Validation Expression

I am using the following regular expression to validate IP addresses. It works fine for IP addresses but I need to be able to enter partial IP addresses as well, such as 10.10.10 or 10.10.
How can I modify the expression to accomplish this:
ValidationExpression
="\b(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b"
...