perfSONAR User Q&A and Other Discussion

[Eli Dart <>]

Hi Pete,

Is flow control enabled between the host and the router?  One possible cause for this circumstance is the host being unable to sink traffic, and sending pause frames to the router (which it should), and the router then filling its queue and dropping packets.

Another possibility would be if you were running owamp and throughput tests on the same host. If the throughput test and the owamp test enter the router via different interfaces (or a common faster interface), then the traffic for both tests might not fit into the interface connected to the host - that could also cause output drops.

Do you feel that either of these circumstances are a good fit for the current config?

Thanks,

Eli

On Wednesday, October 12, 2016, Pete Siemsen <> wrote:

We have a perfSONAR server that is directly connected to a router. The router reports that the "Output drops" counter is going up on the interface that connects to the perfSONAR server. We graph output drops on all interfaces, so I have a nice graph that shows that the drops occur in regular spurts. So, some test that runs regularly causes the drops. Like, every ~20 minutes, there's a spurt of 2000 output drops.

There are 18 tests defined on the server. I want to identify the one that is causing the drops.

I can monitor the interface on the router, and see the "output drops" counter bump up once in a while. I could wait for a spurt, then identify the test that is running "right now". To identify the test running right now, I could do a "top" command and see the "iperf3" or "java" process that is consuming the most CPU. I also see several bwctl processes, each of which shows the remote site name/IP.

This is almost enough, but I feel like I don't have my mind right :-) What's the clueful way to approach this problem?

-- Pete

--

Eli Dart, Network Engineer                          NOC: (510) 486-7600

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