Interface Cost; Electing The Designated Router And Backup; Summarizing Routes - IBM RackSwitch G8000 Application Manual

Interface Cost

Electing the Designated Router and Backup

Summarizing Routes

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RackSwitch G8000: Application Guide
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):
RS G8000(config-ip-if)#
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 G8000. The
command is as follows:
RS G8000(config-ip-if)#
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:
RS G8000(config-ip-if)#
RS G8000(config-ip-if)#
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:
RS G8000(config)# router ospf
RS G8000(config-router-ospf)#
<IP address> <mask>
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
cost value (1-65535)
<
ip ospf cost
ip ospf priority <priority value (0-255)>
ip ospf passive-interface
exit
area-range <range number> address
"Example 3: Summarizing Routes" on page
>
277.