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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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Configuring Resilient Ethernet Protocol
This chapter describes how to use Resilient Ethernet Protocol (REP) on the Cisco ME 3400 Ethernet
Access switch. REP is a Cisco proprietary protocol that provides an alternative to Spanning Tree
Protocol (STP) to control network loops, handle link failures, and improve convergence time. REP
controls a group of ports connected in a segment, ensures that the segment does not create any bridging
loops, and responds to link failures within the segment. REP provides a basis for constructing more
complex networks and supports VLAN load balancing.
The switch supports REP only when it is running the metro IP access or metro access image.
This chapter includes these sections:
• Understanding REP, page 17-1
• Configuring REP, page 17-6
• Monitoring REP, page 17-12

Understanding REP

One REP segment is a chain of ports connected to each other and configured with a segment ID. Each
segment consists of standard (non-edge) segment ports and two user-configured edge ports. A switch can
have no more than two ports that belong to the same segment, and each segment port can have only one
external neighbor. A segment can go through a shared medium, but on any link only two p orts can belong
to the same segment. REP is supported only on Layer 2 trunk interfaces.
Figure 17-1 shows an example of a segment consisting of six ports spread across four switches. Ports E1
and E2 are configured as edge ports. When all ports are operational (as in the segment on the left), a
single port is blocked, shown by the diagonal line. When there is a failure in the network, as shown in
the diagram on the right, the blocked port returns to the forwarding state to minimize network disruption.