can't ping Linux computer by IP address unless it pings the other computer first

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http://www.linuxquestions.org – Hi all, I've got a real doozy of a question. I'm trying to troubleshoot a Samba problem on my computer running Ubuntu 13.04 (Raring Ringtail), and I discovered that pinging it by IP address from another computer times out, unless the Ubuntu computer has pinged the other computer first. Pinging by hostname doesn't work either. The Ubuntu computer is connected to a DSL router via WiFi. The other two computers in the network run Windows XP; one uses WiFi and the other uses ethernet. The computers are all in the usual 192.168.0.x subnet, and all have subnet masks. The Ubuntu co (HowTos)