diff -ur v2.6.9/linux/Documentation/filesystems/proc.txt linux/Documentation/filesystems/proc.txt
--- v2.6.9/linux/Documentation/filesystems/proc.txt	2004-10-19 10:00:33.000000000 +0300
+++ linux/Documentation/filesystems/proc.txt	2004-10-19 11:53:53.438336280 +0300
@@ -1666,6 +1666,16 @@
 
 Determines whether to send ICMP redirects to other hosts.
 
+hidden
+------
+
+Hide  addresses attached  to this device  from other  devices.  Such addresses
+will  never be selected  by source address  autoselection mechanism, host does
+not  answer broadcast ARP requests for them,  does not announce them as source
+address  of ARP requests,  but they are  still reachable via  IP. This flag is
+activated  only if it is enabled both  in specific device section and in "all"
+section.
+
 Routing settings
 ----------------
 
diff -ur v2.6.9/linux/Documentation/networking/ip-sysctl.txt linux/Documentation/networking/ip-sysctl.txt
--- v2.6.9/linux/Documentation/networking/ip-sysctl.txt	2004-10-19 10:00:33.000000000 +0300
+++ linux/Documentation/networking/ip-sysctl.txt	2004-10-19 11:53:53.439336128 +0300
@@ -623,6 +623,14 @@
 
 
 
+hidden - BOOLEAN
+	Hide addresses attached to this device from other devices.
+	Such addresses will never be selected by source address autoselection
+	mechanism, host does not answer broadcast ARP requests for them,
+	does not announce them as source address of ARP requests, but they
+	are still reachable via IP. This flag is activated only if it is
+	enabled both in specific device section and in "all" section.
+
 tag - INTEGER
 	Allows you to write a number, which can be used as required.
 	Default value is 0.
diff -ur v2.6.9/linux/include/linux/inetdevice.h linux/include/linux/inetdevice.h
--- v2.6.9/linux/include/linux/inetdevice.h	2004-10-19 10:00:35.000000000 +0300
+++ linux/include/linux/inetdevice.h	2004-10-19 11:53:53.440335976 +0300
@@ -26,6 +26,7 @@
 	int	no_xfrm;
 	int	no_policy;
 	int	force_igmp_version;
+	int	hidden;
 	void	*sysctl;
 };
 
@@ -63,6 +64,7 @@
 
 #define IN_DEV_LOG_MARTIANS(in_dev)	(ipv4_devconf.log_martians || (in_dev)->cnf.log_martians)
 #define IN_DEV_PROXY_ARP(in_dev)	(ipv4_devconf.proxy_arp || (in_dev)->cnf.proxy_arp)
+#define IN_DEV_HIDDEN(in_dev)		((in_dev)->cnf.hidden && ipv4_devconf.hidden)
 #define IN_DEV_SHARED_MEDIA(in_dev)	(ipv4_devconf.shared_media || (in_dev)->cnf.shared_media)
 #define IN_DEV_TX_REDIRECTS(in_dev)	(ipv4_devconf.send_redirects || (in_dev)->cnf.send_redirects)
 #define IN_DEV_SEC_REDIRECTS(in_dev)	(ipv4_devconf.secure_redirects || (in_dev)->cnf.secure_redirects)
diff -ur v2.6.9/linux/include/linux/sysctl.h linux/include/linux/sysctl.h
--- v2.6.9/linux/include/linux/sysctl.h	2004-10-19 10:00:35.000000000 +0300
+++ linux/include/linux/sysctl.h	2004-10-19 11:53:53.441335824 +0300
@@ -394,6 +394,7 @@
 	NET_IPV4_CONF_FORCE_IGMP_VERSION=17,
 	NET_IPV4_CONF_ARP_ANNOUNCE=18,
 	NET_IPV4_CONF_ARP_IGNORE=19,
+	NET_IPV4_CONF_HIDDEN=20,
 };
 
 /* /proc/sys/net/ipv4/netfilter */
diff -ur v2.6.9/linux/net/ipv4/arp.c linux/net/ipv4/arp.c
--- v2.6.9/linux/net/ipv4/arp.c	2004-10-19 10:00:36.000000000 +0300
+++ linux/net/ipv4/arp.c	2004-10-19 11:54:14.011208728 +0300
@@ -72,6 +72,8 @@
  *					bonding can change the skb before
  *					sending (e.g. insert 8021q tag).
  *		Harald Welte	:	convert to make use of jenkins hash
+ *		Julian Anastasov:	"hidden" flag: hide the
+ *					interface and don't reply for it
  */
 
 #include <linux/module.h>
@@ -332,21 +334,34 @@
 	u32 target = *(u32*)neigh->primary_key;
 	int probes = atomic_read(&neigh->probes);
 	struct in_device *in_dev = in_dev_get(dev);
+	struct in_device *in_dev2 = NULL;
+	struct net_device *dev2 = NULL;
+	int mode;
 
 	if (!in_dev)
 		return;
 
