diff --git a/sys/kern/uipc_socket.c b/sys/kern/uipc_socket.c
--- a/sys/kern/uipc_socket.c
+++ b/sys/kern/uipc_socket.c
@@ -197,6 +197,9 @@
 
 so_gen_t	so_gencnt;	/* generation count for sockets */
 
+so_checkfiballowed_t	so_checkfiballowed;
+soopt_validfib_t	soopt_validfib;
+
 MALLOC_DEFINE(M_SONAME, "soname", "socket name");
 MALLOC_DEFINE(M_PCB, "pcb", "protocol control block");
 
@@ -3143,24 +3146,6 @@
 			SOCK_UNLOCK(so);
 			break;
 
-		case SO_SETFIB:
-			error = sooptcopyin(sopt, &optval, sizeof optval,
-			    sizeof optval);
-			if (error)
-				goto bad;
-
-			if (optval < 0 || optval >= rt_numfibs) {
-				error = EINVAL;
-				goto bad;
-			}
-			if (((so->so_proto->pr_domain->dom_family == PF_INET) ||
-			   (so->so_proto->pr_domain->dom_family == PF_INET6) ||
-			   (so->so_proto->pr_domain->dom_family == PF_ROUTE)))
-				so->so_fibnum = optval;
-			else
-				so->so_fibnum = 0;
-			break;
-
 		case SO_USER_COOKIE:
 			error = sooptcopyin(sopt, &val32, sizeof val32,
 			    sizeof val32);
@@ -3246,6 +3231,15 @@
 			so->so_max_pacing_rate = val32;
 			break;
 
+		case SO_SETFIB:
+			/* Let the protocol-specific ctloutput handle it */
+			if (so->so_proto->pr_ctloutput != NULL) {
+				error = (*so->so_proto->pr_ctloutput)(so,
+				    sopt);
+				goto bad;
+			}
+
+			/* Fall through */
 		default:
 			if (V_socket_hhh[HHOOK_SOCKET_OPT]->hhh_nhooks > 0)
 				error = hhook_run_socket(so, sopt,
@@ -3589,6 +3583,25 @@
 	return (0);
 }
 
+int
+soopt_getfib(struct sockopt *sopt, int *fibnum)
+{
+	int error, optval;
+
+	error = sooptcopyin(sopt, &optval, sizeof optval, sizeof(optval));
+	if (error)
+		return (error);
+
+	if (soopt_validfib != NULL) {	/* Let netstack check FIB */
+		if (!soopt_validfib(sopt, optval))
+			return (EINVAL);
+	} else if (optval != 0)		/* Default only allow FIB 0 */
+		return (EINVAL);
+
+	*fibnum = optval;
+	return (0);
+}
+
 /*
  * sohasoutofband(): protocol notifies socket layer of the arrival of new
  * out-of-band data, which will then notify socket consumers.
@@ -4378,3 +4391,32 @@
 
 	SOCK_UNLOCK(so);
 }
+
+bool
+so_setfiballowed(struct socket *so)
+{
+
+	if (so_checkfiballowed != NULL)
+		return (so_checkfiballowed(so));
+	return (false);
+}
+
+int
+sosetfib(struct socket *so, struct sockopt *sopt)
+{
+	int error, fibnum;
+
+	if (sopt->sopt_level != SOL_SOCKET ||
+	    sopt->sopt_name != SO_SETFIB)
+		return (ENOPROTOOPT);
+
+	error = soopt_getfib(sopt, &fibnum);
+	if (error != 0)
+		return (error);
+
+	if (so_setfiballowed(so))
+		so->so_fibnum = fibnum;
+	else
+		so->so_fibnum = 0;
+	return (0);
+}
diff --git a/sys/kern/uipc_syscalls.c b/sys/kern/uipc_syscalls.c
--- a/sys/kern/uipc_syscalls.c
+++ b/sys/kern/uipc_syscalls.c
@@ -1606,3 +1606,21 @@
 		m_chtype(m, MT_CONTROL);
 	}
 }
+
+/*
+ * Sets fib of a current process.
+ */
+int
+sys_setfib(struct thread *td, struct setfib_args *uap)
+{
+	int error = 0;
+
+	CURVNET_SET(TD_TO_VNET(td));
+	if (soopt_validfib && soopt_validfib(NULL, uap->fibnum))
+		td->td_proc->p_fibnum = uap->fibnum;
+	else
+		error = EINVAL;
+	CURVNET_RESTORE();
+
+	return (error);
+}
diff --git a/sys/kern/uipc_usrreq.c b/sys/kern/uipc_usrreq.c
--- a/sys/kern/uipc_usrreq.c
+++ b/sys/kern/uipc_usrreq.c
@@ -1735,8 +1735,12 @@
 	struct xucred xu;
 	int error, optval;
 
