Support proxy ARP on mirrored TAP interfaces

When VPP has an interface whose address is also applied to a TAP
interface on the host, then VPP's TAP interface will be unnumbered
to the 'real' interface and do proxy ARP from the host.
the curious aspect of this setup is that ARP requests from the host
will come from the VPP's own address.

Change-Id: Ia238790e1034ba3cd3facdab29387b65a31525f2
Signed-off-by: Neale Ranns <nranns@cisco.com>

1 files changed, 16 insertions, 4 deletions

diff --git a/src/vnet/ethernet/arp.c b/src/vnet/ethernet/arp.c
index c22be3fc809..c84ff47bc00 100644
--- a/src/vnet/ethernet/arp.c
+++ b/src/vnet/ethernet/arp.c
@@ -1004,7 +1004,17 @@ arp_input (vlib_main_t * vm, vlib_node_runtime_t * node, vlib_frame_t * frame)
                   if (FIB_ENTRY_FLAG_LOCAL & src_flags)
                     {
                       error0 = ETHERNET_ARP_ERROR_l3_src_address_is_local;
-                      goto drop2;
+                      /*
+                       * When VPP has an interface whose address is also
+                       * applied to a TAP interface on the host, then VPP's
+                       * TAP interface will be unnumbered  to the 'real'
+                       * interface and do proxy ARP from the host.
+                       * The curious aspect of this setup is that ARP requests
+                       * from the host will come from the VPP's own address.
+                       * So don't drop immediately here, instead go see if this
+                       * is a proxy ARP case.
+                       */
+                      goto drop1;
                     }
                   /* A Source must also be local to subnet of matching
                    * interface address. */
@@ -1151,9 +1161,11 @@ arp_input (vlib_main_t * vm, vlib_node_runtime_t * node, vlib_frame_t * frame)
 		}
 	    }
 
-	  /* We are going to reply to this request, so learn the sender */
-	  error0 = arp_learn (vnm, am, sw_if_index0,
-			      &arp0->ip4_over_ethernet[1]);
+	  /* We are going to reply to this request, so, in the absence of
+	     errors, learn the sender */
+	  if (!error0)
+	    error0 = arp_learn (vnm, am, sw_if_index0,
+				&arp0->ip4_over_ethernet[1]);
 
 	  vlib_validate_buffer_enqueue_x1 (vm, node, next_index, to_next,
 					   n_left_to_next, pi0, next0);