IP Address Validation

Hi,
I need to check whether the input string is in ip address format or not in one of my pl/pgsql functions.
What function should be used to accomplish this

I tried using
if inet(strInput)

However, it throws an exception if the input string is not in IP address format.

I could have caught this exception but really don't know what type of exception category would this exception come under..

Any kind of help would be highly appreciated.

Thanks,

Jas