grepcidr - 2.0-2+b1 main

grepcidr can be used to filter a list of IP addresses against one or
more Classless Inter-Domain Routing (CIDR) specifications, or
arbitrary networks specified by an address range. As with grep, there
are options to invert matching and load patterns from a file.
grepcidr is capable of comparing thousands or even millions of IPs
to networks with little memory usage and in reasonable computation
time.
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grepcidr has endless uses in network software, including: mail
filtering and processing, network security, log analysis, and many
custom applications.