Dell Brocade DCX, Configuration Manual

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704 BigIron RX Series Configuration Guide
53-1001810-01
Configuring OSPF
25
NOTE
For an external route that is redistributed into OSPF through a route map, the metric value of the
route remains the same unless the metric is set by a set metric command inside the route map. The
default-metric
<num> command has no effect on the route. This behavior is different from a route
that is redistributed without using a route map. For a route redistributed without using a route map,
the metric is set by the default-metric
<num> command.
Disable or re-enable load sharing
BigIron RX can load share among up to eight equal-cost IP routes to a destination. By default, IP
load sharing is enabled. The default is 4 equal-cost paths but you can specify from 2 – 8 paths.
The router software can use the route information it learns through OSPF to determine the paths
and costs.
Figure 108 shows an example of an OSPF network containing multiple paths to a
destination (in this case, R1).
FIGURE 108
Example OSPF network with four equal-cost paths
In the example in Figure 108 , the BigIron RX has four paths to R1:
•
BigIron RX ->R3
•
BigIron RX ->R4
•
BigIron RX ->R5
•
BigIron RX ->R6
Normally, the device will choose the path to the R1 with the lower metric. For example, if R3’s
metric is 1400 and R4’s metric is 600, the device will always choose R4.
However, suppose the metric is the same for all four routers in this example. If the costs are the
same, the router now has four equal-cost paths to R1. To allow the router to load share among the
equal cost routes, enable IP load sharing. The software supports four equal-cost OSPF paths by
default when you enable load sharing. You can specify from 2 – 8 paths.
OSPF Area 0
H1
H2
H3
H4
R1
R3
R4
R5
R6
BigIron RX