(ipcalc "192.168.0.23/21")produces a new buffer with:
Address: 192.168.0.23 11000000101010000000000000010111 Netmask: 255.255.248.0 = 21 11111111111111111111100000000000 Wildcard: 0.0.7.255 00000000000000000000011111111111 => Network: 192.168.0.0 11000000101010000000000000000000 HostMin: 192.168.0.1 11000000101010000000000000000001 HostMax: 192.168.7.254 11000000101010000000011111111110 Broadcast: 192.168.7.255 11000000101010000000011111111111 Hosts/Net: 2046
The package is to be found on MELPA.
If using use-package:
(use-package ipcalc
  :ensure t)To execute tests, either open the file ./ipcalc-tests.el and execute
  an (eval-buffer), or run them in batch mode with the command make
  test