isisd: Fix Attach-bit processing

The purpose of the Attach-bit is to accomplish inter-area routing.  In other
venders, the Attached-bit is automatically set when a router is configured
as a L1|L2 router and has two adjacencies.  When a L1 router receives a LSP
with the Attached-bit set it is supposed to create a default route pointing
toward the neighbor to provide a default path out of the L1 area.

ISIS implementation has been fixed to support the above definition:
Setting the Attach-bit is now the default behavior and we allow the user to
turn it off.

We will only set the Default Attach-bit when creating a L1 LSP, if we are
a L1|L2 router and have a L2 adjacency up.

When a L1 router receives a LSP with the Attach-bit set, we will create a
default route pointing to the L1|L2 router as the nexthop.

The default route will be removed if the LSP is received with the Attach-bit
cleared.

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

1 files changed, 49 insertions, 4 deletions

diff --git a/isisd/isis_cli.c b/isisd/isis_cli.c
index 5ca70eab0f..b48da9312f 100644
--- a/isisd/isis_cli.c
+++ b/isisd/isis_cli.c
@@ -593,6 +593,10 @@ void cli_show_isis_overload(struct vty *vty, struct lyd_node *dnode,
 	vty_out(vty, " set-overload-bit\n");
 }
 
+#if CONFDATE > 20220119
+CPP_NOTICE(
+	"Use of `set-attached-bit` is deprecated please use attached-bit [send | receive]")
+#endif
 /*
  * XPath: /frr-isisd:isis/instance/attached
  */
@@ -600,18 +604,57 @@ DEFPY_YANG(set_attached_bit, set_attached_bit_cmd, "[no] set-attached-bit",
       "Reset attached bit\n"
       "Set attached bit to identify as L1/L2 router for inter-area traffic\n")
 {
-	nb_cli_enqueue_change(vty, "./attached", NB_OP_MODIFY,
+	vty_out(vty,
+		"set-attached-bit deprecated please use attached-bit [send | receive]\n");
+
+	return CMD_SUCCESS;
+}
+
+/*
+ * XPath: /frr-isisd:isis/instance/attach-send
+ */
+DEFPY_YANG(attached_bit_send, attached_bit_send_cmd, "[no] attached-bit send",
+	   "Reset attached bit\n"
+	   "Set attached bit for inter-area traffic\n"
+	   "Set attached bit in LSP sent to L1 router\n")
+{
+	nb_cli_enqueue_change(vty, "./attach-send", NB_OP_MODIFY,
 			      no ? "false" : "true");
 
 	return nb_cli_apply_changes(vty, NULL);
 }
 
-void cli_show_isis_attached(struct vty *vty, struct lyd_node *dnode,
-			    bool show_defaults)
+void cli_show_isis_attached_send(struct vty *vty, struct lyd_node *dnode,
+				 bool show_defaults)
+{
+	if (!yang_dnode_get_bool(dnode, NULL))
+		vty_out(vty, " no");
+	vty_out(vty, " attached-bit send\n");
+}
+
+/*
+ * XPath: /frr-isisd:isis/instance/attach-receive-ignore
+ */
+DEFPY_YANG(
+	attached_bit_receive_ignore, attached_bit_receive_ignore_cmd,
+	"[no] attached-bit receive ignore",
+	"Reset attached bit\n"
+	"Set attach bit for inter-area traffic\n"
+	"If LSP received with attached bit set, create default route to neighbor\n"
+	"Do not process attached bit\n")
+{
+	nb_cli_enqueue_change(vty, "./attach-receive-ignore", NB_OP_MODIFY,
+			      no ? "false" : "true");
+
+	return nb_cli_apply_changes(vty, NULL);
+}
+
+void cli_show_isis_attached_receive(struct vty *vty, struct lyd_node *dnode,
+				    bool show_defaults)
 {
 	if (!yang_dnode_get_bool(dnode, NULL))
 		vty_out(vty, " no");
-	vty_out(vty, " set-attached-bit\n");
+	vty_out(vty, " attached-bit receive ignore\n");
 }
 
 /*
@@ -3206,6 +3249,8 @@ void isis_cli_init(void)
 
 	install_element(ISIS_NODE, &set_overload_bit_cmd);
 	install_element(ISIS_NODE, &set_attached_bit_cmd);
+	install_element(ISIS_NODE, &attached_bit_send_cmd);
+	install_element(ISIS_NODE, &attached_bit_receive_ignore_cmd);
 
 	install_element(ISIS_NODE, &metric_style_cmd);
 	install_element(ISIS_NODE, &no_metric_style_cmd);