FIB Inherited Srouce

forwarding provided by the source is pushed to all other entries
it covers in the sub-tree

Change-Id: I2a45222ef653358f55c2436de3e3c6353cfadba2
Signed-off-by: Neale Ranns <nranns@cisco.com>

15 files changed, 1615 insertions, 119 deletions

diff --git a/src/vnet/fib/fib_entry.c b/src/vnet/fib/fib_entry.c
index 35716cacc29..fed42129cff 100644
--- a/src/vnet/fib/fib_entry.c
+++ b/src/vnet/fib/fib_entry.c
@@ -34,6 +34,7 @@
  */
 static const char *fib_source_names[] = FIB_SOURCES;
 static const char *fib_attribute_names[] = FIB_ENTRY_ATTRIBUTES;
+static const char *fib_src_attribute_names[] = FIB_ENTRY_SRC_ATTRIBUTES;
 
 /*
  * Pool for all fib_entries
@@ -102,6 +103,7 @@ format_fib_source (u8 * s, va_list * args)
 u8 *
 format_fib_entry (u8 * s, va_list * args)
 {
+    fib_entry_src_attribute_t sattr;
     fib_forward_chain_type_t fct;
     fib_entry_attribute_t attr;
     fib_entry_t *fib_entry;
@@ -126,15 +128,23 @@ format_fib_entry (u8 * s, va_list * args)
         ({
 	    s = format (s, "\n  %U", format_fib_source, source);
 	    s = fib_entry_src_format(fib_entry, source, s);
-	    s = format (s, " refs:%d ", src->fes_ref_count);
+	    s = format (s, " refs:%d", src->fes_ref_count);
 	    if (FIB_ENTRY_FLAG_NONE != src->fes_entry_flags) {
-		s = format(s, "flags:");
+		s = format(s, " entry-flags:");
 		FOR_EACH_FIB_ATTRIBUTE(attr) {
 		    if ((1<<attr) & src->fes_entry_flags) {
 			s = format (s, "%s,", fib_attribute_names[attr]);
 		    }
 		}
 	    }
+	    if (FIB_ENTRY_SRC_FLAG_NONE != src->fes_flags) {
+		s = format(s, " src-flags:");
+		FOR_EACH_FIB_SRC_ATTRIBUTE(sattr) {
+		    if ((1<<sattr) & src->fes_flags) {
+			s = format (s, "%s,", fib_src_attribute_names[sattr]);
+		    }
+		}
+	    }
 	    s = format (s, "\n");
 	    if (FIB_NODE_INDEX_INVALID != src->fes_pl)
 	    {
@@ -584,7 +594,6 @@ fib_entry_alloc (u32 fib_index,
 
 static fib_entry_t*
 fib_entry_post_flag_update_actions (fib_entry_t *fib_entry,
-				    fib_source_t source,
 				    fib_entry_flag_t old_flags)
 {
     fib_node_index_t fei;
@@ -658,7 +667,6 @@ fib_entry_post_install_actions (fib_entry_t *fib_entry,
 				fib_entry_flag_t old_flags)
 {
     fib_entry = fib_entry_post_flag_update_actions(fib_entry,
-                                                   source,
                                                    old_flags);
     fib_entry_src_action_installed(fib_entry, source);
 }
@@ -748,26 +756,25 @@ fib_entry_post_update_actions (fib_entry_t *fib_entry,
     fib_entry_post_install_actions(fib_entry, source, old_flags);
 }
 
-static void
+void
 fib_entry_source_change (fib_entry_t *fib_entry,
-			 fib_source_t best_source,
-			 fib_source_t new_source,
-			 fib_entry_flag_t old_flags)
+                         fib_source_t old_source,
+			 fib_source_t new_source)
 {
-    /*
-     * if the path list for the source passed is invalid,
-     * then we need to create a new one. else we are updating
-     * an existing.
-     */
-    if (new_source < best_source)
+    fib_entry_flag_t old_flags;
+
+    old_flags = fib_entry_get_flags_for_source(
+        fib_entry_get_index(fib_entry), old_source);
+
+    if (new_source < old_source)
     {
 	/*
 	 * we have a new winning source.
 	 */
-	fib_entry_src_action_deactivate(fib_entry, best_source);
+	fib_entry_src_action_deactivate(fib_entry, old_source);
 	fib_entry_src_action_activate(fib_entry, new_source);
     }
-    else if (new_source > best_source)
+    else if (new_source > old_source)
     {
 	/*
 	 * the new source loses. nothing to do here.
@@ -782,8 +789,7 @@ fib_entry_source_change (fib_entry_t *fib_entry,
 	 * But the path-list was updated, which will contribute new forwarding,
 	 * so install it.
 	 */
-	fib_entry_src_action_deactivate(fib_entry, new_source);
-	fib_entry_src_action_activate(fib_entry, new_source);
+        fib_entry_src_action_reactivate(fib_entry, new_source);
     }
 
     fib_entry_post_update_actions(fib_entry, new_source, old_flags);
@@ -796,18 +802,13 @@ fib_entry_special_add (fib_node_index_t fib_entry_index,
 		       const dpo_id_t *dpo)
 {
     fib_source_t best_source;
-    fib_entry_flag_t bflags;
     fib_entry_t *fib_entry;
-    fib_entry_src_t *bsrc;
 
     fib_entry = fib_entry_get(fib_entry_index);
-
-    bsrc = fib_entry_get_best_src_i(fib_entry);
-    best_source = fib_entry_src_get_source(bsrc);
-    bflags = fib_entry_src_get_flags(bsrc);
+    best_source = fib_entry_get_best_source(fib_entry_index);
 
     fib_entry = fib_entry_src_action_add(fib_entry, source, flags, dpo);
-    fib_entry_source_change(fib_entry, best_source, source, bflags);
+    fib_entry_source_change(fib_entry, best_source, source);
 }
 
 void
@@ -817,18 +818,13 @@ fib_entry_special_update (fib_node_index_t fib_entry_index,
 			  const dpo_id_t *dpo)
 {
     fib_source_t best_source;
-    fib_entry_flag_t bflags;
     fib_entry_t *fib_entry;
-    fib_entry_src_t *bsrc;
 
     fib_entry = fib_entry_get(fib_entry_index);
-
-    bsrc = fib_entry_get_best_src_i(fib_entry);
-    best_source = fib_entry_src_get_source(bsrc);
-    bflags = fib_entry_src_get_flags(bsrc);
+    best_source = fib_entry_get_best_source(fib_entry_index);
 
     fib_entry = fib_entry_src_action_update(fib_entry, source, flags, dpo);
-    fib_entry_source_change(fib_entry, best_source, source, bflags);
+    fib_entry_source_change(fib_entry, best_source, source);
 }
 
 
@@ -882,13 +878,78 @@ fib_entry_path_add (fib_node_index_t fib_entry_index,
 	 * But the path-list was updated, which will contribute new forwarding,
 	 * so install it.
 	 */
-	fib_entry_src_action_deactivate(fib_entry, source);
-	fib_entry_src_action_activate(fib_entry, source);
+	fib_entry_src_action_reactivate(fib_entry, source);
     }
 
     fib_entry_post_update_actions(fib_entry, source, bflags);
 }
 
+static fib_entry_src_flag_t
+fib_entry_src_burn_only_inherited (fib_entry_t *fib_entry)
+{
+    fib_entry_src_t *src;
+    fib_source_t source;
+    int has_only_inherited_sources = 1;
+
+    FOR_EACH_SRC_ADDED(fib_entry, src, source,
+    ({
+        if (!(src->fes_flags & FIB_ENTRY_SRC_FLAG_INHERITED))
+        {
+            has_only_inherited_sources = 0;
+            break;
+        }
+    }));
+    if (has_only_inherited_sources)
+    {
+        FOR_EACH_SRC_ADDED(fib_entry, src, source,
+        ({
+            fib_entry_src_action_remove(fib_entry, source);
+        }));
+        return (FIB_ENTRY_SRC_FLAG_NONE);
+    }
+    else
+    {
+        return (FIB_ENTRY_SRC_FLAG_ADDED);
+    }
+}
+
+static fib_entry_src_flag_t
+fib_entry_source_removed (fib_entry_t *fib_entry,
+                          fib_entry_flag_t old_flags)
+{
+    const fib_entry_src_t *bsrc;
+    fib_source_t best_source;
+
+    /*
+     * if all that is left are inherited sources, then burn them
+     */
+    fib_entry_src_burn_only_inherited(fib_entry);
+
+    bsrc = fib_entry_get_best_src_i(fib_entry);
+    best_source = fib_entry_src_get_source(bsrc);
+
+    if (FIB_SOURCE_MAX == best_source) {
+        /*
+         * no more sources left. this entry is toast.
+         */
+        fib_entry = fib_entry_post_flag_update_actions(fib_entry, old_flags);
+        fib_entry_src_action_uninstall(fib_entry);
+
+        return (FIB_ENTRY_SRC_FLAG_NONE);
+    }
+    else
+    {
+        fib_entry_src_action_activate(fib_entry, best_source);
+    }
+
+    fib_entry_post_update_actions(fib_entry, best_source, old_flags);
+
+    /*
+     * still have sources
+     */
+    return (FIB_ENTRY_SRC_FLAG_ADDED);
+}
+
 /*
  * fib_entry_path_remove
  *
@@ -922,7 +983,7 @@ fib_entry_path_remove (fib_node_index_t fib_entry_index,
      * then we need to create a new one. else we are updating
      * an existing.
      */
-    if (source < best_source )
+    if (source < best_source)
     {
 	/*
 	 * Que! removing a path from a source that is better than the
@@ -933,9 +994,23 @@ fib_entry_path_remove (fib_node_index_t fib_entry_index,
     else if (source > best_source )
     {
 	/*
-	 * the source is not the best. nothing to do.
+	 * the source is not the best. no need to update forwarding
 	 */
-	return (FIB_ENTRY_SRC_FLAG_ADDED);
+	if (FIB_ENTRY_SRC_FLAG_ADDED & sflag)
+        {
+            /*
+             * the source being removed still has paths
+             */
+            return (FIB_ENTRY_SRC_FLAG_ADDED);
+        }
+        else
+        {
+            /*
+             * that was the last path from this source, check if those
+             * that remain are non-inherited
+             */
+            return (fib_entry_src_burn_only_inherited(fib_entry));
+       }
     }
     else
     {
@@ -948,33 +1023,14 @@ fib_entry_path_remove (fib_node_index_t fib_entry_index,
 	     * the last path from the source was removed.
 	     * fallback to lower source
 	     */
-	    bsrc = fib_entry_get_best_src_i(fib_entry);
-	    best_source = fib_entry_src_get_source(bsrc);
-
-	    if (FIB_SOURCE_MAX == best_source) {
-		/*
-		 * no more sources left. this entry is toast.
-		 */
-		fib_entry = fib_entry_post_flag_update_actions(fib_entry,
-                                                               source,
-                                                               bflags);
-		fib_entry_src_action_uninstall(fib_entry);
-
-		return (FIB_ENTRY_SRC_FLAG_NONE);
-	    }
-	    else
-	    {
-		fib_entry_src_action_activate(fib_entry, best_source);
-		source = best_source;
-	    }
+            return (fib_entry_source_removed(fib_entry, bflags));
 	}
 	else
 	{
 	    /*
 	     * re-install the new forwarding information
 	     */
-	    fib_entry_src_action_deactivate(fib_entry, source);
-	    fib_entry_src_action_activate(fib_entry, source);
+	    fib_entry_src_action_reactivate(fib_entry, source);
 	}
     }
 
