Context : Infrared-dark clouds ( IRDCs ) are the precursors to massive stars and stellar clusters . G011.11 - 0.12 is a well-studied filamentary IRDC , though , to date , the absence of far-infrared data with sufficient spatial resolution has limited the understanding of the structure and star-formation activity . Aims : We use Herschel to study the embedded population of young pre- and protostellar cores in this IRDC . Methods : We examine the cloud structure , which appears in absorption at short wavelength and in emission at longer wavelength . We derive the properties of the massive cores from the spectral energy distributions of bright far-infrared point sources detected with the PACS instrument aboard Herschel . Results : We report on the detection and characterization of pre- and protostellar cores in a massive filamentary infrared-dark cloud G011.11 - 0.12 using PACS . We characterize 18 cores directly associated with the filament , two of which have masses over 50 M _ { \sun } , making them the best candidates to become massive stars in G011.11 - 0.12 . These cores are likely at various stages of protostar formation , showing elevated temperature ( < T > \sim 22 K ) with respect to the ambient gas reservoir . The core masses ( < M > \sim 24 M _ { \sun } ) are small compared to that in the cold filament . The mean core separation is 0.9 pc , well in excess of the Jeans length in the filament . Conclusions : We confirm that star formation in IRDCs is underway and diverse , and IRDCs have the capability of forming massive stars and clusters .