My daughter has a user account on our iMac. She is not an administrator, and parental controls are not enabled.
When she logs in, she has about ten minutes of connectivity before host resolution fails. If she logs out, and logs back in, everything is OK for another ten minutes.
There is no spyware or malware on the machine.
When I log in as me, I have no such problems.
dig command works fine; it can happily resolve hostnames.
ping fails with an error indicating that it cannot resolve the same hostname.
Where should I begin looking to solve this vexing problem?