@@ -1009,7 +1065,7 @@ fib_entry_special_remove (fib_node_index_t fib_entry_index,
     best_source = fib_entry_src_get_source(bsrc);
     bflags = fib_entry_src_get_flags(bsrc);
 
-    sflag = fib_entry_src_action_remove(fib_entry, source);
+    sflag = fib_entry_src_action_remove_or_update_inherit(fib_entry, source);
 
     /*
      * if the path list for the source passed is invalid,
@@ -1027,9 +1083,32 @@ fib_entry_special_remove (fib_node_index_t fib_entry_index,
     }
     else if (source > best_source ) {
 	/*
-	 * the source is not the best. nothing to do.
+	 * the source is not the best. no need to update forwarding
 	 */
-	return (FIB_ENTRY_SRC_FLAG_ADDED);
+	if (FIB_ENTRY_SRC_FLAG_ADDED & sflag)
+        {
+            /*
+             * the source being removed still has paths
+             */
+            return (FIB_ENTRY_SRC_FLAG_ADDED);
+        }
+        else
+        {
+            /*
+             * that was the last path from this source, check if those
+             * that remain are non-inherited
+             */
+            if (FIB_ENTRY_SRC_FLAG_NONE == fib_entry_src_burn_only_inherited(fib_entry))
+            {
+                /*
+                 * no more sources left. this entry is toast.
+                 */
+                fib_entry = fib_entry_post_flag_update_actions(fib_entry, bflags);
+                fib_entry_src_action_uninstall(fib_entry);
+                return (FIB_ENTRY_SRC_FLAG_NONE);
+            }
+            return (FIB_ENTRY_SRC_FLAG_ADDED);
+        }
     }
     else
     {
@@ -1038,25 +1117,7 @@ fib_entry_special_remove (fib_node_index_t fib_entry_index,
 	    /*
 	     * the source was removed. use the next best.
 	     */
-	    bsrc = fib_entry_get_best_src_i(fib_entry);
-	    best_source = fib_entry_src_get_source(bsrc);
-
-	    if (FIB_SOURCE_MAX == best_source) {
-		/*
-		 * no more sources left. this entry is toast.
-		 */
-		fib_entry = fib_entry_post_flag_update_actions(fib_entry,
-                                                               source,
-                                                               bflags);
-		fib_entry_src_action_uninstall(fib_entry);
-
-		return (FIB_ENTRY_SRC_FLAG_NONE);
-	    }
-	    else
-	    {
-		fib_entry_src_action_activate(fib_entry, best_source);
-		source = best_source;
-	    }
+            return (fib_entry_source_removed(fib_entry, bflags));
 	}
 	else
 	{
@@ -1076,6 +1137,20 @@ fib_entry_special_remove (fib_node_index_t fib_entry_index,
 }
 
 /**
+ * fib_entry_inherit
+ *
+ * If the source on the cover is inherting then push this source
+ * down to the covered.
+ */
+void
+fib_entry_inherit (fib_node_index_t cover,
+                   fib_node_index_t covered)
+{
+    fib_entry_src_inherit(fib_entry_get(cover),
+                          fib_entry_get(covered));
+}
+
+/**
  * fib_entry_delete
  *
  * The source is withdrawing all the paths it provided
@@ -1146,8 +1221,7 @@ fib_entry_update (fib_node_index_t fib_entry_index,
 	 * But the path-list was updated, which will contribute new forwarding,
 	 * so install it.
 	 */
-	fib_entry_src_action_deactivate(fib_entry, source);
-	fib_entry_src_action_activate(fib_entry, source);
+	fib_entry_src_action_reactivate(fib_entry, source);
     }
 
     fib_entry_post_update_actions(fib_entry, source, bflags);
diff --git a/src/vnet/fib/fib_entry.h b/src/vnet/fib/fib_entry.h
index cd2a685b765..273a5e66b15 100644
--- a/src/vnet/fib/fib_entry.h
+++ b/src/vnet/fib/fib_entry.h
@@ -213,9 +213,14 @@ typedef enum fib_entry_attribute_t_ {
      */
     FIB_ENTRY_ATTRIBUTE_URPF_EXEMPT,
     /**
+     * This FIB entry imposes its source information on all prefixes
+     * that is covers
+     */
+    FIB_ENTRY_ATTRIBUTE_COVERED_INHERIT,
+    /**
      * Marker. add new entries before this one.
      */
-    FIB_ENTRY_ATTRIBUTE_LAST = FIB_ENTRY_ATTRIBUTE_URPF_EXEMPT,
+    FIB_ENTRY_ATTRIBUTE_LAST = FIB_ENTRY_ATTRIBUTE_COVERED_INHERIT,
 } fib_entry_attribute_t;
 
 #define FIB_ENTRY_ATTRIBUTES {		       		\
@@ -227,6 +232,7 @@ typedef enum fib_entry_attribute_t_ {
     [FIB_ENTRY_ATTRIBUTE_LOCAL]     = "local",		\
     [FIB_ENTRY_ATTRIBUTE_URPF_EXEMPT] = "uRPF-exempt",  \
     [FIB_ENTRY_ATTRIBUTE_MULTICAST] = "multicast",	\
+    [FIB_ENTRY_ATTRIBUTE_COVERED_INHERIT] = "covered-inherit",  \
 }
 
 #define FOR_EACH_FIB_ATTRIBUTE(_item)			\
@@ -244,6 +250,7 @@ typedef enum fib_entry_flag_t_ {
     FIB_ENTRY_FLAG_IMPORT    = (1 << FIB_ENTRY_ATTRIBUTE_IMPORT),
     FIB_ENTRY_FLAG_LOOSE_URPF_EXEMPT = (1 << FIB_ENTRY_ATTRIBUTE_URPF_EXEMPT),
     FIB_ENTRY_FLAG_MULTICAST = (1 << FIB_ENTRY_ATTRIBUTE_MULTICAST),
+    FIB_ENTRY_FLAG_COVERED_INHERIT = (1 << FIB_ENTRY_ATTRIBUTE_COVERED_INHERIT),
 } __attribute__((packed)) fib_entry_flag_t;
 
 /**
@@ -263,9 +270,13 @@ typedef enum fib_entry_src_attribute_t_ {
      */
     FIB_ENTRY_SRC_ATTRIBUTE_ACTIVE,
     /**
+     * the source is inherited from its cover
+     */
+    FIB_ENTRY_SRC_ATTRIBUTE_INHERITED,
+    /**
      * Marker. add new entries before this one.
      */
-    FIB_ENTRY_SRC_ATTRIBUTE_LAST = FIB_ENTRY_SRC_ATTRIBUTE_ACTIVE,
+    FIB_ENTRY_SRC_ATTRIBUTE_LAST = FIB_ENTRY_SRC_ATTRIBUTE_INHERITED,
 } fib_entry_src_attribute_t;
 
 #define FIB_ENTRY_SRC_ATTRIBUTE_MAX (FIB_ENTRY_SRC_ATTRIBUTE_LAST+1)
@@ -273,12 +284,19 @@ typedef enum fib_entry_src_attribute_t_ {
 #define FIB_ENTRY_SRC_ATTRIBUTES {		 \
     [FIB_ENTRY_SRC_ATTRIBUTE_ADDED]  = "added",	 \
     [FIB_ENTRY_SRC_ATTRIBUTE_ACTIVE] = "active", \
+    [FIB_ENTRY_SRC_ATTRIBUTE_INHERITED] = "inherited", \
 }
 
+#define FOR_EACH_FIB_SRC_ATTRIBUTE(_item)      		\
+    for (_item = FIB_ENTRY_SRC_ATTRIBUTE_FIRST;		\
+	 _item < FIB_ENTRY_SRC_ATTRIBUTE_MAX;		\
+	 _item++)
+
 typedef enum fib_entry_src_flag_t_ {
     FIB_ENTRY_SRC_FLAG_NONE   = 0,
     FIB_ENTRY_SRC_FLAG_ADDED  = (1 << FIB_ENTRY_SRC_ATTRIBUTE_ADDED),
     FIB_ENTRY_SRC_FLAG_ACTIVE = (1 << FIB_ENTRY_SRC_ATTRIBUTE_ACTIVE),
+    FIB_ENTRY_SRC_FLAG_INHERITED = (1 << FIB_ENTRY_SRC_ATTRIBUTE_INHERITED),
 } __attribute__ ((packed)) fib_entry_src_flag_t;
 
 /*
@@ -477,6 +495,10 @@ extern fib_entry_src_flag_t fib_entry_special_remove(fib_node_index_t fib_entry_
 extern fib_entry_src_flag_t fib_entry_path_remove(fib_node_index_t fib_entry_index,
 						  fib_source_t source,
 						  const fib_route_path_t *rpath);
+
+extern void fib_entry_inherit(fib_node_index_t cover,
+                              fib_node_index_t covered);
+
 extern fib_entry_src_flag_t fib_entry_delete(fib_node_index_t fib_entry_index,
 					     fib_source_t source);
 
diff --git a/src/vnet/fib/fib_entry_src.c b/src/vnet/fib/fib_entry_src.c
index 66f5987a7cf..616d77e8b0a 100644
--- a/src/vnet/fib/fib_entry_src.c
+++ b/src/vnet/fib/fib_entry_src.c
@@ -108,8 +108,7 @@ fib_entry_is_sourced (fib_node_index_t fib_entry_index,
 
 static fib_entry_src_t *
 fib_entry_src_find_or_create (fib_entry_t *fib_entry,
-			      fib_source_t source,
-			      u32 *index)
+			      fib_source_t source)
 {
     fib_entry_src_t *esrc;
 
