Merge pull request #12650 from isabelladeleon12/advertise_high_metrics

isisd: Add support for advertise-high-metrics

doc/user/isisd.rst

@@ -79,6 +79,12 @@ writing, *isisd* does not support multiple ISIS processes.
    - wide
      Use new style of TLVs to carry wider metric. FRR uses this as a default value
 
+.. clicmd:: advertise-high-metrics
+
+   Advertise high metric value on all interfaces to gracefully shift traffic off the router. Reference: :rfc:`3277`
+   
+   For narrow metrics, the high metric value is 63; for wide metrics, 16777215; for transition metrics, 62.
+
 .. clicmd:: set-overload-bit
 
    Set overload bit to avoid any transit traffic.

isisd/isis_circuit.c

@@ -1499,6 +1499,10 @@ ferr_r isis_circuit_metric_set(struct isis_circuit *circuit, int level,
 		return ferr_cfg_invalid("metric %d too large for narrow metric",
 					metric);
 
+	/* Don't modify metric if advertise high metrics is configured */
+	if (circuit->area && circuit->area->advertise_high_metrics)
+		return ferr_ok();
+
 	/* inform ldp-sync of metric change
          *   if ldp-sync is running need to save metric
          *   and restore new values after ldp-sync completion.

isisd/isis_cli.c

@@ -439,6 +439,29 @@ void cli_show_isis_overload_on_startup(struct vty *vty,
 		yang_dnode_get_string(dnode, NULL));
 }
 
+/*
+ * XPath: /frr-isisd:isis/instance/advertise-high-metrics
+ */
+DEFPY_YANG(advertise_high_metrics, advertise_high_metrics_cmd,
+	   "[no] advertise-high-metrics",
+	   NO_STR "Advertise high metric value on all interfaces\n")
+{
+	nb_cli_enqueue_change(vty, "./advertise-high-metrics", NB_OP_MODIFY,
+			      no ? "false" : "true");
+
+	return nb_cli_apply_changes(vty, NULL);
+}
+
+void cli_show_advertise_high_metrics(struct vty *vty,
+				     const struct lyd_node *dnode,
+				     bool show_defaults)
+{
+	if (yang_dnode_get_bool(dnode, NULL))
+		vty_out(vty, " advertise-high-metrics\n");
+	else if (show_defaults)
+		vty_out(vty, " no advertise-high-metrics\n");
+}
+
 /*
  * XPath: /frr-isisd:isis/instance/attach-send
  */
@@ -3160,6 +3183,8 @@ void isis_cli_init(void)
 	install_element(ISIS_NODE, &metric_style_cmd);
 	install_element(ISIS_NODE, &no_metric_style_cmd);
 
+	install_element(ISIS_NODE, &advertise_high_metrics_cmd);
+
 	install_element(ISIS_NODE, &area_passwd_cmd);
 	install_element(ISIS_NODE, &domain_passwd_cmd);
 	install_element(ISIS_NODE, &no_area_passwd_cmd);

isisd/isis_nb.c

@@ -81,6 +81,13 @@ const struct frr_yang_module_info frr_isisd_info = {
 				.modify = isis_instance_overload_on_startup_modify,
 			}
 		},
+		{
+			.xpath = "/frr-isisd:isis/instance/advertise-high-metrics",
+			.cbs = {
+				.cli_show = cli_show_advertise_high_metrics,
+				.modify = isis_instance_advertise_high_metrics_modify,
+			}
+		},
 		{
 			.xpath = "/frr-isisd:isis/instance/metric-style",
 			.cbs = {

