--- sys/netinet/tcp_input.c.original	2015-10-06 17:09:43.917601000 +0100
+++ sys/netinet/tcp_input.c	2015-10-06 17:12:40.674590000 +0100
@@ -595,21 +595,12 @@
 		}
 
 		ip6 = mtod(m, struct ip6_hdr *);
-		th = (struct tcphdr *)((caddr_t)ip6 + off0);
 		tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
-		if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
-			if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
-				th->th_sum = m->m_pkthdr.csum_data;
-			else
-				th->th_sum = in6_cksum_pseudo(ip6, tlen,
-				    IPPROTO_TCP, m->m_pkthdr.csum_data);
-			th->th_sum ^= 0xffff;
-		} else
-			th->th_sum = in6_cksum(m, IPPROTO_TCP, off0, tlen);
-		if (th->th_sum) {
+		if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
 			TCPSTAT_INC(tcps_rcvbadsum);
 			goto drop;
 		}
+		th = (struct tcphdr *)((caddr_t)ip6 + off0);
 
 		/*
 		 * Be proactive about unspecified IPv6 address in source.
--- sys/netinet/tcp_output.c.original	2015-10-06 16:48:18.650266000 +0100
+++ sys/netinet/tcp_output.c	2015-10-06 16:59:12.718992000 +0100
@@ -1179,7 +1179,6 @@
 	 * checksum extended header and data.
 	 */
 	m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
-	m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 #ifdef INET6
 	if (isipv6) {
 		/*
@@ -1187,8 +1186,8 @@
 		 * in ip6_output.
 		 */
 		m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
-		th->th_sum = in6_cksum_pseudo(ip6, sizeof(struct tcphdr) +
-		    optlen + len, IPPROTO_TCP, 0);
+		th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr), 
+					sizeof(struct tcphdr) + optlen + len); 
 	}
 #endif
 #if defined(INET6) && defined(INET)
@@ -1197,6 +1196,7 @@
 #ifdef INET
 	{
 		m->m_pkthdr.csum_flags = CSUM_TCP;
+		m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 		th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 		    htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
 
--- sys/netinet/tcp_subr.c.original	2015-10-06 17:00:06.696707000 +0100
+++ sys/netinet/tcp_subr.c	2015-10-06 17:05:52.865283000 +0100
@@ -682,12 +682,12 @@
 		nth->th_win = htons((u_short)win);
 	nth->th_urp = 0;
 
-	m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 #ifdef INET6
 	if (isipv6) {
 		m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
-		nth->th_sum = in6_cksum_pseudo(ip6,
-		    tlen - sizeof(struct ip6_hdr), IPPROTO_TCP, 0);
+		nth->th_sum = in6_cksum(m, IPPROTO_TCP,
+			sizeof(struct ip6_hdr),
+			tlen - sizeof(struct ip6_hdr));
 		ip6->ip6_hlim = in6_selecthlim(tp != NULL ? tp->t_inpcb :
 		    NULL, NULL);
 	}
@@ -698,6 +698,7 @@
 #ifdef INET
 	{
 		m->m_pkthdr.csum_flags = CSUM_TCP;
+		m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 		nth->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 		    htons((u_short)(tlen - sizeof(struct ip) + ip->ip_p)));
 	}
--- sys/netinet/tcp_syncache.c.original	2015-10-06 17:06:19.746207000 +0100
+++ sys/netinet/tcp_syncache.c	2015-10-06 17:07:47.751243000 +0100
@@ -1542,12 +1542,12 @@
 		optlen = 0;
 
 	M_SETFIB(m, sc->sc_inc.inc_fibnum);
-	m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 #ifdef INET6
 	if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 		m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
-		th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
-		    IPPROTO_TCP, 0);
+		th->th_sum = 0;
+		th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen,
+			 tlen + optlen - hlen);
 		ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
 #ifdef TCP_OFFLOAD
 		if (ADDED_BY_TOE(sc)) {
@@ -1567,6 +1567,7 @@
 #ifdef INET
 	{
 		m->m_pkthdr.csum_flags = CSUM_TCP;
+		m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 		th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 		    htons(tlen + optlen - hlen + IPPROTO_TCP));
 #ifdef TCP_OFFLOAD
--- sys/netinet/tcp_timewait.c.original	2015-10-06 17:08:06.793786000 +0100
+++ sys/netinet/tcp_timewait.c	2015-10-06 17:09:12.957608000 +0100
@@ -616,12 +616,11 @@
 	th->th_flags = flags;
 	th->th_win = htons(tw->last_win);
 
-	m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 #ifdef INET6
 	if (isipv6) {
 		m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
-		th->th_sum = in6_cksum_pseudo(ip6,
-		    sizeof(struct tcphdr) + optlen, IPPROTO_TCP, 0);
+		th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),
+			sizeof(struct tcphdr) + optlen);
 		ip6->ip6_hlim = in6_selecthlim(inp, NULL);
 		error = ip6_output(m, inp->in6p_outputopts, NULL,
 		    (tw->tw_so_options & SO_DONTROUTE), NULL, NULL, inp);
@@ -633,6 +632,7 @@
 #ifdef INET
 	{
 		m->m_pkthdr.csum_flags = CSUM_TCP;
+		m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 		th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 		    htons(sizeof(struct tcphdr) + optlen + IPPROTO_TCP));
 		ip->ip_len = htons(m->m_pkthdr.len);
--- sys/netinet6/udp6_usrreq.c.original	2015-10-06 17:14:38.025141000 +0100
+++ sys/netinet6/udp6_usrreq.c	2015-10-06 17:20:35.235141000 +0100
@@ -200,7 +200,6 @@
	int plen, ulen;
	struct sockaddr_in6 fromsa;
	struct m_tag *fwd_tag;
-	uint16_t uh_sum;
	uint8_t nxt;

	ifp = m->m_pkthdr.rcvif;
@@ -260,18 +260,7 @@
 		}
 	}
 
-	if ((m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) &&
-	    !cscov_partial) {
-		if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
-			uh_sum = m->m_pkthdr.csum_data;
-		else
-			uh_sum = in6_cksum_pseudo(ip6, ulen, nxt,
-			    m->m_pkthdr.csum_data);
-		uh_sum ^= 0xffff;
-	} else
-		uh_sum = in6_cksum_partial(m, nxt, off, plen, ulen);
-
-	if (uh_sum != 0) {
+	if (in6_cksum(m, IPPROTO_UDP, off, ulen) != 0) {
 		UDPSTAT_INC(udps_badsum);
 		goto badunlocked;
 	}
@@ -833,9 +822,11 @@
 			    sizeof(struct ip6_hdr), plen, cscov)) == 0)
 				udp6->uh_sum = 0xffff;
 		} else {
-			udp6->uh_sum = in6_cksum_pseudo(ip6, plen, nxt, 0);
-			m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
-			m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
+			if ((udp6->uh_sum = in6_cksum(m, IPPROTO_UDP,
+				sizeof(struct ip6_hdr), plen)) == 0) {
+				udp6->uh_sum = 0xffff;
+				m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
+			}
 		}
 
 		flags = 0;