-	if (sopt->sopt_level != SOL_LOCAL)
+	if (sopt->sopt_level != SOL_LOCAL) {
+		error = sosetfib(so, sopt);
+		if (error != ENOPROTOOPT)
+			return (error);
 		return (EINVAL);
+	}
 
 	unp = sotounpcb(so);
 	KASSERT(unp != NULL, ("uipc_ctloutput: unp == NULL"));
diff --git a/sys/net/route/route_tables.c b/sys/net/route/route_tables.c
--- a/sys/net/route/route_tables.c
+++ b/sys/net/route/route_tables.c
@@ -38,12 +38,14 @@
 #include "opt_route.h"
 
 #include <sys/param.h>
-#include <sys/socket.h>
 #include <sys/systm.h>
 #include <sys/malloc.h>
 #include <sys/jail.h>
 #include <sys/osd.h>
 #include <sys/proc.h>
+#include <sys/protosw.h>
+#include <sys/socket.h>
+#include <sys/socketvar.h>
 #include <sys/sysctl.h>
 #include <sys/syslog.h>
 #include <sys/kernel.h>
@@ -85,6 +87,9 @@
 
 VNET_DEFINE(uint32_t, _rt_numfibs) = RT_NUMFIBS;
 
+static bool rtsocheckfiballowed(struct socket *so);
+static bool rtsooptvalidfib(struct sockopt *sopt, int fibnum);
+
 /*
  * Handler for net.my_fibnum.
  * Returns current fib of the process.
@@ -145,24 +150,6 @@
     NULL, 0, &sysctl_fibs, "IU",
     "set number of fibs");
 
-/*
- * Sets fib of a current process.
- */
-int
-sys_setfib(struct thread *td, struct setfib_args *uap)
-{
-	int error = 0;
-
-	CURVNET_SET(TD_TO_VNET(td));
-	if (uap->fibnum >= 0 && uap->fibnum < V_rt_numfibs)
-		td->td_proc->p_fibnum = uap->fibnum;
-	else
-		error = EINVAL;
-	CURVNET_RESTORE();
-
-	return (error);
-}
-
 static int
 rtables_check_proc_fib(void *obj, void *data)
 {
@@ -192,6 +179,8 @@
 	    [PR_METHOD_ATTACH] =	rtables_check_proc_fib,
 	};
 	osd_jail_register(rtables_prison_destructor, methods);
+	so_checkfiballowed = rtsocheckfiballowed;
+	soopt_validfib = rtsooptvalidfib;
 }
 SYSINIT(rtables_init, SI_SUB_PROTO_DOMAIN, SI_ORDER_THIRD, rtables_init, NULL);
 
@@ -397,3 +386,17 @@
 	    __func__, table, family));
 	return (rnh->rnh_gen);
 }
+
+static bool
+rtsocheckfiballowed(struct socket *so)
+{
+	return (so->so_proto->pr_domain->dom_family == PF_INET ||
+	    so->so_proto->pr_domain->dom_family == PF_INET6 ||
+	    so->so_proto->pr_domain->dom_family == PF_ROUTE);
+}
+
+static bool
+rtsooptvalidfib(struct sockopt *sopt __unused, int fibnum)
+{
+	return ((u_int)fibnum < V_rt_numfibs);
+}
diff --git a/sys/net/rtsock.c b/sys/net/rtsock.c
--- a/sys/net/rtsock.c
+++ b/sys/net/rtsock.c
@@ -380,6 +380,13 @@
 	soisdisconnected(so);
 }
 
+static int
+rts_ctloutput(struct socket *so, struct sockopt *sopt)
+{
+
+	return (sosetfib(so, sopt));
+}
+
 static SYSCTL_NODE(_net, OID_AUTO, rtsock, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
     "Routing socket infrastructure");
 static u_long rts_sendspace = 8192;
@@ -2691,6 +2698,7 @@
 	.pr_shutdown =		rts_shutdown,
 	.pr_disconnect =	rts_disconnect,
 	.pr_close =		rts_close,
+	.pr_ctloutput =		rts_ctloutput,
 };
 
 static struct domain routedomain = {
diff --git a/sys/netinet/ip_output.c b/sys/netinet/ip_output.c
--- a/sys/netinet/ip_output.c
+++ b/sys/netinet/ip_output.c
@@ -1105,10 +1105,14 @@
 				error = 0;
 				break;
 			case SO_SETFIB:
-				INP_WLOCK(inp);
-				inp->inp_inc.inc_fibnum = so->so_fibnum;
-				INP_WUNLOCK(inp);
-				error = 0;
+				error = sosetfib(so, sopt);
+				if (error == 0) {
+					INP_WLOCK(inp);
+					inp->inp_inc.inc_fibnum = so->so_fibnum;
+					INP_WUNLOCK(inp);
+				}
+				if (error == ENOPROTOOPT)
+					error = 0;
 				break;
 			case SO_MAX_PACING_RATE:
 #ifdef RATELIMIT
diff --git a/sys/netinet/raw_ip.c b/sys/netinet/raw_ip.c
--- a/sys/netinet/raw_ip.c
+++ b/sys/netinet/raw_ip.c
@@ -639,11 +639,11 @@
 	int	error, optval;
 
