test: make feature_bind_port_(discover|externalip).py auto-detect the skip condition

diff --git a/test/functional/feature_bind_port_discover.py b/test/functional/feature_bind_port_discover.py
index 613b111b..407b1364 100755
--- a/test/functional/feature_bind_port_discover.py
+++ b/test/functional/feature_bind_port_discover.py
@@ -7,6 +7,9 @@ Test that -discover does not add all interfaces' addresses if we listen on only
 """
 
 from test_framework.test_framework import BitcoinTestFramework, SkipTest
+from test_framework.test_node import (
+    FailedToStartError,
+)
 from test_framework.util import (
     assert_equal,
     assert_not_equal,
@@ -20,18 +23,14 @@ from test_framework.util import (
 # Linux:
 # First find your interfaces: ip addr show
 # Then use your actual interface names (replace INTERFACE_NAME with yours):
-# ip addr add 1.1.1.1/32 dev INTERFACE_NAME && ip addr add 2.2.2.2/32 dev INTERFACE_NAME  # to set up
-# ip addr del 1.1.1.1/32 dev INTERFACE_NAME && ip addr del 2.2.2.2/32 dev INTERFACE_NAME  # to remove it
-#
-# macOS:
-# ifconfig en0 alias 1.1.1.1 && ifconfig en0 alias 2.2.2.2  # to set up
-# ifconfig en0 1.1.1.1 -alias && ifconfig en0 2.2.2.2 -alias  # to remove it, after the test
+# ip addr add 1.1.1.5/32 dev INTERFACE_NAME && ip addr add 1111:1111::5/128 dev INTERFACE_NAME  # to set up
+# ip addr del 1.1.1.5/32 dev INTERFACE_NAME && ip addr del 1111:1111::5/128 dev INTERFACE_NAME  # to remove it
 #
-# FreeBSD:
-# ifconfig em0 1.1.1.1/32 alias && ifconfig wlan0 2.2.2.2/32 alias  # to set up
-# ifconfig em0 1.1.1.1 -alias && ifconfig wlan0 2.2.2.2 -alias  # to remove it, after the test
-ADDR1 = '1.1.1.1'
-ADDR2 = '2.2.2.2'
+# FreeBSD and MacOS:
+# ifconfig INTERFACE_NAME 1.1.1.5/32 alias && ifconfig INTERFACE_NAME inet6 1111:1111::5/128 alias  # to set up
+# ifconfig INTERFACE_NAME 1.1.1.5 -alias && ifconfig INTERFACE_NAME inet6 1111:1111::5 -alias       # to remove it, after the test
+ADDR1 = '1.1.1.5' # This and the address below are set in the CI environment, don't change it just here (keep them in sync).
+ADDR2 = '1111:1111::5'
 
 class BindPortDiscoverTest(BitcoinTestFramework):
     def set_test_params(self):
@@ -69,19 +68,17 @@ class BindPortDiscoverTest(BitcoinTestFramework):
         # False. We do not want any -bind= thus set has_explicit_bind to True.
         for node in self.nodes:
             node.has_explicit_bind = True
-        self.start_nodes()
-
-    def add_options(self, parser):
-        parser.add_argument(
-            "--ihave1111and2222", action='store_true', dest="ihave1111and2222",
-            help=f"Run the test, assuming {ADDR1} and {ADDR2} are configured on the machine",
-            default=False)
 
-    def skip_test_if_missing_module(self):
-        if not self.options.ihave1111and2222:
-            raise SkipTest(
-                f"To run this test make sure that {ADDR1} and {ADDR2} (routable addresses) are "
-                "assigned to the interfaces on this machine and rerun with --ihave1111and2222")
+        try:
+            self.start_nodes()
+        except FailedToStartError as e:
+            self.cleanup_partially_started_nodes()
+            if 'Unable to bind to ' in str(e):
+                raise SkipTest(
+                    f'To run this test make sure that {ADDR1} and {ADDR2} '
+                    '(routable addresses) are assigned to non-loopback '
+                    'interfaces on this machine')
+            raise
 
     def run_test(self):
         self.log.info(
diff --git a/test/functional/feature_bind_port_externalip.py b/test/functional/feature_bind_port_externalip.py
index 0e7764db..074797ac 100755
--- a/test/functional/feature_bind_port_externalip.py
+++ b/test/functional/feature_bind_port_externalip.py
@@ -7,17 +7,24 @@ Test that the proper port is used for -externalip=
 """
 
 from test_framework.test_framework import BitcoinTestFramework, SkipTest
+from test_framework.test_node import (
+    FailedToStartError,
+)
 from test_framework.util import assert_equal, p2p_port
 
