Dell PowerConnect B-RX BigIron RX Series Configuration Guide v02.7.02 - Page 274

7 Configuring forwarding parameters How multiple equal-cost paths enter the IP Route table IP load sharing applies to equal-cost paths in the IP route table. Routes eligible for load sharing can enter the table from the following sources: • IP static routes • Routes learned through RIP, OSPF, and BGP4 Administrative distance The administrative distance is a unique value associated with each type (source) of IP route. Each path has an administrative distance. It is used when evaluating multiple equal-cost paths to the same destination from different sources, such as RIP, OSPF and so on, but not used when performing IP load sharing. The value of the administrative distance is determined by the source of the route. The device is configured with a unique administrative distance value for each IP route source. When the software receives paths from different sources to the same destination, the software compares their administrative distances, selects the one with the lowest distance, and puts it in the IP route table. For example, if the device has a path learned from OSPF and a path learned from RIP for a given destination, only the path with the lower administrative distance enters the IP route table. Here are the default administrative distances on the device: • 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 router will not use this route) Lower administrative distances are preferred over higher distances. For example, if the router receives routes for the same network from OSPF and from RIP, the router will prefer the OSPF route by default. NOTE You can change the administrative distances individually. Refer to 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 paths from the same IP route source to the same destination. 202 BigIron RX Series Configuration Guide 53-1001810-01