Index: head/lib/libc/net/getnameinfo.c
===================================================================
--- head/lib/libc/net/getnameinfo.c
+++ head/lib/libc/net/getnameinfo.c
@@ -224,10 +224,8 @@
 	case AF_INET:
 		v4a = (u_int32_t)
 		    ntohl(((const struct sockaddr_in *)sa)->sin_addr.s_addr);
-		if (IN_MULTICAST(v4a) || IN_EXPERIMENTAL(v4a))
-			flags |= NI_NUMERICHOST;
-		v4a >>= IN_CLASSA_NSHIFT;
-		if (v4a == 0)
+		if (IN_MULTICAST(v4a) || IN_EXPERIMENTAL(v4a) ||
+		    IN_ZERONET(v4a))
 			flags |= NI_NUMERICHOST;
 		break;
 #ifdef INET6
Index: head/sys/fs/nfsclient/nfs_clport.c
===================================================================
--- head/sys/fs/nfsclient/nfs_clport.c
+++ head/sys/fs/nfsclient/nfs_clport.c
@@ -957,8 +957,7 @@
 		if (error != 0)
 			return (NULL);
 
-		if ((ntohl(nh_ext.nh_src.s_addr) >> IN_CLASSA_NSHIFT) ==
-		    IN_LOOPBACKNET) {
+		if (IN_LOOPBACK(ntohl(nh_ext.nh_src.s_addr))) {
 			/* Ignore loopback addresses */
 			return (NULL);
 		}
Index: head/sys/netinet/in.c
===================================================================
--- head/sys/netinet/in.c
+++ head/sys/netinet/in.c
@@ -191,15 +191,10 @@
 in_canforward(struct in_addr in)
 {
 	u_long i = ntohl(in.s_addr);
-	u_long net;
 
-	if (IN_EXPERIMENTAL(i) || IN_MULTICAST(i) || IN_LINKLOCAL(i))
+	if (IN_EXPERIMENTAL(i) || IN_MULTICAST(i) || IN_LINKLOCAL(i) ||
+	    IN_ZERONET(i) || IN_LOOPBACK(i))
 		return (0);
-	if (IN_CLASSA(i)) {
-		net = i & IN_CLASSA_NET;
-		if (net == 0 || net == (IN_LOOPBACKNET << IN_CLASSA_NSHIFT))
-			return (0);
-	}
 	return (1);
 }
 
Index: head/sys/netinet/ip_input.c
===================================================================
--- head/sys/netinet/ip_input.c
+++ head/sys/netinet/ip_input.c
@@ -499,10 +499,10 @@
 
 	IP_PROBE(receive, NULL, NULL, ip, m->m_pkthdr.rcvif, ip, NULL);
 
-	/* 127/8 must not appear on wire - RFC1122 */
+	/* IN_LOOPBACK must not appear on the wire - RFC1122 */
 	ifp = m->m_pkthdr.rcvif;
-	if ((ntohl(ip->ip_dst.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET ||
-	    (ntohl(ip->ip_src.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET) {
+	if (IN_LOOPBACK(ntohl(ip->ip_dst.s_addr)) ||
+	    IN_LOOPBACK(ntohl(ip->ip_src.s_addr))) {
 		if ((ifp->if_flags & IFF_LOOPBACK) == 0) {
 			IPSTAT_INC(ips_badaddr);
 			goto bad;
Index: head/sys/netinet/ip_output.c
===================================================================
--- head/sys/netinet/ip_output.c
+++ head/sys/netinet/ip_output.c
@@ -594,9 +594,9 @@
 		}
 	}
 
-	/* 127/8 must not appear on wire - RFC1122. */
-	if ((ntohl(ip->ip_dst.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET ||
-	    (ntohl(ip->ip_src.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET) {
+	/* IN_LOOPBACK must not appear on the wire - RFC1122. */
+	if (IN_LOOPBACK(ntohl(ip->ip_dst.s_addr)) ||
+	    IN_LOOPBACK(ntohl(ip->ip_src.s_addr))) {
 		if ((ifp->if_flags & IFF_LOOPBACK) == 0) {
 			IPSTAT_INC(ips_badaddr);
 			error = EADDRNOTAVAIL;
Index: head/sys/netinet/netdump/netdump_client.c
===================================================================
--- head/sys/netinet/netdump/netdump_client.c
+++ head/sys/netinet/netdump/netdump_client.c
@@ -557,8 +557,8 @@
 	}
 
 #ifdef INVARIANTS
-	if (((ntohl(ip->ip_dst.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET ||
-	    (ntohl(ip->ip_src.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET) &&
+	if ((IN_LOOPBACK(ntohl(ip->ip_dst.s_addr)) ||
+	    IN_LOOPBACK(ntohl(ip->ip_src.s_addr))) &&
 	    (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) == 0) {
 		NETDDEBUG("Bad IP header (RFC1122)\n");
 		return;
Index: head/sys/netpfil/ipfw/nat64/nat64_translate.h
===================================================================
--- head/sys/netpfil/ipfw/nat64/nat64_translate.h
+++ head/sys/netpfil/ipfw/nat64/nat64_translate.h
@@ -123,14 +123,9 @@
 nat64_check_ip4(in_addr_t ia)
 {
 
-	/* IN_LOOPBACK */
-	if ((ia & htonl(0xff000000)) == htonl(0x7f000000))
-		return (1);
-	/* IN_LINKLOCAL */
-	if ((ia & htonl(0xffff0000)) == htonl(0xa9fe0000))
-		return (1);
-	/* IN_MULTICAST & IN_EXPERIMENTAL */
-	if ((ia & htonl(0xe0000000)) == htonl(0xe0000000))
+	/* These checks are ordered from most likely to least */
+	if (IN_MULTICAST(ntohl(ia)) || IN_LOOPBACK(ntohl(ia)) ||
+	    IN_LINKLOCAL(ntohl(ia)) || IN_EXPERIMENTAL(ntohl(ia)))
 		return (1);
 	return (0);
 }
Index: head/sys/netpfil/pf/pf.c
===================================================================
--- head/sys/netpfil/pf/pf.c
+++ head/sys/netpfil/pf/pf.c
@@ -6170,7 +6170,7 @@
 	    pd.proto == IPPROTO_UDP) && s != NULL && s->nat_rule.ptr != NULL &&
 	    (s->nat_rule.ptr->action == PF_RDR ||
 	    s->nat_rule.ptr->action == PF_BINAT) &&
-	    (ntohl(pd.dst->v4.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET)
+	    IN_LOOPBACK(ntohl(pd.dst->v4.s_addr)))
 		m->m_flags |= M_SKIP_FIREWALL;
 
 	if (action == PF_PASS && r->divert.port && ip_divert_ptr != NULL &&