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12-3
Cisco ASR 901 Series Aggregation Services Router Software Configuration Guide
OL-23826-09
Chapter 12 Configuring Resilient Ethernet Protocol
Understanding Resilient Ethernet Protocol (REP)
• If one or more ports in a segment is not operational, causing a link failure, all ports forward traffic
on all VLANs to ensure connectivity.
• In case of a link failure, the alternate ports are unblocked as quickly as possible. When the failed
link comes back up, a logically blocked port per VLAN is selected with minimal disruption to the
network.
You can construct almost any type of network based on REP segments. REP also supports VLAN
load-balancing, controlled by the primary edge port but occurring at any port in the segment.
In access ring topologies, the neighboring switch might not support REP, as shown in Figure 12-3. In
this case, you can configure the non-REP facing ports (E1 and E2) as edge no-neighbor ports. These
ports inherit all properties of edge ports, and you can configure them the same as any edge port, including
configuring them to send STP or REP topology change notices to the aggregation switch. In this case the
STP topology change notice (TCN) that is sent is a multiple spanning-tree (MST) STP message.
Figure 12-3 No-neighbor Topology
Restrictions
• You must configure each segment port; an incorrect configuration can cause forwarding loops in the
networks.
• REP can manage only a single failed port within the segment; multiple port failures within the REP
segment cause loss of network connectivity.
• You should configure REP only in networks with redundancy. Configuring REP in a network
without redundancy causes loss of connectivity.
E1 and E2 are configured
as edge no-neighbor ports
273792
REP ports
REP not
supported
E2
E1