The story of ping(1)

Posted at 2009-02-18 03.47

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.

4 Comments for 'The story of ping(1)'

    Stephen Quinney
    2009-02-18 | 09.37 +0000

    So, whose DNS server did you manage to DOS?

    2009-02-18 | 20.57 +0000

    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.

    Aneurin Price
    2009-02-18 | 23.51 +0000

    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.

    2009-02-23 | 00.08 +0000

    Oh.. that’s why it’s slow.
    Slow DNS reveals flaw in ping(1) :)

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