Hydrolyzes chitin oligosaccharides; (GlcNAc)4 to (GlcNAc)2 and (GlcNAc)5,6 to (GlcNAc)2 and (GlcNAc)3. Inactive towards chitin, glucosamine oligosaccharides, glycoproteins and glycopeptides containing (GlcNAc)2. Hydrolysis of chitodextrins, releasing N,N'-diacetylchitobiose and small amounts of N,N',N''-triacetylchitotriose. Inhibited by (GlcNAc)4, (GlcNAc)5, (GlcNAc)6, and PNP-(GlcNAc)3. Optimum pH is 6.5-7.0. Optimum temperature is 35-37 degrees Celsius. Glycan degradation; chitin degradation. By (GlcNAc)2. Belongs to the glycosyl hydrolase 18 family.