Hmm, i've finished all four cisco courses and i did fairly well, but never had to troubleshoot anything yet, as im still a student.

Anyways lemme know if im on the right track, if u have 172 private addresses, and one WAN address assigned by the ISP, You would obviously need a router or switch that all addresses connect too, going into the router from the LAN u would also need a LAN address and on the other side(internet) u'd have the WAN address that is assigned by the ISP. so from the net u'd be able to ping the router, and since the LAN address is prb something like 192. . . u wouldnt be able to actually ping those from the outside.

Thats just my opinion i could be wrong of course, and if i am could someone lemme know