Howard: Thanks for the suggestion, I will change the terms to Subnet Mask. The ZIP package and the first post in this thread have now been updated to reference Subnet Masks.

Jooel: It all comes down to simple AND/OR binary calculations. Your Example:
code:
    IP         192. 10.128. 55
AND
    SubnetMask 255.255.255.  0
=
    NetworkID  192. 10.128.  0
See for example http://www.telusplanet.net/public/sparkman/netcalc.htm which allows to to enter IP addresses, network IDs, and subnet masks and then explains the results.

[ 24. May 2003, 23:19: Message edited by: sealeopard ]
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There are two types of vessels, submarines and targets.