Interface Cost; Electing The Designated Router And Backup; Summarizing Routes - Lenovo RackSwitch G8264 Application Manual

Interface Cost

Electing the Designated Router and Backup

Summarizing Routes

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G8264 Application Guide for ENOS 8.4
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. You can manually enter the cost for the output route with the
following command (Interface IP mode):
RS G8264(config­ip­if)# ip ospf cost <cost value (1‐65535)>
In any broadcast type subnet, a Designated Router (DR) is elected as the central
contact for database exchanges among neighbors. On subnets with more the one
device, 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 G8264. The
command is as follows:
RS G8264(config­ip­if)# ip ospf priority <priority value (0‐255)>
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 G8264(config­ip­if)# ip ospf passive­interface
RS G8264(config­ip­if)# exit
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 G8264(config)# router ospf
RS G8264(config­router­ospf)# area­range <range number> address <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 "Example 3: Summarizing Routes" on page 576.