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Cisco IE 2000 Switch Software Configuration Guide
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Chapter 23 Configuring Resilient Ethernet Protocol
Information About Configuring REP
When VLAN load balancing is triggered, the primary edge port sends out a message to alert all interfaces
in the segment about the preemption. When the secondary port receives the message, it is reflected into
the network to notify the alternate port to block the set of VLANs specified in the message and to notify
the primary edge port to block the remaining VLANs.
You can also configure a particular port in the segment to block all VLANs. Only the primary edge port
initiates VLAN load balancing, which is not possible if the segment is not terminated by an edge port on
each end. The primary edge port determines the local VLAN load balancing configuration.
Reconfigure the primary edge port to reconfigure load balancing. When you cha nge the load balancing
configuration, the primary edge port again waits for the rep preempt segment command or for the
configured preempt delay period after a port failure and re covery before executing the new
configuration. If you change an edge port to a regular segment port, th e existing VLAN load balancing
status does not change. Configuring a new edge port might cause a new top ology configuration.
Spanning Tree Interaction
REP does not interact with STP or with the FlexLink feature, but can coexist with both. A port that
belongs to a segment is removed from spanning tree control and STP BPDUs are not accepted or sent
from segment ports. Therefore, STP cannot run on a segment.
To migrate from an STP ring configuration to REP segment configuration, begin by configuring a single
port in the ring as part of the segment and continue by configuring contiguous ports to minimize the
number of segments. Each segment always contains a blocked port, so multiple segments means multiple
blocked ports and a potential loss of connectivity. When the segment has been configured in both
directions up to the location of the edge ports, you then c onfigure the edge ports.
REP Ports
Ports in REP segments are Failed, Open, or Alternate.
• A port configured as a regular segment port starts as a failed port.
• After the neighbor adjacencies are determined, the port transitions to alternate port state, blocking
all VLANs on the interface. Blocked port negotiations occur and when the segment settles, one
blocked port remains in the alternate role and all other ports become open ports.
• When a failure occurs in a link, all ports move to the failed state. When the alternate port receives
the failure notification, it changes to the open state, forwarding all VLANs.
A regular segment port converted to an edge port, or an edge port converted to a regular segment port,
does not always result in a topology change. If you convert an edge port into a regular segment port,
VLAN load balancing is not implemented unless it has been configured. For VLA N load balancing, you
must configure two edge ports in the segment.
A segment port that is reconfigured as a spanning tree port restarts according the spanning tree
configuration. By default, this is a designated blocking port. If PortFast is configured or if STP is
disabled, the port goes into the forwarding state.