Cisco Catalyst 4500 Series, Software Configuration Manual

Page: 761 / 2086

25-5
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 25 Configuring Resilient Ethernet Protocol
About REP
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 never enter an offset value of 1 because
that is the offset number of the primary edge port itself.
Figure 25-4 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 is then
1 and E1 is then -1.
• By entering the preferred keyword to select the port that you previously configured as the preferred
alternate port with the rep segment preferred interface configuration command.
Figure 25-4 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.
•
You can configure a preempt delay time by entering the rep preempt delay seconds interface
configuration command. After a link failure and recovery, VLAN load balancing begins after the
configured preemption time period elapses. Note that the delay timer restarts if another port fails
before the time has elapsed.
Note
When VLAN load balancing is configured, it does not start working until triggered by either manual
intervention or a link failure and recovery.
E2 E1
-1
-2
- 3
-4
-5
-6
-7
- 8
-9
2
1 10
9
8
7
6
5
4
3
201
8
90
E1 = Prim a ry edge port
E2 = S econd a ry edge port
Off s et n u m b er s from the prim a ry edge port
Off s et n u m b er s from the s econd a ry edge
port (neg a tive n u m b er s )