. REP cancels the LSL Hello Message timer and floods the segment with an HFL topology change message.
• Upon receiving an HFL, REP will determine which role the receiving port will take on.

Examples

Current Modeling Limitations

Packet Tracer does not support configuring the primary edge port to send Segment Topology Change Notifications (STCNs) and VLAN load balancing to another port or to other segments.