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Community Member

Impact of changing VLAN bandwidh if my physical port is 10G?

My monitoring system is reporting that VLAN X is 100% utilization in my 6509. That VLAN is used to pass traffic between two 10G access ports in that VLAN X. It seems that by default the VLAN bandwidth is 1G, however i am passing more traffic than that in that 10G connection. Is it safe to just change the bandwidth to the VLAN without impact? I think it is but would like to know if someone has some experience with this.

Thank you,


Community Member

The bandwidth statement is

The bandwidth statement is for dynamic routing protocol this is how it determine cost?


Hi,There should not be any


There should not be any issue by changing it accordingly to the actual speed of the interfaces. Typically the interface bandwidth command would be used to communicate the speed of the interface to Interior Gateway Routing Protocols (IGRP), so they would then calculate their metircs based on that value, the bandwidth value should be accurate, otherwise there would be cases where a routing protocol would rely on wrong values (please see below output) so would consider wrongly a path as equal as another and use them both equally. Please keep in mind also that the bandwidth command does not affect the actual speed of the interface. One more use of the bandwidth command would be in the adjustment of the initial retransmision parameters of tcp.

Switch#sh run int f0/9 | in speed
 speed 10

Switch#sh int f0/9 | in BW
  MTU 1500 bytes, BW 100000 Kbit, DLY 1000 usec,

In this example, an IGRP would calculate its metric considering 100Mbps as the speed of the interface when the real speed is 10Mbps, that's because the bandwidth is set to 100000 Kb and it is the value that would be used by that IGRP.



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