I need a regex that matches a string containing 6 alpha, 2 alphanumeric and 3 OPTIONAL alphanumeric, upper and lower case. I need this for validating strings in ASP.net 2. Eg:. abcdefab345 abcdef22 abcdef5e abcdef3ee5e abcdef55asd abcdefr5 and should not match abcs abcd34d3 abcdef23f abcdefd abcdef