Bandwidth Statements on Router Interfaces

What do bandwidth statements on router interfaces do? I have an IWAN configuration that I use for deployment of DMVPN hub and spoke. We also use bandwidth based policy mapping.

Could a mismatch of actual bandwidth applied to an interface cause issues?

For example we have a 10mb circuit that is carved up between 3 VLANs. One of the VLANS get 4 of the 10 mbs. On the interface I put 10mb for bandwidth but was told it should be 4mb as that is what this VLAN gets while the other two get 4 and 2mb.

I hope this question makes sense.



Hello Ronald

The bandwidth parameter on a router interface doesn’t affect the actual throughput of the interface. It is simply a label that you can adjust that will be used by various other mechanisms to operate. For example, OSPF uses the bandwidth parameter to determine the cost of a link, as does EIGRP.

In your particular case, if you have a 10Mbps link that has subinterfaces for three VLANs (it sounds like a router on a stick situation) and you want to shape the traffic so that each VLAN will have a particular available throughput, then there are various ways to employ this. All of them however have to do with QoS mechanisms.

To answer your question directly, the bandwidth parameter will not have an effect on the amount of traffic that is going through. If you want to shape the traffic that is going through each of the subinterfaces, then you should use a QoS mechanism such as CBWFQ . An example of how this can be applied to subinterfaces can be found at the following lesson:

I hope this has been helpful!


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Your comment does help and make sense. I will have to review customer complaints regarding slow applications after the most recent migration.

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