ldpd: make allowing broken-lsps to be installed with pop operation configurable

If LDP is miss configured in a setup and the router has LSPs with no remote
label, this code installs the LSP with a pop instruction of the top-level
label so the packet can be forwarded using IP.   This is a best-effort
attempt to deliver labeled IP packets to their final destination instead of
dropping them.    If this config is turned off the code will only install
LSPs that have a valid remote label.

Signed-off-by: Lynne Morrison <lynne@voltanet.io>

ldpd/lde.c

@@ -1630,6 +1630,30 @@ lde_nbr_addr_update(struct lde_nbr *ln, struct lde_addr *lde_addr, int removed)
 	}
 }
 
+void
+lde_allow_broken_lsp_update(int new_config)
+{
+	struct fec_node		*fn;
+	struct fec_nh		*fnh;
+	struct fec		*f;
+
+	RB_FOREACH(f, fec_tree, &ft) {
+		fn = (struct fec_node *)f;
+
+		LIST_FOREACH(fnh, &fn->nexthops, entry) {
+			/* allow-broken-lsp config is changing so
+			 * we need to reprogram labeled routes to
+			 * have proper top-level label
+			 */
+			if (!(new_config & F_LDPD_ALLOW_BROKEN_LSP))
+				lde_send_delete_klabel(fn, fnh);
+
+			if (fn->local_label != NO_LABEL)
+				lde_send_change_klabel(fn, fnh);
+		}
+	}
+}
+
 static __inline int
 lde_map_compare(const struct lde_map *a, const struct lde_map *b)
 {

ldpd/lde.h

@@ -200,6 +200,7 @@ void		 lde_route_update_release(struct iface *, int);
 void		 lde_route_update_release_all(int);
 struct lde_addr	*lde_address_find(struct lde_nbr *, int,
 		    union ldpd_addr *);
+void		 lde_allow_broken_lsp_update(int new_config);
 
 /* lde_lib.c */
 void		 fec_init(struct fec_tree *);

ldpd/ldp_vty.h

@@ -34,6 +34,7 @@ extern struct cmd_node ldp_debug_node;
 union ldpd_addr;
 int	 ldp_get_address(const char *, int *, union ldpd_addr *);
 int	 ldp_vty_mpls_ldp (struct vty *, const char *);
+int	 ldp_vty_allow_broken_lsp(struct vty *, const char *);
 int	 ldp_vty_address_family (struct vty *, const char *, const char *);
 int	 ldp_vty_disc_holdtime(struct vty *, const char *, enum hello_type, long);
 int	 ldp_vty_disc_interval(struct vty *, const char *, enum hello_type, long);

ldpd/ldp_vty_cmds.c

@@ -241,6 +241,16 @@ DEFPY  (ldp_wait_for_sync,
 
 }
 
+DEFPY  (ldp_allow_broken_lsps,
+	ldp_allow_broken_lsps_cmd,
+	"[no] install allow-broken-lsps",
+	NO_STR
+	"install lsps\n"
+	"if no remote-label install with imp-null")
+{
+	return (ldp_vty_allow_broken_lsp(vty, no));
+}
+
 DEFPY  (ldp_discovery_targeted_hello_accept,
 	ldp_discovery_targeted_hello_accept_cmd,
 	"[no] discovery targeted-hello accept [from <(1-199)|(1300-2699)|WORD>$from_acl]",
@@ -844,6 +854,7 @@ ldp_vty_init (void)
 	install_element(LDP_NODE, &ldp_router_id_cmd);
 	install_element(LDP_NODE, &ldp_ordered_control_cmd);
 	install_element(LDP_NODE, &ldp_wait_for_sync_cmd);
+	install_element(LDP_NODE, &ldp_allow_broken_lsps_cmd);
 
 	install_element(LDP_IPV4_NODE, &ldp_discovery_link_holdtime_cmd);
 	install_element(LDP_IPV4_NODE, &ldp_discovery_targeted_holdtime_cmd);

ldpd/ldp_vty_conf.c

@@ -290,6 +290,9 @@ ldp_config_write(struct vty *vty)
 		vty_out (vty, " wait-for-sync %u\n",
 		    ldpd_conf->wait_for_sync_interval);
 
+	if (ldpd_conf->flags & F_LDPD_ALLOW_BROKEN_LSP)
+		vty_out(vty, " install allow-broken-lsp\n");
+
 	RB_FOREACH(nbrp, nbrp_head, &ldpd_conf->nbrp_tree) {
 		if (nbrp->flags & F_NBRP_KEEPALIVE)
 			vty_out (vty, " neighbor %pI4 session holdtime %u\n",
@@ -1039,6 +1042,19 @@ int ldp_vty_wait_for_sync_interval(struct vty *vty, const char *negate,
 	return (CMD_SUCCESS);
 }
 
+int
+ldp_vty_allow_broken_lsp(struct vty *vty, const char *negate)
+{
+	if (negate)
+		vty_conf->flags &= ~F_LDPD_ALLOW_BROKEN_LSP;
+	else
+		vty_conf->flags |= F_LDPD_ALLOW_BROKEN_LSP;
+
+	ldp_config_apply(vty, vty_conf);
+
+	return (CMD_SUCCESS);
+}
+
 int
 ldp_vty_ds_cisco_interop(struct vty *vty, const char * negate)
 {

ldpd/ldp_zebra.c

@@ -246,12 +246,17 @@ ldp_zebra_send_mpls_labels(int cmd, struct kroute *kr)
 		zl.route.instance = kr->route_instance;
 	}
 
-	/*
-	 * For broken LSPs, instruct the forwarding plane to pop the top-level
+	/* If allow-broken-lsps is enabled then if an lsp is received with
+	 * no remote label, instruct the forwarding plane to pop the top-level
 	 * label and forward packets normally. This is a best-effort attempt
 	 * to deliver labeled IP packets to their final destination (instead of
 	 * dropping them).
 	 */
+	if (kr->remote_label == NO_LABEL
+	    && !(ldpd_conf->flags & F_LDPD_ALLOW_BROKEN_LSP)
+	    && cmd == ZEBRA_MPLS_LABELS_ADD)
+		return 0;
+
 	if (kr->remote_label == NO_LABEL)
 		kr->remote_label = MPLS_LABEL_IMPLICIT_NULL;
 

ldpd/ldpd.c

@@ -1365,6 +1365,16 @@ merge_global(struct ldpd_conf *conf, struct ldpd_conf *xconf)
 			ldpe_reset_ds_nbrs();
 	}
 
+	/*
+	 * Configuration of allow-broken-lsp requires reprograming all
+	 * labeled routes
+	 */
+	if ((conf->flags & F_LDPD_ALLOW_BROKEN_LSP) !=
+	    (xconf->flags & F_LDPD_ALLOW_BROKEN_LSP)) {
+		if (ldpd_process == PROC_LDE_ENGINE)
+			lde_allow_broken_lsp_update(xconf->flags);
+	}
+
 	if (ldpd_process == PROC_LDP_ENGINE)
 		ldpe_set_config_change_time();
 

ldpd/ldpd.h

@@ -590,7 +590,7 @@ DECLARE_QOBJ_TYPE(ldpd_conf);
 #define	F_LDPD_DS_CISCO_INTEROP	0x0002
 #define	F_LDPD_ENABLED		0x0004
 #define	F_LDPD_ORDERED_CONTROL  0x0008
-
+#define	F_LDPD_ALLOW_BROKEN_LSP 0x0010
 
 struct ldpd_af_global {
 	struct thread		*disc_ev;