Dell PowerConnect B-RX Configuration Manual 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:
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•
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:
•
•
•
•
•
•
•
•
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
IP static routes
Routes learned through RIP, OSPF, and BGP4
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)
BigIron RX Series Configuration Guide
53-1001810-01