So I'm on a hotel WiFi that has been working fine for several days.
Suddenly, I'm not able to use many programs on the internet.
Safari says "Can't find server".
Ping says "Can't resolve: Unknown host".
Meanwhile, I can browse just fine with Google Chrome and
nslookup immediately returns correct results.
sudo dscacheutil -flushcache
sudo killall -HUP mDNSResponder
This has happened to me before, but usually cycling the WiFi, or the commands above or a reboot would fix the problem. Not now.