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Zayo DIA Speed Troubleshooting


I've been beating my head against a wall now for months fighting with Zayo and troubleshooting speed issues we're having with a 1G DIA circuit from them. We're colocated in a datacenter with them, and the uplink from their handoff to our gateway is SMF, about 50 feet away.


Our gateway is a Ubiquiti UISP Console, so it's well up to the task. We also had similar speeds with both a UISP Router, and an Edgerouter X SFP. The SMF uplink is connected through a 1G SFP module.


Running the built in UISP speed test, which originates on the gateway, we always get in the 200-300Mb download range, and 900Mb+ upload. I've gotten the same results from a laptop testing through WifiMan, SpeedTest, TestMy, DSLReports, etc. All the same.


Two weeks ago, Zayo sent out a tech to troubleshoot from their suite adjacent to the datacenter, and found no problem. Interestingly enough though, the day before, and the day of their testing I was able to achieve near 1Gb download test speeds from our gateway. However, the next day the 200-300Mb speeds returned.


They escalated the issue and earlier today I set up an Iperf3 server connected through a switch directly to our SMF uplink so that their tech could test our speeds directly from their end. I was relayed the following;



Based on my testing it appears the TCP buffer on your test box is 254 Kbyte. 

The host I am testing from is 80ms RTT away. 

TCP window of 256 KByte and RTT of 80.0 ms <= 26.21 Mbit/sec. 

So I get 26Mbit for one TCP stream. 

I run 120 parallel stream and get 700 Mbit pushed to your test box. 

For UDP 900+ Mbit already verified. 

Test was ran periodically and those are the averages.


I do not see any limitation except for what is caused by TCP windowing.



I was also sent the logs from their end of the Iperf test, and it does indeed show in the 700Mb range with parallel streams. So theoretically their circuit is good, yet I still can't test out over 300Mb. Logically, testing to our server, maybe TCP Windowing could be the cause. But that doesn't make any sense with testing from our gateway.


Admittedly networking is not my strong suit and I'm not sure where to go from here. Suggestions?

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