With default window size of 64KB, and a delay of 75 msec, you should only get around 7Mbps of throughput with TCP. You would need a window size of about 1MB in order to fill up the 100 Mbps link. 1/0.75 = 13.333 (how many RTTs in a second) 13.333 * 65535 * 8 = 6,990,225.24 (about 7Mbps) You would need to increase the window to 1,048,560 KB, in order to get around 100Mbps. 13.333 * 1,048,560 * 8 = 111,843,603.84 (about 100 Mbps) *Pablo Lucena* *Cooper General Global Services* *Network Administrator* *Office: 305-418-4440 ext. 130* *plucena@coopergeneral.com <plucena@coopergeneral.com>* On Thu, Nov 5, 2015 at 6:31 PM, Bob Evans <bob@fiberinternetcenter.com> wrote:
Eric,
I have seen that happen.
1st double check that the gear is truly full duplex....seems like it may claim it is and you just discovered it is not. That's always been an issue with manufactures claiming they are full duplex and on short distances it's not so noticeable.
Try to perf in both directions at the same time and it become obvious.
Thank You Bob Evans CTO
Hello NANOG,
We've been dealing with an interesting throughput issue with one of our carrier. Specs and topology:
100Mbps EPL, fiber from a national carrier. We do MPLS to the CPE providing a VRF circuit to our customer back to our data center through our MPLS network. Circuit has 75 ms of latency since it's around 5000km.
Linux test machine in customer's VRF <-> SRX100 <-> Carrier CPE (Cisco 2960G) <-> Carrier's MPLS network <-> NNI - MX80 <-> Our MPLS network <-> Terminating edge - MX80 <-> Distribution switch - EX3300 <-> Linux test machine in customer's VRF
We can full the link in UDP traffic with iperf but with TCP, we can reach 80-90% and then the traffic drops to 50% and slowly increase up to 90%.
Any one have dealt with this kind of problem in the past? We've tested by forcing ports to 100-FD at both ends, policing the circuit on our side, called the carrier and escalated to L2/L3 support. They tried to also police the circuit but as far as I know, they didn't modify anything else. I've told our support to make them look for underrun errors on their Cisco switch and they can see some. They're pretty much in the same boat as us and they're not sure where to look at.
Thanks Eric