How we laughed when we discovered that Linux’s ping makes a reverse DNS lookup for every incoming ICMP echo reply! For added mirth and/or merriment, it also happens on flood-ping.
How we laughed when we discovered that Linux’s ping makes a reverse DNS lookup for every incoming ICMP echo reply! For added mirth and/or merriment, it also happens on flood-ping.
So, whose DNS server did you manage to DOS?
It’s even funnier when those DNS lookups are slow. You get second-long pauses between the pings, yet every one of them claims a round-trip time of 20ms.
So *that’s* why ping responses can take three seconds while claiming a ping time of 123ms, or pause for a while and then seven arrive at once, all claiming to have taken the same time.
That’s bugged me for years. Maybe I'll start using dnsmasq or something.
Oh.. that’s why it’s slow.
Slow DNS reveals flaw in ping(1) :)