Interface Bandwidth & Bursting

[Limitless1801]

Hi,

I have a 50Mbps MetroE connection between two sites. This link can go up to 100Mbps (bursting). My question is, should I configure the interface with the bandwidth command using 50Mbps or 100Mbps? We have a tool that monitors this interface and I would like to get the reports as accurate as possible.

Next step I want to do is to configure QoS; therefore, here is my subsequent question, should I do this based on 50Mbps or 100Mbps?

Thanks in advanced !!!!!

RG

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

You normally set the bandwidth statement to "mirror" maximum bandwidth that the interface will pass.  Otherwise, in a case like yours, monitoring that uses this value will incorrectly report utilization percentages.

You also configure (queuing) QoS to deal with congestion.  Unless you shape, you shouldn't have congestion until you exceed 100 Mbps.

You might want to find out what exactly your 50 Mbps that can burst to 100 Mbps really means.  For example, it might mean your have a CIR of 50 Mbps that's policed, but the physical media supports 100 Mbps.  Or it might mean, you can use 100 Mbps anytime but pay a surcharge for usage above 50 Mbps.  How your link supports 50 Mbps vs. 100 Mbps can greatly influence how you may want to configure QoS and the bandwidth statement.

[Limitless1801]

Your Post: you can use 100 Mbps anytime but pay a surcharge for usage above 50 Mbps

This is exactly how we are doing it. We are paying monthly for being able to burst up to 100 Mbps but our CIR is 50 Mbps. My concern is mostly on what happens to the bursting traffic because after 50 Mbps I would assume is all best effort which the carrier should respect but who knows

To start doing QoS, I need to do some calculations based on the bandwidth so I have to options: do I calculate the % based on 50 Mbps or 100 Mbps? If I use 50, I can guarantee that everything is going to the other side with no problems but I can't say the same if I use 100 Mbps.

Now, if I use 50Mbps: does it mean that the other 50Mbps (bursting) is going to be used for the default class since it is remaining?

I appreciate your feedback.

[Joseph W. Doherty]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

Generally, if you're paying a surcharge for bandwidth in excess of your CIR, the provider often doesn't treat traffic above or below your CIR any differently.  (In cases where they allow bursting above CIR but don't charge extra for it, such traffic might be subject to dropping [first] if there's provider congestion.)

Again, I would suggest setting bandwidths and/or percentages to what's allowed across the interface.

Depending on exactly how your provider "clocks" your bandwidth over CIR, and your actual traffic needs, you might find it worthwhile to shape to avoid going over your CIR.