Rep Configuration Guidelines - Cisco IE-4000 Software Configuration Manual

Configuring Resilient Ethernet Protocol
REP Segments
When VLAN load balancing is enabled, the default is manual preemption with the delay timer disabled. If VLAN load
balancing is not configured, the default after manual preemption is to block all VLANs at the primary edge port.

REP Configuration Guidelines

Follow these guidelines when configuring REP:

We recommend that you begin by configuring one port and then configure the contiguous ports to minimize the
number of segments and the number of blocked ports.

If more than two ports in a segment fail when no external neighbors are configured, one port changes to a forwarding
state for the data path to help maintain connectivity during configuration. In the show rep interface privileged EXEC
command output, the Port Role for this port shows as Fail Logical Open; the Port Role for the other failed port shows
as Fail No Ext Neighbor. When the external neighbors for the failed ports are configured, the ports go through the
alternate port state transitions and eventually go to an open state or remain as the alternate port, based on the
alternate port election mechanism.

REP ports must be Layer 2 trunk ports.

Be careful when configuring REP through a Telnet connection. Because REP blocks all VLANs until another REP
interface sends a message to unblock it, you might lose connectivity to the switch if you enable REP in a Telnet
session that accesses the switch through the same interface.

You cannot run REP and STP or REP and Flex Links on the same segment or interface.

If you connect an STP network to the REP segment, be sure that the connection is at the segment edge. An STP
connection that is not at the edge could cause a bridging loop because STP does not run on REP segments. All STP
BPDUs are dropped at REP interfaces.

You must configure all trunk ports in the segment with the same set of allowed VLANs, or a misconfiguration occurs.

REP ports follow these rules:
— There is no limit to the number of REP ports on a switch; however, only two ports on a switch can belong to the
same REP segment.
— If only one port on a switch is configured in a segment, the port should be an edge port.
— If two ports on a switch belong to the same segment, they must be both edge ports, both regular segment ports,
or one regular port and one edge no-neighbor port. An edge port and regular segment port on a switch cannot
belong to the same segment.
— If two ports on a switch belong to the same segment and one is configured as an edge port and one as a regular
segment port (a misconfiguration), the edge port is treated as a regular segment port.

REP interfaces come up in a blocked state and remains in a blocked state until notified that it is safe to unblock. You
need to be aware of this to avoid sudden connection losses.

REP sends all LSL PDUs in untagged frames on the native VLAN. The BPA message sent to the Cisco multicast
address is sent on the administration VLAN, which is VLAN 1 by default.

You can configure how long a REP interface remains up without receiving a hello from a neighbor. You can use the
rep lsl-age-timer value interface configuration command to set the time from 120 ms to 10000 ms. The LSL hello
timer is then set to the age-timer value divided by 3. In normal operation, three LSL hellos are sent before the age
timer on the peer switch expires and checks for hello messages.
— In Cisco IOS Release 12.2(52)SE, the LSL age-timer range changed from 3000 to 10000 ms in 500-ms
increments to 120 to 10000 ms in 40-ms increments. If the REP neighbor device is not running Cisco IOS release
12.2(52)SE or later, do not configure a timer value less than 3000 ms. Configuring a value less than 3000 ms
causes the port to shut down because the neighbor switch does not respond within the requested time period.
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