@@ -654,6 +653,249 @@ fib_entry_recursive_loop_detect_i (fib_node_index_t path_list_index)
     vec_free(entries);
 }
 
+/*
+ * fib_entry_src_action_copy
+ *
+ * copy a source data from another entry to this one
+ */
+fib_entry_t *
+fib_entry_src_action_copy (fib_entry_t *fib_entry,
+                           const fib_entry_src_t *orig_src)
+{
+    fib_entry_src_t *esrc;
+
+    esrc = fib_entry_src_find_or_create(fib_entry, orig_src->fes_src);
+
+    *esrc = *orig_src;
+    esrc->fes_ref_count = 1;
+    esrc->fes_flags |= FIB_ENTRY_SRC_FLAG_INHERITED;
+    esrc->fes_flags &= ~FIB_ENTRY_SRC_FLAG_ACTIVE;
+    esrc->fes_entry_flags &= ~FIB_ENTRY_FLAG_COVERED_INHERIT;
+
+    /*
+     * the source owns a lock on the entry
+     */
+    fib_path_list_lock(esrc->fes_pl);
+    fib_entry_lock(fib_entry_get_index(fib_entry));
+
+    return (fib_entry);
+}
+
+/*
+ * fib_entry_src_action_update
+ *
+ * copy a source data from another entry to this one
+ */
+static fib_entry_src_t *
+fib_entry_src_action_update_from_cover (fib_entry_t *fib_entry,
+                                        const fib_entry_src_t *orig_src)
+{
+    fib_entry_src_t *esrc;
+
+    esrc = fib_entry_src_find_or_create(fib_entry, orig_src->fes_src);
+
+    /*
+     * the source owns a lock on the entry
+     */
+    fib_path_list_unlock(esrc->fes_pl);
+    esrc->fes_pl = orig_src->fes_pl;
+    fib_path_list_lock(esrc->fes_pl);
+
+    return (esrc);
+}
+
+static fib_table_walk_rc_t
+fib_entry_src_covered_inherit_add_i (fib_entry_t *fib_entry,
+                                     const fib_entry_src_t *cover_src)
+{
+    fib_entry_src_t *esrc;
+
+    esrc = fib_entry_src_find(fib_entry, cover_src->fes_src, NULL);
+
+    if (cover_src == esrc)
+    {
+        return (FIB_TABLE_WALK_CONTINUE);
+    }
+
+    if (NULL != esrc)
+    {
+        /*
+         * the covered entry already has this source.
+         */
+        if (esrc->fes_entry_flags & FIB_ENTRY_FLAG_COVERED_INHERIT)
+        {
+            /*
+             * the covered source is itself a COVERED_INHERIT, i.e.
+             * it also pushes this source down the sub-tree.
+             * We consider this more specfic covered to be the owner
+             * of the sub-tree from this point down.
+             */
+            return (FIB_TABLE_WALK_SUB_TREE_STOP);
+        }
+        if (esrc->fes_flags & FIB_ENTRY_SRC_FLAG_INHERITED)
+        {
+            /*
+             * The covered's source data has been inherited, presumably
+             * from this cover, i.e. this is a modify.
+             */
+            esrc = fib_entry_src_action_update_from_cover(fib_entry, cover_src);
+            fib_entry_source_change(fib_entry, esrc->fes_src, esrc->fes_src);
+        }
+        else
+        {
+            /*
+             * The covered's source was not inherited and it is also
+             * not inherting. Nevertheless, it still owns the sub-tree from 
+             * this point down.
+             */
+            return (FIB_TABLE_WALK_SUB_TREE_STOP);
+        }
+    }
+    else
+    {
+        /*
+         * The covered does not have this source - add it.
+         */
+        fib_source_t best_source;
+
+        best_source = fib_entry_get_best_source(
+            fib_entry_get_index(fib_entry));
+
+        fib_entry_src_action_copy(fib_entry, cover_src);
+        fib_entry_source_change(fib_entry, best_source, cover_src->fes_src);
+
+    }
+    return (FIB_TABLE_WALK_CONTINUE);
+}
+
+static fib_table_walk_rc_t
+fib_entry_src_covered_inherit_walk_add (fib_node_index_t fei,
+                                        void *ctx)
+{
+    return (fib_entry_src_covered_inherit_add_i(fib_entry_get(fei), ctx));
+}
+
+static fib_table_walk_rc_t
+fib_entry_src_covered_inherit_walk_remove (fib_node_index_t fei,
+                                           void *ctx)
+{
+    fib_entry_src_t *cover_src, *esrc;
+    fib_entry_t *fib_entry;
+
+    fib_entry = fib_entry_get(fei);
+
+    cover_src = ctx;
+    esrc = fib_entry_src_find(fib_entry, cover_src->fes_src, NULL);
+
+    if (cover_src == esrc)
+    {
+        return (FIB_TABLE_WALK_CONTINUE);
+    }
+
+    if (NULL != esrc)
+    {
+        /*
+         * the covered entry already has this source.
+         */
+        if (esrc->fes_entry_flags & FIB_ENTRY_FLAG_COVERED_INHERIT)
+        {
+            /*
+             * the covered source is itself a COVERED_INHERIT, i.e.
+             * it also pushes this source down the sub-tree.
+             * We consider this more specfic covered to be the owner
+             * of the sub-tree from this point down.
+             */
+            return (FIB_TABLE_WALK_SUB_TREE_STOP);
+        }
+        if (esrc->fes_flags & FIB_ENTRY_SRC_FLAG_INHERITED)
+        {
+            /*
+             * The covered's source data has been inherited, presumably
+             * from this cover
+             */
+            fib_entry_src_flag_t remaining;
+
+            remaining = fib_entry_special_remove(fei, cover_src->fes_src);
+
+            ASSERT(FIB_ENTRY_SRC_FLAG_ADDED == remaining);
+        }
+        else
+        {
+            /*
+             * The covered's source was not inherited and it is also
+             * not inherting. Nevertheless, it still owns the sub-tree from 
+             * this point down.
+             */
+            return (FIB_TABLE_WALK_SUB_TREE_STOP);
+        }
+    }
+    else
+    {
+        /*
+         * The covered does not have this source - that's an error,
+         * since it should have inherited, but there is nothing we can do
+         * about it now.
+         */
+    }
+    return (FIB_TABLE_WALK_CONTINUE);
+}
+
+void
+fib_entry_src_inherit (const fib_entry_t *cover,
+                       fib_entry_t *covered)
+{
+    CLIB_UNUSED(fib_source_t source);
+    const fib_entry_src_t *src;
+
+    FOR_EACH_SRC_ADDED(cover, src, source,
+    ({
+        if ((src->fes_entry_flags & FIB_ENTRY_FLAG_COVERED_INHERIT) ||
+            (src->fes_flags & FIB_ENTRY_SRC_FLAG_INHERITED))
+        {
+            fib_entry_src_covered_inherit_add_i(covered, src);
+        }
+    }))
+}
+
+static void
+fib_entry_src_covered_inherit_add (fib_entry_t *fib_entry,
+                                   fib_source_t source)
+
+{
+    fib_entry_src_t *esrc;
+
+    esrc = fib_entry_src_find(fib_entry, source, NULL);
+
+    ASSERT(esrc->fes_flags & FIB_ENTRY_SRC_FLAG_ACTIVE);
+
+    if ((esrc->fes_entry_flags & FIB_ENTRY_FLAG_COVERED_INHERIT) ||
+        (esrc->fes_flags & FIB_ENTRY_SRC_FLAG_INHERITED))
+    {
+        fib_table_sub_tree_walk(fib_entry->fe_fib_index,
+                                fib_entry->fe_prefix.fp_proto,
+                                &fib_entry->fe_prefix,
+                                fib_entry_src_covered_inherit_walk_add,
+                                esrc);
+    }
+}
+
+static void
+fib_entry_src_covered_inherit_remove (fib_entry_t *fib_entry,
+                                      fib_entry_src_t *esrc)
+
+{
+    ASSERT(!(esrc->fes_flags & FIB_ENTRY_SRC_FLAG_ACTIVE));
+
+    if (esrc->fes_entry_flags & FIB_ENTRY_FLAG_COVERED_INHERIT)
+    {
+        fib_table_sub_tree_walk(fib_entry->fe_fib_index,
+                                fib_entry->fe_prefix.fp_proto,
+                                &fib_entry->fe_prefix,
+                                fib_entry_src_covered_inherit_walk_remove,
+                                esrc);
+    }
+}
+
 void
 fib_entry_src_action_activate (fib_entry_t *fib_entry,
 			       fib_source_t source)
@@ -698,6 +940,11 @@ fib_entry_src_action_activate (fib_entry_t *fib_entry,
     FIB_ENTRY_DBG(fib_entry, "activate: %d",
 		  fib_entry->fe_parent);
 
+    /*
+     * If this source should push its state to covered prefixs, do that now.
+     */
+    fib_entry_src_covered_inherit_add(fib_entry, source);
+
     if (0 != houston_we_are_go_for_install)
     {
 	fib_entry_src_action_install(fib_entry, source);
@@ -730,6 +977,14 @@ fib_entry_src_action_deactivate (fib_entry_t *fib_entry,
     FIB_ENTRY_DBG(fib_entry, "deactivate: %d", fib_entry->fe_parent);
 
     /*
+     * If this source should pull its state from covered prefixs, do that now.
+     * If this source also has the INHERITED flag set then it has a cover
+     * that wants to push down forwarding. We only want the covereds to see
+     * one update.
+     */
+    fib_entry_src_covered_inherit_remove(fib_entry, esrc);
+
+    /*
      * un-link from an old path-list. Check for any loops this will clear
      */
     path_list_index = fib_entry->fe_parent;
@@ -778,6 +1033,8 @@ fib_entry_src_action_reactivate (fib_entry_t *fib_entry,
 
     if (fib_entry->fe_parent != esrc->fes_pl)
     {
+        int remain_installed;
+
 	/*
 	 * un-link from an old path-list. Check for any loops this will clear
 	 */
@@ -811,6 +1068,30 @@ fib_entry_src_action_reactivate (fib_entry_t *fib_entry,
 
 	fib_entry_recursive_loop_detect_i(fib_entry->fe_parent);
 	fib_path_list_unlock(path_list_index);
+
+        /*
+         * call the source to reactive and get the go/no-go to remain installed
+         */
+        if (NULL != fib_entry_src_vft[source].fesv_reactivate)
+        {
+            remain_installed =
+                fib_entry_src_vft[source].fesv_reactivate(esrc, fib_entry);
+        }
+        else
+        {
+            remain_installed = 1;
+        }
+
+        /*
+         * If this source should push its state to covered prefixs, do that now.
+         */
+        fib_entry_src_covered_inherit_add(fib_entry, source);
+
+        if (!remain_installed)
+        {
+            fib_entry_src_action_uninstall(fib_entry);
+            return;
+        }
     }
     fib_entry_src_action_install(fib_entry, source);
     fib_entry_src_action_fwd_update(fib_entry, source);
@@ -850,7 +1131,7 @@ fib_entry_src_action_add (fib_entry_t *fib_entry,
     fib_node_index_t fib_entry_index;
     fib_entry_src_t *esrc;
 