isisd/isis_nb.h

@@ -26,6 +26,7 @@ int isis_instance_attached_receive_modify(struct nb_cb_modify_args *args);
 int isis_instance_attached_modify(struct nb_cb_modify_args *args);
 int isis_instance_overload_enabled_modify(struct nb_cb_modify_args *args);
 int isis_instance_overload_on_startup_modify(struct nb_cb_modify_args *args);
+int isis_instance_advertise_high_metrics_modify(struct nb_cb_modify_args *args);
 int isis_instance_metric_style_modify(struct nb_cb_modify_args *args);
 int isis_instance_purge_originator_modify(struct nb_cb_modify_args *args);
 int isis_instance_lsp_mtu_modify(struct nb_cb_modify_args *args);
@@ -464,6 +465,9 @@ void cli_show_isis_overload(struct vty *vty, const struct lyd_node *dnode,
 void cli_show_isis_overload_on_startup(struct vty *vty,
 				       const struct lyd_node *dnode,
 				       bool show_defaults);
+void cli_show_advertise_high_metrics(struct vty *vty,
+				     const struct lyd_node *dnode,
+				     bool show_defaults);
 void cli_show_isis_metric_style(struct vty *vty, const struct lyd_node *dnode,
 				bool show_defaults);
 void cli_show_isis_area_pwd(struct vty *vty, const struct lyd_node *dnode,

isisd/isis_nb_config.c

@@ -360,6 +360,24 @@ int isis_instance_overload_on_startup_modify(struct nb_cb_modify_args *args)
 	return NB_OK;
 }
 
+/*
+ * XPath: /frr-isisd:isis/instance/advertise-high-metrics
+ */
+int isis_instance_advertise_high_metrics_modify(struct nb_cb_modify_args *args)
+{
+	struct isis_area *area;
+	bool advertise_high_metrics;
+
+	if (args->event != NB_EV_APPLY)
+		return NB_OK;
+
+	advertise_high_metrics = yang_dnode_get_bool(args->dnode, NULL);
+	area = nb_running_get_entry(args->dnode, NULL, true);
+	isis_area_advertise_high_metrics_set(area, advertise_high_metrics);
+
+	return NB_OK;
+}
+
 /*
  * XPath: /frr-isisd:isis/instance/metric-style
  */

isisd/isisd.c

@@ -2503,6 +2503,9 @@ static void common_isis_summary_vty(struct vty *vty, struct isis *isis)
 		vty_out(vty, "  RX counters per PDU type:\n");
 		pdu_counter_print(vty, "    ", area->pdu_rx_counters);
 
+		vty_out(vty, "  Advertise high metrics: %s\n",
+			area->advertise_high_metrics ? "Enabled" : "Disabled");
+
 		for (level = ISIS_LEVEL1; level <= ISIS_LEVELS; level++) {
 			if ((area->is_type & level) == 0)
 				continue;
@@ -3247,6 +3250,58 @@ void config_end_lsp_generate(struct isis_area *area)
 	}
 }
 
+void isis_area_advertise_high_metrics_set(struct isis_area *area,
+					  bool advertise_high_metrics)
+{
+	struct listnode *node;
+	struct isis_circuit *circuit;
+	int max_metric;
+	char xpath[XPATH_MAXLEN];
+	struct lyd_node *dnode;
+	int configured_metric_l1;
+	int configured_metric_l2;
+
+	if (area->advertise_high_metrics == advertise_high_metrics)
+		return;
+
+	if (advertise_high_metrics) {
+		if (area->oldmetric && area->newmetric)
+			max_metric = ISIS_NARROW_METRIC_INFINITY;
+		else if (area->newmetric)
+			max_metric = MAX_WIDE_LINK_METRIC;
+		else
+			max_metric = MAX_NARROW_LINK_METRIC;
+
+		for (ALL_LIST_ELEMENTS_RO(area->circuit_list, node, circuit)) {
+			isis_circuit_metric_set(circuit, IS_LEVEL_1,
+						max_metric);
+			isis_circuit_metric_set(circuit, IS_LEVEL_2,
+						max_metric);
+		}
+
+		area->advertise_high_metrics = true;
+	} else {
+		area->advertise_high_metrics = false;
+		for (ALL_LIST_ELEMENTS_RO(area->circuit_list, node, circuit)) {
+			/* Get configured metric */
+			snprintf(xpath, XPATH_MAXLEN,
+				 "/frr-interface:lib/interface[name='%s']",
+				 circuit->interface->name);
+			dnode = yang_dnode_get(running_config->dnode, xpath);
+
+			configured_metric_l1 = yang_dnode_get_uint32(
+				dnode, "./frr-isisd:isis/metric/level-1");
+			configured_metric_l2 = yang_dnode_get_uint32(
+				dnode, "./frr-isisd:isis/metric/level-2");
+
+			isis_circuit_metric_set(circuit, IS_LEVEL_1,
+						configured_metric_l1);
+			isis_circuit_metric_set(circuit, IS_LEVEL_2,
+						configured_metric_l2);
+		}
+	}
+}
+
 /*
  * Returns the path of the file (non-volatile memory) that contains restart
  * information.

