Author: Timo Teräs <timo.teras@iki.fi>

Date:   Tue Sep 30 11:31:53 2014 +0300

    bgpd: implement route-map set as-path prepend last-as

    It picks up the AS to add from the aspath, or uses the peers
    AS number. Useful mostly in iBGP setups.

    Signed-off-by: Timo Teräs <timo.teras@iki.fi>
    Reviewed-by: Paul Jakma <paul@opensourcerouting.org>

bgpd/bgp_aspath.c

@@ -490,6 +490,19 @@ aspath_highest (struct aspath *aspath)
   return highest;
 }
 
+/* Return the left-most ASN in path */
+as_t
+aspath_leftmost (struct aspath *aspath)
+{
+  struct assegment *seg = aspath->segments;
+  as_t leftmost = 0;
+
+  if (seg && seg->length && seg->type == AS_SEQUENCE)
+    leftmost = seg->as[0];
+
+  return leftmost;
+}
+
 /* Return 1 if there are any 4-byte ASes in the path */
 unsigned int
 aspath_has_as4 (struct aspath *aspath)
@@ -1569,46 +1582,50 @@ aspath_filter_exclude (struct aspath * source, struct aspath * exclude_list)
 
 /* Add specified AS to the leftmost of aspath. */
 static struct aspath *
-aspath_add_one_as (struct aspath *aspath, as_t asno, u_char type)
+aspath_add_asns (struct aspath *aspath, as_t asno, u_char type, unsigned num)
 {
   struct assegment *assegment = aspath->segments;
+  unsigned i;
 
-  /* In case of empty aspath. */
+  if (assegment && assegment->type == type)
-  if (assegment == NULL || assegment->length == 0)
     {
-      aspath->segments = assegment_new (type, 1);
+      /* extend existing segment */
-      aspath->segments->as[0] = asno;
+      aspath->segments = assegment_prepend_asns (aspath->segments, asno, num);
-      
-      if (assegment)
-	assegment_free (assegment);
-
-      return aspath;
     }
-
-  if (assegment->type == type)
-    aspath->segments = assegment_prepend_asns (aspath->segments, asno, 1);
   else 
     {
-      /* create new segment
+      /* prepend with new segment */
-       * push it onto head of aspath's segment chain 
+      struct assegment *newsegment = assegment_new (type, num);
-       */
+      for (i = 0; i < num; i++)
-      struct assegment *newsegment;
+	newsegment->as[i] = asno;
-      
-      newsegment = assegment_new (type, 1);
-      newsegment->as[0] = asno;
 
+      /* insert potentially replacing empty segment */
+      if (assegment && assegment->length == 0)
+	{
+	  newsegment->next = assegment->next;
+	  assegment_free (assegment);
+	}
+       else
 	  newsegment->next = assegment;
       aspath->segments = newsegment;
     }
 
+  aspath_str_update (aspath);
   return aspath;
 }
 
+/* Add specified AS to the leftmost of aspath num times. */
+struct aspath *
+aspath_add_seq_n (struct aspath *aspath, as_t asno, unsigned num)
+{
+  return aspath_add_asns (aspath, asno, AS_SEQUENCE, num);
+}
+
 /* Add specified AS to the leftmost of aspath. */
 struct aspath *
 aspath_add_seq (struct aspath *aspath, as_t asno)
 {
-  return aspath_add_one_as (aspath, asno, AS_SEQUENCE);
+  return aspath_add_asns (aspath, asno, AS_SEQUENCE, 1);
 }
 
 /* Compare leftmost AS value for MED check.  If as1's leftmost AS and
@@ -1831,7 +1848,7 @@ aspath_delete_confed_seq (struct aspath *aspath)
 struct aspath*
 aspath_add_confed_seq (struct aspath *aspath, as_t asno)
 {
-  return aspath_add_one_as (aspath, asno, AS_CONFED_SEQUENCE);
+  return aspath_add_asns (aspath, asno, AS_CONFED_SEQUENCE, 1);
 }
 
