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.
Best Answer
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: