HP 445946-001 manual Interface cost, Using the area ID to assign the Ospf area number

OSPF

Using the area ID to assign the OSPF area number

The OSPF area number is defined in the areaid <IP address> option. The octet format is used in order to be compatible with two different systems of notation used by other OSPF network vendors. There are two valid ways to designate an area ID:

•Placing the area number in the last octet (0.0.0.n)

Most common OSPF vendors express the area ID number as a single number. For example, the Cisco IOS-based router command network 1.1.1.0 0.0.0.255 area 1 defines the area number simply as area 1. On the switch, using the last octet in the area ID, area 1 is equivalent to areaid 0.0.0.1.

•Multi-octet (IP address)

Some OSPF vendors express the area ID number in multi-octet format. For example, area 2.2.2.2 represents OSPF area 2 and can be specified directly on the switch as areaid 2.2.2.2.

NOTE: Although both types of area ID formats are supported, be sure that the area IDs are in the same format throughout an area.

Attaching an area to a network

Once an OSPF area has been defined, it must be associated with a network. To attach the area to a network, you must assign the OSPF area index to an IP interface that participates in the area. The format for the command is as follows:

>> # /cfg/l3/ospf/if <interface number>/aindex <area index>

For example, the following commands could be used to configure IP interface 14 for a presence on the 10.10.10.1/24 network, to define OSPF area 1, and to attach the area to the network:

>># /cfg/l3/if 14 (Select menu for IP interface 14)

>>IP Interface 14# addr 10.10.10.1(Define IP address on backbone network)

>>IP Interface 14# mask 255.255.255.0(Define IP mask on backbone)

>> IP Interface 14# ena (Enable IP interface 14)

>>IP Interface 14# ../ospf/aindex 1(Select menu for area index 1)

>>OSPF Area (index) 1 # areaid 0.0.0.1(Define area ID as OSPF area 1)

>> OSPF Area (index)	1	#	ena	(Enable area index	1)
>> OSPF Area (index)	1	#	../if 14	(Select OSPF menu for interface 14)
>> OSPF Interface 14# aindex 1				(Attach area to network on
				interface 14)
>> OSPF Interface 14# enable				(Enable interface 14	for area index 1)

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:

>># /cfg/l3/ospf/if <OSPF interface number>/cost <cost value (1-65535)>

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