-# We need to bind to a routable address for this test to exercise the relevant code.
-# To set a routable address on the machine use:
+# We need to bind to a routable address for this test to exercise the relevant
+# code. Those addresses must be on an interface that is UP and is not a loopback
+# interface (IFF_LOOPBACK).
+# To set these routable addresses on the machine, use:
 # Linux:
-# ifconfig lo:0 1.1.1.1/32 up  # to set up
-# ifconfig lo:0 down  # to remove it, after the test
-# FreeBSD:
-# ifconfig lo0 1.1.1.1/32 alias  # to set up
-# ifconfig lo0 1.1.1.1 -alias  # to remove it, after the test
-ADDR = '1.1.1.1'
+# First find your interfaces: ip addr show
+# Then use your actual interface names (replace INTERFACE_NAME with yours):
+# ip addr add 1.1.1.5/32 dev INTERFACE_NAME  # to set up
+# ip addr del 1.1.1.5/32 dev INTERFACE_NAME  # to remove it
+# FreeBSD and MacOS:
+# ifconfig INTERFACE_NAME 1.1.1.5/32 alias  # to set up
+# ifconfig INTERFACE_NAME 1.1.1.5 -alias  # to remove it, after the test
+ADDR = '1.1.1.5' # This is set in the CI environment, don't change it just here (keep them in sync).
 
 # array of tuples [arguments, expected port in localaddresses]
 EXPECTED = [
@@ -45,17 +52,25 @@ class BindPortExternalIPTest(BitcoinTestFramework):
         self.num_nodes = len(EXPECTED)
         self.extra_args = list(map(lambda e: e[0], EXPECTED))
 
-    def add_options(self, parser):
-        parser.add_argument(
-            "--ihave1111", action='store_true', dest="ihave1111",
-            help=f"Run the test, assuming {ADDR} is configured on the machine",
-            default=False)
+    def setup_network(self):
+        self.setup_nodes()
 
-    def skip_test_if_missing_module(self):
-        if not self.options.ihave1111:
-            raise SkipTest(
-                f"To run this test make sure that {ADDR} (a routable address) is assigned "
-                "to one of the interfaces on this machine and rerun with --ihave1111")
+    def setup_nodes(self):
+        self.add_nodes(self.num_nodes, self.extra_args)
+        # TestNode.start() will add -bind= to extra_args if has_explicit_bind is
+        # False. We do not want any -bind= thus set has_explicit_bind to True.
+        for node in self.nodes:
+            node.has_explicit_bind = True
+        try:
+            self.start_nodes()
+        except FailedToStartError as e:
+            self.cleanup_partially_started_nodes()
+            if 'Unable to bind to ' in str(e):
+                raise SkipTest(
+                    f'To run this test make sure that {ADDR} '
+                    '(routable address) is assigned to non-loopback '
+                    'interface on this machine')
+            raise
 
     def run_test(self):
         self.log.info("Test the proper port is used for -externalip=")
diff --git a/test/functional/test_framework/test_framework.py b/test/functional/test_framework/test_framework.py
index b809e68f..8cc7121f 100755
--- a/test/functional/test_framework/test_framework.py
+++ b/test/functional/test_framework/test_framework.py
@@ -535,6 +535,27 @@ class BitcoinTestFramework(metaclass=BitcoinTestMetaClass):
             # Wait for nodes to stop
             node.wait_until_stopped()
 
+    def cleanup_partially_started_nodes(self):
+        """Tear down nodes left running after a failed start_nodes().
+
+        After start_nodes() raises (e.g. FailedToStartError), some nodes may be
+        RPC-connected, some may have a live process without RPC, and some may
+        already have exited. Stop the connected ones cleanly and force-kill the
+        rest so the framework's teardown can proceed.
+        """
+        for node in self.nodes:
+            if not node.running:
+                continue
+            if node.rpc_connected:
+                node.stop_node(wait=node.rpc_timeout)
+            else:
+                node.process.kill()
+                node.process.wait(timeout=node.rpc_timeout)
+                node.process = None
+                node.stdout.close()
+                node.stderr.close()
+                node.running = False
+
     def restart_node(self, i, extra_args=None, clear_addrman=False, *, expected_stderr=''):
         """Stop and start a test node"""
         self.stop_node(i, expected_stderr=expected_stderr)