grepcidr - Filter IP addresses matching IPv4 CIDR specification
grepcidr can be used as a stream filter when you need to compare a list of IP
addresses against one or more Classless Inter-Domain Routing (CIDR) mask
specifications. Think of grepcidr as a CIDR-aware grep; instead of using
'grep 18.104.22.168' you can use 'grepcidr -e 22.214.171.124/30', for example. Multiple
specifications, of arbitrary mask lengths, can be specified both on the
command line or loaded from a file.