-    esrc = fib_entry_src_find_or_create(fib_entry, source, NULL);
+    esrc = fib_entry_src_find_or_create(fib_entry, source);
 
     esrc->fes_ref_count++;
 
@@ -909,10 +1190,12 @@ fib_entry_src_action_update (fib_entry_t *fib_entry,
     fib_node_index_t fib_entry_index, old_path_list_index;
     fib_entry_src_t *esrc;
 
-    esrc = fib_entry_src_find_or_create(fib_entry, source, NULL);
+    esrc = fib_entry_src_find_or_create(fib_entry, source);
 
     if (NULL == esrc)
+    {
 	return (fib_entry_src_action_add(fib_entry, source, flags, dpo));
+    }
 
     old_path_list_index = esrc->fes_pl;
     esrc->fes_entry_flags = flags;
@@ -941,6 +1224,60 @@ fib_entry_src_action_update (fib_entry_t *fib_entry,
     return (fib_entry);
 }
 
+fib_entry_src_flag_t
+fib_entry_src_action_remove_or_update_inherit (fib_entry_t *fib_entry,
+                                               fib_source_t source)
+{
+    fib_entry_src_t *esrc;
+
+    esrc = fib_entry_src_find(fib_entry, source, NULL);
+
+    if (NULL == esrc)
+        return (FIB_ENTRY_SRC_FLAG_ACTIVE);
+
+    if ((esrc->fes_entry_flags & FIB_ENTRY_FLAG_COVERED_INHERIT) &&
+        (esrc->fes_flags & FIB_ENTRY_SRC_FLAG_INHERITED))
+    {
+        fib_entry_src_t *cover_src;
+        fib_node_index_t coveri;
+        fib_entry_t *cover;
+
+        /*
+         * this source was pushing inherited state, but so is its
+         * cover. Now that this source is going away, we need to
+         * pull the covers forwarding and use it to update the covereds.
+         * Go grab the path-list from the cover, rather than start a walk from
+         * the cover, so we don't recursively update this entry.
+         */
+        coveri = fib_table_get_less_specific(fib_entry->fe_fib_index,
+                                             &fib_entry->fe_prefix);
+
+        /*
+         * only the default route has itself as its own cover, but the
+         * default route cannot have inherited from something else.
+         */
+        ASSERT(coveri != fib_entry_get_index(fib_entry));
+
+        cover = fib_entry_get(coveri);
+        cover_src = fib_entry_src_find(cover, source, NULL);
+
+        ASSERT(NULL != cover_src);
+
+        esrc = fib_entry_src_action_update_from_cover(fib_entry, cover_src);
+        esrc->fes_entry_flags &= ~FIB_ENTRY_FLAG_COVERED_INHERIT;
+
+        /*
+         * Now push the new state from the cover down to the covereds
+         */
+        fib_entry_src_covered_inherit_add(fib_entry, source);
+
+        return (esrc->fes_flags);
+    }
+    else
+    {
+        return (fib_entry_src_action_remove(fib_entry, source));
+    }
+}
 
 fib_entry_src_flag_t
 fib_entry_src_action_remove (fib_entry_t *fib_entry,
@@ -969,7 +1306,7 @@ fib_entry_src_action_remove (fib_entry_t *fib_entry,
 
     if (esrc->fes_flags & FIB_ENTRY_SRC_FLAG_ACTIVE)
     {
-	fib_entry_src_action_deactivate(fib_entry, source);
+        fib_entry_src_action_deactivate(fib_entry, source);
     }
 
     old_path_list = esrc->fes_pl;
@@ -1185,6 +1522,10 @@ fib_entry_src_action_path_swap (fib_entry_t *fib_entry,
                                                  fib_entry_get_dpo_proto(fib_entry)));
 	esrc = fib_entry_src_find(fib_entry, source, NULL);
     }
+    else
+    {
+        esrc->fes_entry_flags = flags;
+    }
 
     /*
      * swapping paths may create a new path-list (or may use an existing shared)
@@ -1258,7 +1599,7 @@ fib_entry_src_action_path_remove (fib_entry_t *fib_entry,
 	/*
 	 * no more paths left from this source
 	 */
-	fib_entry_src_action_remove(fib_entry, source);
+	fib_entry_src_action_remove_or_update_inherit(fib_entry, source);
 	return (FIB_ENTRY_SRC_FLAG_NONE);
     }
 }
diff --git a/src/vnet/fib/fib_entry_src.h b/src/vnet/fib/fib_entry_src.h
index 35c43936a1f..57840d555ee 100644
--- a/src/vnet/fib/fib_entry_src.h
+++ b/src/vnet/fib/fib_entry_src.h
@@ -60,6 +60,13 @@ typedef int (*fib_entry_src_activate_t)(fib_entry_src_t *src,
 					 const fib_entry_t *fib_entry);
 
 /**
+ * Source re-activation. Called when the source is updated and remains
+ * the best source.
+ */
+typedef int (*fib_entry_src_reactivate_t)(fib_entry_src_t *src,
+                                          const fib_entry_t *fib_entry);
+
+/**
  * Source Deactivate. 
  * Called when the source is no longer best source on the entry
  */
@@ -173,6 +180,7 @@ typedef struct fib_entry_src_vft_t_ {
     fib_entry_src_deinit_t fesv_deinit;
     fib_entry_src_activate_t fesv_activate;
     fib_entry_src_deactivate_t fesv_deactivate;
+    fib_entry_src_reactivate_t fesv_reactivate;
     fib_entry_src_add_t fesv_add;
     fib_entry_src_remove_t fesv_remove;
     fib_entry_src_path_swap_t fesv_path_swap;
@@ -240,6 +248,9 @@ extern fib_entry_t* fib_entry_src_action_update(fib_entry_t *fib_entry,
 
 extern fib_entry_src_flag_t fib_entry_src_action_remove(fib_entry_t *fib_entry,
 							fib_source_t source);
+extern fib_entry_src_flag_t
+fib_entry_src_action_remove_or_update_inherit(fib_entry_t *fib_entry,
+                                              fib_source_t source);
 
 extern void fib_entry_src_action_install(fib_entry_t *fib_entry,
 					 fib_source_t source);
@@ -262,10 +273,13 @@ extern fib_entry_src_flag_t fib_entry_src_action_path_remove(fib_entry_t *fib_en
 
 extern void fib_entry_src_action_installed(const fib_entry_t *fib_entry,
 					   fib_source_t source);
+extern void fib_entry_src_inherit (const fib_entry_t *cover,
+                                   fib_entry_t *covered);
 
 extern fib_forward_chain_type_t fib_entry_get_default_chain_type(
     const fib_entry_t *fib_entry);
 extern fib_entry_flag_t fib_entry_get_flags_i(const fib_entry_t *fib_entry);
+
 extern fib_path_list_flags_t fib_entry_src_flags_2_path_list_flags(
     fib_entry_flag_t eflags);
 
@@ -280,6 +294,10 @@ extern void fib_entry_src_mk_lb (fib_entry_t *fib_entry,
 extern fib_protocol_t fib_entry_get_proto(const fib_entry_t * fib_entry);
 extern dpo_proto_t fib_entry_get_dpo_proto(const fib_entry_t * fib_entry);
 
+extern void fib_entry_source_change(fib_entry_t *fib_entry,
+                                    fib_source_t old_source,
+                                    fib_source_t new_source);
+
 /*
  * Per-source registration. declared here so we save a separate .h file for each
  */
diff --git a/src/vnet/fib/fib_entry_src_adj.c b/src/vnet/fib/fib_entry_src_adj.c
index 9ea2b17e6b9..04c5c8dc1f7 100644
--- a/src/vnet/fib/fib_entry_src_adj.c
+++ b/src/vnet/fib/fib_entry_src_adj.c
@@ -201,10 +201,6 @@ fib_entry_src_adj_path_list_walk (fib_node_index_t pl_index,
     return (FIB_PATH_LIST_WALK_CONTINUE);
 }
 
-/*
- * Source activate.
- * Called when the source is the new longer best source on the entry
- */
 static int
 fib_entry_src_adj_activate (fib_entry_src_t *src,
                             const fib_entry_t *fib_entry)
@@ -262,6 +258,28 @@ fib_entry_src_adj_activate (fib_entry_src_t *src,
 }
 
