如何使用asp.net对文本框进行验证

I have a Textbox on my webform, for instance 2012 entered in single text box the following text box must enter 2014 or else should give error.Iam trying to validate it by using compare validation but am unable to meet the exact condition what i want.Can i know how can it be done?thnks in advanceI have a Textbox on my webform, for instance 20