On RH9 at least, ping isd part of the iputils package. Assuming you're using FC2 as your profile states, you can find the source RPM fpor that packages and install it, which will put the source into /usr/src/REDHAT IIRC. Then you can look at the source. You can probably find a tar.gz of the source of the iputils package too, if you Google on it.
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