With regards to the failing test, it looks like the test basically boils down to testing whether loop.getaddrinfo('fe80::1%1', 80, type=socket.SOCK_STREAM) returns (<socket.AF_INET6>, <socket.SOCK_STREAM>, *, *, ('fe80::1', 80, 0, 1)). This feels like a dangerous assumption to make, since it's tied to the operating system's behavior. Maybe AIX's getaddrinfo() in fact does not resolve scoped addresses correctly; maybe it only resolves scope ids correctly for real addresses that actually exist on the network; Maybe AIX assigns scope ids differently and do not use small integers; etc.