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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
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 ports can belong
to the same segment. REP is supported only on Layer 2 trunk interfaces.
Figure 23-1 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 disrup tion.
Figure 23-1 REP Open Segments
The segment shown in Figure 23-1 is an open segment; there is no connectivity between the two edge
ports. The REP segment cannot cause a bridging loop and it is safe to connect the segment edges to any
network. All hosts connected to switches inside the segment have two possible connections to the rest
of the network through the edge ports, but only one connection is accessible at any time. If a failure
causes a host to be unable to access its usual gateway, REP unblocks all ports to ensure that connectivity
is available through the other gateway.
The segment shown in Figure 23-2, with both edge ports located on the same switch, is a ring segment.
In this configuration, there is connectivity between the edge ports through the segment. With this
configuration, you can create a redundant connection between a ny two switches in the segment.
Figure 23-2 REP Ring Segment
E2E1 E2E1
E1 Edge port
Blocked port
Link failure
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E2E1
201889