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BLADEOS 6.5.2 Application Guide
BMD00220, October 2010 Chapter 20: OSPF 281
Interface Cost
The OSPF link-state algorithm (Dijkstra’s algorithm) places each routing device at the root of a tree
and determines the cumulative cost required to reach each destination. Usually, the cost is inversely
proportional to the bandwidth of the interface. Low cost indicates high bandwidth. You can
manually enter the cost for the output route with the following command (Interface IP mode):
Electing the Designated Router and Backup
In any area with more than two routing devices, a Designated Router (DR) is elected as the central
contact for database exchanges among neighbors, and a Backup Designated Router (BDR) is
elected in case the DR fails.
DR and BDR elections are made through the hello process. The election can be influenced by
assigning a priority value to the OSPF interfaces on the G8124. The command is as follows:
A priority value of 255 is the highest, and 1 is the lowest. A priority value of 0 specifies that the
interface cannot be used as a DR or BDR. In case of a tie, the routing device with the highest router
ID wins. Interfaces configured as passive do not participate in the DR or BDR election process:
Summarizing Routes
Route summarization condenses routing information. Without summarization, each routing device
in an OSPF network would retain a route to every subnet in the network. With summarization,
routing devices can reduce some sets of routes to a single advertisement, reducing both the load on
the routing device and the perceived complexity of the network. The importance of route
summarization increases with network size.
Summary routes can be defined for up to 16 IP address ranges using the following command:
where <range number> is a number 1 to 16, <IP address> is the base IP address for the range, and
<mask> is the IP address mask for the range. For a detailed configuration example, see
“Example 3: Summarizing Routes” on page 295.
RS G8124(config-ip-if)# ip ospf cost <cost value (1-65535)>
RS G8124(config-ip-if)#
ip ospf priority <priority value (0-255)>
RS G8124(config-ip-if)# ip ospf passive-interface
RS G8124(config-ip-if)# exit
RS G8124(config)# router ospf
RS G8124(config-router-ospf)#
area-range <range number> address
<IP address> <mask>