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I've been investigating intermittently dropping RDP connections from my laptop and decided to ping another machine on the same subnet to see if there are any dropped packets or slow responses. The results I see are very confusing to me, so I wonder if someone can point me in the right direction for further investigation.

What I see is this: If I ping machine X from my laptop, I get, on average, 300ms responses (which seems kinda slow for a very uncongested home network), but no packets are lost. Also the responses are all over the place, from 65ms to 1500ms. However, when I ping my laptop from machine X, the responses average about 3ms and don't vary very much. So that's 100 times faster from X to my laptop.

Here is my setup: Dual-band wireless router, both machines are connected over WiFi, machine X is on 5GHz band, the laptop is on 2.4GHz band (unfortunately it doesn't support 5GHz). The same local subnet. Both machines are running Ubuntu. Both WiFi adapters report very strong signals.

Any ideas for what can account for such a vast difference in response times in just one direction and what can I check to investigate the issue further?

Thank you for your time and help.

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    It may be caused by wi-fi, but confirming this requires special tools (at least, a wireless sniffer. Try to move the machines, bring them closer, etc. It may be caused by something on machine X not related to wireless, Try to connect them with a cable. Run performance monitor on X.
    – ddbug
    May 30, 2017 at 23:20
  • Run a packet capture on machine X while you ping it from your laptop. How long does it take machine X to respond to the ping?
    – joeqwerty
    May 31, 2017 at 0:45
  • Does changing power settings of either machines make a difference?
    – Cameron Kerr
    May 31, 2017 at 6:14

2 Answers 2

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It looks like machine X might have 802.11 power saving enabled, so it enters lower power mode between pings and has to wake up each time you ping it. When going in the other direction, your laptop does not enter power saving mode, so it answers right away. This is taken from the answer here:

https://superuser.com/questions/716596/how-to-diagnose-long-asymmetric-ping-times-to-a-linux-host

You can prove this is the case by shortening the interval between pings until the pings come so rapidly that machine X does not enter low power mode:

sudo ping -i 0.1 x.x.x.x
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If there is anything between server X and the router, it could be getting ratty data. In radio fundamentals, the lower the bandwidth, the better the signal can get through walls. That would explain why the 2.4GHz machine is getting a better response than the 5GHz machine.

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    Do you mean lower frequencies permeate walls better? You said bandwidth, but referenced frequencies.
    – Cory Knutson
    Jun 2, 2017 at 18:51
  • Sorry, yes I meant frequency. I come from a radio background, and we refer to frequency groups as bands, so I got myself turned around.
    – BBAV
    Jun 2, 2017 at 19:16

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