# OSPF Reference Bandwidth I have R1 who has a G0/0/0 and a S4/0/0/0 interface. The reference bandwidth (which is 108 bps) can be changed on Huawei routers. The reason of changing it, is because when you have a Gigabit Ethernet interface (like in our case) we will have issues because the reference bandwidth is 100 Mbps and the Gigabit Ethernet is 1000 Mbps. The lowest value of the cost can be 1, that’s why we need to increase the reference bandwidth when we need to use Gigabit Ethernet interfaces or bigger interfaces, otherwise they will do load balancing with interfaces having 100 Mbps speed because they also will have a cost of 1.

For now, let’s check the IP addresses that are set on R1’s interfaces. Let’s enable OSPF on R1 and advertise the connected network to it.

[mepr-show rules=”319″ unauth=”message”] Let’s check what is the bandwidth under Serial 4/0/0. I see that the bandwidth on the interface S4/0/0/ is 64000 bps.

So the cost should be:

Cost = Reference bandwidth / Interface bandwidth

Cost = 100.000.000 / 64.000

Cost = 1562,5

Normally, Huawei will round up the value of the cost, that means we should have the cost of 1562.

Let’s verify that. Here it is, the cost is exactly the same as we have calculated.

What about the interface G0/0/0? What cost should it have?

If we do the calculation then the cost will be 0.1. But Huawei doesn’t accept a value less than 1. Let me show you that. The cost on the interface G0/0/0 is 1. But that’s not really fair, because now the Gigabit Ethernet interface has the same cost as the Fast Ethernet interface while it is 10 faster than the Fast Ethernet interface and that’s all because the reference bandwidth is set to 108 that means that in case I have another Fast Ethernet interface routing me to the same destination then it will do load balancing with the Gigabit Ethernet interface and that’s not really fair at all.

In this case, I can change the reference bandwidth on the router and make it higher. I will make it 109 then the Gigabit Ethernet interface will have a cost of 1 while the Fast Ethernet interface will have a cost of 10. Let me show you how this can be changed. I have changed the reference bandwidth to 1000 Mbps which is 109 (Huawei works with Mbps for the reference bandwidth).

That means now the cost on the G0/0/0 will be 1 but the correct 1, and the cost on the serial interface should be increased.

Let’s check 1st the cost on the G0/0/0 interface. So the cost is 1, that’s true.

The Serial interface will have a higher number because now the number which is being dividing by the interface bandwidth speed is 109 and not 108 . Here we go!!!! The cost is higher than the number that we have seen before we changed the reference bandwidth.

[/mepr-show]