C H A P T E R 22 Configuring Resilient Ethernet Protocol - Cisco Catalyst 4500 Series Configuration Manual

About REP
Figure 22-1
E1
The segment shown in
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
In this configuration, there is connectivity between the edge ports through the segment. With this
configuration, you can create a redundant connection between any two switches in the segment.
Figure 22-2
REP segments have these characteristics:
• If all ports in the segment are operational, one port (referred to as the alternate port) is in the blocked
state for each VLAN. If VLAN load balancing is configured, two ports in the segment control the
blocked state of VLANs.
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.
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
22-2
REP Open Segments
E2
Figure 22-1 is an open segment; there is no connectivity between the two edge
Figure 22-2, with both edge ports located on the same switch, is a ring segment.
REP Ring Segment
E1 E2
Chapter 22 Configuring Resilient Ethernet Protocol
E1
Edge port
E1
Blocked port
Link failure
E2
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