Index: share/man/man4/ip.4
===================================================================
--- share/man/man4/ip.4
+++ share/man/man4/ip.4
@@ -92,8 +92,8 @@
 .Dv IP_TOS
 and
 .Dv IP_TTL
-may be used to set the type-of-service and time-to-live
-fields in the
+may be used to set the differential service codepoint (DSCP) and
+time-to-live (TTL) fields in the
 .Tn IP
 header for
 .Dv SOCK_STREAM , SOCK_DGRAM ,
@@ -102,8 +102,8 @@
 sockets.
 For example,
 .Bd -literal
-int tos = IPTOS_LOWDELAY;       /* see <netinet/ip.h> */
-setsockopt(s, IPPROTO_IP, IP_TOS, &tos, sizeof(tos));
+int dscp = IPTOS_DSCP_EF;       /* see <netinet/ip.h> */
+setsockopt(s, IPPROTO_IP, IP_TOS, &dscp, sizeof(dscp));
 
 int ttl = 60;                   /* max = 255 */
 setsockopt(s, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
Index: sys/netinet/ip.h
===================================================================
--- sys/netinet/ip.h
+++ sys/netinet/ip.h
@@ -79,7 +79,7 @@
 #define	IPTOS_LOWDELAY		0x10
 #define	IPTOS_THROUGHPUT	0x08
 #define	IPTOS_RELIABILITY	0x04
-#define	IPTOS_MINCOST		0x02
+#define	IPTOS_MINCOST		IPTOS_DSCP_CS0
 
 /*
  * Definitions for IP precedence (also in ip_tos) (deprecated).
Index: sys/netinet/tcp_usrreq.c
===================================================================
--- sys/netinet/tcp_usrreq.c
+++ sys/netinet/tcp_usrreq.c
@@ -82,6 +82,7 @@
 #include <netinet/in_pcb.h>
 #include <netinet/in_systm.h>
 #include <netinet/in_var.h>
+#include <netinet/ip.h>
 #include <netinet/ip_var.h>
 #ifdef INET6
 #include <netinet/ip6.h>
@@ -1757,6 +1758,12 @@
 		case IPPROTO_IP:
 			switch (sopt->sopt_name) {
 			case IP_TOS:
+				int optval;
+				if (sooptcopyin(sopt, &optval, sizeof optval,
+						    sizeof optval))
+					break;
+				inp->inp_ip_tos = optval & ~IPTOS_ECN_MASK;
+				break;
 			case IP_TTL:
 				/* Notify tcp stacks that care (e.g. RACK). */
 				break;