when i try to attch a port to a extternal network using the rest api or CLI i get this error

{ "QuantumError" : "External network 09403640-62fb-402f-bec5-0aaedf759504 is not reachable from subnet a589c818-8943-43eb-89de-f2b178e418a0. Therefore, cannot associate Port 23ab32aa-aa76-4498-bcff-271873119f60 with a Floating IP." }

Dont know if i need to do anything to make my subnet on private network talk to external network