Involved in lipopolysaccharide (LPS) biosynthesis. Catalyzes the transfer of two 3-deoxy-D-manno-octulosonate (Kdo) residues from CMP-Kdo to lipid IV(A), the tetraacyldisaccharide-1,4'-bisphosphate precursor of lipid A. CMP-3-deoxy-beta-D-manno-octulosonate + lipid IVA (E. coli) = alpha-Kdo-(2->6)-lipid IVA + CMP + H(+) alpha-Kdo-(2->6)-lipid IVA + CMP-3-deoxy-beta-D-manno-octulosonate = alpha-Kdo-(2->4)-alpha-Kdo-(2->6)-lipid IVA + CMP + H(+) Glycolipid biosynthesis; KDO(2)-lipid A biosynthesis; KDO(2)-lipid A from CMP-3-deoxy-D-manno-octulosonate and lipid IV(A): step 1/4. Glycolipid biosynthesis; KDO(2)-lipid A biosynthesis; KDO(2)-lipid A from CMP-3-deoxy-D-manno-octulosonate and lipid IV(A): step 2/4. Bacterial outer membrane biogenesis; LPS core biosynthesis. Belongs to the glycosyltransferase group 1 family. Glycosyltransferase 30 subfamily.