Have you coded in Python or Perl?
Do know that there is a special interface in Linux called the "tap" interface?
The tap interface appears to the 5921 ESR as an Ethernet interface and can be used to have your custom application communicate directly with the router.
Perhaps. you prefer TCL.
Yes, TCL is also available within the IOS environment of the 5921.
Feel free to share and discuss your unique creations here!