... Check your WiFi router. Looks for a setting called "isolation". It's a "security" feature where two wireless clients are not allowed to see each other.
..
I don't have too wireless clients, n800 is wireless, mac in on ethernet (same router physically), plus I don't see "isolation" option on my router.

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Re passwords:

a) what is the scope of openssh installation defined "root" password? It doen't work with su or sudo?

b) how do I change my USER password?

(su and sudo use the same password (root) don't they?)

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more q later after i digest the rest.