ip: source address selection

Implement a simple source address selection algorithm
for IPv4 and IPv6.
IPv6 does not yet implement RFC6724 but supports link-locals.
ping now chooses correct source address for link-local destination.
Added ping support for link-local multicast (e.g. allnodes).

Type: feature
Signed-off-by: Ole Troan <ot@cisco.com>
Change-Id: I1a3382c1f7d4ace0386c2c19e4e47b045b73a3ed
Signed-off-by: Ole Troan <ot@cisco.com>
diff --git a/src/vnet/ip/icmp6.c b/src/vnet/ip/icmp6.c
index 4bba430..b6ed3ea 100644
--- a/src/vnet/ip/icmp6.c
+++ b/src/vnet/ip/icmp6.c
@@ -40,6 +40,7 @@
 #include <vlib/vlib.h>
 #include <vnet/ip/ip.h>
 #include <vnet/pg/pg.h>
+#include <vnet/ip/ip_sas.h>
 
 static u8 *
 format_ip6_icmp_type_and_code (u8 * s, va_list * args)
@@ -475,8 +476,6 @@
   u32 *from, *to_next;
   uword n_left_from, n_left_to_next;
   ip6_icmp_error_next_t next_index;
-  ip6_main_t *im = &ip6_main;
-  ip_lookup_main_t *lm = &im->lookup_main;
 
   from = vlib_frame_vector_args (frame);
   n_left_from = frame->n_vectors;
@@ -507,7 +506,7 @@
 	  vlib_buffer_t *p0, *org_p0;
 	  ip6_header_t *ip0, *out_ip0;
 	  icmp46_header_t *icmp0;
-	  u32 sw_if_index0, if_add_index0;
+	  u32 sw_if_index0;
 	  int bogus_length;
 
 	  org_p0 = vlib_get_buffer (vm, org_pi0);
@@ -547,18 +546,10 @@
 	  out_ip0->protocol = IP_PROTOCOL_ICMP6;
 	  out_ip0->hop_limit = 0xff;
 	  out_ip0->dst_address = ip0->src_address;
-	  if_add_index0 =
-	    lm->if_address_pool_index_by_sw_if_index[sw_if_index0];
-	  if (PREDICT_TRUE (if_add_index0 != ~0))
-	    {
-	      ip_interface_address_t *if_add =
-		pool_elt_at_index (lm->if_address_pool, if_add_index0);
-	      ip6_address_t *if_ip =
-		ip_interface_address_get_address (lm, if_add);
-	      out_ip0->src_address = *if_ip;
-	    }
-	  else			/* interface has no IP6 address - should not happen */
-	    {
+	  /* Prefer a source address from "offending interface" */
+	  if (!ip6_sas_by_sw_if_index (sw_if_index0, &out_ip0->dst_address,
+				       &out_ip0->src_address))
+	    { /* interface has no IP6 address - should not happen */
 	      next0 = IP6_ICMP_ERROR_NEXT_DROP;
 	      error0 = ICMP6_ERROR_DROP;
 	    }