isisd/isisd.h

@@ -175,6 +175,8 @@ struct isis_area {
 	uint32_t overload_on_startup_time;
 	/* advertise prefixes of passive interfaces only? */
 	bool advertise_passive_only;
+	/* Are we advertising high metrics? */
+	bool advertise_high_metrics;
 	/* L1/L2 router identifier for inter-area traffic */
 	char attached_bit_send;
 	char attached_bit_rcv_ignore;
@@ -289,6 +291,8 @@ void isis_area_switchover_routes(struct isis_area *area, int family,
 void isis_area_overload_bit_set(struct isis_area *area, bool overload_bit);
 void isis_area_overload_on_startup_set(struct isis_area *area,
 				       uint32_t startup_time);
+void isis_area_advertise_high_metrics_set(struct isis_area *area,
+					  bool advertise_high_metrics);
 void isis_area_attached_bit_send_set(struct isis_area *area, bool attached_bit);
 void isis_area_attached_bit_receive_set(struct isis_area *area,
 					bool attached_bit);

tests/topotests/isis_advertise_high_metrics/r1/isisd.conf

@@ -0,0 +1,19 @@
+hostname r1
+! debug isis adj-packets
+! debug isis events
+! debug isis update-packets
+interface eth-r2
+ ip router isis 1
+ isis circuit-type level-2-only
+ isis network point-to-point
+!
+interface eth-r3
+ ip router isis 1
+ isis circuit-type level-2-only
+ isis metric 20
+ isis network point-to-point
+!
+router isis 1
+ is-type level-2-only
+ net 10.0000.0000.0000.0000.0000.0000.0000.0000.0000.00
+!

tests/topotests/isis_advertise_high_metrics/r1/zebra.conf

@@ -0,0 +1,5 @@
+interface eth-r2
+  ip address 192.168.1.0/31
+
+interface eth-r3
+  ip address 192.168.1.2/31

tests/topotests/isis_advertise_high_metrics/r2/isisd.conf

@@ -0,0 +1,18 @@
+hostname r2
+! debug isis adj-packets
+! debug isis events
+! debug isis update-packets
+interface eth-r1
+ ip router isis 1
+ isis circuit-type level-2-only
+ isis network point-to-point
+!
+interface eth-r4
+ ip router isis 1
+ isis circuit-type level-2-only
+ isis network point-to-point
+!
+router isis 1
+ is-type level-2-only
+ net 10.0000.0000.0000.0000.0000.0000.0000.0000.0001.00
+!

tests/topotests/isis_advertise_high_metrics/r2/zebra.conf

@@ -0,0 +1,5 @@
+interface eth-r1
+  ip address 192.168.1.1/31
+
+interface eth-r4
+  ip address 192.168.1.7/31

tests/topotests/isis_advertise_high_metrics/r3/isisd.conf

@@ -0,0 +1,20 @@
+hostname r3
+! debug isis adj-packets
+! debug isis events
+! debug isis update-packets
+interface eth-r1
+ ip router isis 1
+ isis circuit-type level-2-only
+ isis metric 20
+ isis network point-to-point
+!
+interface eth-r4
+ ip router isis 1
+ isis circuit-type level-2-only
+ isis metric 20
+ isis network point-to-point
+!
+router isis 1
+ is-type level-2-only
+ net 10.0000.0000.0000.0000.0000.0000.0000.0000.0002.00
+!

