diff -ur v2.4.25/linux/Documentation/filesystems/proc.txt linux/Documentation/filesystems/proc.txt
--- v2.4.25/linux/Documentation/filesystems/proc.txt	2003-06-14 08:41:59.000000000 +0300
+++ linux/Documentation/filesystems/proc.txt	2004-02-19 01:36:53.406998896 +0200
@@ -1550,6 +1550,16 @@
 (external addresses  can  still  be  spoofed), without the need for additional
 firewall rules.
 
+rp_filter_mask
+--------------
+
+Integer value representing bitmask of the mediums for which the reverse path
+protection is disabled. If the source validation results in reverse path
+to interface with medium_id value in the 1..31 range the access is
+allowed if the corresponding bit is set in the bitmask. The bitmask value
+is considered only when rp_filter is enabled. By default the bitmask is
+empty preserving the original rp_filter semantic.
+
 secure_redirects
 ----------------
 
diff -ur v2.4.25/linux/Documentation/networking/ip-sysctl.txt linux/Documentation/networking/ip-sysctl.txt
--- v2.4.25/linux/Documentation/networking/ip-sysctl.txt	2003-06-14 08:41:59.000000000 +0300
+++ linux/Documentation/networking/ip-sysctl.txt	2004-02-19 01:36:53.407998744 +0200
@@ -489,6 +489,16 @@
 Alpha 1/1024s. See the HZ define in /usr/include/asm/param.h for the exact
 value on your system. 
 
+rp_filter_mask - INTEGER
+
+	Integer value representing bitmask of the mediums for which the
+	reverse path protection is disabled. If the source validation
+	results in reverse path to interface with medium_id value in
+	the 1..31 range the access is allowed if the corresponding bit
+	is set in the bitmask. The bitmask value is considered only when
+	rp_filter is enabled. By default the bitmask is empty preserving
+	the original rp_filter semantic.
+
 Alexey Kuznetsov.
 kuznet@ms2.inr.ac.ru
 
diff -ur v2.4.25/linux/include/linux/inetdevice.h linux/include/linux/inetdevice.h
--- v2.4.25/linux/include/linux/inetdevice.h	2004-02-19 00:23:39.000000000 +0200
+++ linux/include/linux/inetdevice.h	2004-02-19 01:37:10.211444232 +0200
@@ -20,6 +20,7 @@
 	int     arp_filter;
 	int	medium_id;
 	int	force_igmp_version;
+	int	rp_filter_mask;
 	void	*sysctl;
 };
 
@@ -61,6 +62,7 @@
 #define IN_DEV_SEC_REDIRECTS(in_dev)	(ipv4_devconf.secure_redirects || (in_dev)->cnf.secure_redirects)
 #define IN_DEV_IDTAG(in_dev)		((in_dev)->cnf.tag)
 #define IN_DEV_MEDIUM_ID(in_dev)	((in_dev)->cnf.medium_id)
+#define IN_DEV_RPFILTER_MASK(in_dev)	((in_dev)->cnf.rp_filter_mask)
 
 #define IN_DEV_RX_REDIRECTS(in_dev) \
 	((IN_DEV_FORWARD(in_dev) && \
diff -ur v2.4.25/linux/include/linux/sysctl.h linux/include/linux/sysctl.h
--- v2.4.25/linux/include/linux/sysctl.h	2004-02-19 00:23:39.000000000 +0200
+++ linux/include/linux/sysctl.h	2004-02-19 01:37:29.927446944 +0200
@@ -360,6 +360,7 @@
 	NET_IPV4_CONF_ARPFILTER=13,
 	NET_IPV4_CONF_MEDIUM_ID=14,
 	NET_IPV4_CONF_FORCE_IGMP_VERSION=17,
+	NET_IPV4_CONF_RP_FILTER_MASK=18,
 };
 
 /* /proc/sys/net/ipv4/netfilter */
diff -ur v2.4.25/linux/net/ipv4/devinet.c linux/net/ipv4/devinet.c
--- v2.4.25/linux/net/ipv4/devinet.c	2004-02-19 00:23:39.000000000 +0200
+++ linux/net/ipv4/devinet.c	2004-02-19 01:37:43.125440544 +0200
@@ -1057,7 +1057,7 @@
 static struct devinet_sysctl_table
 {
 	struct ctl_table_header *sysctl_header;
-	ctl_table devinet_vars[18];
+	ctl_table devinet_vars[19];
 	ctl_table devinet_dev[2];
 	ctl_table devinet_conf_dir[2];
 	ctl_table devinet_proto_dir[2];
@@ -1094,6 +1094,9 @@
 	{NET_IPV4_CONF_MEDIUM_ID, "medium_id",
          &ipv4_devconf.medium_id, sizeof(int), 0644, NULL,
          &proc_dointvec},
+	{NET_IPV4_CONF_RP_FILTER_MASK, "rp_filter_mask",
+         &ipv4_devconf.rp_filter_mask, sizeof(int), 0644, NULL,
+         &proc_dointvec},
 	{NET_IPV4_CONF_BOOTP_RELAY, "bootp_relay",
          &ipv4_devconf.bootp_relay, sizeof(int), 0644, NULL,
          &proc_dointvec},
diff -ur v2.4.25/linux/net/ipv4/fib_frontend.c linux/net/ipv4/fib_frontend.c
--- v2.4.25/linux/net/ipv4/fib_frontend.c	2003-08-25 22:06:13.000000000 +0300
+++ linux/net/ipv4/fib_frontend.c	2004-02-19 01:36:53.405999048 +0200
@@ -210,6 +210,7 @@
 	struct rt_key key;
 	struct fib_result res;
 	int no_addr, rpf;
+	unsigned rpf_mask = 0;
 	int ret;
 
 	key.dst = src;
@@ -225,6 +226,7 @@
 	if (in_dev) {
 		no_addr = in_dev->ifa_list == NULL;
 		rpf = IN_DEV_RPFILTER(in_dev);
+		rpf_mask = IN_DEV_RPFILTER_MASK(in_dev);
 	}
 	read_unlock(&inetdev_lock);
 
@@ -247,6 +249,17 @@
 		fib_res_put(&res);
 		return ret;
 	}
+	if (rpf_mask && rpf) {
+		int omi = 0;
+
+		read_lock(&inetdev_lock);
+		in_dev = __in_dev_get(FIB_RES_DEV(res));
+		if (in_dev)
+			omi = IN_DEV_MEDIUM_ID(in_dev);
+		read_unlock(&inetdev_lock);
+		if (omi >= 1 && omi <= 31 && ((1 << omi) & rpf_mask))
+			rpf = 0;
+	}
 	fib_res_put(&res);
 	if (no_addr)
 		goto last_resort;