Auto-Cost Reference Bandwidth - Allied Telesis AT-AR3050S Command Reference Manual

OSPF C
OMMANDS
-
AUTO COST REFERENCE BANDWIDTH

auto-cost reference bandwidth

Overview This command controls how OSPF calculates default metrics for the interface.
Use the no variant of this command to assign cost based only on the interface
bandwidth.
Syntax auto-cost reference-bandwidth <1-4294967>
no auto-cost reference-bandwidth
Default 1000 Mbps
Usage By default, OSPF calculates the OSPF metric for an interface by dividing the
reference bandwidth by the interface bandwidth. The default for the reference
bandwidth is 1000 Mbps. As a result, if this default is used, there is very little
difference between the metrics applied to interfaces of increasing bandwidth
beyond 1000 Mbps.
The auto-cost command is used to alter this reference bandwidth in order to give
a real difference between the metrics of high bandwidth links of differing
bandwidths. In a network that has multiple links with high bandwidths, specify a
larger reference bandwidth value to differentiate the costs on those links.
Cost is calculated by dividing the reference bandwidth (Mbps) by the layer 3
interface (Switched Virtual Interface (SVI), Loopback or Ethernet interface)
bandwidth. Interface bandwidth may be altered by using the
command as the SVI does not auto detect the bandwidth based on the speed of
associated switch ports.
When the reference bandwidth calculation results in a cost integer greater than 1
but contains a fractional value (value after the decimal point), the result rounds
down to the nearest integer. The following example shows how the cost is
calculated.
The reference bandwidth is 1000 Mbps and the interface bandwidth is 7 Mbps.
Calculation = 1000/7
Calculation result = 142.85 (integer of 142, fractional value of 0.85)
Result after rounding down to the nearest integer = 142 (Interface cost is 142)
When the reference bandwidth calculation results in a cost less than 1, it is
rounded up to the nearest integer which is 1. The following example shows how
the cost is calculated.
The reference bandwidth is 1000 Mbps and the interface bandwidth is 10000
Mbps.
Calculation = 1000/10000
C613-50077-01 REV A
Parameter Description
<1-4294967>
The reference bandwidth in terms of Mbits per second (Mbps).
Command Reference for AT-AR3050S
AlliedWare Plus™ Operating System - Version 5.4.5-2.x
bandwidth
749