tests/topotests/isis_advertise_high_metrics/r3/zebra.conf

@@ -0,0 +1,5 @@
+interface eth-r1
+  ip address 192.168.1.3/31
+
+interface eth-r4
+  ip address 192.168.1.4/31

tests/topotests/isis_advertise_high_metrics/r4/isisd.conf

@@ -0,0 +1,19 @@
+hostname r4
+! debug isis adj-packets
+! debug isis events
+! debug isis update-packets
+interface eth-r2
+ ip router isis 1
+ isis circuit-type level-2-only
+ isis network point-to-point
+!
+interface eth-r3
+ ip router isis 1
+ isis circuit-type level-2-only
+ isis metric 20
+ isis network point-to-point
+!
+router isis 1
+ is-type level-2-only
+ net 10.0000.0000.0000.0000.0000.0000.0000.0000.0003.00
+!

tests/topotests/isis_advertise_high_metrics/r4/zebra.conf

@@ -0,0 +1,5 @@
+interface eth-r2
+  ip address 192.168.1.6/31
+
+interface eth-r3
+  ip address 192.168.1.5/31

tests/topotests/isis_advertise_high_metrics/test_isis_advertise_high_metrics.py

@@ -0,0 +1,485 @@
+#!/usr/bin/env python
+
+#
+# test_isis_advertise_high_metrics.py
+# Part of NetDEF Topology Tests
+#
+# Copyright (c) 2020 by Volta Networks
+#
+# Permission to use, copy, modify, and/or distribute this software
+# for any purpose with or without fee is hereby granted, provided
+# that the above copyright notice and this permission notice appear
+# in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND NETDEF DISCLAIMS ALL WARRANTIES
+# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL NETDEF BE LIABLE FOR
+# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY
+# DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
+# WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
+# ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
+# OF THIS SOFTWARE.
+#
+
+r"""
+test_isis_advertise_high_metrics.py: Advertise High Metrics FRR ISIS Test
+"""
+
+import os
+import re
+import sys
+import pytest
+import json
+from time import sleep
+from functools import partial
+
+# Save the Current Working Directory to find configuration files.
+CWD = os.path.dirname(os.path.realpath(__file__))
+sys.path.append(os.path.join(CWD, "../"))
+
+# pylint: disable=C0413
+# Import topogen and topotest helpers
+from lib import topotest
+from lib.common_config import (
+    retry,
+    stop_router,
+    start_router,
+)
+from lib.topogen import Topogen, TopoRouter, get_topogen
+from lib.topolog import logger
+
+# Required to instantiate the topology builder class.
+
+pytestmark = [pytest.mark.isisd]
+
+
+def build_topo(tgen):
+    "Build function"
+
+    # Add ISIS routers:
+    #     r2
+    #    /  \
+    #  r1   r4
+    #    \  /
+    #     r3
+
+    #
+    # Define FRR Routers
+    #
+    for router in ["r1", "r2", "r3", "r4"]:
+        tgen.add_router(router)
+    #
+    # Define connections
+    #
+    switch = tgen.add_switch("s0")
+    switch.add_link(tgen.gears["r1"], nodeif="eth-r2")
+    switch.add_link(tgen.gears["r2"], nodeif="eth-r1")
+
+    switch = tgen.add_switch("s1")
+    switch.add_link(tgen.gears["r1"], nodeif="eth-r3")
+    switch.add_link(tgen.gears["r3"], nodeif="eth-r1")
+
+    switch = tgen.add_switch("s2")
+    switch.add_link(tgen.gears["r2"], nodeif="eth-r4")
+    switch.add_link(tgen.gears["r4"], nodeif="eth-r2")
+
+    switch = tgen.add_switch("s3")
+    switch.add_link(tgen.gears["r3"], nodeif="eth-r4")
+    switch.add_link(tgen.gears["r4"], nodeif="eth-r3")
+
+
+def setup_module(mod):
+    "Sets up the pytest environment"
+    tgen = Topogen(build_topo, mod.__name__)
+    tgen.start_topology()
+
+    # For all registered routers, load the zebra configuration file
+    for rname, router in tgen.routers().items():
+        router.load_config(
+            TopoRouter.RD_ZEBRA, os.path.join(CWD, "{}/zebra.conf".format(rname))
+        )
