--- /dev/null
+#!/usr/bin/env python
+# SPDX-License-Identifier: ISC
+
+#
+# Copyright (c) 2023 by
+# Donatas Abraitis <donatas@opensourcerouting.org>
+#
+
+"""
+Test if TCP MSS is synced with passive neighbor.
+"""
+
+import os
+import sys
+import json
+import pytest
+import functools
+
+CWD = os.path.dirname(os.path.realpath(__file__))
+sys.path.append(os.path.join(CWD, "../"))
+
+# pylint: disable=C0413
+from lib import topotest
+from lib.topogen import Topogen, TopoRouter, get_topogen
+
+pytestmark = [pytest.mark.bgpd]
+
+
+def build_topo(tgen):
+ for routern in range(1, 3):
+ tgen.add_router("r{}".format(routern))
+
+ switch = tgen.add_switch("s1")
+ switch.add_link(tgen.gears["r1"])
+ switch.add_link(tgen.gears["r2"])
+
+
+def setup_module(mod):
+ tgen = Topogen(build_topo, mod.__name__)
+ tgen.start_topology()
+
+ router_list = tgen.routers()
+
+ for i, (rname, router) in enumerate(router_list.items(), 1):
+ router.load_frr_config(os.path.join(CWD, "{}/frr.conf".format(rname)))
+
+ tgen.start_router()
+
+
+def teardown_module(mod):
+ tgen = get_topogen()
+ tgen.stop_topology()
+
+
+def test_bgp_tcp_mss_passive():
+ tgen = get_topogen()
+
+ if tgen.routers_have_failure():
+ pytest.skip(tgen.errors)
+
+ def _bgp_check_tcp_mss_configured(router, neighbor, mss):
+ output = json.loads(router.vtysh_cmd("show bgp neighbors json"))
+ expected = {
+ neighbor: {
+ "bgpTcpMssConfigured": mss,
+ }
+ }
+ return topotest.json_cmp(output, expected)
+
+ test_func = functools.partial(
+ _bgp_check_tcp_mss_configured, tgen.gears["r1"], "192.168.1.2", 300
+ )
+ _, result = topotest.run_and_expect(test_func, None, count=30, wait=1)
+ assert result is None, "r1 is not configured with TCP MSS 300"
+
+ test_func = functools.partial(
+ _bgp_check_tcp_mss_configured, tgen.gears["r2"], "192.168.1.1", 0
+ )
+ _, result = topotest.run_and_expect(test_func, None, count=30, wait=1)
+ assert result is None, "r2 is not configured with the default TCP MSS (1500)"
+
+ def _bgp_check_tcp_mss_synced(router, neighbor, mss):
+ output = json.loads(router.vtysh_cmd("show bgp neighbors json"))
+ expected = {
+ neighbor: {
+ "bgpTcpMssSynced": mss,
+ }
+ }
+ return topotest.json_cmp(output, expected)
+
+ test_func = functools.partial(
+ _bgp_check_tcp_mss_synced, tgen.gears["r1"], "192.168.1.2", 288
+ )
+ _, result = topotest.run_and_expect(test_func, None, count=30, wait=1)
+ assert result is None, "r1 is not synced with TCP MSS 300"
+
+ test_func = functools.partial(
+ _bgp_check_tcp_mss_synced, tgen.gears["r2"], "192.168.1.1", 288
+ )
+ _, result = topotest.run_and_expect(test_func, None, count=30, wait=1)
+ assert result is None, "r2 is not synced with the default TCP MSS (1488)"
+
+
+if __name__ == "__main__":
+ args = ["-s"] + sys.argv[1:]
+ sys.exit(pytest.main(args))