 /*
+ * Source re-activate.
+ * Called when the source path lit has changed and the source is still
+ * the best source
+ */
+static int
+fib_entry_src_adj_reactivate (fib_entry_src_t *src,
+                              const fib_entry_t *fib_entry)
+{
+    fib_entry_src_path_list_walk_cxt_t ctx = {
+        .cover_itf = fib_entry_get_resolving_interface(src->adj.fesa_cover),
+        .flags = FIB_PATH_EXT_ADJ_FLAG_NONE,
+        .src = src,
+    };
+
+    fib_path_list_walk(src->fes_pl,
+                       fib_entry_src_adj_path_list_walk,
+                       &ctx);
+
+    return (FIB_PATH_EXT_ADJ_FLAG_REFINES_COVER & ctx.flags);
+}
+
+/*
  * Source Deactivate.
  * Called when the source is no longer best source on the entry
  */
@@ -291,7 +309,7 @@ static u8*
 fib_entry_src_adj_format (fib_entry_src_t *src,
                          u8* s)
 {
-    return (format(s, "cover:%d", src->adj.fesa_cover));
+    return (format(s, " cover:%d", src->adj.fesa_cover));
 }
 
 static void
@@ -368,6 +386,7 @@ const static fib_entry_src_vft_t adj_src_vft = {
     .fesv_remove = fib_entry_src_adj_remove,
     .fesv_activate = fib_entry_src_adj_activate,
     .fesv_deactivate = fib_entry_src_adj_deactivate,
+    .fesv_reactivate = fib_entry_src_adj_reactivate,
     .fesv_format = fib_entry_src_adj_format,
     .fesv_installed = fib_entry_src_adj_installed,
     .fesv_cover_change = fib_entry_src_adj_cover_change,
diff --git a/src/vnet/fib/fib_entry_src_default.c b/src/vnet/fib/fib_entry_src_default.c
index 9846cf56e64..18a039afbd6 100644
--- a/src/vnet/fib/fib_entry_src_default.c
+++ b/src/vnet/fib/fib_entry_src_default.c
@@ -95,7 +95,7 @@ fib_entry_src_default_add (fib_entry_src_t *src,
 }
 
 static void
-fib_entry_src_default_remove (fib_entry_src_t *src)			     
+fib_entry_src_default_remove (fib_entry_src_t *src)
 {
 }
 
diff --git a/src/vnet/fib/fib_entry_src_interface.c b/src/vnet/fib/fib_entry_src_interface.c
index 6c087f34552..f79be72c45a 100644
--- a/src/vnet/fib/fib_entry_src_interface.c
+++ b/src/vnet/fib/fib_entry_src_interface.c
@@ -190,7 +190,7 @@ static u8*
 fib_entry_src_interface_format (fib_entry_src_t *src,
 				u8* s)
 {
-    return (format(s, "cover:%d", src->interface.fesi_cover));
+    return (format(s, " cover:%d", src->interface.fesi_cover));
 }
 
 const static fib_entry_src_vft_t interface_src_vft = {
diff --git a/src/vnet/fib/fib_entry_src_rr.c b/src/vnet/fib/fib_entry_src_rr.c
index 1153f3f1da4..b6f4bc3ba45 100644
--- a/src/vnet/fib/fib_entry_src_rr.c
+++ b/src/vnet/fib/fib_entry_src_rr.c
@@ -280,7 +280,7 @@ static u8*
 fib_entry_src_rr_format (fib_entry_src_t *src,
 			 u8* s)
 {
-    return (format(s, "cover:%d", src->rr.fesr_cover));
+    return (format(s, " cover:%d", src->rr.fesr_cover));
 }
 
 const static fib_entry_src_vft_t rr_src_vft = {
diff --git a/src/vnet/fib/fib_table.c b/src/vnet/fib/fib_table.c
index 80e5a0fe1a0..c20bb255ddf 100644
--- a/src/vnet/fib/fib_table.c
+++ b/src/vnet/fib/fib_table.c
@@ -181,8 +181,7 @@ fib_table_post_insert_actions (fib_table_t *fib_table,
 	return;
 
     /*
-     * find and inform the covering entry that a new more specific
-     * has been inserted beneath it
+     * find  the covering entry
      */
     fib_entry_cover_index = fib_table_get_less_specific_i(fib_table, prefix);
     /*
@@ -190,6 +189,16 @@ fib_table_post_insert_actions (fib_table_t *fib_table,
      */
     if (fib_entry_cover_index != fib_entry_index)
     {
+        /*
+         * push any inherting sources from the cover onto the covered
+         */
+        fib_entry_inherit(fib_entry_cover_index,
+                          fib_entry_index);
+
+        /*
+         * inform the covering entry that a new more specific
+         * has been inserted beneath it
+         */
 	fib_entry_cover_change_notify(fib_entry_cover_index,
 				      fib_entry_index);
     }
@@ -982,7 +991,7 @@ typedef struct fib_table_set_flow_hash_config_ctx_t_
     flow_hash_config_t hash_config;
 } fib_table_set_flow_hash_config_ctx_t;
 
-static int
+static fib_table_walk_rc_t
 fib_table_set_flow_hash_config_cb (fib_node_index_t fib_entry_index,
                                    void *arg)
 {
@@ -990,7 +999,7 @@ fib_table_set_flow_hash_config_cb (fib_node_index_t fib_entry_index,
 
     fib_entry_set_flow_hash_config(fib_entry_index, ctx->hash_config);
 
-    return (1);
+    return (FIB_TABLE_WALK_CONTINUE);
 }
 
 void
@@ -1177,6 +1186,26 @@ fib_table_walk (u32 fib_index,
 }
 
 void
+fib_table_sub_tree_walk (u32 fib_index,
+                         fib_protocol_t proto,
+                         const fib_prefix_t *root,
+                         fib_table_walk_fn_t fn,
+                         void *ctx)
+{
+    switch (proto)
+    {
+    case FIB_PROTOCOL_IP4:
+	ip4_fib_table_sub_tree_walk(ip4_fib_get(fib_index), root, fn, ctx);
+	break;
+    case FIB_PROTOCOL_IP6:
+	ip6_fib_table_sub_tree_walk(fib_index, root, fn, ctx);
+	break;
+    case FIB_PROTOCOL_MPLS:
+	break;
+    }
+}
+
+void
 fib_table_unlock (u32 fib_index,
 		  fib_protocol_t proto,
                   fib_source_t source)
@@ -1260,7 +1289,7 @@ typedef struct fib_table_flush_ctx_t_
     fib_source_t ftf_source;
 } fib_table_flush_ctx_t;
 
-static int
+static fib_table_walk_rc_t
 fib_table_flush_cb (fib_node_index_t fib_entry_index,
                     void *arg)
 {
@@ -1270,7 +1299,7 @@ fib_table_flush_cb (fib_node_index_t fib_entry_index,
     {
         vec_add1(ctx->ftf_entries, fib_entry_index);
     }
-    return (1);
+    return (FIB_TABLE_WALK_CONTINUE);
 }
 
 
diff --git a/src/vnet/fib/fib_table.h b/src/vnet/fib/fib_table.h
index 8a0c73968fb..14ac7054059 100644
--- a/src/vnet/fib/fib_table.h
+++ b/src/vnet/fib/fib_table.h
@@ -793,10 +793,29 @@ extern fib_table_t *fib_table_get(fib_node_index_t index,
 				  fib_protocol_t proto);
 
 /**
+ * @brief return code controlling how a table walk proceeds
+ */
+typedef enum fib_table_walk_rc_t_
+{
+    /**
+     * Continue on to the next entry
+     */
+    FIB_TABLE_WALK_CONTINUE,
+    /**
+     * Do no traverse down this sub-tree
+     */
+    FIB_TABLE_WALK_SUB_TREE_STOP,
+    /**
+     * Stop the walk completely
+     */
+    FIB_TABLE_WALK_STOP,
+} fib_table_walk_rc_t;
+
+/**
  * @brief Call back function when walking entries in a FIB table
  */
-typedef int (*fib_table_walk_fn_t)(fib_node_index_t fei,
-                                   void *ctx);
+typedef fib_table_walk_rc_t (*fib_table_walk_fn_t)(fib_node_index_t fei,
+                                                   void *ctx);
 
 /**
  * @brief Walk all entries in a FIB table
@@ -809,6 +828,18 @@ extern void fib_table_walk(u32 fib_index,
                            void *ctx);
 
 /**
+ * @brief Walk all entries in a sub-tree FIB table. The 'root' paraneter
+ * is the prefix at the root of the sub-tree.
+ * N.B: This is NOT safe to deletes. If you need to delete walk the whole
+ * table and store elements in a vector, then delete the elements
+ */
+extern void fib_table_sub_tree_walk(u32 fib_index,
+                                    fib_protocol_t proto,
+                                    const fib_prefix_t *root,
+                                    fib_table_walk_fn_t fn,
+                                    void *ctx);
+
+/**
  * @brief format (display) the memory used by the FIB tables
  */
 extern u8 *format_fib_table_memory(u8 *s, va_list *args);
diff --git a/src/vnet/fib/fib_test.c b/src/vnet/fib/fib_test.c
index 9a8febb1396..61b290b8b8f 100644
--- a/src/vnet/fib/fib_test.c
+++ b/src/vnet/fib/fib_test.c
@@ -661,7 +661,8 @@ fib_test_validate_entry (fib_node_index_t fei,
         const load_balance_t *lb;
 
         FIB_TEST_LB((DPO_LOAD_BALANCE == dpo.dpoi_type),
-                    "Entry links to %U",
+                    "%U Entry links to %U",
+                    format_fib_prefix, &pfx,
                     format_dpo_type, dpo.dpoi_type);
 
         lb = load_balance_get(dpo.dpoi_index);
@@ -698,7 +699,7 @@ fib_test_validate_entry (fib_node_index_t fei,
                 fw_lbi = 0;
             }
             FIB_TEST_LB((fw_lbi == dpo.dpoi_index),
-                        "Contributed LB = FW LB: %U\n %U",
+                        "Contributed LB = FW LB:\n fwd:%U\n cont:%U",
                         format_load_balance, fw_lbi, 0,
                         format_load_balance, dpo.dpoi_index, 0);
         }
@@ -8781,6 +8782,796 @@ lfib_test (void)
     return (0);
 }
 
