As originally posted, your script has the "DoOneEvent" call outside of the inner-most "for" loop, running the range of numbers in the fourth part of the IP addresses. If you have been trying the script with the default values for the start and stop IP addresses (1.1.1.1 - 1.1.1.255), this means that you run 255 iterations of the inner-most loop (calling Net::SNMP->session each time, with a 2-sec time-out) before you get to the first "DoOneEvent" call.

Have you allowed the script to run for at least 8 min. 30 sec, to let that inner loop finish? How about putting the DoOneEvent call inside that loop, rather than after it? Better yet, you might want to add a label widget with a "-textvariable =>\$status_string option, update that variable with the ip address being scanned, and call that widget's update method within the inner-most loop, so you can see what's happening inside that loop as it happens.

A few other comments about your code:

• Since your "start-ip" and "end-ip" entry widgets use variables with the "-textvariable" option, why not just reference those variables in the Strtscan sub, rather than getting the values from the widgets?
• You are using quotes around variables when you don't need to (e.g. in the C-style for loop conditions).
• Maybe I'm missing something, but it looks like nothing happens in the Tk window unless there's an error in the SNMP $session->get_request call. So during all the time that the scan is moving along with no errors, nothing is showing up to tell the user what's happening. If there is nothing to be shown to the user except when there's an error, why is this a Tk GUI? (Why not just a plain-text command-line tool?)