+void
+sock_set_v6only(int s)
+{
+#ifdef IPV6_V6ONLY
+ int on = 1;
+
+ debug3("%s: set socket %d IPV6_V6ONLY", __func__, s);
+ if (setsockopt(s, IPPROTO_IPV6, IPV6_V6ONLY, &on, sizeof(on)) == -1)
+ error("setsockopt IPV6_V6ONLY: %s", strerror(errno));
+#endif
+}