I posted in Windows because it's the only forum that's described specifically as "networking". The question wasn't specific to any OS, as far as I was guessing. It would have been better to put it in Linux, after thinking more about it, since it was about NFS, and exports might be limited in their format (for example, * and ? might work in some cases, but are not supported or recommended).
Anyway, after playing around with some online IP tools I was going to go with 192.168.1.100/28, which apparently specifies 6 IP addresses, but put it back to a single IP after discovering that there are no free NFS clients for Windows....the other linux box has no reason to access the NFS share.
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/ >) My 84-year-old non-techy mom uses Debian Linux. It ain't that hard.