+static int
+fib_test_inherit (void)
+{
+    fib_node_index_t fei;
+    test_main_t *tm;
+    int n_feis;
+
+    n_feis = fib_entry_pool_size();
+    tm = &test_main;
+
+    const ip46_address_t nh_10_10_10_1 = {
+	.ip4.as_u32 = clib_host_to_net_u32(0x0a0a0a01),
+    };
+    const ip46_address_t nh_10_10_10_2 = {
+	.ip4.as_u32 = clib_host_to_net_u32(0x0a0a0a02),
+    };
+    const ip46_address_t nh_10_10_10_16 = {
+	.ip4.as_u32 = clib_host_to_net_u32(0x0a0a0a10),
+    };
+    const ip46_address_t nh_10_10_10_20 = {
+	.ip4.as_u32 = clib_host_to_net_u32(0x0a0a0a14),
+    };
+    const ip46_address_t nh_10_10_10_21 = {
+	.ip4.as_u32 = clib_host_to_net_u32(0x0a0a0a15),
+    };
+    const ip46_address_t nh_10_10_10_22 = {
+	.ip4.as_u32 = clib_host_to_net_u32(0x0a0a0a16),
+    };
+    const ip46_address_t nh_10_10_10_255 = {
+	.ip4.as_u32 = clib_host_to_net_u32(0x0a0a0aff),
+    };
+    const ip46_address_t nh_10_10_10_0 = {
+	.ip4.as_u32 = clib_host_to_net_u32(0x0a0a0a00),
+    };
+    const ip46_address_t nh_10_10_0_0 = {
+	.ip4.as_u32 = clib_host_to_net_u32(0x0a0a0000),
+    };
+
+    /*
+     * prefixes at the base of a sub-tree
+     */
+    const fib_prefix_t pfx_10_10_10_21_s_32 = {
+        .fp_len = 32,
+        .fp_proto = FIB_PROTOCOL_IP4,
+        .fp_addr = nh_10_10_10_21,
+    };
+    const fib_prefix_t pfx_10_10_10_22_s_32 = {
+        .fp_len = 32,
+        .fp_proto = FIB_PROTOCOL_IP4,
+        .fp_addr = nh_10_10_10_22,
+    };
+    const fib_prefix_t pfx_10_10_10_255_s_32 = {
+        .fp_len = 32,
+        .fp_proto = FIB_PROTOCOL_IP4,
+        .fp_addr = nh_10_10_10_255,
+    };
+
+    fib_table_entry_special_add(0,
+				&pfx_10_10_10_21_s_32,
+				FIB_SOURCE_CLI,
+				FIB_ENTRY_FLAG_DROP);
+    fib_table_entry_special_add(0,
+				&pfx_10_10_10_22_s_32,
+				FIB_SOURCE_CLI,
+				FIB_ENTRY_FLAG_DROP);
+    fib_table_entry_special_add(0,
+				&pfx_10_10_10_255_s_32,
+				FIB_SOURCE_CLI,
+				FIB_ENTRY_FLAG_DROP);
+
+    /*
+     * source an entry that pushes its state down the sub-tree
+     */
+    const fib_prefix_t pfx_10_10_10_16_s_28 = {
+        .fp_len = 28,
+        .fp_proto = FIB_PROTOCOL_IP4,
+        .fp_addr = nh_10_10_10_16,
+    };
+    fib_table_entry_update_one_path(0,
+                                    &pfx_10_10_10_16_s_28,
+				    FIB_SOURCE_API,
+				    FIB_ENTRY_FLAG_COVERED_INHERIT,
+				    DPO_PROTO_IP4,
+                                    &nh_10_10_10_1,
+				    tm->hw[0]->sw_if_index,
+				    ~0,
+				    1,
+				    NULL,
+				    FIB_ROUTE_PATH_FLAG_NONE);
+
+    /*
+     * this covering entry and all those below it should have
+     * the same forwarding information.
+     */
+    adj_index_t ai_10_10_10_1 = adj_nbr_add_or_lock(FIB_PROTOCOL_IP4,
+                                                    VNET_LINK_IP4,
+                                                    &nh_10_10_10_1,
+                                                    tm->hw[0]->sw_if_index);
+    fib_test_lb_bucket_t adj_o_10_10_10_1 = {
+	.type = FT_LB_ADJ,
+	.adj = {
+	    .adj = ai_10_10_10_1,
+	},
+    };
+
+    fei = fib_table_lookup(0, &pfx_10_10_10_16_s_28);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_16_s_28);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_21_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_21_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_22_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_22_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_255_s_32);
+    FIB_TEST(load_balance_is_drop(fib_entry_contribute_ip_forwarding(fei)),
+             "%U resolves via drop",
+             format_fib_prefix, &pfx_10_10_10_255_s_32);
+
+    /*
+     * remove the inherting cover - covereds go back to drop
+     */
+    fib_table_entry_delete(0, &pfx_10_10_10_16_s_28, FIB_SOURCE_API);
+
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_21_s_32);
+    FIB_TEST(load_balance_is_drop(fib_entry_contribute_ip_forwarding(fei)),
+             "%U resolves via drop",
+             format_fib_prefix, &pfx_10_10_10_21_s_32);
+
+    /*
+     * source an entry that pushes its state down the sub-tree
+     */
+    const fib_prefix_t pfx_10_10_10_0_s_24 = {
+        .fp_len = 24,
+        .fp_proto = FIB_PROTOCOL_IP4,
+        .fp_addr = nh_10_10_10_0,
+    };
+    fib_table_entry_update_one_path(0,
+                                    &pfx_10_10_10_0_s_24,
+				    FIB_SOURCE_API,
+				    FIB_ENTRY_FLAG_COVERED_INHERIT,
+				    DPO_PROTO_IP4,
+                                    &nh_10_10_10_1,
+				    tm->hw[0]->sw_if_index,
+				    ~0,
+				    1,
+				    NULL,
+				    FIB_ROUTE_PATH_FLAG_NONE);
+
+    /*
+     * whole sub-tree now covered
+     */
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_0_s_24);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_0_s_24);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_21_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_21_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_22_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_22_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_255_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_255_s_32);
+
+    /*
+     * insert a more specific into the sub-tree - expect inheritance
+     *  this one is directly covered by the root
+     */
+    fib_table_entry_special_add(0,
+				&pfx_10_10_10_16_s_28,
+				FIB_SOURCE_CLI,
+				FIB_ENTRY_FLAG_DROP);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_16_s_28);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_16_s_28);
+
+    /*
+     * insert a more specific into the sub-tree - expect inheritance
+     *  this one is indirectly covered by the root
+     */
+    const fib_prefix_t pfx_10_10_10_20_s_30 = {
+        .fp_len = 30,
+        .fp_proto = FIB_PROTOCOL_IP4,
+        .fp_addr = nh_10_10_10_20,
+    };
+    fib_table_entry_special_add(0,
+				&pfx_10_10_10_20_s_30,
+				FIB_SOURCE_CLI,
+				FIB_ENTRY_FLAG_DROP);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_20_s_30);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_20_s_30);
+
+    /*
+     * remove the prefix from the middle of the sub-tree
+     *  the inherited source will be the only one remaining - expect
+     *  it to be withdrawn and hence the prefix is removed.
+     */
+    fib_table_entry_special_remove(0,
+                                   &pfx_10_10_10_20_s_30,
+                                   FIB_SOURCE_CLI);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_20_s_30);
+    FIB_TEST((FIB_NODE_INDEX_INVALID == fei),
+             "%U gone",
+             format_fib_prefix, &pfx_10_10_10_20_s_30);
+
+    /*
+     * inheriting source is modifed - expect the modification to be present
+     *  throughout the sub-tree
+     */
+    adj_index_t ai_10_10_10_2 = adj_nbr_add_or_lock(FIB_PROTOCOL_IP4,
+                                                    VNET_LINK_IP4,
+                                                    &nh_10_10_10_2,
+                                                    tm->hw[0]->sw_if_index);
+    fib_test_lb_bucket_t adj_o_10_10_10_2 = {
+	.type = FT_LB_ADJ,
+	.adj = {
+	    .adj = ai_10_10_10_2,
+	},
+    };
+
+    fib_table_entry_update_one_path(0,
+                                    &pfx_10_10_10_0_s_24,
+				    FIB_SOURCE_API,
+				    FIB_ENTRY_FLAG_COVERED_INHERIT,
+				    DPO_PROTO_IP4,
+                                    &nh_10_10_10_2,
+				    tm->hw[0]->sw_if_index,
+				    ~0,
+				    1,
+				    NULL,
+				    FIB_ROUTE_PATH_FLAG_NONE);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_21_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_21_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_22_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_22_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_255_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_255_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_0_s_24);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_0_s_24);
+
+    /*
+     * add the source that replaces inherited state.
+     * inheriting source is not the best, so it doesn't push state.
+     */
+    fib_table_entry_update_one_path(0,
+                                    &pfx_10_10_10_0_s_24,
+				    FIB_SOURCE_PLUGIN_HI,
+				    FIB_ENTRY_FLAG_NONE,
+				    DPO_PROTO_IP4,
+                                    &nh_10_10_10_1,
+				    tm->hw[0]->sw_if_index,
+				    ~0,
+				    1,
+				    NULL,
+				    FIB_ROUTE_PATH_FLAG_NONE);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_0_s_24);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_0_s_24);
+
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_21_s_32);
+    FIB_TEST(load_balance_is_drop(fib_entry_contribute_ip_forwarding(fei)),
+             "%U resolves via drop",
+             format_fib_prefix, &pfx_10_10_10_21_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_22_s_32);
+    FIB_TEST(load_balance_is_drop(fib_entry_contribute_ip_forwarding(fei)),
+             "%U resolves via drop",
+             format_fib_prefix, &pfx_10_10_10_22_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_255_s_32);
+    FIB_TEST(load_balance_is_drop(fib_entry_contribute_ip_forwarding(fei)),
+             "%U resolves via drop",
+             format_fib_prefix, &pfx_10_10_10_255_s_32);
+        fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_16_s_28);
+    FIB_TEST(load_balance_is_drop(fib_entry_contribute_ip_forwarding(fei)),
+             "%U resolves via drop",
+             format_fib_prefix, &pfx_10_10_10_16_s_28);
+
+    /*
+     * withdraw the higher priority source and expect the inherited to return
+     * throughout the sub-tree
+     */
+    fib_table_entry_delete(0, &pfx_10_10_10_0_s_24, FIB_SOURCE_PLUGIN_HI);
+
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_21_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_21_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_22_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_22_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_255_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_255_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_0_s_24);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_0_s_24);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_16_s_28);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_16_s_28);
+
+    /*
+     * source a covered entry in the sub-tree with the same inherting source
+     *  - expect that it now owns the sub-tree and thus over-rides its cover
+     */
+    fib_table_entry_update_one_path(0,
+                                    &pfx_10_10_10_16_s_28,
+				    FIB_SOURCE_API,
+				    FIB_ENTRY_FLAG_COVERED_INHERIT,
+				    DPO_PROTO_IP4,
+                                    &nh_10_10_10_1,
+				    tm->hw[0]->sw_if_index,
+				    ~0,
+				    1,
+				    NULL,
