Index: sys/netinet/udp_usrreq.c
===================================================================
--- sys/netinet/udp_usrreq.c
+++ sys/netinet/udp_usrreq.c
@@ -162,7 +162,7 @@
 #ifdef INET
 static void	udp_detach(struct socket *so);
 static int	udp_output(struct inpcb *, struct mbuf *, struct sockaddr *,
-		    struct mbuf *, struct thread *);
+		    struct mbuf *, struct thread *, int);
 #endif
 
 static void
@@ -1084,7 +1084,7 @@
 #ifdef INET
 static int
 udp_output(struct inpcb *inp, struct mbuf *m, struct sockaddr *addr,
-    struct mbuf *control, struct thread *td)
+    struct mbuf *control, struct thread *td, int flags)
 {
 	struct udpiphdr *ui;
 	int len = m->m_pkthdr.len;
@@ -1148,6 +1148,60 @@
 				error = EINVAL;
 				break;
 			}
+#ifdef INET6
+			if ((flags & PRUS_IPV6) != 0 &&
+			    cm->cmsg_level == IPPROTO_IPV6 &&
+			    (cm->cmsg_type == IPV6_2292PKTINFO ||
+			    cm->cmsg_type == IPV6_PKTINFO)) {
+				struct ifnet *ifp = NULL;
+				struct in6_pktinfo *pktinfo;
+
+				if (cm->cmsg_len !=
+				    CMSG_LEN(sizeof(struct in6_pktinfo))) {
+					error = EINVAL;
+					goto err;
+				}
+
+				pktinfo = (struct in6_pktinfo *)CMSG_DATA(cm);
+				if (!IN6_IS_ADDR_V4MAPPED(&pktinfo->ipi6_addr) ||
+				    !IN6_IS_ADDR_UNSPECIFIED(&pktinfo->ipi6_addr))
+				{
+					error = EINVAL;
+					goto err;
+				}
+				/* Validate the interface index if specified. */
+				if (pktinfo->ipi6_ifindex > V_if_index) {
+					error = ENXIO;
+					goto err;
+				}
+				if (pktinfo->ipi6_ifindex) {
+					ifp = ifnet_byindex(pktinfo->ipi6_ifindex);
+					if (ifp == NULL) {
+						error = ENXIO;
+						goto err;
+					}
+				}
+				if (ifp != NULL &&
+				    !IN6_IS_ADDR_UNSPECIFIED(&pktinfo->ipi6_addr)) {
+					struct in_addr ia;
+
+					ia.s_addr =
+					    pktinfo->ipi6_addr.s6_addr32[3];
+					if (in_ifhasaddr(ifp, ia) == 0) {
+						error = EADDRNOTAVAIL;
+						goto err;
+					}
+				}
+				bzero(&src, sizeof(src));
+				src.sin_family = AF_INET;
+				src.sin_len = sizeof(src);
+				src.sin_port = inp->inp_lport;
+				src.sin_addr.s_addr =
+				    pktinfo->ipi6_addr.s6_addr32[3];
+				continue;
+			}
+#endif
+
 			if (cm->cmsg_level != IPPROTO_IP)
 				continue;
 
@@ -1203,6 +1257,9 @@
 				error = ENOPROTOOPT;
 				break;
 			}
+#ifdef INET6
+err:
+#endif
 			if (error)
 				break;
 		}
@@ -1695,7 +1752,7 @@
 
 	inp = sotoinpcb(so);
 	KASSERT(inp != NULL, ("udp_send: inp == NULL"));
-	return (udp_output(inp, m, addr, control, td));
+	return (udp_output(inp, m, addr, control, td, flags));
 }
 #endif /* INET */
 
Index: sys/netinet6/udp6_usrreq.c
===================================================================
--- sys/netinet6/udp6_usrreq.c
+++ sys/netinet6/udp6_usrreq.c
@@ -784,7 +784,7 @@
 				in6_sin6_2_sin_in_sock((struct sockaddr *)sin6);
 			pru = inetsw[ip_protox[nxt]].pr_usrreqs;
 			/* addr will just be freed in sendit(). */
-			return ((*pru->pru_send)(so, flags_arg, m,
+			return ((*pru->pru_send)(so, flags_arg | PRUS_IPV6, m,
 			    (struct sockaddr *)sin6, control, td));
 		}
 	} else
Index: sys/sys/protosw.h
===================================================================
--- sys/sys/protosw.h
+++ sys/sys/protosw.h
@@ -210,6 +210,7 @@
 #define	PRUS_EOF	0x2
 #define	PRUS_MORETOCOME	0x4
 #define	PRUS_NOTREADY	0x8
+#define	PRUS_IPV6	0x10
 	int	(*pru_ready)(struct socket *so, struct mbuf *m, int count);
 	int	(*pru_sense)(struct socket *so, struct stat *sb);
 	int	(*pru_shutdown)(struct socket *so);