In general, techniques are described for using routing information obtained by operation of network routing protocols to dynamically generate network and cost maps for an application-layer traffic optimization (ALTO) service. For example, an ALTO server of an autonomous system (AS) receives routing information from routers of the AS by listening for routing protocol updates outputted by the routers and uses the received topology information to dynamically generate a network map of PIDs that reflects a current topology of the AS and/or of the broader network that includes the AS. Additionally, the ALTO server dynamically calculates inter-PID costs using received routing information that reflects current link metrics. The ALTO server then assembles the inter-PID costs into a cost map that the ALTO server may provide, along with the network map, to clients of the ALTO service.