Index: share/man/man4/carp.4
===================================================================
--- share/man/man4/carp.4
+++ share/man/man4/carp.4
@@ -26,7 +26,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd February 21, 2013
+.Dd February 23, 2018
 .Dt CARP 4
 .Os
 .Sh NAME
@@ -102,6 +102,13 @@
 When enabled, a vhid in a backup state would preempt a master that
 is announcing itself with a lower advskew.
 Disabled by default.
+.It Va net.inet.carp.dscp
+Set DSCP value in carp packet
+When enabled, set Class of Service to CS7 (network control) in outgoing
+carp packets.
+When disabled, Class of Service is set to TOS LOW_DELAY.
+TOS values were deprecated and replaced by DSCP in 1998.
+Disabled by default.
 .It Va net.inet.carp.log
 Determines what events relating to
 .Nm
Index: sys/netinet/ip6.h
===================================================================
--- sys/netinet/ip6.h
+++ sys/netinet/ip6.h
@@ -102,6 +102,7 @@
 #define IPV6_FLOWLABEL_MASK	0xffff0f00	/* flow label (20 bits) */
 #endif /* LITTLE_ENDIAN */
 #endif
+#define IPV6_FLOWLABEL_LEN	20
 #if 1
 /* ECN bits proposed by Sally Floyd */
 #define IP6TOS_CE		0x01	/* congestion experienced */
Index: sys/netinet/ip_carp.c
===================================================================
--- sys/netinet/ip_carp.c
+++ sys/netinet/ip_carp.c
@@ -190,6 +190,10 @@
 static VNET_DEFINE(int, carp_allow) = 1;
 #define	V_carp_allow	VNET(carp_allow)
 
+/* Set DSCP in outgoing CARP packets. */
+static VNET_DEFINE(int, carp_dscp) = 1;
+#define	V_carp_dscp	VNET(carp_dscp)
+
 /* Preempt slower nodes. */
 static VNET_DEFINE(int, carp_preempt) = 0;
 #define	V_carp_preempt	VNET(carp_preempt)
@@ -215,6 +219,8 @@
 SYSCTL_NODE(_net_inet, IPPROTO_CARP,	carp,	CTLFLAG_RW, 0,	"CARP");
 SYSCTL_INT(_net_inet_carp, OID_AUTO, allow, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(carp_allow), 0, "Accept incoming CARP packets");
+SYSCTL_INT(_net_inet_carp, OID_AUTO, dscp, CTLFLAG_VNET | CTLFLAG_RW,
+    &VNET_NAME(carp_dscp), 0, "Use DSCP CS7 for carp packets");
 SYSCTL_INT(_net_inet_carp, OID_AUTO, preempt, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(carp_preempt), 0, "High-priority backup preemption mode");
 SYSCTL_INT(_net_inet_carp, OID_AUTO, log, CTLFLAG_VNET | CTLFLAG_RW,
@@ -931,7 +937,11 @@
 		ip = mtod(m, struct ip *);
 		ip->ip_v = IPVERSION;
 		ip->ip_hl = sizeof(*ip) >> 2;
-		ip->ip_tos = IPTOS_LOWDELAY;
+		if (V_carp_dscp) {
+			ip->ip_tos = IPTOS_DSCP_CS7;
+		} else {
+			ip->ip_tos = IPTOS_LOWDELAY;
+		}	
 		ip->ip_len = htons(len);
 		ip->ip_off = htons(IP_DF);
 		ip->ip_ttl = CARP_DFLTTL;
@@ -981,6 +991,11 @@
 		ip6 = mtod(m, struct ip6_hdr *);
 		bzero(ip6, sizeof(*ip6));
 		ip6->ip6_vfc |= IPV6_VERSION;
+                if (V_carp_dscp) {
+			/* Traffic class isn't defined in ip6 struct instead  
+			 * it gets offset into flowlabel field */
+                	ip6->ip6_flow |= htonl(IPTOS_DSCP_CS7 << IPV6_FLOWLABEL_LEN);
+		}
 		ip6->ip6_hlim = CARP_DFLTTL;
 		ip6->ip6_nxt = IPPROTO_CARP;