- if ((ptr->ai_family != AF_INET6)
- || setsockopt (fd, SOL_IPV6, IPV6_V6ONLY, &(int){ 0 },
- sizeof (int)))
-#endif
- {
- msg_Err (obj, "Multiple network protocols present");
- msg_Err (obj, "Please select network protocol manually");
- }
+ /* If IPv6 was forced, set IPv6-only mode.
+ * If IPv4 was forced, do nothing extraordinary.
+ * If nothing was forced, try dual-mode IPv6. */
+ if (ptr->ai_family == AF_INET6)
+ {
+ int on = (family == AF_INET6);
+ setsockopt (fd, SOL_IPV6, IPV6_V6ONLY, &on, sizeof (on));
+ }
+ else if (ptr->ai_family == AF_INET && family == AF_UNSPEC)
+ {
+ for (const struct addrinfo *p = ptr; p != NULL; p = p->ai_next)
+ if (p->ai_family == AF_INET6)
+ {
+ net_Close (fd);
+ fd = -1;
+ break;
+ }
+ if (fd == -1)
+ continue;
+ }
+#else
+ if (family == AF_UNSPEC && ptr->ai_next != NULL)
+ {
+ msg_Warn (obj, "ambiguous network protocol specification");
+ msg_Warn (obj, "please select IP version explicitly");