子网掩码划分工具下载

 SubNetter  界面简单，来自大名鼎鼎的Boson
http://bosondownload.com/utils/bos_sub.exe

IP Subnet Calculator可显示出IP位置的相关信息，其中包括指定子网络的某一组IP位置及建议子网掩码等。IP Subnet Calculator提供5种不同方式来选择子网络作业，并提供更美观的作业界面。  
http://www.wildpackets.com/products/free_utilities/ipsubnetcalc/overview

Advanced IP Address Calculator 1.1 (FREE)
Advanced IP Address Calculator is an easy-to-use IP subnet calculator that lets you to calculate every aspect of your subnet configuration in a few mouse clicks! The calculator generates a color-coded bit map, breaking down the network, subnet, and host portion. It shows you the subnet host address range, the subnet ID, and the subnet broadcast address. The binary representation and hexadecimal representations of IP addresses are supported.
http://www.radmin.com/download/ipcalc11.exe

还有PDA上的版本

For PPC: http://www.pocketgear.com/software_detail.asp?id=10287
For PALM: http://www.wildpackets.com/products/free_utilities/ipcalc_palm/overview