First login into your Internet banking.
Now visit services option.
From here select Generate IRCTC pass code given under the head Utilities.
Now Select the option of 5 in Select no of transactions. So that you can use the same pass code for 5 transactions in IRCTC.
This pass code is only for IRCTC transaction.
This pass code will be valid for 4 hours.
Then you will see confirmation page and your pass code will be sent on your registered mobile number.