The door_call() on /etc/.name_service_door, is a fast IPC mechanism used to call the name service cache daemon.
Usually, nscd speeds things up. However, on systems that do a lot of DNS lookups, all such lookups are single threaded through nscd. Nscd itself is multi-threaded, but the resolver library uses one big global lock. On such systems, performance is often best served by disabling the nscd host cache by editing /etc/nscd.conf like this:
enable-cache hosts no