Provide a sysctl switch that allows to install ARP entries

with multicast bit set. FreeBSD refuses to install such
entries since 9.0, and this broke installations running
Microsoft NLB, which are violating standards.

Tested by:	Tarasov Oleg <oleg_tarasov sg-tea.com>

2 files changed, 16 insertions, 3 deletions

diff --git a/sys/netinet/if_ether.c b/sys/netinet/if_ether.c
index 8e2daeb..52d7db2 100644
--- a/sys/netinet/if_ether.c
+++ b/sys/netinet/if_ether.c
@@ -496,6 +496,7 @@ arpintr(struct mbuf *m)
 static int log_arp_wrong_iface = 1;
 static int log_arp_movements = 1;
 static int log_arp_permanent_modify = 1;
+static int allow_multicast = 0;
 
 SYSCTL_INT(_net_link_ether_inet, OID_AUTO, log_arp_wrong_iface, CTLFLAG_RW,
 	&log_arp_wrong_iface, 0,
@@ -506,7 +507,8 @@ SYSCTL_INT(_net_link_ether_inet, OID_AUTO, log_arp_movements, CTLFLAG_RW,
 SYSCTL_INT(_net_link_ether_inet, OID_AUTO, log_arp_permanent_modify, CTLFLAG_RW,
 	&log_arp_permanent_modify, 0,
 	"log arp replies from MACs different than the one in the permanent arp entry");
-
+SYSCTL_INT(_net_link_ether_inet, OID_AUTO, allow_multicast, CTLFLAG_RW,
+	&allow_multicast, 0, "accept multicast addresses");
 
 static void
 in_arpinput(struct mbuf *m)
@@ -551,8 +553,8 @@ in_arpinput(struct mbuf *m)
 		return;
 	}
 
-	if (ETHER_IS_MULTICAST(ar_sha(ah))) {
-		log(LOG_NOTICE, "in_arp: %*D is multicast\n",
+	if (allow_multicast == 0 && ETHER_IS_MULTICAST(ar_sha(ah))) {
+		log(LOG_NOTICE, "arp: %*D is multicast\n",
 		    ifp->if_addrlen, (u_char *)ar_sha(ah), ":");
 		return;
 	}
diff --git a/usr.sbin/arp/arp.4 b/usr.sbin/arp/arp.4
index 980ca71..0ff0f2c 100644
--- a/usr.sbin/arp/arp.4
+++ b/usr.sbin/arp/arp.4
@@ -120,6 +120,12 @@ of the
 .Xr sysctl 3
 MIB.
 .Bl -tag -width "log_arp_permanent_modify"
+.It Va allow_multicast
+Should the kernel install ARP entries with multicast bit set in
+the hardware address.
+Installing such entries is RFC 1812 violation, but some prorietary
+load balancing techniques require routers on network to do so.
+Turned off by default.
 .It Va log_arp_movements
 Should the kernel log movements of IP addresses from one hardware
 address to an other.
@@ -203,6 +209,11 @@ entry in the local ARP table.
 This error will only be logged if the sysctl
 .Va net.link.ether.inet.log_arp_permanent_modify
 is set to 1, which is the system's default behaviour.
+.It "arp: %x:%x:%x:%x:%x:%x is multicast"
+Kernel refused to install an entry with multicast hardware address.
+If you really want such addresses being installed, set the sysctl
+.Va net.link.ether.inet.allow_multicast
+to a positive value.
 .El
 .Sh SEE ALSO
 .Xr inet 4 ,