Resilient Ethernet Protocol (REP) on the Cisco ME 3400E 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. REP Configuration Guidelines

Follow these guidelines when configuring REP:

* We recommend that you begin by configuring one port and then configure the contiguous ports to minimize the number of segments and the number of blocked ports. ·If more than two ports in a segment fail when no external neighbors are configured, one port goes into a forwarding state for the data path to help maintain connectivity during configuration. In the show rep interface privileged EXEC command output, the Port Role for this port shows as Fail Logical Open; the Port Role for the other failed port shows as Fail No Ext Neighbor. When the external neighbors for the failed ports are configured, the ports go through the alternate port state transitions and eventually go to an open state or remain as the alternate port, based on the alternate port election mechanism.
* REP ports must be Layer 2 trunk ports.
* Be careful when configuring REP through a Telnet connection. Because REP blocks all VLANs until another REP interface sends a message to unblock it, you might lose connectivity to the switch if you enable REP in a Telnet session that accesses the switch through the same interface. ·You cannot run REP and STP or REP and Flex Links on the same segment or interface. ·If you connect an STP network to the REP segment, be sure that the connection is at the segment edge. An STP connection that is not at the edge could cause a bridging loop because STP does not run on REP segments. All STP BPDUs are dropped at REP interfaces. ·You must configure all trunk ports in the segment with the same set of allowed VLANs, or a misconfigurations occurs.·If REP is enabled on two ports on a switch, both ports must be either regular segment ports or edge ports.

REP ports follow these rules:
If only one port on a switch is configured in a segment, the port should be an edge port. If two ports on a switch belong to the same segment, both ports must be edge ports or both ports must be regular segment ports.
If two ports on a switch belong to the same segment and one is configured as an edge port and one as a regular segment port (a misconfiguration), the edge port is treated as a regular segment port.

*REP interfaces come up in a blocked state and remains in a blocked state until notified that it is safe to unblock. You need to be aware of this to avoid sudden connection losses. ·REP sends all LSL PDUs in untagged frames on the native VLAN. The BPA message sent to the Cisco multicast address is sent on the administration VLAN, which is VLAN 1 by default. ·REP ports can not be configured as one of these port types:
SPAN destination port
Private VLAN port
Tunnel port
Access port

* On a Cisco ME-3400 switch, REP ports must be network node interfaces (NNI). User-network interfaces (UNIs) cannot be REP ports.
* REP is supported on EtherChannels, but not on an individual port that belongs to an EtherChannel.
* There is a maximum of 64 REP segments per switch.