+				    FIB_ROUTE_PATH_FLAG_NONE);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_16_s_28);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_16_s_28);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_22_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_22_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_21_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_21_s_32);
+
+    /* these two unaffected by the sub-tree change */
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_255_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_255_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_0_s_24);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_0_s_24);
+
+    /*
+     * removes the more specific, expect the /24 to now re-owns the sub-tree
+     */
+    fib_table_entry_delete(0, &pfx_10_10_10_16_s_28, FIB_SOURCE_API);
+
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_21_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_16_s_28);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_21_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_22_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_22_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_255_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_255_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_0_s_24);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_10_0_s_24);
+    /*
+     * modify the /24. expect the new forwarding to be pushed down
+     */
+    fib_table_entry_update_one_path(0,
+                                    &pfx_10_10_10_0_s_24,
+				    FIB_SOURCE_API,
+				    FIB_ENTRY_FLAG_COVERED_INHERIT,
+				    DPO_PROTO_IP4,
+                                    &nh_10_10_10_1,
+				    tm->hw[0]->sw_if_index,
+				    ~0,
+				    1,
+				    NULL,
+				    FIB_ROUTE_PATH_FLAG_NONE);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_21_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_16_s_28);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_21_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_22_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_22_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_255_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_255_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_0_s_24);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_0_s_24);
+
+    /*
+     * add an entry less specific to /24. it should not own the /24's tree
+     */
+    const fib_prefix_t pfx_10_10_0_0_s_16 = {
+        .fp_len = 16,
+        .fp_proto = FIB_PROTOCOL_IP4,
+        .fp_addr = nh_10_10_0_0,
+    };
+    fib_table_entry_update_one_path(0,
+                                    &pfx_10_10_0_0_s_16,
+				    FIB_SOURCE_API,
+				    FIB_ENTRY_FLAG_COVERED_INHERIT,
+				    DPO_PROTO_IP4,
+                                    &nh_10_10_10_2,
+				    tm->hw[0]->sw_if_index,
+				    ~0,
+				    1,
+				    NULL,
+				    FIB_ROUTE_PATH_FLAG_NONE);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_21_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_16_s_28);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_21_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_22_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_22_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_255_s_32);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_255_s_32);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_10_0_s_24);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_1),
+	     "%U via 10.10.10.1",
+             format_fib_prefix, &pfx_10_10_10_0_s_24);
+    fei = fib_table_lookup_exact_match(0, &pfx_10_10_0_0_s_16);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP4,
+				     1,
+				     &adj_o_10_10_10_2),
+	     "%U via 10.10.10.2",
+             format_fib_prefix, &pfx_10_10_0_0_s_16);
+
+    /*
+     * cleanup
+     */
+    fib_table_entry_delete(0, &pfx_10_10_10_21_s_32, FIB_SOURCE_CLI);
+    fib_table_entry_delete(0, &pfx_10_10_10_22_s_32, FIB_SOURCE_CLI);
+    fib_table_entry_delete(0, &pfx_10_10_10_16_s_28, FIB_SOURCE_CLI);
+    fib_table_entry_delete(0, &pfx_10_10_10_255_s_32, FIB_SOURCE_CLI);
+    fib_table_entry_delete(0, &pfx_10_10_10_0_s_24, FIB_SOURCE_API);
+    fib_table_entry_delete(0, &pfx_10_10_0_0_s_16, FIB_SOURCE_API);
+    adj_unlock(ai_10_10_10_1);
+    adj_unlock(ai_10_10_10_2);
+
+    /*
+     * test the v6 tree walk.
+     * a /64 that covers everytinhg. a /96 that covers one /128
+     * a second /128 covered only by the /64.
+     */
+    const fib_prefix_t pfx_2001_s_64 = {
+        .fp_len = 64,
+        .fp_proto = FIB_PROTOCOL_IP6,
+        .fp_addr = {
+            .ip6 = {
+		.as_u64 = {
+		    [0] = clib_host_to_net_u64(0x2001000000000000),
+		    [1] = clib_host_to_net_u64(0x0000000000000000),
+		},
+            },
+        },
+    };
+    const fib_prefix_t pfx_2001_1_s_96 = {
+        .fp_len = 96,
+        .fp_proto = FIB_PROTOCOL_IP6,
+        .fp_addr = {
+            .ip6 = {
+		.as_u64 = {
+		    [0] = clib_host_to_net_u64(0x2001000000000000),
+		    [1] = clib_host_to_net_u64(0x1000000000000000),
+		},
+            },
+        },
+    };
+    const fib_prefix_t pfx_2001_1_1_s_128 = {
+        .fp_len = 128,
+        .fp_proto = FIB_PROTOCOL_IP6,
+        .fp_addr = {
+            .ip6 = {
+		.as_u64 = {
+		    [0] = clib_host_to_net_u64(0x2001000000000000),
+		    [1] = clib_host_to_net_u64(0x1000000000000001),
+		},
+            },
+        },
+    };
+    const fib_prefix_t pfx_2001_0_1_s_128 = {
+        .fp_len = 128,
+        .fp_proto = FIB_PROTOCOL_IP6,
+        .fp_addr = {
+            .ip6 = {
+		.as_u64 = {
+		    [0] = clib_host_to_net_u64(0x2001000000000000),
+		    [1] = clib_host_to_net_u64(0x0000000000000001),
+		},
+            },
+        },
+    };
+    const ip46_address_t nh_3000_1 = {
+        .ip6 = {
+            .as_u64 = {
+                [0] = clib_host_to_net_u64(0x3000000000000000),
+                [1] = clib_host_to_net_u64(0x0000000000000001),
+            },
+        },
+    };
+    const ip46_address_t nh_3000_2 = {
+        .ip6 = {
+            .as_u64 = {
+                [0] = clib_host_to_net_u64(0x3000000000000000),
+                [1] = clib_host_to_net_u64(0x0000000000000002),
+            },
+        },
+    };
+    adj_index_t ai_3000_1 = adj_nbr_add_or_lock(FIB_PROTOCOL_IP6,
+                                                VNET_LINK_IP6,
+                                                &nh_3000_1,
+                                                tm->hw[0]->sw_if_index);
+    adj_index_t ai_3000_2 = adj_nbr_add_or_lock(FIB_PROTOCOL_IP6,
+                                                VNET_LINK_IP6,
+                                                &nh_3000_2,
+                                                tm->hw[0]->sw_if_index);
+    fib_test_lb_bucket_t adj_o_3000_1 = {
+	.type = FT_LB_ADJ,
+	.adj = {
+	    .adj = ai_3000_1,
+	},
+    };
+    fib_test_lb_bucket_t adj_o_3000_2 = {
+	.type = FT_LB_ADJ,
+	.adj = {
+	    .adj = ai_3000_2,
+	},
+    };
+
+    fib_table_entry_special_add(0,
+				&pfx_2001_0_1_s_128,
+				FIB_SOURCE_CLI,
+				FIB_ENTRY_FLAG_DROP);
+    fib_table_entry_special_add(0,
+				&pfx_2001_1_1_s_128,
+				FIB_SOURCE_CLI,
+				FIB_ENTRY_FLAG_DROP);
+
+    /*
+     * /96 has inherited forwarding pushed down to its covered /128
+     */
+    fib_table_entry_update_one_path(0,
+                                    &pfx_2001_1_s_96,
+				    FIB_SOURCE_API,
+				    FIB_ENTRY_FLAG_COVERED_INHERIT,
+				    DPO_PROTO_IP6,
+                                    &nh_3000_1,
+				    tm->hw[0]->sw_if_index,
+				    ~0,
+				    1,
+				    NULL,
+				    FIB_ROUTE_PATH_FLAG_NONE);
+    fei = fib_table_lookup_exact_match(0, &pfx_2001_1_s_96);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP6,
+				     1,
+				     &adj_o_3000_1),
+	     "%U via 3000::1",
+             format_fib_prefix, &pfx_2001_1_s_96);
+    fei = fib_table_lookup_exact_match(0, &pfx_2001_1_1_s_128);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP6,
+				     1,
+				     &adj_o_3000_1),
+	     "%U via 3000::1",
+             format_fib_prefix, &pfx_2001_1_1_s_128);
+    fei = fib_table_lookup_exact_match(0, &pfx_2001_0_1_s_128);
+    FIB_TEST(load_balance_is_drop(fib_entry_contribute_ip_forwarding(fei)),
+             "%U resolves via drop",
+             format_fib_prefix, &pfx_2001_0_1_s_128);
+
+    /*
+     * /64 has inherited forwarding pushed down to all, but the /96
+     * and its sub-tree remain unaffected.
+     */
+    fib_table_entry_update_one_path(0,
+                                    &pfx_2001_s_64,
+				    FIB_SOURCE_API,
+				    FIB_ENTRY_FLAG_COVERED_INHERIT,
+				    DPO_PROTO_IP6,
+                                    &nh_3000_2,
+				    tm->hw[0]->sw_if_index,
+				    ~0,
+				    1,
+				    NULL,
+				    FIB_ROUTE_PATH_FLAG_NONE);
+
+    fei = fib_table_lookup_exact_match(0, &pfx_2001_s_64);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP6,
+				     1,
+				     &adj_o_3000_2),
+	     "%U via 3000::2",
+             format_fib_prefix, &pfx_2001_s_64);
+    fei = fib_table_lookup_exact_match(0, &pfx_2001_0_1_s_128);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP6,
+				     1,
+				     &adj_o_3000_2),
+	     "%U via 3000::1",
+             format_fib_prefix, &pfx_2001_0_1_s_128);
+
+    fei = fib_table_lookup_exact_match(0, &pfx_2001_1_s_96);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP6,
+				     1,
+				     &adj_o_3000_1),
+	     "%U via 3000::1",
+             format_fib_prefix, &pfx_2001_1_s_96);
+    fei = fib_table_lookup_exact_match(0, &pfx_2001_1_1_s_128);
+    FIB_TEST(fib_test_validate_entry(fei,
+				     FIB_FORW_CHAIN_TYPE_UNICAST_IP6,
+				     1,
+				     &adj_o_3000_1),
+	     "%U via 3000::1",
+             format_fib_prefix, &pfx_2001_1_1_s_128);
+
+    /*
+     * Cleanup
+     */
+    fib_table_entry_delete(0, &pfx_2001_0_1_s_128, FIB_SOURCE_CLI);
+    fib_table_entry_delete(0, &pfx_2001_1_1_s_128, FIB_SOURCE_CLI);
+    fib_table_entry_delete(0, &pfx_2001_s_64,      FIB_SOURCE_API);
+    fib_table_entry_delete(0, &pfx_2001_1_s_96,    FIB_SOURCE_API);
+    adj_unlock(ai_3000_1);
+    adj_unlock(ai_3000_2);
+
+    /*
+     * test no-one left behind
+     */
+    FIB_TEST((n_feis == fib_entry_pool_size()), "Entries gone");
+    FIB_TEST(0 == adj_nbr_db_size(), "All adjacencies removed");
+    return (0);
+}
+
 static clib_error_t *
 fib_test (vlib_main_t * vm, 
 	  unformat_input_t * input,
@@ -8825,6 +9616,10 @@ fib_test (vlib_main_t * vm,
     {
 	res += fib_test_bfd();
     }
+    else if (unformat (input, "inherit"))
+    {
+	res += fib_test_inherit();
+    }
     else
     {
 	res += fib_test_v4();
@@ -8833,6 +9628,7 @@ fib_test (vlib_main_t * vm,
 	res += fib_test_bfd();
 	res += fib_test_pref();
 	res += fib_test_label();
+        res += fib_test_inherit();
 	res += lfib_test();
 
