diff --git a/sys/netinet/ip_output.c b/sys/netinet/ip_output.c
index 1a594cd1b68..9ebbf9826ef 100644
--- a/sys/netinet/ip_output.c
+++ b/sys/netinet/ip_output.c
@@ -601,7 +601,8 @@ ip_output(struct mbuf *m, struct mbuf *opt, struct route *ro, int flags,
 	}
 
 	m->m_pkthdr.csum_flags |= CSUM_IP;
-	if (m->m_pkthdr.csum_flags & CSUM_DELAY_DATA & ~ifp->if_hwassist) {
+	if ((m->m_pkthdr.csum_flags & CSUM_DELAY_DATA & ~ifp->if_hwassist) ||
+		(m->m_pkthdr.csum_flags & CSUM_UDP_TRAIL)) {
 		in_delayed_cksum(m);
 		m->m_pkthdr.csum_flags &= ~CSUM_DELAY_DATA;
 	}
diff --git a/sys/netinet/udp_usrreq.c b/sys/netinet/udp_usrreq.c
index 670182ece8b..7ce3f78ed88 100644
--- a/sys/netinet/udp_usrreq.c
+++ b/sys/netinet/udp_usrreq.c
@@ -140,6 +140,12 @@ u_long	udp_recvspace = 40 * (1024 +
 SYSCTL_ULONG(_net_inet_udp, UDPCTL_RECVSPACE, recvspace, CTLFLAG_RW,
     &udp_recvspace, 0, "Maximum space for incoming UDP datagrams");
 
+VNET_DEFINE(int, udp_trailing_data) = 0;
+SYSCTL_INT(_net_inet_udp, OID_AUTO, udp_trailing_data, CTLFLAG_VNET | CTLFLAG_RW,
+       &VNET_NAME(udp_trailing_data), 0,
+	  "dirty hack - send udp trailing data");
+#define	V_udp_trailing_data VNET(udp_trailing_data)
+
 VNET_DEFINE(struct inpcbhead, udb);		/* from udp_var.h */
 VNET_DEFINE(struct inpcbinfo, udbinfo);
 VNET_DEFINE(struct inpcbhead, ulitecb);
@@ -1460,7 +1466,13 @@ udp_output(struct inpcb *inp, struct mbuf *m, struct sockaddr *addr,
 		m->m_pkthdr.csum_flags = CSUM_UDP;
 		m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
 	}
-	((struct ip *)ui)->ip_len = htons(sizeof(struct udpiphdr) + len);
+	if (V_udp_trailing_data) {
+		u_char *trailer = "freebsd";
+		m_append(m, sizeof(trailer), trailer);
+		((struct ip *)ui)->ip_len = htons(sizeof(struct udpiphdr) + len + sizeof(trailer));
+		m->m_pkthdr.csum_flags |= CSUM_UDP_TRAIL;
+	} else
+		((struct ip *)ui)->ip_len = htons(sizeof(struct udpiphdr) + len);
 	((struct ip *)ui)->ip_ttl = inp->inp_ip_ttl;	/* XXX */
 	((struct ip *)ui)->ip_tos = tos;		/* XXX */
 	UDPSTAT_INC(udps_opackets);
diff --git a/sys/sys/mbuf.h b/sys/sys/mbuf.h
index 81aed4e75f8..3265ea6c278 100644
--- a/sys/sys/mbuf.h
+++ b/sys/sys/mbuf.h
@@ -503,6 +503,7 @@ struct mbuf {
 #define	CSUM_IP_SCTP		0x00000008	/* SCTP checksum offload */
 #define	CSUM_IP_TSO		0x00000010	/* TCP segmentation offload */
 #define	CSUM_IP_ISCSI		0x00000020	/* iSCSI checksum offload */
+#define	CSUM_IP_UDP_TRAIL	0x00000040	/* UDP trailing data */
 
 #define	CSUM_IP6_UDP		0x00000200	/* UDP checksum offload */
 #define	CSUM_IP6_TCP		0x00000400	/* TCP checksum offload */
@@ -524,7 +525,7 @@ struct mbuf {
  */
 #define	CSUM_BITS \
     "\20\1CSUM_IP\2CSUM_IP_UDP\3CSUM_IP_TCP\4CSUM_IP_SCTP\5CSUM_IP_TSO" \
-    "\6CSUM_IP_ISCSI" \
+    "\6CSUM_IP_ISCSI\7CSUM_IP_UDP_TRAIL" \
     "\12CSUM_IP6_UDP\13CSUM_IP6_TCP\14CSUM_IP6_SCTP\15CSUM_IP6_TSO" \
     "\16CSUM_IP6_ISCSI" \
     "\31CSUM_L3_CALC\32CSUM_L3_VALID\33CSUM_L4_CALC\34CSUM_L4_VALID" \
@@ -542,6 +543,7 @@ struct mbuf {
 #define	CSUM_DATA_VALID_IPV6	CSUM_DATA_VALID
 #define	CSUM_TCP		CSUM_IP_TCP
 #define	CSUM_UDP		CSUM_IP_UDP
+#define	CSUM_UDP_TRAIL		CSUM_IP_UDP_TRAIL
 #define	CSUM_SCTP		CSUM_IP_SCTP
 #define	CSUM_TSO		(CSUM_IP_TSO|CSUM_IP6_TSO)
 #define	CSUM_UDP_IPV6		CSUM_IP6_UDP