For example, in the OSPF network shown in the following figure, IP load-sharing is enabled on router "A". In this
case, OSPF calculates three equal-cost next-hop routes for each of the subnets and then distributes per-subnet
route assignments across these three routes.
Figure 45: Example of load-sharing traffic to different subnets through equal-cost next-hop routers
Example of a routing table for the network in the preceding figure.
Destination subnet
Router "A" next hop
10.1.0.0/16
Router "C"
10.2.0.0/16
Router "D"
10.3.0.0/16
Router "B"
10.32.0.0/16
Router "B"
10.42.0.0/16
Router "D"
IP load-sharing does not affect routed traffic to different hosts on the same subnet. That is, all traffic for different
hosts on the same subnet will go through the same next-hop router. For example, if subnet 10.32.0.0 includes two
servers at 10.32.0.11 and 10.32.0.22, all traffic from router "A" to these servers will go through router "B".
Global OSPF Cost Setting
The OSPF cost global configuration command implements a parameter at the global level which modifies the
default cost calculation. The configured OSPF cost value can then be modified for a specific VLAN interface,
particular subnet, or complete VLAN. The cost configured with the global command is then used as the default
cost at VLAN level provided it is not explicitly configured locally. When the cost is explicitly configured at VLAN,
this cost will take precedence over the global level cost.
• This global parameter, if configured, must be used as the default value:
Chapter 11 Open Shortest Path First Protocol (OSPF)
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