tests: Nexthop should not be changed if peer X shares a common subnet

Signed-off-by: Donatas Abraitis <donatas.abraitis@gmail.com>

tests/topotests/bgp-ebgp-common-subnet-nexthop-unchanged/r1/bgpd.conf

@@ -0,0 +1,7 @@
+router bgp 65001
+ no bgp ebgp-requires-policy
+ neighbor 192.168.1.101 remote-as external
+ address-family ipv4 unicast
+  redistribute connected
+ exit-address-family
+!

tests/topotests/bgp-ebgp-common-subnet-nexthop-unchanged/r1/zebra.conf

@@ -0,0 +1,7 @@
+!
+int lo
+ ip address 172.16.1.1/32
+!
+int r1-eth0
+ ip address 192.168.1.1/24
+!

tests/topotests/bgp-ebgp-common-subnet-nexthop-unchanged/r2/bgpd.conf

@@ -0,0 +1,3 @@
+router bgp 65103
+ no bgp ebgp-requires-policy
+ neighbor 192.168.1.101 remote-as external

tests/topotests/bgp-ebgp-common-subnet-nexthop-unchanged/r2/zebra.conf

@@ -0,0 +1,4 @@
+!
+int r2-eth0
+ ip address 192.168.1.103/24
+!

tests/topotests/bgp-ebgp-common-subnet-nexthop-unchanged/r3/bgpd.conf

@@ -0,0 +1,5 @@
+router bgp 65000
+ bgp router-id 192.168.1.101
+ no bgp ebgp-requires-policy
+ neighbor 192.168.1.1 remote-as external
+ neighbor 192.168.1.103 remote-as external

tests/topotests/bgp-ebgp-common-subnet-nexthop-unchanged/r3/zebra.conf

@@ -0,0 +1,4 @@
+!
+int r3-eth0
+ ip address 192.168.1.101/24
+!

tests/topotests/bgp-ebgp-common-subnet-nexthop-unchanged/test_bgp-ebgp-common-subnet-nexthop-unchanged.py

@@ -0,0 +1,127 @@
+#!/usr/bin/env python
+
+# Copyright (c) 2021 by
+# Donatas Abraitis <donatas.abraitis@gmail.com>
+#
+# 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.
+#
+
+"""
+https://tools.ietf.org/html/rfc4271
+
+Check if NEXT_HOP attribute is not changed if peer X shares a
+common subnet with this address.
+
+- Otherwise, if the route being announced was learned from an
+  external peer, the speaker can use an IP address of any
+  adjacent router (known from the received NEXT_HOP attribute)
+  that the speaker itself uses for local route calculation in
+  the NEXT_HOP attribute, provided that peer X shares a common
+  subnet with this address.  This is a second form of "third
+  party" NEXT_HOP attribute.
+"""
+
+import os
+import sys
+import json
+import time
+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
+from lib.topolog import logger
+from mininet.topo import Topo
+
+
+class TemplateTopo(Topo):
+    def build(self, *_args, **_opts):
+        tgen = get_topogen(self)
+
+        for routern in range(1, 4):
+            tgen.add_router("r{}".format(routern))
+
+        switch = tgen.add_switch("s1")
+        switch.add_link(tgen.gears["r1"])
+        switch.add_link(tgen.gears["r2"])
+        switch.add_link(tgen.gears["r3"])
+
+
+def setup_module(mod):
+    tgen = Topogen(TemplateTopo, mod.__name__)
+    tgen.start_topology()
+
+    router_list = tgen.routers()
+
+    for i, (rname, router) in enumerate(router_list.items(), 1):
+        router.load_config(
+            TopoRouter.RD_ZEBRA, os.path.join(CWD, "{}/zebra.conf".format(rname))
+        )
+        router.load_config(
+            TopoRouter.RD_BGP, os.path.join(CWD, "{}/bgpd.conf".format(rname))
+        )
+
+    tgen.start_router()
+
+
+def teardown_module(mod):
+    tgen = get_topogen()
+    tgen.stop_topology()
+
+
+def test_bgp_ebgp_common_subnet_nh_unchanged():
+    tgen = get_topogen()
+
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    r2 = tgen.gears["r2"]
+    r3 = tgen.gears["r3"]
+
+    def _bgp_converge(router):
+        output = json.loads(router.vtysh_cmd("show ip bgp summary json"))
+        expected = {
+            "ipv4Unicast": {
+                "peers": {
+                    "192.168.1.1": {"state": "Established"},
+                    "192.168.1.103": {"state": "Established"},
+                }
+            }
+        }
+        return topotest.json_cmp(output, expected)
+
+    test_func = functools.partial(_bgp_converge, r3)
+    success, result = topotest.run_and_expect(test_func, None, count=60, wait=0.5)
+
+    assert result is None, 'Failed bgp convergence in "{}"'.format(r3)
+
+    def _bgp_nh_unchanged(router):
+        output = json.loads(router.vtysh_cmd("show ip bgp 172.16.1.1/32 json"))
+        expected = {"paths": [{"nexthops": [{"ip": "192.168.1.1"}]}]}
+        return topotest.json_cmp(output, expected)
+
+    test_func = functools.partial(_bgp_nh_unchanged, r2)
+    success, result = topotest.run_and_expect(test_func, None, count=60, wait=0.5)
+
+    assert result is None, 'Wrong next-hop in "{}"'.format(r2)
+
+
+if __name__ == "__main__":
+    args = ["-s"] + sys.argv[1:]
+    sys.exit(pytest.main(args))