Old Indian defense variation: 1. d4 d6 2. c4 Nf6 3. Nc3 Nc6 : how should White respond?
White should continue to fight for the center, as always and Black should continue developing so he can pressure Whites pawn center from afar.
I couldn't find this variation discussed anywhere which leads me to think it is likely an inferior line for Black.
I am not surprised-Black is tempting White to overextend by chasing the knight but this is not Alekhine's defense and I think White can get slight advantage from this position.
If so, how should White continue to gain advantage? 4. e4 perhaps ?
e4. White should use this moment to seize the initiative and hinder Black's development. You see, Black's only compensation for giving White the center power is his superior development. He will use it to pressure White's center or undermine it with flank attack. I suggest immediate
d5 as an answer. See the detailed variations below.
1. d4 d6 2. c4 Nf6 3. Nc3 Nc6?! 4.d5! Nb8 ( 4...Nb4? 5.Qa4++- ) ( 4...Na5? 5.Qa4+! c6 6.b4! Nxc4 7.dxc6! b5 ( 7...bxc6? 8.Qxc6++- ) ( 7...Nb6 8.cxb7+!+- Nxa4 9.bxa8=Q Nxc3 10.Qc6+!+- ) 8.Qxb5!?+- ) ( 4...Ne5? 5.f4! Ned7 ( 5...Ng6? 6.e4 e5 7.f5! Ne7 8.Bg5!? ) 6.e4 ) 5.e4
and White is tempo up in all the above variations comparing to the usual King's Indian defense opening moves.
Since every tempo counts in the King's Indian defense this is a big plus-White will be faster in reaching his typical queen side attack while Black will be one tempo behind in generating King side attack. At the very least, this should force Black into long, passive defense since he will not be able to generate typical counter-play.
As for the moves with
!? in the sidelines mentioned in the above diagram, you should consult the engine to find even stronger continuation-I just gave you my thought-it might not be the best move but I like the fact it maintains initiative/pressure.
Hopefully this answer helped you. If you have further questions leave a comment and I will reply.