Netflix fast.com performance

Sun Jun 25 16:22:59 UTC 2017

Hello,

Lately we have been troubleshooting complaints from customers of several ISPs about
relatively low results when testing to Netflix's fast.com
When we started troubleshooting we notice the following:
1. When the latency to the fast.com test server is ~70ms results are significantly lower than speedtest.net results or Google fiber results.
2. When latency to the fast.com server is low (10-20ms, over DSL link) the results are similar between speedtest.net and fast.com

When looking at packet captures of the fast.com test we notice the following:

1. fast.com pushes traffic very aggressively: we have applied a shaper with CIR=100Mbps and 200ms and even 500ms queue limit (cisco jargon)
and still noticed drops when performing fast.com tests.

2. Packets originated from fast.com do not have the tcp push (psh) flag on.

3. It seems that fast.com recovery from packet loss is not very good over high latency (~70ms).
It seems to us that after a packet loss even the server reaches his cwnd and stops transmitting for relatively long periods.

We are interested to know if anybody else experience similar behaviour (with similar latency) or have any other insights into this.
If you would like to take a look at captures performed over 70ms latency please PM and I'll share the files.

Regards

Amos