Long-haul 100Mbps EPL circuit throughput issue

James Bensley jwbensley at gmail.com
Fri Nov 6 19:34:14 UTC 2015

On 5 Nov 2015 21:50, "Eric Dugas" <edugas at unknowndevice.ca> wrote:
> 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
> 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

Hi Eric,

Sounds like a TCP problem off the top of my head, however just throwing it
out there, we use a mix of wholesale access circuit providers and carriers
for locations we haven't PoP'ed and we are an LLU provider (CLEC in US
terms). For such issues I have been developing an app to test below TCP/UDP
and for pseudowires testing etc:


It may or may not shed some light when you have an underlying problem
(although yours sounds TCP related).


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