Configuring IP

Here are the default administrative distances on the HP routing switch:

•Directly connected – 0 (this value is not configurable)

•Static IP route – 1 (applies to all static routes, including default routes and default network routes)

•Exterior Border Gateway Protocol (EBGP) – 20

•OSPF – 110

•RIP – 120

•Interior Gateway Protocol (IBGP) – 200

•Local BGP – 200

•Unknown – 255 (the routing switch will not use this route)

Lower administrative distances are preferred over higher distances. For example, if the routing switch receives routes for the same network from OSPF and from RIP, the routing switch will prefer the OSPF route by default.

NOTE: You can change the administrative distances individually. See the configuration chapter for the route source for information.

Since the software selects only the path with the lowest administrative distance, and the administrative distance is determined by the path’s source, IP load sharing does not apply to paths from different route sources. IP load sharing applies only when the IP route table contains multiple paths to the same destination, from the same IP route source.

IP load sharing does not apply to paths that come from different sources.

Path Cost

The cost parameter provides a common basis of comparison for selecting from among multiple paths to a given destination. Each path in the IP route table has a cost. When the IP route table contains multiple paths to a destination, the routing switch chooses the path with the lowest cost. When the IP route table contains more than one path with the lowest cost to a destination, the routing switch uses IP load sharing to select one of the lowest­ cost paths.

The source of a path’s cost value depends on the source of the path.

•IP static route – The value you assign to the metric parameter when you configure the route. The default metric is 1. See “Configuring Load Balancing and Redundancy Using Multiple Static Routes to the Same Destination” on page 6-41.

•RIP – The number of next-hop routers to the destination.

•OSPF – The Path Cost associated with the path. The paths can come from any combination of inter-area, intra-area, and external Link State Advertisements (LSAs).

•BGP4 – The path’s Multi-Exit Discriminator (MED) value.

NOTE: If the path is redistributed between two or more of the above sources before entering the IP route table, the cost can increase during the redistribution due to settings in redistribution filters.

Static Route, OSPF, and BGP4 Load Sharing

IP load sharing and load sharing for static routes, OSPF routes, and BGP4 routes are individually configured. Multiple equal-cost paths for a destination can enter the IP route table only if the source of the paths is configured to support multiple equal-cost paths. For example, if BGP4 allows only one path with a given cost for a given destination, the BGP4 route table cannot contain equal-cost paths to the destination. Consequently, the IP route table will not receive multiple equal-cost paths from BGP4.

Table 6.6 lists the default and configurable maximum numbers of paths for each IP route source that can provide equal-cost paths to the IP route table. The table also lists where to find configuration information for the route source’s load sharing parameters.

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