+        router.load_config(
+            TopoRouter.RD_ISIS, os.path.join(CWD, "{}/isisd.conf".format(rname))
+        )
+
+    # After loading the configurations, this function loads configured daemons.
+    tgen.start_router()
+
+
+def teardown_module(mod):
+    "Teardown the pytest environment"
+    tgen = get_topogen()
+
+    # This function tears down the whole topology.
+    tgen.stop_topology()
+
+
+@retry(retry_timeout=60)
+def _check_interface_metrics(router, expected_metrics):
+    "Verfiy metrics on router's isis interfaces"
+
+    tgen = get_topogen()
+    router = tgen.gears[router]
+    logger.info(f"check_interface_metrics {router}")
+    isis_interface_output = router.vtysh_cmd(
+        "show isis interface detail json"
+    )
+
+    intf_json = json.loads(isis_interface_output)
+    for i in range(len(expected_metrics)):
+        metric = intf_json["areas"][0]["circuits"][i]["interface"]["levels"][0]["metric"]
+        if (metric != expected_metrics[i]):
+            intf_name = intf_json["areas"][0]["circuits"][i]["interface"]["name"]
+            return "{} with expected metric {} on {} got {}".format(
+                router.name, expected_metrics[i], intf_name, metric
+            )
+    return True
+
+
+def check_interface_metrics(router, expected_metrics):
+    "Verfiy metrics on router's isis interfaces"
+
+    assertmsg = _check_interface_metrics(
+        router, expected_metrics
+    )
+    assert assertmsg is True, assertmsg
+
+
+@retry(retry_timeout=60)
+def _check_lsp_metrics(router, lsp, expected_metrics):
+    "Verfiy metrics on router's lsp"
+    tgen = get_topogen()
+    router = tgen.gears[router]
+    logger.info(f"check_lsp_metrics {router}")
+    isis_lsp_output = router.vtysh_cmd(
+        "show isis database detail {}".format(lsp)
+    )
+
+    metrics_list = [int(i) for i in re.findall(r"Metric: (\d+)", isis_lsp_output)]
+    if len(metrics_list) == 0:
+        return False
+    for metric in metrics_list:
+        if metric not in expected_metrics:
+            return "{} with expected metrics {} got {}".format(
+                router.name, expected_metrics, metrics_list
+            )
+
+    return True
+
+
+def check_lsp_metrics(router, lsp, expected_metrics):
+    "Verfiy metrics on router's lsp"
+
+    assertmsg = _check_lsp_metrics(
+        router, lsp, expected_metrics
+    )
+    assert assertmsg is True, assertmsg
+
+
+@retry(retry_timeout=60)
+def _check_ip_route(router, destination, expected_interface):
+    "Verfiy IS-IS route"
+
+    tgen = get_topogen()
+    router = tgen.gears[router]
+    logger.info(f"check_ip_route {router}")
+    route_output = router.vtysh_cmd(
+        "show ip route {} json".format(destination)
+    )
+    route_json = json.loads(route_output)
+
+    interface = route_json[destination][0]["nexthops"][0]["interfaceName"]
+
+    if (interface != expected_interface):
+        return "{} with expected route to {} got {} expected {}".format(
+            router.name, destination, interface, expected_interface
+        )
+
+    return True
+
+
+def check_ip_route(router, destination, expected_interface):
+    "Verfiy IS-IS route"
+
+    assertmsg = _check_ip_route(
+        router, destination, expected_interface
+    )
+    assert assertmsg is True, assertmsg
+
+
+def test_isis_daemon_up():
+    "Check isis daemon up before starting test"
+    tgen = get_topogen()
+    # Don't run this test if we have any failure.
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    for router in ["r1", "r2", "r3", "r4"]:
+        r = tgen.gears[router]
+        daemons = r.vtysh_cmd(
+            "show daemons"
+        )
+        assert "isisd" in daemons
+
+    # Verify initial metric values.
