OSPF Price –
OSPF makes use of a metric referred to as “Price” to calculate the metric of the trail. The price is a cumulative worth which is an incremental metric.
The price is as a default primarily based on the bandwidth of the interface. The Larger the interface bandwidth the decrease the fee that’s related to that interface.
Associated – OSPF LSA Varieties
To view the fee that’s assigned to any given interface which is collaborating in OSPF, the next command is used –
Router# present ip ospf interface
The output of this command will present the present value given to this interface. The prices of the interface is calculated by taking the bandwidth of the interface and dividing this quantity by a worth often known as the “auto-cost reference-bandwidth“. This auto-cost reference-bandwidth is an integer used to calculate a regular metric throughout OSPF and is ready to 100,000,000. The price is calculated as follows:
100,000,000/BW
If the interface bandwidth is 10Mbps, then the ensuing value could be 10:
100,000,000/10,000,000 = 10
If the interface bandwidth is 100Mbps, then the ensuing value could be 1:
100,000,000/100,000,000 = 1
Beneath desk could also be referred whereas calculating the OSPF value for the interface –
The following instance reveals some deficiencies with the auto-cost reference-bandwidth set at 100,000,000. If we had a 1Gbp interface it’s value might be calculated by OSPF to be the very same quantity as that for the 100Mbps interface.
100,000,000/1000,000,000 = 1
The identical would apply for larger velocity interfaces equivalent to 10Gbps interfaces which might even be interpreted by OSPF as having a value of 1, since OSPF can not outline interface prices as an integer a part of a decimal quantity i.e. 0.5 or 0.125.
In order that OSPF could possibly calculate the price of an interface primarily based on the bandwidth of the interface with nice accuracy we might want to change the worth of the auto-cost reference-bandwidth worth from 100,000,000 to a larger worth.
To vary the reference bandwidth , we are able to use the next instructions:
router(config)#router ospf 1
R1(config-router)#auto-cost reference-bandwidth 10000
% OSPF: Reference bandwidth is modified.
Notice – Please guarantee reference bandwidth is constant throughout all routers.
The auto-cost reference-bandwidth now has a worth of 10000,000,000 (The worth is ready in Mbps), subsequently now the OSPF course of will view the 100Mbps interface as having a value of 100, 1Gbps having a Price of 10 and 10Gbps a value of 1, one other level value mentioning is that the router will immediate you to ensure that the auto-cost reference-bandwidth worth is ready constantly throughout all of your routers.
Notice: The price given to a path is added to the metric solely when the route is acquired inbound on an interface, subsequently must you want to alter the price of the trail you should do that on the inbound interface.
Proceed Studying:
To know extra about OSPF Price Calculation watch this video –