-	switch (IN_DEV_ARP_ANNOUNCE(in_dev)) {
+	mode = IN_DEV_ARP_ANNOUNCE(in_dev);
+	if (mode != 2 && skb && (dev2 = ip_dev_find(skb->nh.iph->saddr)) != NULL &&
+	    (saddr = skb->nh.iph->saddr, in_dev2 = in_dev_get(dev2)) != NULL &&
+	    IN_DEV_HIDDEN(in_dev2)) {
+		saddr = 0;
+		goto get;
+	}
+
+	switch (mode) {
 	default:
 	case 0:		/* By default announce any local IP */
+		if (saddr)
+			break;
 		if (skb && inet_addr_type(skb->nh.iph->saddr) == RTN_LOCAL)
 			saddr = skb->nh.iph->saddr;
 		break;
 	case 1:		/* Restrict announcements of saddr in same subnet */
 		if (!skb)
 			break;
-		saddr = skb->nh.iph->saddr;
-		if (inet_addr_type(saddr) == RTN_LOCAL) {
+		if (saddr || (saddr = skb->nh.iph->saddr,
+			      inet_addr_type(saddr) == RTN_LOCAL)) {
 			/* saddr should be known to target */
 			if (inet_addr_onlink(in_dev, target, saddr))
 				break;
@@ -357,6 +372,12 @@
 		break;
 	}
 
+get:
+	if (dev2) {
+		if (in_dev2)
+			in_dev_put(in_dev2);
+		dev_put(dev2);
+	}
 	if (in_dev)
 		in_dev_put(in_dev);
 	if (!saddr)
@@ -434,6 +455,26 @@
 	return flag; 
 } 
 
+static int arp_hidden(u32 tip, struct net_device *dev)
+{
+	struct net_device *dev2 = NULL;
+	struct in_device *in_dev2 = NULL;
+	int ret = 0;
+
+	if (!ipv4_devconf.hidden)
+		return 0;
+
+	if ((dev2 = ip_dev_find(tip)) && dev2 != dev &&
+	    (in_dev2 = in_dev_get(dev2)) && IN_DEV_HIDDEN(in_dev2))
+		ret = 1;
+	if (dev2) {
+		if (in_dev2)
+			in_dev_put(in_dev2);
+		dev_put(dev2);
+	}
+	return ret;
+}
+
 /* OBSOLETE FUNCTIONS */
 
 /*
@@ -828,6 +869,7 @@
 	if (sip == 0) {
 		if (arp->ar_op == htons(ARPOP_REQUEST) &&
 		    inet_addr_type(tip) == RTN_LOCAL &&
+		    !arp_hidden(tip, dev) &&
 		    !arp_ignore(in_dev,dev,sip,tip))
 			arp_send(ARPOP_REPLY,ETH_P_ARP,tip,dev,tip,sha,dev->dev_addr,dev->dev_addr);
 		goto out;
@@ -848,6 +890,8 @@
 					dont_send |= arp_ignore(in_dev,dev,sip,tip);
 				if (!dont_send && IN_DEV_ARPFILTER(in_dev))
 					dont_send |= arp_filter(sip,tip,dev); 
+				if (!dont_send && skb->pkt_type != PACKET_HOST)
+					dont_send |= arp_hidden(tip,dev); 
 				if (!dont_send)
 					arp_send(ARPOP_REPLY,ETH_P_ARP,sip,dev,tip,sha,dev->dev_addr,sha);
 
diff -ur v2.6.9/linux/net/ipv4/devinet.c linux/net/ipv4/devinet.c
--- v2.6.9/linux/net/ipv4/devinet.c	2004-10-19 10:00:36.000000000 +0300
+++ linux/net/ipv4/devinet.c	2004-10-19 11:53:53.445335216 +0300
@@ -805,7 +805,8 @@
 			continue;
 
 		for_primary_ifa(in_dev) {
-			if (ifa->ifa_scope != RT_SCOPE_LINK &&
+			if (!IN_DEV_HIDDEN(in_dev) &&
+			    ifa->ifa_scope != RT_SCOPE_LINK &&
 			    ifa->ifa_scope <= scope) {
 				addr = ifa->ifa_local;
 				goto out_unlock_both;
@@ -1213,7 +1214,7 @@
 
 static struct devinet_sysctl_table {
 	struct ctl_table_header *sysctl_header;
-	ctl_table		devinet_vars[20];
+	ctl_table		devinet_vars[21];
 	ctl_table		devinet_dev[2];
 	ctl_table		devinet_conf_dir[2];
 	ctl_table		devinet_proto_dir[2];
@@ -1325,6 +1326,14 @@
 			.proc_handler	= &proc_dointvec,
 		},
 		{
+			.ctl_name	= NET_IPV4_CONF_HIDDEN,
+			.procname	= "hidden",
+			.data		= &ipv4_devconf.hidden,
+			.maxlen		= sizeof(int),
+			.mode		= 0644,
+			.proc_handler	= &proc_dointvec,
+		},
+		{
 			.ctl_name	= NET_IPV4_CONF_ARPFILTER,
 			.procname	= "arp_filter",
 			.data		= &ipv4_devconf.arp_filter,
