Methods and apparatus are disclosed for configuring one or more processors to implement service function chains comprising one or more virtualised service functions. A method according to one aspect, performed by a processing module (330) implemented on one or more processors (30), involves steps being performed in respect of at least one new virtualised service function (33) to be included in a service function chain of: determining a position in the service function chain at which the new virtualised service function (33) is to be included; allocating at least one internal address to the new virtualised service function, the at least one internal address being an address to be usable by a switching processor (34); and providing to the switching processor (34) an indication of the at least one internal address allocated to the new virtualised service function (33).