Catalyzes the stereoinversion of LL-2,6-diaminoheptanedioate (L,L-DAP) to meso-diaminoheptanedioate (meso-DAP), a precursor of L-lysine and an essential component of the bacterial peptidoglycan. (2S,6S)-2,6-diaminoheptanedioate = meso-2,6-diaminoheptanedioate Amino-acid biosynthesis; L-lysine biosynthesis via DAP pathway; DL-2,6-diaminopimelate from LL-2,6-diaminopimelate: step 1/1. Homodimer. Belongs to the diaminopimelate epimerase family. Extended N-terminus.