4 IP Subnet Calculator
IP Subnet Calculator is a Web-based resource that is used to calculate the subnet mask
based on several variables. This tool can be used to verify network settings.
http://www.cisco.com/cgi-bin/Support/IpSubnet/home.pl
Copyright © 2004, Cisco Systems, Inc.
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CCNA 2: Routers and Routing Basics v3.1 Instructor Guide – Appendix A