How do/would you handle this situation?

DD1 (nearly 5) and DD2 (nearly 3) can really get at each other sometimes. DD2 is definitely rougher/more violent (she scratches, pulls hair, and sometimes bites, even though she's been reprimanded strongly for this). The bulk of the scolding/discipline used to fall on her, until I realized she is ALWAYS provoked by her older sister - DD1 will take things, call names, or just be whining/complaining excessively, and DD2 reacts. I think DD1 actually enjoys the reaction, until she gets hurt. Then she screams and cries (which provokes or motivates DD2 further).

Obviously they're both wrong. But how do you handle discipline for this situation? Obviously DD2 needs to deal with her emotions less aggressively...and while I do feel badly for DD1, I think she DOES need to learn that she brings some of this on herself with her own behavior - she is choosing to provoke her sister.

Any tips? It's equal parts heartbreaking and enraging to have this happening on a too-regular basis recently...