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/ip_output.c
===================================================================
--- sys/netinet/ip_output.c
+++ sys/netinet/ip_output.c
@@ -1200,7 +1200,7 @@
 
 			switch (sopt->sopt_name) {
 			case IP_TOS:
-				inp->inp_ip_tos = optval;
+				inp->inp_ip_tos = optval & ~IPTOS_ECN_MASK;
 				break;
 
 			case IP_TTL:
Index: sys/netinet/tcp_stacks/rack.c
===================================================================
--- sys/netinet/tcp_stacks/rack.c
+++ sys/netinet/tcp_stacks/rack.c
@@ -20475,7 +20475,7 @@
 			/*
 			 * The DSCP codepoint has changed, update the fsb.
 			 */
-			ip->ip_tos = rack->rc_inp->inp_ip_tos;
+			ip->ip_tos = rack->rc_inp->inp_ip_tos & ~IPTOS_ECN_MASK;
 			break;
 		case IP_TTL:
 			/*