Why is ping slow on domain solving?

Question

Why this big difference in times if the domain name is resolved by ping itself, versus getent externally?

$ time ping -c1 "google.com""
0% packet loss
0m5,064s

$ time (ip=$(getent ahostsv4 "google.es" | awk '{ print $1 }' |
head -n1); ping -c1 "${ip}")
0% packet loss
0m0,042s

time will tell how much time took the command to run, not how much time the ping took. If you ping <bogus ip>, time will tell you i.e. 10s, when there was never a real ping involved. — schrodingerscatcuriosity, Oct 23 '19 at 22:52
That's what I meant, that time isn't the actual ping but the tool trying to solve the name. The difference in times doing that same thing is big. — Alberto Salvia Novella, Oct 23 '19 at 22:54
Try to run the commands several times in a row and you see that there's not a clear pattern... as far as I've tried. — schrodingerscatcuriosity, Oct 23 '19 at 23:00
First case always takes more than 5s, second case always less than 100ms. — Alberto Salvia Novella, Oct 23 '19 at 23:03

score 3 · Answer 1 · answered Oct 24 '19 at 14:56

A work-around that succeeded was, on /etc/resolv.conf, adding:

options single-request-reopen

Suggesting the root issue:

Sets RES_SNGLKUPREOP in _res.options. The resolver uses the same socket for the A and AAAA requests. Some hardware mistakenly sends back only one reply. When that happens the client system will sit and wait for the second reply. Turning this option on changes this behavior so that if two requests from the same port are not handled correctly it will close the socket and open a new one before sending the second request.

So disabling IPv6 on my Google Wifi router fixed the problem.

Why is ping slow on domain solving?

1 Answers1

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