If you need to calculate subnet under Linux use an IP Netmask/broadcast calculator called ipcal. You can calculate IPv4 or IPv6 address. Supported features:
=> Multiple address and netmask input formats.
=> Retrieving of address information from interfaces.
=> Classfull and CIDR output.
=> Multiple address and netmask output formats (dotted quad, hex, number of bits).
=> Output of broadcast address, network class, Cisco wildcard, hosts/range, network range.
=> Output of multiple types of bitmaps.
=> Output of a user-defined number of extra networks.
=> Multiple networks input from commandline.
=> DNS resolutions of hostnames.
=> Compressed and expanded input addresses.
=> Compressed and expanded output.
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