Among other things, this document describes systems, devices, and methods for improving the mapping of end user clients to content servers. In one embodiment, an intermediary DNS server receives a DNS answer with multiple IP addresses. The intermediary DNS server modifies this answer before passing it on to the end user client—that is the end user client that originally requested name resolution of the hostname. Modification can involve filtering the list to remove low-performing IP addresses, re-ordering the list, blocking certain IPs according to policy, or other things. The intermediary DNS server can be operated by a internet service provider (carrier) or an enterprise, for example, or provided on their behalf by a third party as a service. The modification can be based on knowledge of the client-side network, including the location and connectivity of the end user client.