/usr/bin/ipsort is in pnscan 1.11-6.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 | #!/bin/sh
#
# Sort a file using IPv4 addresses in at the beginning of each line
exec sort -t . -k 1,1n -k 2,2n -k 3,3n -k 4,4n "$@"
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