ldpd: be more conservative with labels

On unstable networks, routes can be lost and relearned very often. If
we deallocate the input label every time a route is lost and allocate
a new one when the route is relearned, a lot of changes are made in vain.

This patch introduces a logic in which labels are preserved for at least
five minutes before being deallocated by the LIB garbage collector. This
is consistent with what other implementations do.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>

1 files changed, 11 insertions, 8 deletions

diff --git a/ldpd/lde_lib.c b/ldpd/lde_lib.c
index db2682a173..b074bf3498 100644
--- a/ldpd/lde_lib.c
+++ b/ldpd/lde_lib.c
@@ -383,20 +383,23 @@ lde_kernel_update(struct fec *fec)
 	if (LIST_EMPTY(&fn->nexthops)) {
 		RB_FOREACH(ln, nbr_tree, &lde_nbrs)
 			lde_send_labelwithdraw(ln, fn, NULL, NULL);
-		fn->local_label = NO_LABEL;
 		fn->data = NULL;
-	} else {
-		uint32_t	 previous_label;
 
-		previous_label = fn->local_label;
+		/*
+		 * Do not deallocate the local label now, do that only in the
+		 * LIB garbage collector. This will prevent ldpd from changing
+		 * the input label of some prefixes too often when running on
+		 * an unstable network. Also, restart the garbage collector
+		 * timer so that labels are deallocated only when the network
+		 * is stabilized.
+		 */
+		lde_gc_start_timer();
+	} else {
 		fn->local_label = lde_update_label(fn);
-
-		if (fn->local_label != NO_LABEL &&
-		    fn->local_label != previous_label) {
+		if (fn->local_label != NO_LABEL && RB_EMPTY(&fn->upstream))
 			/* FEC.1: perform lsr label distribution procedure */
 			RB_FOREACH(ln, nbr_tree, &lde_nbrs)
 				lde_send_labelmapping(ln, fn, 1);
-		}
 	}
 
 	LIST_FOREACH(fnh, &fn->nexthops, entry) {