diff -urNp linux-2.6.18/Documentation/filesystems/proc.txt linux-2.6.18/Documentation/filesystems/proc.txt
--- linux-2.6.18/Documentation/filesystems/proc.txt	2006-09-19 20:42:06.000000000 -0700
+++ linux-2.6.18/Documentation/filesystems/proc.txt	2006-10-26 05:13:15.000000000 -0700
@@ -1758,6 +1758,15 @@ max_delay, min_delay
 
 Delays for flushing the routing cache.
 
+mc_src_strict
+-------------
+
+There is a hack in the kernel router which provides compatibility for old
+multicast applications such as vic, vat and friends. Unfortunately, this
+hack also breaks normal behavior of preferred source address selection
+(iproute2 "src" field) with multicast and limited broadcast. Enabling this
+option disables this hack and restores normal (strict) behavior.
+
 redirect_load, redirect_number
 ------------------------------
 
diff -urNp linux-2.6.18/include/linux/sysctl.h linux-2.6.18/include/linux/sysctl.h
--- linux-2.6.18/include/linux/sysctl.h	2006-09-19 20:42:06.000000000 -0700
+++ linux-2.6.18/include/linux/sysctl.h	2006-10-26 04:25:00.000000000 -0700
@@ -434,6 +434,7 @@ enum {
 	NET_IPV4_ROUTE_MIN_ADVMSS=17,
 	NET_IPV4_ROUTE_SECRET_INTERVAL=18,
 	NET_IPV4_ROUTE_GC_MIN_INTERVAL_MS=19,
+	NET_IPV4_ROUTE_MC_SRC_STRICT=20,
 };
 
 enum
diff -urNp linux-2.6.18/net/ipv4/route.c linux-2.6.18/net/ipv4/route.c
--- linux-2.6.18/net/ipv4/route.c	2006-09-19 20:42:06.000000000 -0700
+++ linux-2.6.18/net/ipv4/route.c	2006-10-26 05:11:00.000000000 -0700
@@ -132,6 +132,7 @@ static int ip_rt_mtu_expires		= 10 * 60 
 static int ip_rt_min_pmtu		= 512 + 20 + 20;
 static int ip_rt_min_advmss		= 256;
 static int ip_rt_secret_interval	= 10 * 60 * HZ;
+static int ip_rt_mc_src_strict		= 0;
 static unsigned long rt_deadline;
 
 #define RTprint(a...)	printk(KERN_DEBUG a)
@@ -2416,7 +2417,7 @@ static int ip_route_output_slow(struct r
 		      of another iface. --ANK
 		 */
 
-		if (oldflp->oif == 0
+		if (!ip_rt_mc_src_strict && oldflp->oif == 0
 		    && (MULTICAST(oldflp->fl4_dst) || oldflp->fl4_dst == 0xFFFFFFFF)) {
 			/* Special hack: user can direct multicasts
 			   and limited broadcast via necessary interface
@@ -2431,6 +2432,12 @@ static int ip_route_output_slow(struct r
 			   cannot know, that ttl is zero, so that packet
 			   will not leave this host and route is valid).
 			   Luckily, this hack is good workaround.
+
+			   Unfortunately, it also breaks normal behavior of
+			   source address preference, so I added a sysctl option
+			   to let the user disable this hack and restore normal
+			   behavior. By default, the hack is still enabled (old
+			   compatibility behavior). -- PY
 			 */
 
 			fl.oif = dev_out->ifindex;
@@ -3057,6 +3064,15 @@ ctl_table ipv4_route_table[] = {
 		.proc_handler	= &proc_dointvec_jiffies,
 		.strategy	= &sysctl_jiffies,
 	},
+	{
+		.ctl_name	= NET_IPV4_ROUTE_MC_SRC_STRICT,
+		.procname	= "mc_src_strict",
+		.data		= &ip_rt_mc_src_strict,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= &ipv4_doint_and_flush,
+		.strategy	= &ipv4_doint_and_flush_strategy,
+	},
 	{ .ctl_name = 0 }
 };
 #endif