Brocade Communications Systems ICX 7250 series, Руководство по настройке

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Interface types to which the reference bandwidth does
not apply
Some interface types are not affected by the reference bandwidth and always have the same cost regardless of the reference bandwidth
in use:
• The cost of a loopback interface is always 1.
• The cost of a virtual link is calculated using the Shortest Path First (SPF) algorithm and is not affected by the auto-cost feature.
• The bandwidth for tunnel interfaces is 9 Kbps and is also subject to the auto-cost reference bandwidth setting.
Changing the reference bandwidth for the cost on
OSPFv2 interfaces
Each interface on which OSPFv2 is enabled has a cost associated with it. The device advertises its interfaces and their costs to OSPFv2
neighbors. For example, if an interface has an OSPFv2 cost of ten, the device advertises the interface with a cost of ten to other OSPFv2
routers.
By default, an interface’s OSPFv2 cost is based on the port speed of the interface. The cost is calculated by dividing the reference
bandwidth by the port speed. The default reference bandwidth is 100 Mbps, which results in the following default costs:
• 10 Mbps port - 10
• All other port speeds - 1
You can change the reference bandwidth. The following formula is used to calculate the cost:
Cost = reference-bandwidth/interface-speed
If the resulting cost is less than 1, the cost is rounded up to 1. The default reference bandwidth results in the following costs:
• 10 Mbps port’s cost = 100/10 = 10
• 100 Mbps port’s cost = 100/100 = 1
• 1000 Mbps port’s cost = 100/1000 = 0.10, which is rounded up to 1
• 10 Gbps port’s cost = 100/10000 = 0.01, which is rounded up to 1
The bandwidth for interfaces that consist of more than one physical port is calculated as follows:
• LAG group - The combined bandwidth of all the ports.
• Virtual interface - The combined bandwidth of all the ports in the port-based VLAN that contains the virtual interface.
The default reference bandwidth is 100 Mbps. You can change the reference bandwidth to a value from 1—4294967.
If a change to the reference bandwidth results in a cost change to an interface, the device sends a link-state update to update the costs of
interfaces advertised by the device.
NOTE
If you specify the cost for an individual interface, the cost you specify overrides the cost calculated by the software.
Interface types to which the reference bandwidth does not apply
Brocade FastIron Layer 3 Routing Configuration Guide
232 53-1003903-04