$(foreach host,$(EXTERNAL_HOSTS),cache/switch.$(host)): ;
$(foreach host,$(EXTERNAL_HOSTS),cache/controller.$(host)): ;
$(foreach link,$(EXTERNAL_LINKS),cache/iface.$(link)@2): ;
$(foreach host,$(EXTERNAL_HOSTS),cache/switch.$(host)): ;
$(foreach host,$(EXTERNAL_HOSTS),cache/controller.$(host)): ;
$(foreach link,$(EXTERNAL_LINKS),cache/iface.$(link)@2): ;