Two consecutive numbers

A teacher thinks of two consecutive numbers between 1 and 10—both inclusive—and then tells one number to one student and the other number to a second student. After that, both students talk to each other in the following way:

First student: I do not know your number.

Second student: Neither do I know your number.

First student: Now I know!

What are the four solutions of this easy number puzzle? If you know them, write them down as a comment.