--- utils/sc_rxifd/sc_rxifd.c.orig	2026-06-10 14:04:50.000000000 +0800
+++ utils/sc_rxifd/sc_rxifd.c	2026-07-15 18:28:39.000000000 +0800
@@ -42,10 +42,9 @@
 #endif /* HAVE_QUIC or TEST_RXIFD_H3_REQUEST */
 
 #ifndef TEST_RXIFD_H3_REQUEST
-#if defined(IP_PKTINFO) || \
-  (defined(IP_RECVIF) && defined(IP_RECVDSTADDR) && defined(IP_SENDSRCADDR))
+#if defined(IP_PKTINFO) || (defined(IP_RECVIF) && defined(IP_RECVDSTADDR))
 #define HAVE_RXIF4
-#endif /* IP_PKTINFO or (IP_RECVIF, IP_RECVDSTADDR, IP_SENDSRCADDR) */
+#endif /* IP_PKTINFO or (IP_RECVIF, IP_RECVDSTADDR) */
 
 #if defined(IPV6_PKTINFO)
 #define HAVE_RXIF6
@@ -917,7 +916,11 @@
   cmsg = CMSG_FIRSTHDR(&msg);
   cmsg->cmsg_len = CMSG_LEN(sizeof(struct in_addr));
   cmsg->cmsg_level = IPPROTO_IP;
+#if defined(IP_SENDSRCADDR)
   cmsg->cmsg_type = IP_SENDSRCADDR;
+#else
+  cmsg->cmsg_type = IP_RECVDSTADDR;
+#endif /* IP_SENDSRCADDR */
   memcpy(CMSG_DATA(cmsg), us, sizeof(struct in_addr));
 #endif /* IP_PKTINFO, IP_RECVDSTADDR */
 
@@ -1944,15 +1947,19 @@
 	    continue;
 	  if(them_ss.ss_family == AF_INET)
 	    {
+#ifdef HAVE_RXIF4
 	      udp4_send(quic4, txbuf, msg.data_len,
 			&((struct sockaddr_in *)&us_ss)->sin_addr,
 			(struct sockaddr_in *)&them_ss);
+#endif /* HAVE_RXIF4 */
 	    }
 	  else
 	    {
+#ifdef HAVE_RXIF6
 	      udp6_send(quic6, txbuf, msg.data_len,
 			&((struct sockaddr_in6 *)&us_ss)->sin6_addr,
 			(struct sockaddr_in6 *)&them_ss);
+#endif /* HAVE_RXIF6 */
 	    }
 	}
     }
@@ -2583,7 +2590,11 @@
 #endif /* HAVE_RXIF4 */
 
 #ifdef HAVE_RXIF6
+#ifdef OPT_IPV4
   if((options & OPT_IPV4) == 0)
+#else
+  if(1) /* IPv4 unavailable; always open IPv6 socket */
+#endif /* OPT_IPV4 */
     {
       dns6 = udp6_open(dns_port);
       if(socket_isinvalid(dns6))