What would cause computer A to be able to ping Computers B and C, but B and C be unable to ping A (though they can ping each other)? FWIW, A is on a wireless connection. B and C are ethernet.

[Update a few minutes later]

In answer to the question in comments, I’m pinging by IP. The router is running in DHCP mode.

[going off to try something]

That was it. Zone Alarm was blocking the pings. I shut it down, and it works now. Guess I need to add the local network to its trusted zone.