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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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Chapter 17 Configuring Resilient Ethernet Protocol
Understanding REP
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.
• By entering the neighbor offset number of a port in the segment, which identifies the downstream
neighbor port of an edge port. The neighbor offset number range is –256 to +256; a value of 0 is
invalid. The primary edge port has an offset number of 1; positive numbers above 1 identify
downstream neighbors of the primary edge port. Negative numbers indicate the secondary edge port
(offset number -1) and its downstream neighbors.
Note You configure offset numbers on the primary edge port by identifying a port’s downstream
position from the primary (or secondary) edge port. You would never enter an offset value of 1
because that is the offset number of the primary edge port itself.
Figure 17-3 shows neighbor offset numbers for a segment where E1 is the primary edge port and E2
is the secondary edge port. The red numbers inside the ring are numbers offset from the primary
edge port; the black numbers outside of the ring show the offset numbers from the secondary edge
port. Note that you can identify all ports (except the primary edge port) by either a positive offset
number (downstream position from the primary edge port) or a negative offset number (downstream
position from the secondary edge port). If E2 became the primary edge port, its offset number would
then be 1 and E1 would be -1.
• By entering the preferred keyword to select the port that you previously configured as the preferred
alternate port with the rep segment segment-id preferred interface configuration command.
Figure 17-3 Neighbor Offset Numbers in a Segment
When the REP segment is complete, all VLANs are blocked. When you configure VLAN load balancing,
it is triggered in one of two ways:
• You can manually trigger VLAN load balancing at any time by entering the rep preempt segment
segment-id privileged EXEC command on the switch that has the primary edge port.
E2E1
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E1 = Primary edge port
E2 = Secondary edge port
Offset numbers from the primary edge port
Offset numbers from the secondary edge
port (negative numbers)