--- a/bgpd/bgp_aspath.c
+++ b/bgpd/bgp_aspath.c
@@ -614,6 +614,47 @@ aspath_private_as_check (struct aspath *
   return 1;
 }
 
+/* AS path confed check.  If aspath contains confed set or sequence then return 1. */
+int
+aspath_confed_check (struct aspath *aspath)
+{
+  caddr_t pnt;
+  caddr_t end;
+  struct assegment *assegment;
+
+  if (aspath == NULL)
+    return 0;
+
+  pnt = aspath->data;
+  end = aspath->data + aspath->length;
+
+  while (pnt < end)
+    {
+      assegment = (struct assegment *) pnt;
+      if (assegment->type == AS_CONFED_SET || assegment->type == AS_CONFED_SEQUENCE)
+	  return 1;
+      pnt += (assegment->length * AS_VALUE_SIZE) + AS_HEADER_SIZE;
+    }
+  return 0;
+}
+
+/* Leftmost AS path segment confed check.  If leftmost AS segment is of type
+  AS_CONFED_SEQUENCE or AS_CONFED_SET then return 1.  */
+int
+aspath_left_confed_check (struct aspath *aspath)
+{
+  struct assegment *assegment;
+
+  if (aspath == NULL)
+    return 0;
+
+  assegment = (struct assegment *) aspath->data;
+  if (assegment->type == AS_CONFED_SEQUENCE || assegment->type == AS_CONFED_SET)
+    return 1;
+
+  return 0;
+}
+
 /* Merge as1 to as2.  as2 should be uninterned aspath. */
 struct aspath *
 aspath_merge (struct aspath *as1, struct aspath *as2)
@@ -671,6 +712,10 @@ aspath_prepend (struct aspath *as1, stru
   if (seg1 == NULL)
     return as2;
 
+  /* Delete any AS_CONFED_SEQUENCE segment from as2. */
+  if (seg1->type == AS_SEQUENCE && seg2->type == AS_CONFED_SEQUENCE)
+    as2 = aspath_delete_confed_seq (as2);
+
   /* Compare last segment type of as1 and first segment type of as2. */
   if (seg1->type != seg2->type)
     return aspath_merge (as1, as2);
--- a/bgpd/bgp_aspath.h
+++ b/bgpd/bgp_aspath.h
@@ -76,4 +76,6 @@ unsigned int aspath_key_make (struct asp
 int aspath_loop_check (struct aspath *, as_t);
 int aspath_private_as_check (struct aspath *);
 int aspath_firstas_check (struct aspath *, as_t);
+int aspath_confed_check (struct aspath *);
+int aspath_left_confed_check (struct aspath *);
 unsigned long aspath_count ();
--- a/bgpd/bgp_attr.c
+++ b/bgpd/bgp_attr.c
@@ -673,6 +673,17 @@ bgp_attr_aspath (struct peer *peer, bgp_
       return -1;
     }
 
+  /* Confederation sanity check. */
+  if ((peer_sort (peer) == BGP_PEER_CONFED && ! aspath_left_confed_check (attr->aspath)) ||
+     (peer_sort (peer) == BGP_PEER_EBGP && aspath_confed_check (attr->aspath)))
+    {
+      zlog (peer->log, LOG_ERR, "Malformed AS path from %s", peer->host);
+      bgp_notify_send (peer, 
+		       BGP_NOTIFY_UPDATE_ERR, 
+		       BGP_NOTIFY_UPDATE_MAL_AS_PATH);
+      return -1;
+    }
+
   bgp = peer->bgp;
     
   /* First AS check for EBGP. */
