If you mean the next program down the line should finally decide whether the IP address is valid, I disagree.

In this situation this regexp should deal with the lower level checking of the basic address validity. 999.000.999.000 is not a valid IP address. Otherwise you're allowing garbage input further down the chain of execution, while you bask in your cerebral interpretation of the definition of "taint" :)


you'll have to check what characters that program accepts.

What program that deals with IP addresses will accept "999.000.999.000" as valid? Do you mean we have drop everything, and go check with that program first?