ip: add loose reverse path filtering

Extend existing reverse path filter option to allow strict or loose
filtering. (See http://en.wikipedia.org/wiki/Reverse_path_filtering).

For compatibility with existing usage, the value 1 is chosen for strict mode
and 2 for loose mode.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 15 insertions, 9 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index ff3f219ee4d7..71041c21af9b 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -699,16 +699,22 @@ accept_source_route - BOOLEAN
         default TRUE (router)
                 FALSE (host)
 
-rp_filter - BOOLEAN
-        1 - do source validation by reversed path, as specified in RFC1812
-            Recommended option for single homed hosts and stub network
-            routers. Could cause troubles for complicated (not loop free)
-            networks running a slow unreliable protocol (sort of RIP),
-            or using static routes.
-
+rp_filter - INTEGER
         0 - No source validation.
-
-        conf/all/rp_filter must also be set to TRUE to do source validation
+        1 - Strict mode as defined in RFC3704 Strict Reverse Path
+            Each incoming packet is tested against the FIB and if the interface
+            is not the best reverse path the packet check will fail.
+            By default failed packets are discarded.
+        2 - Loose mode as defined in RFC3704 Loose Reverse Path
+            Each incoming packet's source address is also tested against the FIB
+            and if the source address is not reachable via any interface
+            the packet check will fail.
+
+        Current recommended practice in RFC3704 is to enable strict mode
+        to prevent IP spoofin from DDos attacks. If using asymmetric routing
+        or other complicated routing,t hen loose mode is recommended.
+
+        conf/all/rp_filter must also be set to non-zero to do source validation
         on the interface
 
         Default value is 0. Note that some distributions enable it