Need to confirm if an mx960 with a MPC7E line card and a RE-S-2X00x6 would require a license to configure an IP sec tunnel

No symptoms observed, the customer just have a question before configuring the IP Sec

The answer is no, there is no need for any extra license to configure IP sec tunnels, there are indeed some related licenses but those are for advance feature and applicable for other devices, mostly SRX devices.