diff -ru linux-2.4.5-pre4.orig/net/ipv4/arp.c linux-2.4.5-pre4/net/ipv4/arp.c
--- linux-2.4.5-pre4.orig/net/ipv4/arp.c	Sun May 20 20:54:17 2001
+++ linux-2.4.5-pre4/net/ipv4/arp.c	Tue May 22 09:58:24 2001
@@ -321,11 +321,24 @@
 	struct net_device *dev = neigh->dev;
 	u32 target = *(u32*)neigh->primary_key;
 	int probes = atomic_read(&neigh->probes);
+	struct rtable *rt;
 
-	if (skb && inet_addr_type(skb->nh.iph->saddr) == RTN_LOCAL)
-		saddr = skb->nh.iph->saddr;
-	else
-		saddr = inet_select_addr(dev, target, RT_SCOPE_LINK);
+	/* Determine source IP for the probing packet. */
+	saddr = 0;
+	if (skb != NULL) {
+		rt = (struct rtable*)skb->dst;
+		if (!rt->rt_iif)
+			saddr = rt->rt_src;
+	}
+	if (!saddr) {
+		if (ip_route_output(&rt, target, 0, 0, dev->ifindex) < 0)
+			/* Never send probes with 0 source as we used to. */
+			return;
+		saddr = rt->rt_src;
+		ip_rt_put(rt);
+	}
+	if (!saddr)
+		return;
 
 	if ((probes -= neigh->parms->ucast_probes) < 0) {
 		if (!(neigh->nud_state&NUD_VALID))
@@ -345,20 +358,35 @@
 		read_unlock_bh(&neigh->lock);
 }
 
-static int arp_filter(__u32 sip, __u32 tip, struct net_device *dev)
+static int arp_filter(struct sk_buff *skb, __u32 sip, __u32 tip,
+		struct in_device *in_dev)
 {
 	struct rtable *rt;
 	int flag = 0; 
-	/*unsigned long now; */
 
+	if (!IN_DEV_ARPFILTER(in_dev))
+		return 0;
+
+	/* Always answer direct queries. */
+	if (skb->pkt_type == PACKET_HOST)
+		return 0;
+
+	/* Then check routes:
+	 * primarily, this check is used to not to answer to some requests if
+	 * several interfaces are connected to the same segment.
+	 * This check also may be used for manual control of who sees IP
+	 * addresses at which link-level addresses by installing prohibiting
+	 * routes.  -- 2001/05/20  SAW
+	 */
 	if (ip_route_output(&rt, sip, tip, 0, 0) < 0) 
 		return 1;
-	if (rt->u.dst.dev != dev) { 
+	if (rt->u.dst.dev != in_dev->dev) { 
 		NET_INC_STATS_BH(ArpFilter);
 		flag = 1;
 	} 
 	ip_rt_put(rt); 
-	return flag; 
+
+	return flag;
 } 
 
 /* OBSOLETE FUNCTIONS */
@@ -757,10 +785,7 @@
 		if (addr_type == RTN_LOCAL) {
 			n = neigh_event_ns(&arp_tbl, sha, &sip, dev);
 			if (n) {
-				int dont_send = 0;
-				if (IN_DEV_ARPFILTER(in_dev))
-					dont_send |= arp_filter(sip,tip,dev); 
-				if (!dont_send)
+				if (!arp_filter(skb, sip, tip, in_dev))
 					arp_send(ARPOP_REPLY,ETH_P_ARP,sip,dev,tip,sha,dev->dev_addr,sha);
 
 				neigh_release(n);