How do I get a country to stop supporting independence?

[delta180]

Currently, one of my rivals is supporting the independence of one of my vassals, but because I am a tributary of Ming, I don't think they will ever declare war.
I am more than happy to declare on my rival (although I would not be satisfied with taking the stability hit from declaring war on my vassal), but what sort of peace deal would I need? Would white peace do?

 

[InvisibleBison]

I'm pretty sure a truce with you, regardless of the peace deal that produced it, will block a nation from supporting your subject's independence.

 

[bokorthedust]

Just by declaring on your rival the support would break, and as @InvisibleBison said he won't be able to offer it again for the duration of the truce. So just a white peace would do it too, unless you feel you need longer than 5 years to get your vassal under 50 LD, in that case extending the truce as long as you could wouldn't hurt.