Did FRA-(LH)-BLR-(6E)-HYD last year. Planned layover was ~4h and that was plenty, even with a ~20Min delay into BLR.
BUT, 2h will be asking for it. I advise you get out of the plane as fast as possible and dont stop before being in the queue for immigrations - they ARE slow (about 20 in front of me took ~30Min with four counters open...).
Also have the domestic ticket printed(!) and ready to show when changing from international to domestic.
Oh, and be alert about the part that BLR domestic (and some others) are "silent" airports. Check the boards, they wont "call" for boarding over PA.