+    check_lsp_metrics("r1", "r1.00-00", [10, 20])
+    check_lsp_metrics("r2", "r2.00-00", [10, 10])
+    check_lsp_metrics("r3", "r3.00-00", [20, 20])
+    check_lsp_metrics("r4", "r4.00-00", [10, 20])
+
+
+def test_isis_advertise_high_metrics():
+    "Check that advertise high metrics behaves as expected"
+
+    tgen = get_topogen()
+    net = get_topogen().net
+
+    # Don't run this test if we have any failure.
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    logger.info("Testing advertise high metrics basic behavior")
+
+    # Confirm low metrics values on each isis interface on r1
+    r1 = tgen.gears["r1"]
+    check_interface_metrics("r1", [10, 20])
+
+    # Confirm low metrics values within isis database on r1
+    check_lsp_metrics("r1", "r1.00-00", [10, 20])
+
+    # Configure advertise high metrics
+    r1.vtysh_cmd(
+        f"""
+          configure
+            router isis 1
+              advertise-high-metrics
+        """
+    )
+
+    # Confirm high wide metrics values on each isis interface on r1
+    check_interface_metrics("r1", [16777215])
+
+    # Confirm high wide metrics values within isis database on r1
+    check_lsp_metrics("r1", "r1.00-00", [16777215])
+
+    # Remove advertise high metrics
+    r1.vtysh_cmd(
+        f"""
+          configure
+            router isis 1
+              no advertise-high-metrics
+        """
+    )
+
+    # Confirm low metrics values on each isis interface on r1
+    check_interface_metrics("r1", [10, 20])
+
+    # Confirm low metrics values within isis database on r1
+    check_lsp_metrics("r1", "r1.00-00", [10, 20])
+
+
+def test_isis_advertise_high_metrics_narrow():
+    "Check that advertise high metrics behaves as expected with narrow metrics"
+
+    tgen = get_topogen()
+    net = get_topogen().net
+
+    # Don't run this test if we have any failure.
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    logger.info("Testing advertise high metrics with narrow metric style")
+
+    r1 = tgen.gears["r1"]
+
+    # Configure narrow metric-style
+    r1.vtysh_cmd(
+        f"""
+          configure
+            router isis 1
+              metric-style narrow
+        """
+    )
+
+    # Confirm low metrics values on each isis interface on r1
+    check_interface_metrics("r1", [10, 20])
+
+    # Confirm low metrics values within isis database on r1
+    check_lsp_metrics("r1", "r1.00-00", [10, 20])
+
+    # Configure advertise high metrics
+    r1.vtysh_cmd(
+        f"""
+          configure
+            router isis 1
+              advertise-high-metrics
+        """
+    )
+
+    # Confirm high narrow metrics values on each isis interface on r1
+    check_interface_metrics("r1", [63])
+
+    # Confirm high narrow metrics values within isis database on r1
+    check_lsp_metrics("r1", "r1.00-00", [63])
+
+    # Remove advertise high metrics
+    r1.vtysh_cmd(
+        f"""
+          configure
+            router isis 1
+              no advertise-high-metrics
+        """
+    )
+
+    # Confirm low metrics values on each isis interface on r1
+    check_interface_metrics("r1", [10, 20])
+
+    # Confirm low metrics values within isis database on r1
+    check_lsp_metrics("r1", "r1.00-00", [10, 20])
+
+    # Remove narrow metric-style
+    r1.vtysh_cmd(
+        f"""
+          configure
+            router isis 1
+              no metric-style narrow
+        """
+    )
+
+
+def test_isis_advertise_high_metrics_transition():
+    "Check that advertise high metrics behaves as expected with transition metrics"
+    tgen = get_topogen()
+    net = get_topogen().net
+
+    # Don't run this test if we have any failure.
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    logger.info("Testing advertise high metrics with transition metric style")
