Advanced Configuration and Management Guide

Disable or Re-enable Load Sharing

HP routing switches 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 routing switch software can use the route information it learns through OSPF to determine the paths and costs. Figure 8.8 shows an example of an OSPF network containing multiple paths to a destination (in this case, R1).

 

OSPF Area 0

H1

R3

 

 

R1

H2

R4

H3

HP9308M

 

 

R5

H4

 

 

R6

Figure 8.8 Example OSPF network with four equal-cost paths

In the example in Figure 8.8, the HP routing switch has four paths to R1:

•HP9308M->R3

•HP9308M->R4

•HP9308M->R5

•HP9308M->R6

Normally, the HP routing switch 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 HP routing switch will always choose R4.

However, suppose the metric is the same for all four routing switches in this example. If the costs are the same, the routing switch now has four equal-cost paths to R1. To allow the routing switch 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.

NOTE: The HP routing switch is not source routing in these examples. The routing switch is concerned only with the paths to the next-hop routers, not the entire paths to the destination hosts.

OSPF load sharing is enabled by default when IP load sharing is enabled. To configure IP load sharing parameters, see “Configuring IP Load Sharing” on page 6-48.

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