GCDAsyncUdpSocket immediately closes when sending to an IPv6 address

Question

I\'m connecting via UDP to a server on a different device which is advertised by Bonjour. When both the iOS device which this code is running on, and the server, are on our

Answer 1

fe80 is a link-local IPv6 address. The machine to which you're connecting must have more than one network interface -- most do, e.g. Ethernet and WiFi. To fully specific an IPv6 address, the scope_id is required. This is the sin6_scope_id from:

// IPv6 AF_INET6 sockets:

struct sockaddr_in6 {
    u_int16_t       sin6_family;   // address family, AF_INET6
    u_int16_t       sin6_port;     // port number, Network Byte Order
    u_int32_t       sin6_flowinfo; // IPv6 flow information
    struct in6_addr sin6_addr;     // IPv6 address
    u_int32_t       sin6_scope_id; // Scope ID
};

and when combined with the address and converted to a string looks like this: fe80::e2f8:47ff:fe23:5392%eth1

When the DNS is resolved, the NSData wrapping a sockaddr struct includes this information. However, in your code, you are extracting the sin6_port and sin6_addr, then feeding them back to GCDAsyncUDPSocket devoid of the sin6_flowinfo (which you don't need) and the sin6_scope_id (which in this case you do).

Use -[GCDAsyncUDPSocket connectToAddress:error:] directly, using the NSData you get directly from your resolve service, and you should be good to go.