+
+    r1 = tgen.gears["r1"]
+
+    # Configure transition metric-style
+    r1.vtysh_cmd(
+        f"""
+          configure
+            router isis 1
+              metric-style transition
+        """
+    )
+
+    # Confirm low metrics values on each isis interface on r1
+    check_interface_metrics("r1", [10, 20])
+
+    # Confirm low metrics values within isis database on r1
+    check_lsp_metrics("r1", "r1.00-00", [10, 20])
+
+    # Configure advertise high metrics
+    r1.vtysh_cmd(
+        f"""
+          configure
+            router isis 1
+              advertise-high-metrics
+        """
+    )
+
+    # Confirm high transition metrics values on each isis interface on r1
+    check_interface_metrics("r1", [62])
+
+    # Confirm high transition metrics values within isis database on r1
+    check_lsp_metrics("r1", "r1.00-00", [62])
+
+    # Remove advertise high metrics
+    r1.vtysh_cmd(
+        f"""
+          configure
+            router isis 1
+              no advertise-high-metrics
+        """
+    )
+
+    # Confirm low metrics values on each isis interface on r1
+    check_interface_metrics("r1", [10, 20])
+
+    # Confirm low metrics values within isis database on r1
+    check_lsp_metrics("r1", "r1.00-00", [10, 20])
+
+    # Remove narrow metric-style
+    r1.vtysh_cmd(
+        f"""
+          configure
+            router isis 1
+              no metric-style transition
+        """
+    )
+
+
+def test_isis_advertise_high_metrics_route():
+    """
+    Topology:
+    
+         r2
+        /  \
+      r1   r4
+        \  /
+         r3
+    
+    Devices are configured with preferred route between r1 and r4:
+    r1 -> r2 -> r4
+    Configure "advertise-high-metrics" on r2 and check that preferred route is:
+    r1 -> r3 -> r4.
+    Shut r3 and check that preferred route is:
+    r1 -> r2 -> r4.
+    """
+    tgen = get_topogen()
+    net = get_topogen().net
+
+    # Don't run this test if we have any failure.
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    logger.info("Testing advertise high metrics route behavior")
+
+    r1 = tgen.gears["r1"]
+    r2 = tgen.gears["r2"]
+
+    # Verify the preferred path from r1 to r4 (192.168.1.6) is currently via 192.168.1.1, eth-r2
+    check_ip_route("r1", "192.168.1.6/31", "eth-r2")
+
+    # Configure advertise high metrics on r2
+    r2.vtysh_cmd(
+        f"""
+          configure
+            router isis 1
+              advertise-high-metrics
+        """
+    )
+
+    # Verify the preferred path from r1 to r4 (192.168.1.6) is now via 192.168.1.3, eth-r3
+    check_ip_route("r1", "192.168.1.6/31", "eth-r3")
+
+    # Shutdown r3
+    logger.info("Stop router r3")
+    stop_router(tgen, "r3")
+
+    # Verify the preferred path from r1 to r4 (192.168.1.6) is now via 192.168.1.1, eth-r2
+    check_ip_route("r1", "192.168.1.6/31", "eth-r2")
+
+    # Start r3
+    logger.info("Start router r3")
+    start_router(tgen, "r3")
+
+
+def test_memory_leak():
+    "Run the memory leak test and report results."
+    tgen = get_topogen()
+    if not tgen.is_memleak_enabled():
+        pytest.skip("Memory leak test/report is disabled")
+
+    tgen.report_memory_leaks()
+
+
+if __name__ == "__main__":
+    args = ["-s"] + sys.argv[1:]
+    sys.exit(pytest.main(args))

yang/frr-isisd.yang

@@ -1169,6 +1169,13 @@ module frr-isisd {
           "Define the style of TLVs metric supported.";
       }
 
+      leaf advertise-high-metrics {
+        type boolean;
+        default "false";
+        description
+          "Advertise high metric value on all interfaces.";
+      }
+
       leaf purge-originator {
         type boolean;
         default "false";