         /*
diff --git a/src/vnet/fib/ip4_fib.c b/src/vnet/fib/ip4_fib.c
index 0f2d3f7ad89..ef3324645c3 100644
--- a/src/vnet/fib/ip4_fib.c
+++ b/src/vnet/fib/ip4_fib.c
@@ -417,22 +417,95 @@ ip4_fib_table_walk (ip4_fib_t *fib,
                     fib_table_walk_fn_t fn,
                     void *ctx)
 {
+    fib_prefix_t root = {
+        .fp_proto = FIB_PROTOCOL_IP4,
+        // address and length default to all 0
+    };
+
+    /*
+     * A full tree walk is the dengenerate case of a sub-tree from
+     * the very root
+     */
+    return (ip4_fib_table_sub_tree_walk(fib, &root, fn, ctx));
+}
+
+void
+ip4_fib_table_sub_tree_walk (ip4_fib_t *fib,
+                             const fib_prefix_t *root,
+                             fib_table_walk_fn_t fn,
+                             void *ctx)
+{
+    fib_prefix_t *sub_trees = NULL;
     int i;
 
-    for (i = 0; i < ARRAY_LEN (fib->fib_entry_by_dst_address); i++)
+    /*
+     * There is no efficent way to walk this array of hash tables.
+     * so we walk each table with a mask length greater than and equal to
+     * the required root and check it is covered by the root.
+     */
+    for (i = root->fp_len;
+         i < ARRAY_LEN (fib->fib_entry_by_dst_address);
+         i++)
     {
 	uword * hash = fib->fib_entry_by_dst_address[i];
 
 	if (NULL != hash)
 	{
+            ip4_address_t key;
 	    hash_pair_t * p;
 
 	    hash_foreach_pair (p, hash,
 	    ({
-		fn(p->value[0], ctx);
+                key.as_u32 = p->key;
+                if (ip4_destination_matches_route(&ip4_main,
+                                                  &key,
+                                                  &root->fp_addr.ip4,
+                                                  root->fp_len))
+                {
+                    const fib_prefix_t *sub_tree;
+                    int skip = 0;
+
+                    /*
+                     * exclude sub-trees the walk does not want to explore
+                     */
+                    vec_foreach(sub_tree, sub_trees)
+                    {
+                        if (ip4_destination_matches_route(&ip4_main,
+                                                          &key,
+                                                          &sub_tree->fp_addr.ip4,
+                                                          sub_tree->fp_len))
+                        {
+                            skip = 1;
+                            break;
+                        }
+                    }
+
+                    if (!skip)
+                    {
+                        switch (fn(p->value[0], ctx))
+                        {
+                        case FIB_TABLE_WALK_CONTINUE:
+                            break;
+                        case FIB_TABLE_WALK_SUB_TREE_STOP: {
+                            fib_prefix_t pfx = {
+                                .fp_proto = FIB_PROTOCOL_IP4,
+                                .fp_len = i,
+                                .fp_addr.ip4 = key,
+                            };
+                            vec_add1(sub_trees, pfx);
+                            break;
+                        }
+                        case FIB_TABLE_WALK_STOP:
+                            goto done;
+                        }
+                    }
+                }
 	    }));
 	}
     }
+done:
+    vec_free(sub_trees);
+    return;
 }
 
 /**
@@ -443,7 +516,7 @@ typedef struct ip4_fib_show_walk_ctx_t_
     fib_node_index_t *ifsw_indicies;
 } ip4_fib_show_walk_ctx_t;
 
-static int
+static fib_table_walk_rc_t
 ip4_fib_show_walk_cb (fib_node_index_t fib_entry_index,
                       void *arg)
 {
@@ -451,7 +524,7 @@ ip4_fib_show_walk_cb (fib_node_index_t fib_entry_index,
 
     vec_add1(ctx->ifsw_indicies, fib_entry_index);
 
-    return (1);
+    return (FIB_TABLE_WALK_CONTINUE);
 }
 
 static void
diff --git a/src/vnet/fib/ip4_fib.h b/src/vnet/fib/ip4_fib.h
index 438eb2405bf..84800eb2397 100644
--- a/src/vnet/fib/ip4_fib.h
+++ b/src/vnet/fib/ip4_fib.h
@@ -99,6 +99,16 @@ extern void ip4_fib_table_walk(ip4_fib_t *fib,
                                void *ctx);
 
 /**
+ * @brief Walk all entries in a sub-tree of the FIB table
+ * N.B: This is NOT safe to deletes. If you need to delete walk the whole
+ * table and store elements in a vector, then delete the elements
+ */
+extern void ip4_fib_table_sub_tree_walk(ip4_fib_t *fib,
+                                        const fib_prefix_t *root,
+                                        fib_table_walk_fn_t fn,
+                                        void *ctx);
+
+/**
  * @brief Get the FIB at the given index
  */
 static inline ip4_fib_t *
diff --git a/src/vnet/fib/ip6_fib.c b/src/vnet/fib/ip6_fib.c
index 3400987018f..bb092cea1bf 100644
--- a/src/vnet/fib/ip6_fib.c
+++ b/src/vnet/fib/ip6_fib.c
@@ -437,6 +437,8 @@ typedef struct ip6_fib_walk_ctx_t_
     u32 i6w_fib_index;
     fib_table_walk_fn_t i6w_fn;
     void *i6w_ctx;
+    fib_prefix_t i6w_root;
+    fib_prefix_t *i6w_sub_trees;
 } ip6_fib_walk_ctx_t;
 
 static int
@@ -444,11 +446,58 @@ ip6_fib_walk_cb (clib_bihash_kv_24_8_t * kvp,
                  void *arg)
 {
     ip6_fib_walk_ctx_t *ctx = arg;
+    ip6_address_t key;
 
     if ((kvp->key[2] >> 32) == ctx->i6w_fib_index)
     {
-        ctx->i6w_fn(kvp->value, ctx->i6w_ctx);
+        key.as_u64[0] = kvp->key[0];
+        key.as_u64[1] = kvp->key[1];
+
+        if (ip6_destination_matches_route(&ip6_main,
+                                          &key,
+                                          &ctx->i6w_root.fp_addr.ip6,
+                                          ctx->i6w_root.fp_len))
+        {
+            const fib_prefix_t *sub_tree;
+            int skip = 0;
+
+            /*
+             * exclude sub-trees the walk does not want to explore
+             */
+            vec_foreach(sub_tree, ctx->i6w_sub_trees)
+            {
+                if (ip6_destination_matches_route(&ip6_main,
+                                                  &key,
+                                                  &sub_tree->fp_addr.ip6,
+                                                  sub_tree->fp_len))
+                {
+                    skip = 1;
+                    break;
+                }
+            }
+
+            if (!skip)
+            {
+                switch (ctx->i6w_fn(kvp->value, ctx->i6w_ctx))
+                {
+                case FIB_TABLE_WALK_CONTINUE:
+                    break;
+                case FIB_TABLE_WALK_SUB_TREE_STOP: {
+                    fib_prefix_t pfx = {
+                        .fp_proto = FIB_PROTOCOL_IP6,
+                        .fp_len = kvp->key[2] & 0xffffffff,
+                        .fp_addr.ip6 = key,
+                    };
+                    vec_add1(ctx->i6w_sub_trees, pfx);
+                    break;
+                }
+                case FIB_TABLE_WALK_STOP:
+                    goto done;
+                }
+            }
+        }
     }
+done:
 
     return (1);
 }
@@ -462,20 +511,44 @@ ip6_fib_table_walk (u32 fib_index,
         .i6w_fib_index = fib_index,
         .i6w_fn = fn,
         .i6w_ctx = arg,
+        .i6w_root = {
+            .fp_proto = FIB_PROTOCOL_IP6,
+        },
+        .i6w_sub_trees = NULL,
     };
-    ip6_main_t *im = &ip6_main;
 
-    BV(clib_bihash_foreach_key_value_pair)(&im->ip6_table[IP6_FIB_TABLE_NON_FWDING].ip6_hash,
-					   ip6_fib_walk_cb,
-					   &ctx);
+    BV(clib_bihash_foreach_key_value_pair)(
+        &ip6_main.ip6_table[IP6_FIB_TABLE_NON_FWDING].ip6_hash,
+        ip6_fib_walk_cb,
+        &ctx);
 
+    vec_free(ctx.i6w_sub_trees);
+}
+
+void
+ip6_fib_table_sub_tree_walk (u32 fib_index,
+                             const fib_prefix_t *root,
+                             fib_table_walk_fn_t fn,
+                             void *arg)
+{
+    ip6_fib_walk_ctx_t ctx = {
+        .i6w_fib_index = fib_index,
+        .i6w_fn = fn,
+        .i6w_ctx = arg,
+        .i6w_root = *root,
+    };
+
+    BV(clib_bihash_foreach_key_value_pair)(
+        &ip6_main.ip6_table[IP6_FIB_TABLE_NON_FWDING].ip6_hash,
+        ip6_fib_walk_cb,
+        &ctx);
 }
 
 typedef struct ip6_fib_show_ctx_t_ {
     fib_node_index_t *entries;
 } ip6_fib_show_ctx_t;
 
-static int
+static fib_table_walk_rc_t
 ip6_fib_table_show_walk (fib_node_index_t fib_entry_index,
                          void *arg)
 {
@@ -483,7 +556,7 @@ ip6_fib_table_show_walk (fib_node_index_t fib_entry_index,
 
     vec_add1(ctx->entries, fib_entry_index);
 
-    return (1);
+    return (FIB_TABLE_WALK_CONTINUE);
 }
 
 static void
diff --git a/src/vnet/fib/ip6_fib.h b/src/vnet/fib/ip6_fib.h
index eda53628b01..dcd6c301bec 100644
--- a/src/vnet/fib/ip6_fib.h
+++ b/src/vnet/fib/ip6_fib.h
@@ -103,6 +103,16 @@ ip6_fib_table_fwding_lookup (ip6_main_t * im,
 }
 
 /**
+ * @brief Walk all entries in a sub-tree of the FIB table
+ * N.B: This is NOT safe to deletes. If you need to delete walk the whole
+ * table and store elements in a vector, then delete the elements
+ */
+extern void ip6_fib_table_sub_tree_walk(u32 fib_index,
+                                        const fib_prefix_t *root,
+                                        fib_table_walk_fn_t fn,
+                                        void *ctx);
+
+/**
  * @brief return the DPO that the LB stacks on.
  */
 always_inline u32