p2141-ipbf705marunouchi.tokyo.ocn.ne.jp -> 222.145.169.141
p3089-ipbf409marunouchi.tokyo.ocn.ne.jp -> 218.43.37.89

222.145.169.141 -> 3270180799D4F62311B7FFC82DD0663A
218.43.37.89 -> 40F1932CF051E326A2D2B7BA6DF3663A

>$idnum = substr($idnum,-4);
222.145.169.141 -> 663A
218.43.37.89 -> 663A
?