Bandwidth mistery

[Ernesto Borges]

Hello,

I have a 3650 switch with a routed port connecting to a ISP circuit, 300 Mbps. the interface is a Gigabit interface, the provider did a test and it showed the full 300 Mbps throughput; however, the 5 min rate on the interface never shows more than 200 Mbps, just some times (once or two times a day it bursts up to 225-240 Mbps)

Any comment is highly appreciated

Thank you

[trfinkenstadt]

Ernesto,

The 5 min rate is averaged over the entire 300 seconds.  If you or the ISP did an extended test longer than 5 minutes you should see your interface get up to 300 mbps.  Alternatively, try setting the load-interval on the interface to 30 and you'll see 30 second rate average.  

best regards,

tim

[Carlos Villagran]

Hi!

Your link is 1Gig capable. The ISP is policing that capability to only 300 Mbps.

This means that anytime your output link traffic exceeds this 3000 Mbps, the policy will slow it down to 300 Mbps. 

What you are seeing is only the throughput average in 5 minutes (or 30 seconds, it depends of your configuration). It only means how much traffic has been traversing your link in 5 minutes average. 

Hope it helps, best regards!

JC

[Joseph W. Doherty]

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Posting

As the others have already noted, your link might not be busy enough, over the measured time period, to push your link to 300 Mbps.

Another possibility, and it's not mutually exclusive, if most of your traffic is TCP, if the traffic is being subjected to drops when it hits 300 Mbps, it often will half its transmission rate.  This will bring your average transmission rate down under the maximum.

[Ernesto Borges]

Thank you all for the replies!!

Let me clarify little more, I know it is not an easy answer. Yes, QoS is shaping to 300Mbps, problem is it is never getting that high, shaper is not even doing the job. Max burst for a single day might be 225 Mbps. The traffic is being pushed by a Data Center, it is 1,000 Mbps circuit (VPLS mesh) pushing towards lower size circuit (300 Mbps). traffic is mostly SQL replication and Exchange Server replication; supposedly it should be overwhelming the 300 circuit with traffic, and I was expecting to see the shaping in progress all the time. 

To Joseph:

Link should be busy enough 24/7 (more than TB of data replicating) and I agree traffic would be dropping packets when it hits the 300 Mbps mark.... problem it never does

[Joseph W. Doherty · Accepted solution]

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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.

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In no event shall Author be liable for any damages wha2tsoever (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

If you have a gig hand-off, the policing (and drops) I had in mind would be on the provider's portion of the network.

If certainly possible that your traffic is unable to drive 300 Mbps.  Are you familiar with BDP (bandwidth delay product) TCP considerations?  If not, you might want to read up on it.

[Ernesto Borges]

Thank you! I request a RFC test and came back OK, showing full 300 Mbps circuit. My sysadmin told me that Windows 2012 is automatically adjusting the Window Size of the packets, I also blamed on that.

I will read for sure about BDP, thank you!

[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.

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In no event shall Author be liable for any damages wha2tsoever (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

If I remember correctly, user Windows will try to use large RWINs since Vista.  Windows, servers though, at least the least the earlier versions that supported large RWINs don't enable the feature, by default.