Cisco IE 4000, Software Configuration Manual

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Configuring Resilient Ethernet Protocol
Information About Configuring REP

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.
Link Integrity
REP does not use an end-to-end polling mechanism between edge ports to verify link integrity. It implements local link
failure detection. The REP Link Status Layer (LSL) detects its REP-aware neighbor and establishes connectivity within
the segment. All VLANs are blocked on an interface until it detects the neighbor. After the neighbor is identified, REP
determines which neighbor port should become the alternate port and which ports should forward traffic.
Each port in a segment has a unique port ID. The port ID format is similar to that used by the spanning tree algorithm: a
port number (unique on the bridge), associated to a MAC address (unique in the network). When a segment port is
coming up, its LSL starts sending packets that include the segment ID and the port ID. The port is declared as operational
after it performs a three-way handshake with a neighbor in the same segment.
A segment port does not become operational if:

No neighbor has the same segment ID.

More than one neighbor has the same segment ID.

The neighbor does not acknowledge the local port as a peer.
Each port creates an adjacency with its immediate neighbor. Once the neighbor adjacencies are created, the ports
negotiate to determine one blocked port for the segment, the alternate port. All other ports become unblocked. By
default, REP packets are sent to a BPDU class MAC address. The packets can also be sent to the Cisco multicast address,
which is used only to send blocked port advertisement (BPA) messages when there is a failure in the segment. The
packets are dropped by devices not running REP.
Fast Convergence
Because REP runs on a physical link basis and not a per-VLAN basis, only one hello message is required for all VLANs,
reducing the load on the protocol. We recommend that you create VLANs consistently on all switches in a given segment
and configure the same allowed VLANs on the REP trunk ports. To avoid the delay introduced by relaying messages in
software, REP also allows some packets to be flooded to a regular multicast address. These messages operate at the
hardware flood layer (HFL) and are flooded to the whole network, not just the REP segment. Switches that do not belong
to the segment treat them as data traffic. You can control flooding of these messages by configuring a dedicated
administrative VLAN for the whole domain.
The estimated convergence recovery time on fiber interfaces is less than 200 ms for the local segment with 200 VLANs
configured. Convergence for VLAN load balancing is 300 ms or less.
VLAN Load Balancing
One edge port in the REP segment acts as the primary edge port; the other as the secondary edge port. It is the primary
edge port that always participates in VLAN load balancing in the segment. REP VLAN balancing is achieved by blocking
some VLANs at a configured alternate port and all other VLANs at the primary edge port. When you configure VLAN load
balancing, you can specify the alternate port in one of three ways:

By entering the port ID of the interface. To identify the port ID of a port in the segment, enter the show interface rep
detail interface configuration command for the port.