Though this is quite an old post, I thought it'll be worthwhile to add the following for future reference:
Both above regex patterns will also return true for
225*1*1*1:3000 or
225a1b1c1:3000 etc. This is because you're not using the literal "." in your pattern. Therefore, escaping the "."s in the above pattern would be a good idea, like so:
@"^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}:\d{1,5}$"
so that the literal "." character is not confused with the "." metacharacter for regular expressions.