Configuring Cost Calculation For A Link - HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual

IP Routing—Configuring RIP, OSPF, BGP, and PBR
Configuring OSPF
13-54

Configuring Cost Calculation for a Link

OSPF was designed for great flexibility in computing a route's metric. An
OSPF route's metric is the sum of the cost for each link between the router
and the destination. Originally, network administrators were supposed to be
able to configure routers to calculate a link's cost according to several fields
in a type of service (ToS) header. However, in practice, OSPF determines cost
primarily by inverse bandwidth.
Typically, there is no need to configure an interface with the link's cost. The
ProCurve Secure Router handles metric computations automatically. It
divides 100 by the bandwidth of the link in Mbps and assigns that value to
the link.
However, you can override the cost the ProCurve Secure Router computes.
For example, you may want to assign a higher cost to a high-speed but
frequently congested link. Or you may want to assign a lower cost to a lower-
speed but cheaper connection.
You assign cost from the configuration mode context of the logical interface
for the link. For example, if the logical interface is Frame Relay, you enter the
command from the Frame Relay subinterface configuration mode context.
For an Ethernet link, you enter it from the Ethernet interface configuration
mode context. You might enter:
ProCurve(config-fr 1.101)# ip ospf cost 130
ProCurve(config-eth 0/1)# ip ospf cost 20
You can also affect the cost the router calculates for a link by changing the
bandwidth the interface reports to OSPF. You would lower the bandwidth
value to raise the cost and raise the bandwidth value to lower the cost. Enter
the following command from the interface configuration mode context:
Syntax: bandwidth <Kbps>
The range for the bandwidth is between 1 and 4,294,967,295 Kbps. For
example, you might enter:
ProCurve(config-fr 1.101)# bandwidth 10000
For a network with high-speed links (links over 100 Mbps), you may need to
change the way the router computes all metrics. The router assigns every
interface its cost by dividing a reference bandwidth by the interface's band-
width. That is, an interface with the same bandwidth as the reference has a
cost of one. An interface with a lower bandwidth has a higher cost.