 /* Add new as value to as path structure. */

bgpd/bgp_aspath.h

@@ -84,6 +84,7 @@ extern struct aspath *aspath_dup (struct aspath *);
 extern struct aspath *aspath_aggregate (struct aspath *, struct aspath *);
 extern struct aspath *aspath_prepend (struct aspath *, struct aspath *);
 extern struct aspath *aspath_filter_exclude (struct aspath *, struct aspath *);
+extern struct aspath *aspath_add_seq_n (struct aspath *, as_t, unsigned);
 extern struct aspath *aspath_add_seq (struct aspath *, as_t);
 extern struct aspath *aspath_add_confed_seq (struct aspath *, as_t);
 extern int aspath_cmp (const void *, const void *);
@@ -115,6 +116,7 @@ extern unsigned int aspath_count_hops (const struct aspath *);
 extern unsigned int aspath_count_confeds (struct aspath *);
 extern unsigned int aspath_size (struct aspath *);
 extern as_t aspath_highest (struct aspath *);
+extern as_t aspath_leftmost (struct aspath *);
 extern size_t aspath_put (struct stream *, struct aspath *, int);
 
 extern struct aspath *aspath_reconcile_as4 (struct aspath *, struct aspath *);

bgpd/bgp_routemap.c

@@ -1435,7 +1435,6 @@ route_set_aspath_prepend (void *rule, struct prefix *prefix, route_map_object_t
 
   if (type == RMAP_BGP)
     {
-      aspath = rule;
       binfo = object;
     
       if (binfo->attr->aspath->refcnt)
@@ -1443,20 +1442,50 @@ route_set_aspath_prepend (void *rule, struct prefix *prefix, route_map_object_t
       else
 	new = binfo->attr->aspath;
 
+      if ((uintptr_t)rule > 10)
+      {
+	aspath = rule;
 	aspath_prepend (aspath, new);
+      }
+      else
+      {
+	as_t as = aspath_leftmost(new);
+	if (!as) as = binfo->peer->as;
+	new = aspath_add_seq_n (new, as, (uintptr_t) rule);
+      }
+
       binfo->attr->aspath = new;
     }
 
   return RMAP_OKAY;
 }
 
+static void *
+route_set_aspath_prepend_compile (const char *arg)
+{
+  unsigned int num;
+
+  if (sscanf(arg, "last-as %u", &num) == 1 && num > 0 && num < 10)
+    return (void*)(uintptr_t)num;
+
+  return route_aspath_compile(arg);
+}
+
+static void
+route_set_aspath_prepend_free (void *rule)
+{
+  if ((uintptr_t)rule > 10)
+    route_aspath_free(rule);
+}
+
+
 /* Set as-path prepend rule structure. */
 struct route_map_rule_cmd route_set_aspath_prepend_cmd = 
 {
   "as-path prepend",
   route_set_aspath_prepend,
-  route_aspath_compile,
+  route_set_aspath_prepend_compile,
-  route_aspath_free,
+  route_set_aspath_prepend_free,
 };
 
 /* `set as-path exclude ASn' */
@@ -3803,6 +3832,15 @@ DEFUN (set_aspath_prepend,
   return ret;
 }
 
+ALIAS (set_aspath_prepend,
+       set_aspath_prepend_lastas_cmd,
+       "set as-path prepend (last-as) <1-10>",
+       SET_STR
+       "Transform BGP AS_PATH attribute\n"
+       "Prepend to the as-path\n"
+       "Use the peer's AS-number\n"
+       "Number of times to insert");
+
 DEFUN (no_set_aspath_prepend,
        no_set_aspath_prepend_cmd,
        "no set as-path prepend",
@@ -4681,6 +4719,7 @@ bgp_route_map_init (void)
   install_element (RMAP_NODE, &no_set_metric_cmd);
   install_element (RMAP_NODE, &no_set_metric_val_cmd);
   install_element (RMAP_NODE, &set_aspath_prepend_cmd);
+  install_element (RMAP_NODE, &set_aspath_prepend_lastas_cmd);
   install_element (RMAP_NODE, &set_aspath_exclude_cmd);
   install_element (RMAP_NODE, &no_set_aspath_prepend_cmd);
   install_element (RMAP_NODE, &no_set_aspath_prepend_val_cmd);