 	if (sopt->sopt_level != IPPROTO_IP) {
-		if ((sopt->sopt_level == SOL_SOCKET) &&
-		    (sopt->sopt_name == SO_SETFIB)) {
+		error = sosetfib(so, sopt);
+		if (error == 0)
 			inp->inp_inc.inc_fibnum = so->so_fibnum;
-			return (0);
-		}
+		if (error != ENOPROTOOPT)
+			return (error);
 		return (EINVAL);
 	}
 
diff --git a/sys/netinet6/ip6_output.c b/sys/netinet6/ip6_output.c
--- a/sys/netinet6/ip6_output.c
+++ b/sys/netinet6/ip6_output.c
@@ -1663,10 +1663,15 @@
 				error = 0;
 				break;
 			case SO_SETFIB:
-				INP_WLOCK(inp);
-				inp->inp_inc.inc_fibnum = so->so_fibnum;
-				INP_WUNLOCK(inp);
-				error = 0;
+				error = sosetfib(so, sopt);
+				if (error == 0) {
+					INP_WLOCK(inp);
+					inp->inp_inc.inc_fibnum =
+					    so->so_fibnum;
+					INP_WUNLOCK(inp);
+				}
+				if (error == ENOPROTOOPT)
+					error = 0;
 				break;
 			case SO_MAX_PACING_RATE:
 #ifdef RATELIMIT
diff --git a/sys/netinet6/raw_ip6.c b/sys/netinet6/raw_ip6.c
--- a/sys/netinet6/raw_ip6.c
+++ b/sys/netinet6/raw_ip6.c
@@ -580,13 +580,14 @@
 		 */
 		return (icmp6_ctloutput(so, sopt));
 	else if (sopt->sopt_level != IPPROTO_IPV6) {
-		if (sopt->sopt_level == SOL_SOCKET &&
-		    sopt->sopt_name == SO_SETFIB) {
+		error = sosetfib(so, sopt);
+		if (error == 0) {
 			INP_WLOCK(inp);
 			inp->inp_inc.inc_fibnum = so->so_fibnum;
 			INP_WUNLOCK(inp);
-			return (0);
 		}
+		if (error != ENOPROTOOPT)
+			return (error);
 		return (EINVAL);
 	}
 
diff --git a/sys/sys/socket.h b/sys/sys/socket.h
--- a/sys/sys/socket.h
+++ b/sys/sys/socket.h
@@ -722,6 +722,10 @@
 #ifdef _KERNEL
 struct socket;
 
+typedef bool (*so_checkfiballowed_t)(struct socket *so);
+
+extern so_checkfiballowed_t so_checkfiballowed;
+
 struct inpcb *so_sotoinpcb(struct socket *so);
 struct sockbuf *so_sockbuf_snd(struct socket *);
 struct sockbuf *so_sockbuf_rcv(struct socket *);
@@ -741,6 +745,8 @@
 struct protosw *so_protosw_get(const struct socket *);
 void so_protosw_set(struct socket *, struct protosw *);
 
+bool so_setfiballowed(struct socket *so);
+
 void so_sorwakeup_locked(struct socket *so);
 void so_sowwakeup_locked(struct socket *so);
 
diff --git a/sys/sys/sockopt.h b/sys/sys/sockopt.h
--- a/sys/sys/sockopt.h
+++ b/sys/sys/sockopt.h
@@ -57,10 +57,16 @@
 	struct	thread *sopt_td; /* calling thread or null if kernel */
 };
 
+typedef bool (*soopt_validfib_t)(struct sockopt *sopt, int fibnum);
+
+extern soopt_validfib_t soopt_validfib;
+
 int	sosetopt(struct socket *so, struct sockopt *sopt);
 int	sogetopt(struct socket *so, struct sockopt *sopt);
+int	sosetfib(struct socket *so, struct sockopt *sopt);
 int	sooptcopyin(struct sockopt *sopt, void *buf, size_t len, size_t minlen);
 int	sooptcopyout(struct sockopt *sopt, const void *buf, size_t len);
+int	soopt_getfib(struct sockopt *sopt, int *fibnum);
 int	soopt_getm(struct sockopt *sopt, struct mbuf **mp);
 int	soopt_mcopyin(struct sockopt *sopt, struct mbuf *m);
 int	soopt_mcopyout(struct sockopt *sopt, struct mbuf *m);