Caro-kann exchange main line

@1

4 c4 is the Panov-Botvinnik attack.
The main line of the exchange variation is 4 Bd3, which prevents ...Bf5
https://www.chessgames.com/perl/chessgame?gid=1044326

E4

Different approaches, with different positional motifs. 4.c4 leads to highly asymmetrical IQP positions which can also come from other openings (Nimzoindian, Semi-Tarrasch etc) while 4.Bd3 is a QGD Karlsbad formation with colors reversed.

Opening variations are often named differently if the pawn structures are different. If White goes for c4, it's the Panov, not the Exchange. The Exchange is where White goes c3.

The main line of the Exchange is Bd3 and c3. If White plays this, I recommend Nc6 and Qc7. The idea of Qc7 is to control the diagonal to f4 before the bishop arrives there. One line worth knowing is 1. e4 c6 2. d4 d5 3. exd5 cxd5 4. Bd3 Nc6 5. c3 Qc7 6. Ne2, trying to re-establish control of f4, 6...Bg4 7. f3 Bd7 8. Bf4 e5! Unusual to play e5 in a Caro like this, but in this instance it works out well.

If White doesn't play Bd3 and c3, if White just puts the knights out etc, then the move orders become a lot less critical and you can just develop normally.

There are various ways to play against the Panov. When I played the Caro I liked 4. c4 Nf6 5. Nc3 Nc6. Now if White plays 6. Nf3 I like ...a6 and there are plenty of ways for White to go wrong. If White plays 6. Bg5 though, the positions tend to get really tactical and you really have to know your theory there.